Composite materials comprising graphene-coated hollow particles useful in high frequency applications

Abstract

A composite material comprising a polymeric matrix and coated particles dispersed within the polymeric matrix. The coated particles comprise a hollow particle made of an electrically resistive material and a coating comprising graphene platelets in direct contact with the outer surface of the hollow particle. The hollow particles are made by mechanically exfoliating layered graphene to produce graphene platelets and coating the hollow particles with the graphene platelets. The composite material can be used as an electromagnetic interference (EMI) mitigation material in high frequency applications.

Description

Background Technology

[0001] Electromagnetic interference (“EMI”) is becoming increasingly problematic in many commercial microelectronics applications due to the growing demand for more powerful and compact electronic devices. EMI is a disturbance caused by electromagnetic radiation that can interfere with the operation of electronic equipment or, in some cases, render it completely inoperable. Many EMI sources exist. In some cases, EMI sources are external to the electronic equipment. However, in other cases, components inside the electronic equipment can become EMI sources, potentially affecting other components within that electronic equipment and / or other nearby electronic equipment. Although the normal performance of the electronic equipment is usually restored after the EMI source is eliminated, temporary malfunctions caused by EMI can be critical.

[0002] Generally, reducing or eliminating unwanted EMI can be achieved by reflecting electromagnetic radiation, absorbing electromagnetic radiation, or both. A common solution is to use a highly conductive metal sheet (called an electromagnetic (EM) shield) to reflect unwanted electromagnetic radiation away from the device. However, this shield may not provide sufficient reflectivity, or depending on the application, the reflected radiation may cause additional problems, such as interference with other nearby electronic equipment. In such cases, absorption of electromagnetic radiation is the preferred mitigation method. Therefore, there is considerable interest in next-generation EMI mitigation materials that shield electronic devices by absorbing electromagnetic radiation or a combination of absorption and reflection, especially for applications in higher frequency ranges, such as 1–40 GHz for telecommunications applications and 70–110 GHz for automotive applications. Summary of the Invention

[0003] This disclosure provides composite materials that can be used as EMI mitigation materials in high-frequency applications. These composite materials can exhibit high absorption, low reflection, and / or extremely low transmission of high-frequency electromagnetic radiation.

[0004] In one embodiment, this disclosure provides a composite material comprising a polymer matrix and coated particles dispersed within the polymer matrix. The coated particles comprise hollow particles made of a resistive material and a coating, each hollow particle having an outer surface, the coating comprising a graphene sheet in direct contact with the outer surface. In some embodiments, the coating does not contain a binder. In some embodiments, the hollow particles are glass bubbles, nanotubes, or combinations thereof.

[0005] In another embodiment, this disclosure provides an article comprising a composite material. In some embodiments, the article is an electronic mobile device.

[0006] In yet another embodiment, this disclosure provides a method for preparing a composite material, the method comprising mixing coated particles with a curable polymer matrix material, and curing the polymer matrix material to form a composite material.

[0007] In another embodiment, this disclosure provides coated particles.

[0008] In another embodiment, this disclosure provides a method for preparing coated particles, the method comprising mixing hollow particles with layered graphene, mechanically exfoliating the layered graphene to produce graphene flakes, and coating the hollow particles with the graphene flakes.

[0009] As used in this article: The term "comprising" and its variations are not intended to be limiting wherever they appear in the specification and claims. Such terms are to be understood as implying the inclusion of the stated steps or elements or groups of steps or elements, but not excluding any other steps or elements or groups of steps or elements. The phrase "consisting of..." means including and limited to what follows the phrase "consisting of...". Therefore, the phrase "consisting of..." indicates that the listed elements are required or mandatory, and that no other elements may be present. The phrase "substantially consisting of..." means including any elements listed after this phrase, and is limited to other elements that do not impede or contribute to the activity or effect specified for the listed elements in this disclosure. Therefore, the phrase "substantially consisting of..." indicates that the listed elements are required or mandatory, but other elements are optional and may or may not be present depending on whether they substantially affect the activity or effect of the listed elements.

[0010] The terms “a,” “an,” “the,” and “the” are used interchangeably, wherein “at least one” refers to one or more of the said components.

[0011] The term “and / or” means one or all of the listed elements, or any combination of two or more of the listed elements.

[0012] The term "some embodiments" refers to specific features, configurations, compositions, or properties described in connection with embodiments that are included in at least one embodiment of this disclosure. Therefore, such phrases appearing throughout this specification do not necessarily refer to the same embodiments as described in this disclosure. Furthermore, specific features, configurations, compositions, or properties may be combined in any suitable manner in one or more embodiments.

[0013] The terms "preferred" and "ideal" refer to embodiments of this disclosure that may provide certain benefits in certain circumstances; however, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this disclosure.

[0014] All figures are assumed to be modified by the term “approximately”. As used herein, with respect to the quantity being measured, the term “approximately” refers to a deviation in the quantity being measured that would be expected by a technician who would take measurements with a certain degree of care, