Reversible adhesive compositions, related methods, related articles, and related apparatus

Abstract

The disclosure relates to a reversibly assembled part including two substrate surfaces joined via an adhesive composition including an adhesive polymer matrix and electromagnetically excitable, ferromagnetic carbon particles (FMCPs) distributed throughout the adhesive polymer matrix. The FMCPs include ferromagnetic nanoparticles adhered to a carbon-containing substrate, for example metal-containing nanoparticles adhered to a graphene nanoplatelet. When subjected to an electromagnetic induction field, the FMCPs are selectively heated, with little or no direct heating of the polymer matrix material, although heat conduction from the FMCPs into and through the carbon substrate assists in the more even distribution of the initially localized heating throughout the polymer matrix. The parts can be reversibly assembled, disassembled, and / or repaired by application of an electromagnetic induction field to the FMCPs. Also disclosed is a variable frequency induction applicator (VFIA) apparatus that can be used to analyze FMCP samples at different induction field properties to identify induction conditions for optimal heating of the FMCPs in a part.

Description

Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONREVERSIBLE ADHESIVE COMPOSITIONS, RELATED METHODS, RELATED ARTICLES, AND RELATED APPARATUSCROSS REFERENCE TO RELATED APPLICATION

[0001] Priority is claimed to U.S. Provisional Application No. 63 / 634,617 (filed April 16, 2024), which is incorporated herein by reference in its entirety.STATEMENT OF GOVERNMENT INTEREST

[0002] This invention was made with government support under HQ0034-15-2-0007, RC107160, and RC108606 awarded by the U.S. Department of Defense. The government has certain rights in the invention.BACKGROUND OF THE DISCLOSUREField of the Disclosure

[0003] The disclosure relates to a reversibly assembled part including two substrate surfaces joined via an adhesive composition including an adhesive polymer matrix and electromagnetically excitable, ferromagnetic carbon particles (FMCPs) distributed throughout the adhesive polymer matrix. The FMCPs include ferromagnetic nanoparticles adhered to a carbon-containing substrate. When subjected to an electromagnetic induction field, the FMCPs are selectively heated. The parts can be reversibly assembled, disassembled, and / or repaired by application of an electromagnetic induction field to the FMCPs.Background

[0004] Lightweight and reliable dissimilar material joining is of special interest in automotive, aerospace, defense and marine industries. Conventional and well-established methods for dissimilar materials joining include friction stir welding (FSW), ultrasonic welding, arc welding, laser welding, plasma welding, explosive welding / bonding using chemical explosives, conventional brazing or soldering, rivets, bolts, and other conventional mechanical fasteners, conventional adhesive joining. However, each of those techniques has its own advantages and drawbacks.

[0005] Adhesively bonded joints are gaining popularity in place of conventional fasteners as they provide light-weight designs, reduce stress concentrations, enable joining of dissimilar materials, and are often cheaper than conventional fasteners. Bonded joints provide larger contact area than bolted joints thereby providing efficient stress distribution, enabling higher efficiency and improved fatigue life. Nevertheless, the quality of adhesively bonded joints depends on various factors including manufacturing techniques,Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONmanufacturing defects, physical damage and deterioration due to accidental impacts, moisture absorption, improper handling, etc. These factors can significantly affect the strength of resulting bonded joints leading to an increased need for a successful monitoring technique that can provide information about the adhesive layer and its resulting joint.Moreover, the resulting joint cannot be disassembled or reassembled.

[0006] Haq et al. US 2016 / 0284449 is directed to reversible bonded structural joints using active adhesive compositions that can allow for dis-assembly, repair, and re-assembly. The adhesive composition includes a thermoplastic adhesive material that can be remotely activated for targeted heating via the inclusion of electromagnetically excitable particles (EEPs) in the adhesive composition. Examples of EEPs include ferromagnetic nanoparticles, graphene nanoplatelets, alumina nanoparticles, metal-doped graphene microparticles, and / or metal-doped graphene nanoparticles.

[0007] He et al. (Carbon; vol. 58, pp. 175-184; 2013) is directed to the formation of graphene nanosheet-FesC hybrids and syndiotactic polystyrene composites including the graphene nanosheet-FesC hybrids. The hybrid materials are formed via solvothermal reduction of graphene oxide and deposition of Fe3C>4 nanoparticles on the reduced graphene nanosheet surface.

[0008] Garaio et al. (Meas. Sci. Technol. vol. 25, no. 115702 (10 pages); 2014) is directed to a multifrequency electromagnetic applicator with an integrated AC magnetometer for magnetic hyperthermia experiments. The apparatus is based on a parallel LCC resonant circuit fed by a linear power amplifier. The device is used to evaluate magnetic nanoparticles for using an anti-cancer magnetic hyperthemia therapy.SUMMARY

[0009] In one aspect, the disclosure relates to a reversibly assembled part (or article) comprising: at least one substrate defining a first surface and a second surface reversibly joined at a joint interface in an assembled part; an adhesive composition in a solid state and in contact with and bonded to the first surface and the second surface at the joint interface of the assembled part, wherein the adhesive composition comprises: at least one of a thermoplastic polymer matrix and a thermoset polymer matrix (e.g., thermoplastic or thermoset adhesive polymer), and electromagnetically excitable, ferromagnetic carbon (e.g., carbon-containing) particles (FMCPs) distributed throughout the thermoplastic and / or thermoset polymer matrix, each FMCP comprising a plurality of ferromagnetic nanoparticles (e.g., metal-containing nanoparticles) adhered to a carbon-containing substrate (e.g., particle with micro- and / or nano-scale dimensions).Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0010] Various refinements of the disclosed articles are possible.

[0011] In a refinement, the FMCPs comprise ferromagnetic graphene nanoparticles (FMGnPs) in which: the ferromagnetic nanoparticles of the FMCP comprise metal-containing nanoparticles (e.g., Fe3O4 nanoparticles); and the carbon-containing substrate of the FMCP comprises a graphene nanoplatelet. The nanoplatelet can include one or more of graphene, graphene oxide, and reduced graphene oxide (e.g., as separate carbon-containing substrates in admixture).

[0012] The FMCPs (or FMGnPs more specifically) are characterized by ferromagnetic nanoparticles (e.g., FesO^ fixedly adhered or otherwise bound to a carbon-containing particulate substrate (e.g., graphene nanoplatelet substrate), for example as a result of a process in which the ferromagnetic nanoparticles are directly grown on the carbon-containing substrate in a deposition process. The ferromagnetic nanoparticles typically range from about 5-25 nm in diameter, for example at least 5, 7, 10, 12, or 15 nm and / or up to 6, 8, 10, 12, 15, 20, or 25 nm, such as representing the breadth of a size distribution or an average size (e.g., number-, weight-, volume-, area-weighted average). The resulting FMCPs exhibit enhanced mechanical performance, improved particle dispersion, and improved heating in the adhesive composition of the corresponding assembled part. When subjected to an electromagnetic induction field, the ferromagnetic nanoparticles are selectively heated. When subjected to the electromagnetic induction field, there is typically negligible or little (or no intended) direct heating of the polymer matrix or carbon substrate. The main thermal response resulting from the electromagnetic induction field is in the ferromagnetic nanoparticles. Heat conduction from the ferromagnetic nanoparticles into and through the carbon substrate assists in the more even distribution of the localized heating throughout the polymer matrix by correspondingly (i) reducing the higher temperature gradient at the ferromagnetic nanoparticle-polymer interface and (ii) creating a lower temperature gradient at the carbon substrate-polymer interface (i.e., resulting from heat conduction from the ferromagnetic nanoparticles into the carbon substrate) for a more even distribution of heat into the polymer matrix. Using the carbon substrate as a support for the ferromagnetic nanoparticles also helps to ensure that the ferromagnetic nanoparticles are more evenly distributed throughout the polymer matrix: Once the ferromagnetic nanoparticles are adhered / fixed on the carbon substrate, then an even distribution or well-mixed state for the carbon substrate particles ensures that the ferromagnetic nanoparticles are also evenly distributed (i.e., preventing aggregation of ferromagnetic nanoparticles and / or otherwise limiting areas where locally high concentrations of ferromagnetic nanoparticles would result in locally very high induction heating temperatures and localAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONpolymer matrix damage as well as inefficient or insufficient heating of the polymer matrix in other areas).

[0013] The FMCPs (or FMGnPs more specifically) are distinct from the electromagnetically excitable particles disclosed in Haq et al. U.S. Patent No. 10,099,458 (“Haq”). For example, Haq discloses metal doped nano-graphene particles, which would include graphene structures in which some lattice carbon atoms are replaced with metal atoms (e.g., throughout the body of the carbon substrate, including surface and internal regions of the bulk carbon material having lattice carbon atoms substituted or replaced with metal or other dopant atoms). In contrast, the FMCPs / FMGnPs include ferromagnetic nanoparticles grown directly on the graphene or other carbon-containing particular substrate, but they do not involve doping or other replacement of carbon atoms in the underlying (or internal) carbon substrate structure.

[0014] Further, other methods to “combine” carbon and metal materials do not work as well as the FMCP / FMGnP particles. Simply attempting to attach already-formed metal particles (or ferromagnetic nanoparticles) onto graphene sheets results in relatively weak attachment and aggregates of unbound metal particles in a polymer matrix. Unbound metal particles or ferromagnetic nanoparticles and aggregates thereof can result in an uneven induction heating distribution and corresponding damage to the polymer matrix. Similar problems occur by simply mixing separate metal particles and graphene particles as two types of materials in a polymer matrix. In contrast, FMCP / FMGnP particles ensure that all metal particles are attached to a graphene substrate or other carbon-containing substrate, which in turn helps ensure that the metal particles are evenly distributed in the polymer matrix and facilitates heat conduction through the graphene and into the polymer matrix from the locally induction-heated metal particles.

[0015] In general, the FMGnPs display a saturation magnetization in excess of a specific value in a specific magnetic fields, given that a non-zero hysteresis loop is required for heating in this range of magnetic fields. In a particular refinement, the FMGnPs can display a saturation magnetization of non-zero value in magnetic fields of 100 kHz to 2 MHz of flux densities in excess of 5 kA / m, for example a saturation magnetization of (at least) 20 A / m in a 5kA / m field, saturation magnetization of (at least) 40 A / m in a 10 kA / m field, and / or saturation magnetization of (at least) 80 A / m in a 20kA / m field. In a particular refinement, the FMGnPs can have a non-zero hysteresis loop area in magnetic fields of 100 kHz to 2 MHz of flux densities in excess of 5 kA / m such that the coercivity of the particle defines an energy loss, for example approaching or being in excess of 0.3 (kA / m)A2 in fields ofAtty. Docket No. 32213 / 58079B / US PATENT APPLICATION10 kA / m. These properties are illustrated in the examples for particle SDR3. In contrast, to these properties, some Fe3C>4-containing materials known in the art do not exhibit the hysteresis properties required for induction heating, such as the graphene nanosheet-FesC hybrids of He.

[0016] In a refinement, the adhesive composition is substantially free from free (or unbound) ferromagnetic nanoparticles (e.g., not adhered to a carbon-containing substrate). The adhesive composition suitably contains not more than 1 , 0.1 , or 0.01 wt.% (and / or at least 0.0001 or 0.001 wt.%) free ferromagnetic nanoparticles, which can be expressed relative to the adhesive composition as a whole or relative to the total amount of ferromagnetic nanoparticles (i.e., combined amount of those primarily bound / adhered to the carbon-containing substrate as well as those unbound / not adhered to the carbon-containing substrate). This reflects a benefit of the disclosed FMCPs in that they prevent or limit the presence of free ferromagnetic nanoparticles that can result in poor / uneven heating, whereas simple mixing of ferromagnetic nanoparticles with carbon particles or weak attachment of already formed ferromagnetic nanoparticles to carbon particles resulting in detachment can result in the free ferromagnetic nanoparticles in the adhesive composition. Similarly, the adhesive composition suitably contains not more than 1 , 0.1 , or 0.01 wt.% (and / or at least 0.0001 or 0.001 wt.%) non-ferromagnetic carbon particles (e.g., carbon-containing particles such as graphene nanoplatelets that are not functionalized with ferromagnetic nanoparticles bound thereto), which can be expressed relative to the adhesive composition as a whole or relative to the total amount of carbon particles (i.e., combined amount of ferromagnetic carbon particles and non-ferromagnetic carbon particles).

[0017] In a refinement, the adhesive composition comprises the thermoset polymer matrix and the thermoplastic polymer matrix.

[0018] In a refinement, the adhesive composition comprises the thermoplastic polymer matrix; and the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyurethanes, acrylonitrile-butadiene-styrene (ABS) copolymers, styrene block copolymers, polycarbonates, polyolefins, ethylene-vinyl acetate copolymers, ethyleneacrylate copolymers, and combinations thereof.

[0019] In a refinement, the thermoplastic polymer is in a solid state at a temperature ranging from 20 °C to 30 °C. The same property can apply to the thermoset polymer when present in the adhesive composition matrix.

[0020] In a refinement, the thermoplastic polymer is present in the adhesive composition in an amount ranging from 50 wt.% to 99.9 wt.%, for example at least 50, 55, 60, 65, 70, 75,Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION80, 85, 90, or 95 wt.% and / or up to 60, 65, 70, 75, 80, 85, 90, 95, 98, 99, or 99.9 wt.%. The same amounts can apply to the thermoset polymer when present in the adhesive composition matrix.

[0021] In a refinement, the adhesive composition comprises the thermoset polymer matrix; and the thermoset polymer is selected from the group consisting of thermoset epoxy resins, thermoset (meth)acrylate resins, thermoset polyurethane resins, and combinations thereof.

[0022] In a refinement, the electromagnetically excitable, ferromagnetic carbon particles comprise a chemical functionalization moiety for compatibilization with the thermoplastic polymer matrix.

[0023] In a refinement, the carbon-containing substrate is selected from the group consisting of graphite particles, exfoliated graphite nanoplatelets, carbon nanotubes, carbon fibers, carbon black, and combinations thereof.

[0024] In a refinement, the electromagnetically excitable particles are present in the adhesive composition in an amount ranging from 0.1 wt.% to 50 wt.%, 2.5 wt.% to 20 wt.%, 5 wt.% to 15 wt.%, or about 7.5 wt.%. For example, the electromagnetically excitable particles can be present in amounts of at least 0.1 , 0.2, 0.5, 1 , 2.5, 4, 5, 6, 8, or 10 wt.% and / or up to 3, 7, 10, 12, 15, 20, 25, 30, 40, or 50 wt.%.

[0025] In a refinement, the electromagnetically excitable particles comprise nanoparticles having a size ranging from 1 nm to 1000 nm.

[0026] In a refinement, the electromagnetically excitable particles comprise microparticles having a size ranging from 1 pm to 100 pm.

[0027] In a refinement, (i) the first surface is a surface of a first substrate; and (ii) the second surface is a surface of a second substrate separate from the first substrate.

[0028] In a refinement, the first surface and the second surface are surfaces of a single substrate.

[0029] In a refinement, the first surface and the second surface are formed from different materials, for example where the first surface comprises a metal material, and the second surface comprises a polymeric material and / or a non-metallic material. Alternatively or additionally, the reversibly assembled part can include joints of two or more substrates containing at least one substrate of non-electrically conductive composition and may include joints of substrates of differing materials of all compositions, conductive or otherwise, as longAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONas the configuration allows exposure of the adhesive composition to the electromagnetic field through at least one non-conductive material.

[0030] In a refinement, the reversibly assembled part further comprises I one or more additives selected from the group consisting of tackifying resins, waxes, plasticizers, antioxidants, ultraviolet stabilizers, colorants, biocides, flame retardants, antistatic agents, fillers, and combinations thereof; wherein the additives are present in the adhesive composition in an amount ranging from 0.5 wt.% to 40 wt.%.

[0031] In a refinement, the first surface and the second surface are bonded at a joint interface selected from the group consisting of a lap joint, a double-lap joint, a butt joint, a scarf joint, a corner / L-joint, and a T- / Pi-joint.

[0032] In a refinement, the assembled part is a vehicle component part.

[0033] In another aspect, the disclosure relates to a method for assembling a part, the method comprising: (a) contacting an adhesive composition (i) with a first surface and a second surface of at least one substrate defining the first surface and the second surface (ii) at a joint interface of a part to be assembled, wherein the adhesive composition comprises: at least one of a thermoplastic polymer matrix and a thermoset polymer matrix, and electromagnetically excitable, ferromagnetic carbon particles (FMCPs) distributed throughout the thermoplastic or thermoset polymer matrix, each FMCP comprising a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate; (b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, wherein the electromagnetic radiation comprises a variable magnetic field generating electromagnetic induction; and (c) removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the second surface at the joint interface. The adhesive composition can generally include any of the various embodiments described above. In some alternative embodiments, the heating in step (b) need not (fully) transform the adhesive composition to flowable or moldable state, because not all materials require heating all the way to melt or flow to allow for mechanical separation of the joint. In such cases, the heating can be to a degree sufficient such that the matrix of the adhesive composition is altered to a stage of reduced structural integrity at which separation of the joint via mechanical means becomes possible, such as but not limited to surpassing the temperature by which the matrix flows, releases, or degrades.

[0034] Various refinements of the disclosed method for assembling a part are possible.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0035] In a refinement, the electromagnetic radiation is free from microwave radiation, such as where only induction heating is used to selectively heat the ferromagnetic nanoparticles, and there is no microwave or other heating to heat the carbon-containing substrate of the FMCP. For example, induction fields typically suitable for this method can range from about 100 kHz to about 5 MHz, whereas the microwave regime is generally accepted to begin at about 300 MHz.

[0036] In a refinement, the method further comprises heating the adhesive composition to a limited degree sufficient avoid or prevent heat-induced damage to one or both of the first surface and the second surface.

[0037] In a refinement, the method further comprises applying pressure to one or both of the first surface and the second surface when heating the adhesive composition, thereby causing the thermoplastic polymer to expand and contact an increased surface area at the joint interface.

[0038] In a refinement, (i) the first surface is a surface of a first substrate; and (ii) the second surface is a surface of a second substrate separate from the first substrate.

[0039] In a refinement, wherein the first surface and the second surface are surfaces of a single substrate.

[0040] In a refinement, the first surface and the second surface are formed from different materials.

[0041] In a refinement, the method further comprises placing one or more spacers between the first surface and the second surface, the spacers maintaining a constant specified separation distance between the first surface and the second surface.

[0042] In a refinement, the first surface and the second surface are bonded at a joint interface selected from the group consisting of a lap joint, a double-lap joint, a butt joint, a scarf joint, a corner / L-joint, and a T- / Pi-joint.

[0043] In another aspect, the disclosure relates to a method for disassembling a part, the method comprising: (a) providing an assembled part according to any of the variously disclosed refinements, embodiments, etc. comprising the adhesive composition in a solid state and in contact with and bonded to a first surface and a second surface at a joint interface of the assembled part; (b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to a flowable or moldable state, wherein the electromagnetic radiation comprises a variable magnetic field generating electromagnetic induction; and (c) separating the first surface fromAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONthe second surface. In some alternative embodiments, the heating in step (b) need not (fully) transform the adhesive composition to flowable or moldable state, because not all materials require heating all the way to melt or flow to allow for mechanical separation of the joint. In such cases, the heating can be to a degree sufficient such that the matrix of the adhesive composition is altered to a stage of reduced structural integrity at which separation of the joint via mechanical means becomes possible, such as but not limited to surpassing the temperature by which the matrix flows, releases, or degrades.

[0044] Various refinements of the disclosed method for disassembling a part are possible.

[0045] In a refinement, the method further comprises: (d) re-contacting the adhesive composition with the first surface and the second surface at the joint interface, directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, and removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the second surface at the joint interface.

[0046] In a refinement, the method further comprises: (d) providing a third surface as a replacement for the second surface (e.g., the third surface can have the same shape and / or be formed from the same material as the second surface); and I contacting the adhesive composition with the first surface and the third surface at the joint interface, directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, and removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the third surface at the joint interface.

[0047] In a refinement, wherein the electromagnetic radiation is free from microwave radiation.

[0048] In a refinement, wherein: (i) the first surface is a surface of a first substrate; and (ii) the second surface is a surface of a second substrate separate from the first substrate.

[0049] In a refinement, wherein the first surface and the second surface are surfaces of a single substrate.

[0050] In a refinement, wherein the first surface and the second surface are formed from different materials.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0051] In another aspect, the disclosure relates to a method for repairing a part, the method comprising: (a) providing an assembled part according to any of the variously disclosed refinements, embodiments, etc. comprising the adhesive composition in a solid state and in contact with and bonded to a first surface and a second surface at a joint interface of the assembled part, wherein the assembled part further comprises one or more defects at the joint interface; (b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, thereby allowing the adhesive composition to flow at least partially into the one or more defects, wherein the electromagnetic radiation comprises a variable magnetic field generating electromagnetic induction; and (c) removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface, the second surface, and the one or more defects at the joint interface. In some alternative embodiments, the heating in step (b) need not (fully) transform the adhesive composition to flowable or moldable state, because not all materials require heating all the way to melt or flow to allow for mechanical separation of the joint. In such cases, the heating can be to a degree sufficient such that the matrix of the adhesive composition is altered to a stage of reduced structural integrity at which separation of the joint via mechanical means becomes possible, such as but not limited to surpassing the temperature by which the matrix flows, releases, or degrades.

[0052] Various refinements of the disclosed method for repairing a part are possible.

[0053] In a refinement, the method further comprises: applying pressure to one or both of the first surface and the second surface when heating the adhesive composition, thereby causing the thermoplastic polymer (i) to expand and contact an increased surface area at the joint interface and (ii) to flow at least partially into the one or more defects.

[0054] In a refinement, wherein the electromagnetic radiation is free from microwave radiation.

[0055] In a refinement, wherein: (i) the first surface is a surface of a first substrate; and (ii) the second surface is a surface of a second substrate separate from the first substrate.

[0056] In a refinement, the first surface and the second surface are surfaces of a single substrate.

[0057] In a refinement, the first surface and the second surface are formed from different materials.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0058] In another aspect, the disclosure relates to a variable frequency induction applicator (VFIA), comprising: a capacitor array including a plurality of capacitors; a plurality of AC contactors selectively controllable to electrically couple the plurality of capacitors in one or more arrangements; a plurality of relays electrically coupled to respective ones of a plurality of control terminals of respective ones of the plurality of AC contactors, wherein a state of each AC contactor is responsive to a state of the respective relay; an applicator coil coupled to the capacitor array, and configured to generate an electromagnetic field responsive an alternating current (AC) signal applied to the capacitor array; and a processor configured to control the plurality of relays to control one or more properties of the electromagnetic field generated by the applicator coil.

[0059] Various refinements of the disclosed variable frequency induction applicator (VFIA) are possible.

[0060] In a refinement, the VFIA further comprises differential vibrating-sample magnetometer (VSM) coils positioned in the applicator coil; and a meter coupled to the differential VSM coils, and configured to measure the one or more properties of the generated electromagnetic field; wherein the processor is coupled to the meter, and is configured to control the plurality of relays based on differences between (i) the one or more measured properties of the generated electromagnetic field, and (ii) one or more desired properties of an electromagnetic field.

[0061] In a refinement, the VFIA further comprises a thermocouple configured to measure temperatures of a sample positioned in the applicator coil; wherein the processor is coupled to the thermocouple, and is configured to collect one or more temperature measurements from the thermocouple responsive to controlling the plurality of relays to cause the applicator coil to generate one or more electromagnetic fields.

[0062] In a refinement, the processor is configured to control the plurality of relays over time to measure energy absorption of a sample positioned in the applicator coil responsive to one or more of field strength, field frequency, or duration of the electromagnetic field.

[0063] In another aspect, the disclosure relates to a method for analyzing a sample, the method comprising: providing a sample comprising ferromagnetic nanoparticles (FMNPs) (e.g., an aqueous dispersion of FMNPs such as FMCPs); analyzing the sample with the VFIA according to any of the variously disclosed refinements, embodiments, etc. by measuring hysteresis (e.g., energy input) and temperature (e.g., energy output represented by temperature rate or heating rate such as SAR) of the sample positioned in the applicatorAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONcoil of the VFIA at (i) a plurality of different field frequencies and (ii) a plurality of different field strengths.

[0064] Various refinements of the disclosed method for analyzing a sample are possible.

[0065] In a refinement, the FMNPs comprise electromagnetically excitable, ferromagnetic carbon particles (FMCPs), each FMCP comprising a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate. In a further refinement. The FMCPs comprise ferromagnetic graphene nanoparticles (FMGnPs) in which: the ferromagnetic nanoparticles of the FMCP comprise metal-containing nanoparticles (e.g., FesC ); and the carbon-containing substrate of the FMCP comprises a graphene nanoplatelet such as a reduced graphene oxide nanoplatelet. Alternatively, the FMNPs can comprise free or unbound ferromagnetic nanoparticles (e.g., FesC or otherwise that is not bound or adhered to a carbon-containing substrate).

[0066] In a refinement, the sample is in the form of an aqueous dispersion of the FMNPs (e.g., continuous water or water-containing medium with the FMNPs dispersed therein).

[0067] In a refinement, the plurality of different field frequencies is in a range of 100 kHz to 2 MHz; and the plurality of different field strengths is in a range of 0 kA / m to 20 kA / m. More generally, the plurality of different field frequencies can be at least 100, 200, 300, 400, 500, 700, or 1000 kHz and / or up to 500, 1000, 1500, or 2000 kHz. Alternatively or additionally, the plurality of different field strengths can be at least 0, 1 , 2, 3, 4, 5, 7, 10, or 12 kA / m and / or up to 4, 8, 12, 16, or 20 kA / m. In embodiments, the plurality of measurements for hysteresis and / or temperature of the sample can be in a range of 2 to 100 measurements, for example at least 2, 3, 4, 5, 7, 10, 12, 15, 20, or 30 and / or up to 4, 8, 12, 16, 20, 30, 40, 50, 60, 80, or 100 measurements at different field frequencies and / or different field strengths. The number of different field frequency measurements can be the same as or different from the number of different field strength measurements.

[0068] In a refinement, the method further comprises: selecting specific FMNPs and / or specific induction field properties (e.g., field frequency and / or field strength) based on VFIA analysis of the sample (or a plurality of samples with different FMNPs) to optimize (e.g., increase or maximize) induction heating of the FMNPs (e.g., in an adhesive composition matrix); and performing a method for assembling, disassembling, or repairing a part using an adhesive composition comprising the selected FMNPs and using the selected induction field properties (e.g., when directed electromagnetic radiation to heat the adhesive composition). More generally, the VFIA can be used to measure the FMNP response to develop optimal field-particle coupling to maximize the heating within the adhesive composition when theAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONparticles are incorporated into the matrix and exposed to the induction field. The variability of the VFIA unit allows high throughput testing of FMNPs in an optimum suspension state with a broad range of field conditions. Once the particles and field have been selected via VFIA testing, they are scaled, incorporated into the adhesive composition, and then a singlefrequency induction unit / applicator could be purchased and used to match the optimized induction field when assembling, disassembling, or repairing a part according to the method generally described herein.

[0069] Additional features of the disclosure may become apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the drawings, examples, and appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0070] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:

[0071] Figure 1 is a side cross-sectional view of an assembled part incorporating an adhesive composition according to the disclosure.

[0072] Figure 2 includes side cross-sectional views of an assembled part incorporating an adhesive composition according to the disclosure and in various joint interface configurations: (a) lap joint, (b) double lap joint, (c) butt joint, (d) scarf joint, (e) corner / L-joint, and (f) Pi- / T-joint.

[0073] Figure 3 illustrates a method for assembling a part incorporating an adhesive composition according to the disclosure.

[0074] Figure 4 illustrates a method for disassembling a part incorporating an adhesive composition according to the disclosure.

[0075] Figure 5 illustrates a method for repairing a part incorporating an adhesive composition according to the disclosure.

[0076] Figure 6 illustrates a variable frequency induction applicator (VFIA) according to the disclosure.

[0077] Figure 7 is a graph illustrating heating (AT) as function of heating time and electromagnetic induction excitation frequency for (A) electromagnetically excitable, ferromagnetic carbon particles (FMCPs) according to the disclosure and (B) electromagnetically excitable, ferromagnetic nanoparticles (FMNPs).Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0078] Figure 8 is a graph illustrating hysteresis loop area as function of electromagnetic induction excitation frequency for FMCPs according to the disclosure.

[0079] Figure 9 is a graph illustrating hysteresis loops for FMCPs according to the disclosure formed used a graphene oxide (GO):tris(acetylacetonato) iron(lll) (Fe(acac)s) precursor ratios of (a) 1 :1 , (b) 1 :2, (c) 1 :3, and (d) 1 :4.

[0080] While the disclosed articles, compositions, and methods are susceptible of embodiments in various forms, specific embodiments of the disclosure are illustrated (and will hereafter be described) with the understanding that the disclosure is intended to be illustrative, and is not intended to limit the claims to the specific embodiments described and illustrated herein.DETAILED DESCRIPTION

[0081] The disclosure relates to a reversibly assembled part or article including two substrate surfaces joined via an adhesive composition including an adhesive polymer matrix (e.g., thermoplastic polymer matrix) with electromagnetically excitable, ferromagnetic carbon (e.g., carbon-containing) particles (FMCPs) distributed throughout the adhesive polymer matrix. The FMCPs include a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate, for example metal-containing nanoparticles (e.g., FesC ) adhered to a graphene nanoplatelet, such as a reduced graphene oxide nanoplatelet. When subjected to an electromagnetic induction field, the FMCPs are selectively heated, with little or no direct heating of the polymer matrix material, although heat conduction from the FMCPs into and through the carbon substrate assists in the more even distribution of the initially localized heating throughout the polymer matrix. The parts or articles can be reversibly assembled, disassembled, and / or repaired by application of an electromagnetic induction field to the FMCPs. Also disclosed is a variable frequency induction applicator (VFIA) apparatus that can be used to analyze FMCP samples at a plurality of different induction field properties to identify induction conditions for optimal heating of the FMCPs in an adhesive polymer matrix.

[0082] The disclosure is directed to reversibly bonded structural joints using active adhesives that can allow for dis-assembly, repair and re-assembly. This will allow for recyclability of parts at the end of their lifetime. Currently recyclability, in-situ repair and reassembly are desirable properties in assembled parts.

[0083] The disclosure particularly relates to adhesive composition material itself, irrespective of the type of the substrate. The substrate can either be any metal material (e.g., aluminum, steel, magnesium, etc.), any composite material (e.g., carbon fiber-reinforcedAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONpolymer (CFRP), glass fiber-reinforced polymer (GRFP)), any hybrid material (e.g., multimaterials), or otherwise. Secondly, the adhesive composition can include any thermoplastic material (such as nylon, ABS, etc.) that can be modified such that it can be remotely activated for targeted heating of just the adhesive composition (e.g., and not the surrounding substrates being joined). Thermoplastics melt when exposed to temperatures beyond their melting point. Heating large surface areas of structural joints is cumbersome, time, energy and cost consuming. More importantly, if one or more of the substrates is a composite, heating at high temperatures degrades the adherends. The disclosure is directed to rapid, targeted (or localized) heating of an adhesive composition, with little or no heating of the surrounding substrate materials. While the adherends in the vicinity of the adhesive, the surrounding material of the joined surfaces will get heated (e.g., via conduction from the hot adhesive composition), but the adherends will not get degraded as they are exposed to a maximum heat (e.g., equivalent to the melting point of adhesive) for a very short period of time.

[0084] The adhesive composition includes ferromagnetic carbon (e.g., carbon-containing) particles (FMCPs) to permit rapid, localized, selective heating of the adhesive composition. FMCPs (e.g., nano-scale and / or micro-scale) are incorporated or embedded in the polymer matrix of the adhesive composition. The FMCPs include a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate, for example metal-containing nanoparticles (e.g., FesC ) adhered to a graphene nanoplatelet, such as a reduced graphene oxide nanoplatelet. The choice of the polymer for the adhesive matrix is dependent on the desired application, and the polymer can include one or more thermoplastic polymers, one or more thermoset polymers, or a blend of at least one of each thermoplastic and thermoset polymers.

[0085] In addition to an assembled part 20 (described below), Figure 1 illustrates an electromagnetically excitable, ferromagnetic carbon (e.g., carbon-containing) particle (FMCP) 14 according to the disclosure. The FMCP 14 includes a plurality of ferromagnetic nanoparticles 14A (or more generally metal-containing nanoparticles) adhered to a carbon-containing substrate 14B, which can be a particle with micro- and / or nano-scale dimensions. In some embodiments, the ferromagnetic nanoparticles 14A can include metal-containing nanoparticles such as Fe3O4 nanoparticles. In some embodiments, the carbon-containing substrate 14B can be a graphene nanoplatelet. The nanoplatelet can include one or more of graphene, graphene oxide, and reduced graphene oxide (e.g., as separate carbon-containing substrates in admixture). Graphene oxide and reduced graphene oxide can include various oxygen-containing functional groups on the base graphene sheet structure,Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONfor example including hydroxy (-OH), epoxide (-O-), carbonyl (-C(=O)-), and / or carboxylic (-C(=O)OH) groups. The element distribution between carbon and oxygen for graphene oxide is generally about 62-65% C and about 35-38% O relative to total C+O, on molar or weight basis. The element distribution between carbon and oxygen for reduced graphene oxide is generally about 77-87% C and about 13-22% O relative to total C+O, on molar or weight basis. The foregoing ranges can vary depending on the specific methods used to oxidize graphene to graphene oxide and / or to reduce graphene oxide to reduced graphene oxide. Several suitable methods for forming graphene oxide and reduced graphene oxide are known in the art. Graphene (i.e., a non-oxidized form) generally does not contain any substantial amount of oxygen (e.g., not more than 0.01 , 0.1 , or 1% relative to total carbon or total graphene). In a particular embodiment, the FMCP 14 can be a ferromagnetic graphene nanoparticle (FMGnP) when it includes metal-containing nanoparticles such as Fe3C>4 and graphene nanoplatelets such as reduced graphene oxide nanoplatelets. In embodiments, the carbon-containing substrate 14B can include graphite particles, exfoliated graphite nanoplatelets, carbon nanotubes, carbon fibers, carbon black, and combinations thereof. The foregoing carbon-containing substrates 14B can include non-oxidized, oxidized, or reduced oxidized forms of the various materials, for example with the relative carbon / oxygen distributions described above.

[0086] The FMCPs (or FMGnPs) 14 are characterized by ferromagnetic nanoparticles 14A (e.g., FesC ) fixedly adhered or otherwise bound to a carbon-containing particulate substrate 14B, for example as a result of a process in which the ferromagnetic nanoparticles are directly grown on the carbon-containing substrate in a deposition process, for example a deposition process that also reduces a graphene oxide substrate to a reduced graphene oxide substrate in the final FMCP 14. The ferromagnetic nanoparticles 14A typically range from about 5-25 nm in diameter, for example at least 5, 7, 10, 12, or 15 nm and / or up to 6, 8, 10, 12, 15, 20, or 25 nm, such as representing the breadth of a size distribution or an average size (e.g., number-, weight-, volume-, area-weighted average). The resulting FMCPs 14 exhibit enhanced mechanical performance, improved particle dispersion, and improved heating in the adhesive composition of the corresponding assembled part.

[0087] When subjected to an electromagnetic induction field, the ferromagnetic nanoparticles 14A of the FMCPs 14 are selectively heated. When subjected to the electromagnetic induction field, there is typically negligible or little (or no intended) direct heating of the polymer matrix 12 or carbon substrate 14B. The main thermal response resulting from the electromagnetic induction field is in the ferromagnetic nanoparticles 14A. Heat conduction from the ferromagnetic nanoparticles 14A into and through the carbonAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONsubstrate 14B assists in the more even distribution of the localized heating throughout the polymer matrix 12 by correspondingly (i) reducing the higher temperature gradient at the ferromagnetic nanoparticle-polymer interface and (ii) creating a lower temperature gradient at the carbon substrate-polymer interface (i.e., resulting from heat conduction from the ferromagnetic nanoparticles 14A into the carbon substrate 14B) for a more even distribution of heat into the polymer matrix 12. Using the carbon substrate 14B as a support for the ferromagnetic nanoparticles 14A also helps to ensure that the ferromagnetic nanoparticles 14A are more evenly distributed throughout the polymer matrix: Once the ferromagnetic nanoparticles 14A are adhered / fixed on the carbon substrate 14B, then an even distribution or well-mixed state for the carbon substrate 14B particles ensures that the ferromagnetic nanoparticles 14A are also evenly distributed, thus preventing aggregation of ferromagnetic nanoparticles 14A and / or otherwise limiting areas where locally high concentrations of ferromagnetic nanoparticles 14A would result in locally very high induction heating temperatures and local polymer matrix 12 damage as well as inefficient or insufficient heating of the polymer matrix 12 in other areas. Depending on the power, frequency, and exposure time of the electromagnetic induction field, the polymer matrix 12 can melt (e.g., when it is a thermoplastic polymer) and detaches / dis-assembles the two substrates. For example, joints / adherends can be separated in times ranging between 30 to 300 seconds.

[0088] Further, it is possible to heat the polymer matrix in an already formed, assembled part sufficiently to close any cracks, or micro-degradation. Thus, it is possible to refresh the adhesive and repair the joint seal to its original form. For example, if a joint with the adhesive composition in an assembled part has undergone several million cycles of fatigue loading due to in-service loads, then such cyclic fatigue loads can degrade the properties of the adhesive composition and resulting joints. With the adhesive compositions according to the disclosure, it is possible to refresh or perform in-situ repair of the joint without disassembly. This can provide considerable cost-savings, for example in the auto industry with respect to vehicle repairs of assembled part. Moreover, the simple dis-assembly of parts allows for repair and replacement of only required / necessary parts rather than repair or replace the entire component, which is more expensive.

[0089] Furthermore, the FMCPs dispersed throughout the polymer matrix lead to uniform heating of the adhesive throughout the bond area. This is an important feature in the ability of the adhesive composition to form an assembled joint with large bond areas / surfaces. Furthermore, the heat generated can be mapped using IR cameras or other devices. If processing parameters are set such that it heats the entire bond surface by a very small amount and creates a low temperature rise (i.e., not affecting the properties of the adhesive,Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONfor example heating to a temperature well below a glass transition and / or a melting temperature of the adhesive composition), then an IR camera can be used to monitor the health of the joints. The dissipation of heat around cracks and defects will be different than that of the healthy joint. Thus, a combination of low-grade electromagnetic excitation / heating with thermal interrogation (e.g., via an IR camera) can be used to non-invasively monitor joint integrity and to determine when joint repair or (partial) replacement is necessary.

[0090] Remote electromagnetic activation / heating of the adhesive composition can be used for bonding / joining / assembly, dis-assembly and repair. The disclosed adhesive composition provides the ability to perform in-situ repair, e.g., heating the TP adhesive just enough to close any cracks, or micro-degradation, thus refreshing the adhesive to a state as if it were in a new, freshly assembled part.

[0091] Figures 1-5 below generally illustrate an adhesive composition 10 as well as a corresponding part 20 incorporating the adhesive composition 10, for example as a standalone part 20 or in various methods for assembling, disassembling, and / or repairing the part 20. The adhesive composition 10 includes a polymer matrix 12 throughout which electromagnetically excitable, ferromagnetic carbon particles (FMCPs) 14 are distributed (e.g., homogeneously or substantially homogeneously distributed). The polymer matrix 12 can include a thermoplastic polymer (e.g., thermoplastic polymer adhesive or matrix), a thermoset polymer, or a blend of at least one thermoplastic and at least one thermoset polymer. The FMCPs 14 can be nanoparticles and / or microparticles, and the adhesive composition 10 can include more than one type of FMCP (e.g., one type, two or more types, for example two, three, or four different types of FMCPs), where different types can be based on different materials, shapes, and / or (average) sizes, etc. of the FMCPs. As described in more detail below, the FMCPs 14 are formed from suitable materials so that they can permit targeted, remote heating of the polymer matrix 12 (e.g., a thermoplastic or other component thereof including the FMCPs) using non-contact electromagnetic methods such as eddy current induction heating by directed corresponding electromagnetic radiation into the adhesive composition 10 where the FMCPs 14 absorb the radiation and convert it to thermal energy. In addition to providing a means for non-contact heating, the FMCPs 14 also can serve as a composite reinforcement (e.g., depending on shape, size, and material of the FMCPs 14) for the matrix 12 to improve the mechanical properties of the adhesive composition 10, in particular as incorporated into an assembled part 20.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0092] The specific thermoplastic polymer (or combination of polymers in admixture) used for the matrix 12 is not particularly limited and can include any thermoplastic polymer adhesive materials known in the art. The thermoplastic polymer is generally in a solid state at normal usage temperatures of the final part 20 into which it will be incorporated. For example, the glass transition temperature and / or the melting temperature of the thermoplastic polymer is such that the thermoplastic polymer is in a solid state at a temperature ranging from 10°C or 20qC to 30 °C, 40 °C, or 50 °C (e.g., or lower; such as at about 10 °C, 20°C, 25°C, 30 °C, 40qC, or 50°C or lower). For example, the glass transition temperature and / or the melting temperature of the thermoplastic polymer can be at least 50 °C, 100‘C, 150 °C, 200 °C, or 250 °C and / or up to 100 °C, 150^, 200 °C, 300 °C or 400 °C independently. Examples of suitable thermoplastic polymers include polyamides (nylons; such as polyamide- / nylon-6 or 66), polyesters, polyurethanes (e.g., including polyester and / or polyether soft segments), acrylonitrile-butadiene-styrene (ABS) copolymers, styrene block copolymers (e.g., styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene / butylene-styrene (SEBS), styrene-ethylene / propylene (SEP)), polycarbonates, polyolefins (e.g., polyethylene (low-density LDPE, high-density HDPE), polypropylene), ethylene-vinyl acetate copolymers, and / or ethylene-acrylate copolymers, for instance as single polymers or in admixture.

[0093] The thermoplastic polymer can be present as a substantial portion of the matrix 12. For example, the thermoplastic polymer forming the matrix 12 can be present in the adhesive composition 10 in an amount ranging from 50 wt.% to 99.9 wt.%. More generally, the thermoplastic polymer forming the matrix 12 can be present in the adhesive composition 10 in an amount of at least 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.%, 90 wt.%, 95 wt.%, or 98 wt.% and / or up to 80 wt.%, 90 wt.%, 95 wt.%, 98 wt.%, 99 wt.%, 99.5 wt.%, or 99.9 wt.%.

[0094] The specific thermoset polymer (or combination of polymers in admixture) used for the matrix 12 is not particularly limited and can include any thermoset polymer materials known in the art. Examples of suitable thermoset polymer include thermoset epoxy resins, thermoset (meth)acrylate resins, and thermoset polyurethane resins, for instance as single polymers or in admixture. The thermoset polymer can be present as a substantial portion of the matrix 12. For example, the thermoset polymer forming the matrix 12 can be present in the adhesive composition 10 in an amount ranging from 50 wt.% to 99.9 wt.%. More generally, the thermoplastic polymer forming the matrix 12 can be present in the adhesive composition 10 in an amount of at least 50 wt.%, 60 wt.%, 70 wt.%, 80 wt.%, 90 wt.%, 95 wt.%, or 98 wt.% and / or up to 80 wt.%, 90 wt.%, 95 wt.%, 98 wt.%, 99 wt.%, 99.5 wt.%, or 99.9 wt.%.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0095] In embodiments, the polymer matrix 12 can include at least one thermoplastic polymer and at least one thermoset polymer, for example with the FMCPs 14 being distributed throughout one or both of the thermoplastic polymer matrix and the thermoset polymer matrix. Upon curing of the matrix 12 components (e.g., crosslinking of the thermoset polymer in the presence of the thermoplastic polymer and FMCPs), the reversibility of the thermoplastic adhesive composition can be added or imparted to the thermoset-containing matrix 12. Inclusion of the thermoplastic and FMCP can toughen the matrix 12 and can allow for healing of fatigue-induced damage (e.g., internal cracks, voids, etc. that can be internally filled or repaired by heating and flowing the thermoplastic portion of the matrix 12). The matrix 12 can include any distribution between the thermoplastic component(s) and the thermoset component(s), such as at least and / or up to 1 , 2, 5, 10, 20, 30, 40 ,50, 60, 70, 80, 90, 95, 98, or 99 wt.% and ranges therebetween for the thermoplastic component(s) or the thermoset component(s), relative to the total matrix.

[0096] As described above, the FMCPs 14 are able to absorb electromagnetic radiation and convert it to thermal energy, thus permitting targeted, remote heating of the polymer matrix 12 using non-contact electromagnetic methods such as eddy current induction heating by directing corresponding electromagnetic radiation into the adhesive composition 10. A variety of conventional materials are suitable for their ability to absorb and convert electromagnetic radiation, and such materials can include metal-containing materials, for example being partially, completely, or substantially completely formed from metals, metal alloys, and metallic compounds such as metal oxides. Examples of suitable metals include iron (e.g., in the form of oxides such as Fe2Os and / or FesC ) and aluminum (e.g., in the form of oxides such as AI2O3). Metal-containing materials are particularly suited for absorption of electromagnetic radiation from a variable magnetic field, which in turn generates electromagnetic induction heating within the metal-containing material. The metal-containing materials can be used as the nanoparticle 14A component of the FMCPs 14.

[0097] The FMCPs 14 can be nanoparticles and / or microparticles. For example, nanoparticle FMCPs 14, or the carbon-containing substrate 14B thereof, can have a size ranging from 1 nm to 1000 nm, such as at least 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 50 nm, or 100 nm and / or up to 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 500 nm, or 1000 nm. The nanoparticle sizes can represent a diameter or equivalent diameter of a granular, spherical, or semi-spherical nanoparticle, a thickness of a platelet-shaped nanoparticle, or a length or diameter of a rod-shaped nanoparticle. Similarly, microparticle FMCPs 14, or the carbon-containing substrate 14B thereof, can have a size ranging from 1 pm to 100 pm, such as at least 1 pm, 2 pm, 5 pm, 10 pm, or 20 pm and / or up to 10 pm, 20 pm, 50 pm, or 100 pm.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONThe microparticle sizes can represent a diameter or equivalent diameter of a granular, spherical, or semi-spherical microparticle, a diameter of a platelet-shaped microparticle, or a length or diameter of a rod-shaped microparticle. The ferromagnetic nanoparticles 14A on the FMCPs 14 typically range from about 5-25 nm in diameter or size, for example at least 5, 7, 10, 12, or 15 nm and / or up to 6, 8, 10, 12, 15, 20, or 25 nm. The size of the nanoparticles 14A can represent a diameter or equivalent diameter of a granular, spherical, or semi-spherical nanoparticle. For either nanoparticles or microparticles, the foregoing ranges can represent a size range for a particle size distribution, or a range for an average (weight-, number-, or volume-average) size for a particle size distribution. Some FMCPs 14 can have nano- and micro-particle characteristics dimensions. For example, platelet-shaped FMCPs 14, or the carbon-containing substrate 14B thereof (e.g., exfoliated graphite nanoplatelets), can have a micrometer-scale diameter or equivalent diameter and a nanometer-scale thickness.

[0098] The FMCPs 14 can be present in any desired amount in the adhesive composition 10, taking into consideration a loading level that is sufficient to absorb electromagnetic radiation and heat the surrounding polymer matrix 12 to a desired temperature. Generally, a higher loading of FMCPs 14 corresponds to higher heat transfer rates and / or higher peak temperatures given a particular level of excitation energy for the incident electromagnetic radiation. A desirable achievable peak temperature in the matrix 12 can be selected based on the polymer(s) forming the matrix such that the peak temperature is high enough (e.g., above the glass transition and / or melting temperature of the thermoplastic polymer) to make a thermoplastic polymer in the matrix flowable, whether on its own or under an applied pressure or force. Similarly, the peak temperature in the matrix 12 during normal use should be less than any thermal degradation temperature of the polymer(s) in the matrix 12.Further, the amount of FMCPs 14 can be selected in view of any desirable mechanical properties imparted by the FMCPs 14 to the matrix 12 as type of composite reinforcement. Suitably, the FMCPs 14 are present in the adhesive composition 10 in an amount ranging from 0.1 wt.% to 20 wt.%, for example at least 0.1 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 5 wt.%, 6 wt.%, 8 wt.%, or 10 wt.% and / or up to 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.%, 10 wt.%, 12 wt.%, 15 wt.%, or 20 wt.%. For example, the FMCPs 14 can be present in amounts from 2 wt.% to 20 wt.%, 5 wt.% to 15 wt.%, 6 wt.% to 12 wt.%, or 8 wt.% to 10 wt.% relative to the adhesive composition 10, such as in amounts providing synergistic benefits of rapid and / or sufficiently high-temperature heating combined with advantageous mechanical properties for the composite adhesive composition 10. The foregoing amounts and ranges can apply independently either to all FMCPs 14 present in the matrix 12 or the individual types ofAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONFMCPs 14 present in the matrix 12 (e.g., when there are two or more different kinds of FMCPs 14 present in the matrix 12).

[0099] In some embodiments, the FMCPs 14 can include a chemical functionalization moiety for compatibilization with the thermoplastic polymer of the matrix 12 to promote mixing, homogeneous distribution, and / or adhesion between the two composite phases. The chemical functionalization moiety can be incorporated into or onto one or both of the ferromagnetic nanoparticles 14A and / or carbon-containing substrate 14B of the FMCPs. Enhancements in mechanical, thermal, and / or damage-resistance properties offered by addition of the FMCPs 14 in the thermoplastic polymer of the matrix 12 can be further enhanced by chemical functionalization (e.g., creating chemical compatibility between the matrix polymer(s) and FMCPs 14). For example, the FMCPs 14 can include a surface compatibilizing agent which is covalently bonded or otherwise bound (e.g., as an adsorbed or absorbed coating) to the surface of the FMCPs 14 and which contains the same, similar, or otherwise chemically compatible functional groups relative to the thermoplastic polymer matrix in the adhesive composition. For example, compatibilizing functional groups can include amide, amine, hydroxy, ester, ether, ketone, urethane, aliphatic hydrocarbon, aromatic hydrocarbon, etc. Examples of specific compatibilizing functional groups include aliphatic epoxy (AE), phase-separated carboxyl-terminated acrylonitrile butadiene rubber (CTBN), and styrene-butadiene-methyl-methacrylate (SBM) triblock, which can be useful with carbon-based FMCPs 14 (e.g., graphene nanoplatelets or otherwise) and / or metalbased FMCPs 14 (e.g., iron-based material such as ferromagnetic nanoparticles or otherwise).

[0100] In some embodiments, the adhesive composition 10 can further include one or more additives common for thermoplastic adhesives. For example, the composition 10 can include one or more of tackifying resins, waxes, plasticizers, antioxidants, ultraviolet stabilizers, colorants, biocides, flame retardants, antistatic agents, and fillers (e.g., calcium carbonate, clays or nanoclays, talc, silica, etc.). Such additives can be included in amounts ranging from 0.5 wt.% to 40 wt.% (e.g., at least 0.5 wt.%, 1 wt.%, 2 wt.%, 5 wt.%, or 10 wt.% and / or up to 5 wt.%, 10 wt.%, 20 wt.%, 30 wt.%, or 40 wt.%), where such amount ranges can apply independently to all additives combined or to different types of additive individually.

[0101] In addition to illustrating the adhesive composition 10 in its various embodiments as described above, Figure 1 further illustrates an assembled part 20 incorporating the adhesive composition 10 in a finished product. The adhesive composition 10 can be used toAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONfixedly but removably join (i.e., with application of electromagnetic radiation-induced heating) to substrates 22 and 24 at a joint interface 21. As illustrated in Figure 1 , a first surface 22A (e.g., of the first substrate 22 or otherwise) and a second surface 24A (e.g., of the second substrate 24 or otherwise) are both bonded to the adhesive composition 10 at the joint interface 21 while the composition 10 is in a solid state. Although illustrated as two separate structures, the first and second surfaces 22A, 24A can be portions of the same or different / separate substrates. For example, as particularly illustrated in Figure 1 , the first surface 22A is a surface of the first substrate 22 and the second surface 24A is a surface of the second substrate 24 which is separate or otherwise discontinuous from the first substrate 22 (e.g., two separate substrate pieces to be joined in the assembled part 20). In another embodiment, the first and second surface 22A, 24A are surfaces of a single substrate (e.g., two separate surfaces of a single substrate piece that curve or otherwise wrap around to be joined together).

[0102] The materials forming the surfaces 22A, 24A and / or substrates 22, 24 are not particularly limited and generally can include any desired material to which the adhesive composition 10 will adhere or bond upon cooling or solidifying to a solid state. In some embodiments, the surfaces 22A, 24A and / or substrates 22, 24 are formed from the same materials. In some embodiments, the surfaces 22A, 24A and / or substrates 22, 24 are formed from different materials. Examples of suitable materials for the surfaces 22A, 24A and / or substrates 22, 24 include a metal material (e.g., steel, aluminum, magnesium), a polymeric material (e.g., composite material such as a glass or other fiber-reinforced polymer, glass-mat thermoplastic composite, sheet-molding compound composite), and a non-metallic material. In a particular embodiment where the surfaces 22A, 24A and / or substrates 22, 24 are formed from different materials, one is formed from a metal material and the other is formed from a polymeric material or other non-metallic material.

[0103] Figure 1 illustrates an assembled part 20 using the adhesive composition 10 in particular for an in-plane or lap joint, but the adhesive composition 10 can be used to form a bond and seal at any type of structural joint interface 21. Moreover, any combinations / types of substrates / adherends can be used. As illustrated in Figure 2, suitable joint interfaces 21 can include (a) a lap joint, (b) a double-lap joint, (c) a butt joint, (d) a scarf joint, (e) a corner / L-joint, and (f) a T- / Pi-joint.

[0104] The distance between the first and second surfaces 22A, 24A in the assembled part is not particularly limited. In some embodiments, the distance can be at least 10 pm, 20 pm, 50 pm, 100 pm, or 200 pm and / or up to 100 pm, 200 pm, 500 pm, or 1000 pm.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONAlternatively or additionally, the distance between the first and second surfaces 22A, 24A can be selected to be a constant separation distance. One manner of forming the part 20 with the constant separation distance is to place one or more spacers between the first surface 22A (or first substrate 22) and the second surface 24A (or second substrate 24) (not shown) when the part 20 is being assembled and engaging or compression forces are being applied to the two opposing surfaces 22A, 24A, which spacers have a thickness corresponding to the desired constant separation distance.

[0105] Figure 3 illustrates a method of assembling the part 20 using the adhesive composition 10 according to the disclosure. As shown in panel (A), the adhesive composition 10 is contacted with the first surface 22A and the second surface 24A at the location of the eventual joint interface 21 of the part 20 to be assembled, for example with the application of an engaging force or pressure 42 at one or both of the surfaces 22A, 24A (or corresponding substrates 22, 24). As shown in panel (B), electromagnetic radiation 32 from an electromagnetic radiation source 30 (e.g., electromagnet or electromagnetic induction source) is directed to the adhesive composition 10 to heat the composition 10 and to transform the composition 10 to flowable or moldable state. For example, the radiation 32 is applied for a time sufficient and / or at an intensity sufficient to indirectly heat the FMCPs 14, thereby raising the temperature of the polymer in the matrix 12 sufficiently high to transform a thermoplastic polymer matrix 12 component to a flowable or moldable state, such as heating to a temperature at or above the glass transition temperature or the melting temperature of the thermoplastic polymer. As illustrated, the engaging force or pressure 42 can be applied to one or both of the surfaces 22A, 24A when heating the adhesive composition 10, thereby causing the thermoplastic polymer to expand radially / laterally outwardly and contact an increased surface area at the joint interface 21 (e.g., an increased area relative to the adhesive composition 10 prior to heating via the electromagnetic radiation 32). The degree of heating of the adhesive composition 10 is suitably limited or controlled (e.g., via radiation time and / or intensity, FMCPs 14 loading amount) to a degree sufficient avoid or prevent heat-induced damage to one or both of the surfaces 22A, 24A (or corresponding substrates 22, 24). For example, the peak or maximum temperature of the adhesive composition 10 is controlled to be below a damage threshold temperature for the surfaces 22A, 24A. In some cases, the electromagnetic radiation heating can be cycled between high and low intensities or application times to avoid damage. After sufficient heating and contact time while the composition 10 is in the flowable or moldable state, application of the electromagnetic radiation 32 is halted and the adhesive composition 10 is cooled (e.g., passive cooling / heat dissipation to the environment; active / forced cooling),Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONthereby transforming the adhesive composition 10 to a solid state in contact with and bonded to the surfaces 22A, 24A surface at the joint interface 21 and creating the assembled part 20.

[0106] The specific type of electromagnetic radiation 32 is not particularly limited, but it is generally selected to be complementary to the FMCP 14 materials such that it is a type of radiation that is absorbed as converted to thermal energy within the FMCPs 14 for subsequent heat transfer to the polymer matrix 12. In embodiments, the electromagnetic radiation 32 includes a variable magnetic field generating electromagnetic induction heating within the FMCPs 14 (e.g., the ferromagnetic nanoparticles 14A thereof). Such electromagnetic radiation 32 for induction heating can be applied at an excitation or field frequency of about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, or 1500 kHz and ranges therebetween. Alternatively or additionally, the electromagnetic radiation 32 for induction heating can be applied at a field strength or flux density of at least 0, 1 , 2, 3, 4, 5, 7, 10, or 12 kA / m and / or up to 4, 8, 12, 16, or 20 kA / m. Selection of the excitation frequency can be used to increase, decrease, or otherwise the heating rate of the matrix 12, for example resulting from direct induction heating of the ferromagnetic nanoparticles 14A, conduction heating from the nanoparticles 14A into and through the carbon-containing particulate substrate14B and surrounding matrix 12. In embodiments, the electromagnetic radiation 32 uses a variable magnetic field generating electromagnetic induction, and / or does not include or is otherwise free from microwave radiation (e.g., which could otherwise directly heat the carbon-containing particulate substrate 14B).

[0107] Figure 4 illustrates a method of disassembling the part 20 using the adhesive composition 10 according to the disclosure. As shown in panel (A), the assembled part 20 is provided in an initial state with the adhesive composition 10 in a solid state and in contact with and bonded to the first surface 22A and the second surface 24A at the joint interface 21 of the assembled part 20. As further shown in panel (A), electromagnetic radiation 32 is directed to the adhesive composition 10 to heat the composition and to transform it to a flowable or moldable state (e.g., thereby de-bonding the adhesive composition 10 with one or both of the first and second surfaces 22A, 24A). As shown in panel (B), the first surface 22A and the second surface 24A can be separated from each other, for example with application of a disengaging or pulling force 44 on at least one of the surface 22A, 24A (or substrates 22, 24) such that surfaces 22A, 24A are no longer in contact with each other via the composition 10 (e.g., one or both of the surfaces 22A, 24A can be in contact with a portion of the composition 10, but the composition 10 does not provide a continuous bondAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONbetween the two surfaces 22A, 24A. The two surfaces 22A, 24A (or substrates 22, 24) are disengaged, for example without causing any damage or substantial damage to the two surfaces 22A, 24A (or substrates 22, 24).

[0108] Disassembly of the part 20 can be performed, for example, to repair or provide maintenance to the one or more of the part components. As illustrated, for instance, the second surface 24A / substrate 24 can include a defect 28 (e.g., a void area / volume such as crack, crevice, hole, breakage, or other microdegradation structure) resulting from continuous use / cycle fatigue of the part 20 over time or from a single damaging event (e.g., a one-time impact, stress, or strain). For example, in some cases, after disassembly, the foregoing assembly method can be performed to re-bond the first surface 22A and the second surface 24A at the joint interface 21 , such as after performing some maintenance or repair on a component of the part 20 itself (e.g., to repair the defect 28) or another part accessible after disassembly of the joined part 20. As another example as shown in panels (C) and (D) of Figure 3, a third surface 26A (or third substrate 26) can be provided as a replacement part, such as for the second surface 24A (or second substrate 24). Then, the foregoing assembly method can be performed to bond the first surface 22A and the third surface 26A at the joint interface 21 , such as to assemble the part 20 after disassembly with the replacement part. Similarly, a replacement part for the first surface 22A also could be used and replaced (e.g., a fourth surface or substrate, not shown). Suitably, the third surface 26A (or corresponding third substrate 26) has the same shape and / or is formed from the same material as the second surface 24A (or second substrate 24), such as where the third surface 26A is a replacement part for the second surface 24A in its original form when originally assembled and without damage or wear. In some embodiments, additional, supplemental, or replacement adhesive composition 10 can be used to re-bond the first surface 22A and second or third surface 24A, 26A, for example when some or all of the adhesive composition 10 in the original assembled part 20 is lost when disassembling the part 20 (e.g., when some adhesive composition 10 remains on the second surface 24A that is replaced by the third surface 26A).

[0109] Figure 5 illustrates a method of repairing an assembled (but damaged) part 20 using the adhesive composition 10 according to the disclosure. As shown in panel (A), the assembled part 20 includes the adhesive composition 10 in a solid state and in contact with and bonded to the surfaces 22A, 24A at the joint interface 21 including a defect 28, for example resulting from continuous use / cycle fatigue of the part 20 over time or from a single damaging event (e.g., a one-time impact, stress, or strain). One or more defects 28 (e.g., a void area / volume such as crack, crevice, hole, breakage, or other microdegradationAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONstructure) can be present in the first surface 22A / substrate 22, the second surface 24A / substrate 24, and / or the adhesive composition 10 (e.g., a void or other internal defect etc. in the matrix 12). As illustrated in Figure 5 by way of example, the second surface 24A / substrate 24 includes the defect 28. As shown in panel (B), electromagnetic radiation 32 is directed to the adhesive composition 10 to heat the composition and to transform it to a flowable or moldable state. Once the thermoplastic polymer of the matrix 12 has been sufficiently heated, the adhesive composition 10 (e.g., thermoplastic polymer component thereof) can flow into the defects 28, thereby at least partially filling voids, cracks, etc. to repair part 20 structures at the joint interface 21. While in some cases the heated adhesive composition 10 can be flowable under gravity into the defects 28, in other cases it is desirable to apply pressure or other compression / engaging force 42 to one or both of the surfaces 22A, 24A (or substrate 22, 24) when heating the adhesive composition 10, thereby causing the thermoplastic polymer to expand, contact an increased surface area at the joint interface 21 , and flow into the defect 28 void areas (e.g., at least partially, substantially completely, or completely filling the defect 28 void areas). Once the damaged part 20 has undergone heating and any desired compression for a sufficient period for repair (e.g., to result in a desired level of defect 28 void filling), application of the electromagnetic radiation 32 is halted and the adhesive composition 10 is cooled (e.g., passive cooling / heat dissipation to the environment; active / forced cooling), thereby transforming the composition 10 back to a solid state in contact with and bonded to the surfaces 22A, 24A as well as the defect 28 void areas or volumes at the joint interface 21 (e.g., at least partially, substantially completely, or completely bonded to the defect 28 void surfaces). A part 20 with a joint interface 21 repaired in this manner can recover a substantial amount of their original strength, for example having a tensile (shear) strength of at least 80%, 85%, 90%, 95%, or 98% and / or up to 90%, 95%, 98%, 99% or 100% relative to that of a corresponding pristine part 20 as originally formed (e.g., with new substrates 22, 24 and new adhesive composition 10), for example where the part 20 / joint interface 21 prior to repair has a (damaged) tensile (shear) strength of at least 20%, 30%, 40%, 50%, or 60% and / or up to 30%, 50%, 60%, 70% or 80% relative to that of the corresponding pristine part 20 as originally formed.

[0110] Figure 6 illustrates a variable frequency induction applicator (VFIA) 50 according to the disclosure. The VFIA 50 generally includes a capacitor array coupled with a high-power linear amplifier (e.g., producing 1000 W of quasi linear Class AB power over a frequency range from 10 kHz - 2 MHz.) that creates uniform fields of specific flux density at each discrete frequency setting. The VIFA can generate electromagnetic radiation for induction heating at excitation frequency generally ranging from 100 kHz to 2 MHz, forAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONexample at least and / or up to 100, 200, 400, 700, 1000, 1200, 1500, or 2000 kHz and ranges therebetween, based on the number and specific type of capacitors used in the array. Data collection for a sample (an aqueous or other liquid dispersion of FMCPs) being tested by the VFIA is accomplished using differential sensing coils for hysteresis loops and an (optical) thermocouple for measurement of the sample heating rate.

[0111] As illustrated in Figure 6, the VFIA 50 includes a capacitor array 100 including a plurality of capacitors 110, for example arranged in parallel with a total of “n” capacitors 110 (i.e., i = 1 to n as illustrated). The parallel capacitor array 100 can be modeled as an equivalent parallel LCC resonant circuit. The capacitors 110 can have the same or different capacitance values, and specific capacitance values can be selected to provide a desired range of excitation frequencies for the VFIA 50. The VFIA 50 further includes a plurality 200 of AC contactors 210, which can be independently open or closed, between adjacent capacitors 110. As illustrated, the VFIA 50 includes “n” pairs of AC contactors 210 (i.e., i = 1 to n). The AC contactors 210 are selectively controllable to electrically couple the plurality of capacitors 210 in one or more arrangements to control the effective capacitance values of the equivalent parallel LCC resonant circuit and the output excitation frequency. The VFIA 50 further includes a plurality 300 of relays 310 electrically coupled to respective AC contactors 210 such that a state of each AC contactor 210 is responsive to a state of its respective relay 310 (e.g., open or closed). The VFIA 50 further includes an applicator coil 400 coupled to the capacitor array 100, for example with one electrical connection at the first capacitor 110 and one electrical connection at the last (or nth) capacitor 110. The applicator coil 400 generates an electromagnetic field in response to an alternating current (AC) signal applied to the capacitor array 100, for example being delivered by an AC power source 600 at the first capacitor 110. The applicator coil 400 can include any suitable number of turns, for example 6, 7, 8, 9, 10, 11 , or 12 turns. The applicator coil 400 be fluid-cooled (e.g., water-cooled), such as a coil 400 in the form of a tube with internal coolant fluid flow channels. In an illustrative embodiment, the VFIA 50 used in the examples below includes seven capacitors 110 in parallel with capacitance values of 50 nF (i=1 ; first capacitor), 50 nF (i=2), 100 nF (i=3), 100 nF (i=4), 100 nF (i=5), 50 nF (i=6), 50 nF (i=7; last or nthcapacitor), which in turn provides selectable excitation frequencies of 197, 400, 530, 669, 795, 937, 1075, 1191, 1253, and 1389 kHz. The VFIA 50 further includes processor 500 configured to control the plurality of relays 310 to control one or more properties of the electromagnetic field generated by the applicator coil 400. The processor (or computer) 500 can include one or more computing components such as a microprocessor, memory, remote or local storage,Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONwired or wireless network connections, software for controlling the VFIA 50 components, data storage, and data analysis, etc.

[0112] In embodiments, the VFIA 50 further includes differential vibrating-sample magnetometer (VSM) coils 402 positioned in the applicator coil 400 for hysteresis loop measurement. The VFIA 50 can further includes a scout coil 404 (e.g., for field parameter verification), with both coils 402, 404 being coupled to a suitable meter (not shown), for example a multichannel oscilloscope. The coils and meter are configured to measure the one or more properties of the generated electromagnetic field. The processor 500 is electronically coupled to the meter, and is configured to control the relays 310 based on differences between the one or more measured properties of the generated electromagnetic field, and one or more desired properties of an electromagnetic field. The VFIA 50 can include a sample holder 410, typically a non-conductive, adjustable holder positioned within the applicator coil 400 around the VSM and scout coils 402, 404, such that the sample holder 410 can receive a sample 420 to be analyzed with the coils 400, 402, 404 around the sample 420. The VFIA 50 can include a thermocouple 430 configured to measure temperatures of the sample 420 positioned in the applicator coil 400. The processor 500 is electronically coupled to the thermocouple 430, and is configured to collect one or more temperature measurements from the thermocouple 430 responsive to controlling the relays 310 to cause the applicator coil 400 to generate one or more electromagnetic fields. The processor 500 also can be configured to control the relays 310 over time to measure energy absorption of the sample 420 responsive to one or more of field strength, field frequency, or duration of the electromagnetic field.Examples

[0113] The examples illustrate the disclosed apparatus, compositions, articles, and methods, but are not intended to limit the scope of any claims thereto. In particular, the examples illustrate the synthesis and testing of electromagnetically excitable, ferromagnetic nanoparticles (FMNPs) and electromagnetically excitable, ferromagnetic carbon particles (FMCPs) according to the disclosure. The nanoparticles were tested for their heating and hysteresis properties when subjected to electromagnetic induction fields of varying field frequencies using a variable frequency induction applicator (VFIA) as described above and illustrated in Figure 6.

[0114] Electromagnetically Excitable, Ferromagnetic Nanoparticles (FMNPs): FMNPs were produced with a nearly mono-disperse particle size distribution having an average size of about 10 nm, which is directly above the superparamagnetic domain limit of FesC . TheAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONFesC FMNPs were formed by pyrolysis of organometallic iron acetylacetonate [Fe(acac)3] using oleic acid and oleylamine as capping ligands in 1 -octadecene using trioctylphosphine oxide as a terminating agent. The size and eccentricity of the resulting FMNPs was controlled by modifying dwell times at nucleation temperature (about 200 °C) and at growth temperatures (about 260 °C or greater).

[0115] Briefly, iron acetylacetonate [Fe(acac)3] and trioctylphosphine-oxide [TOPO] at a 10:1 molar ratio were loaded into a reactor containing 1 :20 ratio of molar salts to ml octadecene. The reactor was purged and filled with an argon mixture, brought to 120°C, and a 4:10 molar ratio of oleic acid and oleylamine was added. The reactor was brought to 200 °C and held for about 30 minutes to promote nucleation, and then the reactor was brought to 260 °C or 310 °C to promote FMNP growth and refluxed for 2 hours under mixing before cooling to room temperature. The product was precipitated with ethanol and hexane and yielded ligand stabilized spherical Fe3O4 nanoparticles with average diameters ranging from about 9.5 nm to 16 nm. The product can be isolated as is or further functionalized with silane via ligand exchange.

[0116] Sample BP2 (FMNP) tested below was formed at a nucleation temperature of 200 °C (0.5 hr dwell time) followed by a growth temperature of 310 °C (2 hr dwell time), resulting in FesC FMNPs having an average diameter of 9.5 nm and an average eccentricity of 0.73.

[0117] Electromagneticallv Excitable, Ferromagnetic Carbon Particles (FMCPs): FMCPs according to the disclosure were formed via solvothermal decomposition and reduction. A graphene oxide (GO) was reduced to form reduced graphene oxide (rGO) as a carbon-containing substrate while simultaneously precipitating FesO4 ferromagnetic nanoparticles adhered to the rGO substrate. The Fe3O4 nanoparticles were formed by pyrolysis decomposition of organometallic iron acetylacetonate [Fe(acac)3] using triethylene glycol as a solvent in an inert atmosphere.

[0118] Briefly, GO was produced via a modified Hummers method as generally known in the art. The GO and [Fe(acac)3] reactants were combined in GO:[Fe(acac)3] ratios of 1 :1 , 1 :2, 1 :3, and 1 :4 (w / w) in about 60 ml of triethylene glycol. The mixture was homogenized via sonication and then transferred to a polytetrafluoroethylene (PTFE or TEFLON)-lined stainless steel autoclave to react at 200 °C for 12 hours, thereby reducing the GO to rGO and precipitating Fe3O4 nanoparticles thereon to form the FMCPs (or FMGnPs). The resulting FMCP material was collected, washed with ethanol, and vacuum-dried at 60 °C for 24 hours.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0119] Samples SDR1 , SDR2, SDR3, and SDR4 (FMCPs) tested below were formed at GO:[Fe(acac)3] ratios of 1 :1 , 1 :2, 1 :3, and 1 :4 (w / w), respectively, resulting in rGO surface- adhered Fe3O4 FMNPs having an average diameter of about 12 nm with individual particles ranging in diameter from about 8 nm to 15 nm.

[0120] FMCP Materials and Compositions: While graphene oxide (GO) is more reactive and easier to disperse than graphene (G), it comes at the cost of thermal / electrical conductivity and mechanical properties. Pristine graphene is one of the strongest materials in the world, but is difficult to react with due to the stability of the carbon lattice on the basal planes. Utilizing graphene oxide (rGO) strikes a balance between ease of dispersion, thermal conductivity, mechanical properties. Table 1 below provides a comparison various properties of GO, rGO, and G. Table 2 below provides the results of an atomic composition analysis of FMCP Samples SDR1 and SDR2.Table 1. Comparison of Graphene MaterialsProperty GO rGO GC, O Element (%) C (-62-65%), C (-77-87%), C (-99%), O (-)O (-35-38%) O (-13-22%)Crystal Size 21.14 nm 15.13-15.95 nm 175.49 nm d Spacing 0.96 nm 0.36 nm 0.33 nm Plane Size 1-2 pm 1-7 pm 0.5-5 pm Number of Layers 1, 2, or 3 1, 2, or 3 3, 4, or 5 Layer Thickness 0.76-0.84 nm 0.35-0.36 nm 0.34 nm Stack Thickness in 1.00-1.20 nm 125-175 nm 180-230 nm Water DispersionRaman (ID / IG) Ratio 0.79 1.10-1.16 0.25Table 2. Atomic Composition of FMCP SamplesSample C O N s Fe SDR1 78.6% 18.2% 0.6% 0.8% 1.8%SDR2 69.5% 24.8% 0.0% 0.1% 5.6%

[0121] Variable Frequency Induction Applicator (VFIA) Analysis: Samples SDR1 -SDR4 (FMCPs) and BP2 (FMNP) were formulated as aqueous dispersions and were tested for their heating and hysteresis properties when subjected to electromagnetic induction fields of varying field frequencies and varying field strengths (or flux densities) using the VFIA as described above and illustrated in Figure 6.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION

[0122] Figure 7 is a graph illustrating heating (AT) as function of heating time and electromagnetic induction excitation frequency for (A) electromagnetically excitable, ferromagnetic carbon particles (Sample SDR3) according to the disclosure and (B) electromagnetically excitable, ferromagnetic nanoparticles (Sample BP2). The illustrated heating curves were generated at a 10 kA / m field strength for field frequencies ranging from 197 kHz to 1389 kHz (full sweep). The results indicate that binding the Fe3O4 nanoparticles to rGO carbon substrate (i.e., FMCPs) delays heating relative to the FesC nanoparticles alone (i.e., FMNPs), for example matrix heating in a corresponding composite material including the FMCPs or FMNPs therein. The heating curve for Sample SDR3 (panel A) showed essentially little to no heating for about 15-20 seconds, followed by an exponential heating ramp transitioning to an eventual linear increase in temperature (or constant heating rate). In contrast, the heating curve for Sample BP2 (panel B) showed an immediate exponential heating ramp as the FMNPs saturate to the curie temperature, and then transitioning to an eventual linear increase in temperature (or constant heating rate). The delayed heating profile of the FMCPs is desirable, because it prevents rapid, localized, high-heating zones that are capable of scorching and destroying the adhesive matrix (e.g., as can happen with FMNPs). By utilizing the carbon substrate (e.g., rGO in this example), to assist in conductive distribution of the inductively generated heat, the presence of potentially damaging high temperature gradients is reduced or eliminated via the delayed heating profile.

[0123] Figure 8 is a graph illustrating hysteresis loop area as function of electromagnetic induction excitation frequency for FMCPs (Sample SDR3) according to the disclosure. The illustrated hysteresis loop areas were generated at a 10 kA / m field strength for field frequencies ranging from 197 kHz to 1253 kHz. Similar non-zero (positive) hysteresis loop areas were observed at field strengths of about 5, 10, and 19 kA / m for field frequencies ranging from 197 kHz to 1253 kHz for Samples SDR3 and SDR4 (results not shown). These hysteresis properties demonstrate the coercivity of the FMCPs according to the disclosure, which in turn make them capable of induction heating in an electromagnetic field (i.e., in contrast to the graphene nanosheet-Fe304 hybrids of He, which do not exhibit hysteresis properties required for induction heating).

[0124] Figure 9 is a graph illustrating hysteresis loops for FMCP samples including (a) SDR1, (b) SDR2, (c) SDR3, and (d) SDR4. The illustrated hysteresis loops were generated at magnetic field strengths (H) ranging from -10,000 to 10,000 Oe at a field frequency of about 1 kHz. The hysteresis loops for the different precursor ratios showed a superparamagnetic response with a magnetic saturation (M) that increases proportionally toAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONthe iron content (or Fe3C>4 content) of the FMCPs. There was no observable remanence or coercivity due to the small particle size (about 12 nm) at this relatively small measurement frequency (about 1 kHz).

[0125] Because other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the disclosure is not considered limited to the example chosen for purposes of illustration, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this disclosure.

[0126] Accordingly, the foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the disclosure may be apparent to those having ordinary skill in the art.

[0127] All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In case of conflict, the present description, including definitions, will control.

[0128] Throughout the specification, where the compositions, processes, kits, or apparatus are described as including components, steps, or materials, it is contemplated that the compositions, processes, or apparatus can also comprise, consist essentially of, or consist of, any combination of the recited components or materials, unless described otherwise. Component concentrations can be expressed in terms of weight concentrations, unless specifically indicated otherwise. Combinations of components are contemplated to include homogeneous and / or heterogeneous mixtures, as would be understood by a person of ordinary skill in the art in view of the foregoing disclosure.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONList of Figure Elements10 adhesive composition12 polymer matrix polymer (e.g., thermoplastic and / or thermoset; thermoplastic polymer adhesive)14 electromagnetically excitable, ferromagnetic carbon particles (FMCPs) (14A ferromagnetic nanoparticles / metal-containing nanoparticle; 14B carbon-containing substrate / reduced graphene oxide nanoplatelet)20 part to be assembled, disassembled, repaired, etc.21 joint interface22, 24, 26 first, second, third substrate (22A, 24A, 26A first, second, third surface thereof) 28 cracks or defects30 electromagnetic radiation source (e.g., electromagnet)32 electromagnetic radiation42 engaging force or pressure44 disengaging or separation force50 variable frequency induction applicator (VFIA)100 capacitor array (110 capacitor)200 plurality of AC contactors (210 AC contactor)300 plurality of relays (310 relay)400 coil applicator402 VSM coil404 scout coil410 sample holder420 sample430 thermocouple500 processor

Claims

Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONWhat is claimed is:

1. A reversibly assembled part comprising:at least one substrate defining a first surface and a second surface reversibly joined at a joint interface in an assembled part;an adhesive composition in a solid state and in contact with and bonded to the first surface and the second surface at the joint interface of the assembled part, wherein the adhesive composition comprises:at least one of a thermoset polymer matrix and a thermoplastic polymer matrix, andelectromagnetically excitable, ferromagnetic carbon particles (FMCPs) distributed throughout the at least one of the thermoset polymer matrix and the thermoplastic polymer matrix, each FMCP comprising a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate.

2. The reversibly assembled part of claim of claim 1 , wherein the FMCPs comprise ferromagnetic graphene nanoparticles (FMGnPs) in which:the ferromagnetic nanoparticles of the FMCP comprise metal-containing nanoparticles; andthe carbon-containing substrate of the FMCP comprises a graphene nanoplatelet.

3. The reversibly assembled part of claim of claim 2, wherein:the metal-containing nanoparticles comprise FesC nanoparticles; andthe graphene nanoplatelet comprises a reduced graphene oxide nanoplatelet.

4. The reversibly assembled part of claim of claim 2, wherein the FMGnPs display a saturation magnetization of non-zero value in magnetic fields of 100 kHz to 2 MHz of flux densities in excess of 5 kA / m.

5. The reversibly assembled part of claim of claim 2, wherein the FMGnPs have a non-zero hysteresis loop area in magnetic fields of 100 kHz to 2 MHz of flux densities in excess of 5 kA / m such that the coercivity of the particle defines an energy loss.

6. The reversibly assembled part of claim of claim 1 , wherein the adhesive composition is substantially free from free ferromagnetic nanoparticles.

7. The reversibly assembled part of claim of claim 1 , wherein the adhesive composition comprises the thermoset polymer matrix and the thermoplastic polymer matrix.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION8. The reversibly assembled part of claim of claim 1 , wherein:the adhesive composition comprises the thermoplastic polymer matrix; and the thermoplastic polymer is selected from the group consisting of polyamides, polyesters, polyurethanes, acrylonitrile-butadiene-styrene (ABS) copolymers, styrene block copolymers, polycarbonates, polyolefins, ethylene-vinyl acetate copolymers, ethyleneacrylate copolymers, and combinations thereof.

9. The reversibly assembled part of claim of claim 1 , wherein the thermoplastic polymer is in a solid state at a temperature ranging from 20 °C to 30 °C.

10. The reversibly assembled part of claim of claim 1 , wherein the thermoplastic polymer is present in the adhesive composition in an amount ranging from 50 wt.% to 99.9 wt.%.

11. The reversibly assembled part of claim of claim 1, wherein:the adhesive composition comprises the thermoset polymer matrix; andthe thermoset polymer is selected from the group consisting of thermoset epoxy resins, thermoset (meth)acrylate resins, thermoset polyurethane resins, and combinations thereof.

12. The reversibly assembled part of claim of claim 1 , wherein the electromagnetically excitable, ferromagnetic carbon particles comprise a chemical functionalization moiety for compatibilization with the thermoplastic polymer matrix.

13. The reversibly assembled part of claim of claim 1 , wherein the carbon-containing substrate is selected from the group consisting of graphite particles, exfoliated graphite nanoplatelets, carbon nanotubes, carbon fibers, carbon black, and combinations thereof.

14. The reversibly assembled part of claim of claim 1 , the electromagnetically excitable particles are present in the adhesive composition in an amount ranging from 0.1 wt.% to 50 wt.%.

15. The reversibly assembled part of claim of claim 1 , wherein the electromagnetically excitable particles comprise nanoparticles having a size ranging from 1 nm to 1000 nm.

16. The reversibly assembled part of claim of claim 1 , wherein the electromagnetically excitable particles comprise microparticles having a size ranging from 1 pm to 100 pm.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION17. The reversibly assembled part of claim of claim 1 , wherein:(i) the first surface is a surface of a first substrate; and(ii) the second surface is a surface of a second substrate separate from the first substrate.

18. The reversibly assembled part of claim of claim 1 , wherein the first surface and the second surface are surfaces of a single substrate.

19. The reversibly assembled part of claim of claim 1 , wherein the first surface and the second surface are formed from different materials.

20. The reversibly assembled part of claim of claim 1 , further comprising:(c) one or more additives selected from the group consisting of tackifying resins, waxes, plasticizers, antioxidants, ultraviolet stabilizers, colorants, biocides, flame retardants, antistatic agents, fillers, and combinations thereof;wherein the additives are present in the adhesive composition in an amount ranging from 0.5 wt.% to 40 wt.%.

21. The reversibly assembled part of claim of claim 1 , wherein the first surface and the second surface are bonded at a joint interface selected from the group consisting of a lap joint, a double-lap joint, a butt joint, a scarf joint, a corner / L-joint, and a T- / Pi-joint.

22. The reversibly assembled part of claim of claim 1 , wherein the assembled part is a vehicle component part.

23. A method for assembling a part, the method comprising:(a) contacting an adhesive composition (i) with a first surface and a second surface of at least one substrate defining the first surface and the second surface (ii) at a joint interface of a part to be assembled, wherein the adhesive composition comprises:at least one of a thermoplastic polymer matrix and a thermoset polymer matrix, andelectromagnetically excitable, ferromagnetic carbon particles (FMCPs) distributed throughout the at least one of the thermoplastic polymer matrix and the thermoset polymer matrix, each FMCP comprising a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate;(b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, wherein the electromagnetic radiation comprises a variable magnetic field generatingAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONelectromagnetic induction; and(c) removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the second surface at the joint interface.

24. The method of claim 23, wherein the electromagnetic radiation is free from microwave radiation.

25. The method of claim 23, comprising heating the adhesive composition to a limited degree sufficient avoid or prevent heat-induced damage to one or both of the first surface and the second surface.

26. The method of claim 23, further comprising applying pressure to one or both of the first surface and the second surface when heating the adhesive composition, thereby causing the thermoplastic polymer to expand and contact an increased surface area at the joint interface.

27. The method of claim 23, wherein:(i) the first surface is a surface of a first substrate; and(ii) the second surface is a surface of a second substrate separate from the first substrate.

28. The method of claim 23, wherein the first surface and the second surface are surfaces of a single substrate.

29. The method of claim 23, wherein the first surface and the second surface are formed from different materials.

30. The method of claim 23, further comprising placing one or more spacers between the first surface and the second surface, the spacers maintaining a constant specified separation distance between the first surface and the second surface.

31. The method of claim 23, wherein the first surface and the second surface are bonded at a joint interface selected from the group consisting of a lap joint, a double-lap joint, a butt joint, a scarf joint, a corner / L-joint, and a T- / Pi-joint.

32. A method for disassembling a part, the method comprising:(a) providing an assembled part according to claim 1 comprising the adhesive composition in a solid state and in contact with and bonded to a first surface and a secondAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONsurface at a joint interface of the assembled part;(b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to a flowable or moldable state, wherein the electromagnetic radiation comprises a variable magnetic field generating electromagnetic induction; and(c) separating the first surface from the second surface.

33. The method of claim 32, further comprising:(d) re-contacting the adhesive composition with the first surface and the second surface at the joint interface, directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, and removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the second surface at the joint interface.

34. The method of claim 32, further comprising:(d) providing a third surface as a replacement for the second surface (e.g., the third surface can have the same shape and / or be formed from the same material as the second surface); and(e) contacting the adhesive composition with the first surface and the third surface at the joint interface, directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, and removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface and the third surface at the joint interface.

35. The method of claim 32, wherein the electromagnetic radiation is free from microwave radiation.

36. The method of claim 32, wherein:(i) the first surface is a surface of a first substrate; and(ii) the second surface is a surface of a second substrate separate from the first substrate.

37. The method of claim 32, wherein the first surface and the second surface are surfaces of a single substrate.Atty. Docket No. 32213 / 58079B / US PATENT APPLICATION38. The method of claim 32, wherein the first surface and the second surface are formed from different materials.

39. A method for repairing a part, the method comprising:(a) providing an assembled part according to claim 1 comprising the adhesive composition in a solid state and in contact with and bonded to a first surface and a second surface at a joint interface of the assembled part, wherein the assembled part further comprises one or more defects at the joint interface;(b) directing electromagnetic radiation to the adhesive composition to heat the adhesive composition and to transform the adhesive composition to flowable or moldable state, thereby allowing the adhesive composition to flow at least partially into the one or more defects, wherein the electromagnetic radiation comprises a variable magnetic field generating electromagnetic induction; and(c) removing the electromagnetic radiation and cooling the adhesive composition, thereby transforming the adhesive composition to a solid state in contact with and bonded to the first surface, the second surface, and the one or more defects at the joint interface.

40. The method of claim 39, further comprising applying pressure to one or both of the first surface and the second surface when heating the adhesive composition, thereby causing the thermoplastic polymer (i) to expand and contact an increased surface area at the joint interface and (ii) to flow at least partially into the one or more defects.

41. The method of claim 39, wherein the electromagnetic radiation is free from microwave radiation.

42. The method of claim 39, wherein:(i) the first surface is a surface of a first substrate; and(ii) the second surface is a surface of a second substrate separate from the first substrate.

43. The method of claim 39, wherein the first surface and the second surface are surfaces of a single substrate.

44. The method of claim 39, wherein the first surface and the second surface are formed from different materials.

45. A variable frequency induction applicator (VFIA), comprising:a capacitor array including a plurality of capacitors;Atty. Docket No. 32213 / 58079B / US PATENT APPLICATIONa plurality of AC contactors selectively controllable to electrically couple the plurality of capacitors in one or more arrangements;a plurality of relays electrically coupled to respective ones of a plurality of control terminals of respective ones of the plurality of AC contactors, wherein a state of each AC contactor is responsive to a state of the respective relay;an applicator coil coupled to the capacitor array, and configured to generate an electromagnetic field responsive an alternating current (AC) signal applied to the capacitor array; anda processor configured to control the plurality of relays to control one or more properties of the electromagnetic field generated by the applicator coil.

46. The variable frequency induction applicator of claim 45, further comprising: differential vibrating-sample magnetometer (VSM) coils positioned in the applicator coil; anda meter coupled to the differential VSM coils, and configured to measure the one or more properties of the generated electromagnetic field;wherein the processor is coupled to the meter, and is configured to control the plurality of relays based on differences between (i) the one or more measured properties of the generated electromagnetic field, and (ii) one or more desired properties of an electromagnetic field.

47. The variable frequency induction applicator of claim 45, further comprising: a thermocouple configured to measure temperatures of a sample positioned in the applicator coil;wherein the processor is coupled to the thermocouple, and is configured to collect one or more temperature measurements from the thermocouple responsive to controlling the plurality of relays to cause the applicator coil to generate one or more electromagnetic fields.

48. The variable frequency induction applicator of claim 45, wherein the processor is configured to control the plurality of relays over time to measure energy absorption of a sample positioned in the applicator coil responsive to one or more of field strength, field frequency, or duration of the electromagnetic field.

49. A method for analyzing a sample, the method comprising:providing a sample comprising ferromagnetic nanoparticles (FMNPs);analyzing the sample with the VFIA of any one of claims 45 to 48 by measuringAtty. Docket No. 32213 / 58079B / US PATENT APPLICATIONhysteresis and temperature of the sample positioned in the applicator coil of the VFIA at (i) a plurality of different field frequencies and (ii) a plurality of different field strengths.

50. The method of claim 49, wherein the FMNPs comprise electromagnetically excitable, ferromagnetic carbon particles (FMCPs), each FMCP comprising a plurality of ferromagnetic nanoparticles adhered to a carbon-containing substrate.

51. The method of claim 50, wherein the FMCPs comprise ferromagnetic graphene nanoparticles (FMGnPs) in which:the ferromagnetic nanoparticles of the FMCP comprise metal-containing nanoparticles; andthe carbon-containing substrate of the FMCP comprises a graphene nanoplatelet.

52. The method of claim 49, wherein the sample is in the form of an aqueous dispersion of the FMNPs.

53. The method of claim 49, wherein:the plurality of different field frequencies is in a range of 100 kHz to 2 MHz; and the plurality of different field strengths is in a range of 0 kA / m to 20 kA / m.

54. The method of claim 49, further comprising:selecting specific FMNPs and / or specific induction field properties based on VFIA analysis of the sample to optimize induction heating of the FMNPs; andperforming a method for assembling, disassembling, or repairing a part using an adhesive composition comprising the selected FMNPs and using the selected induction field properties.

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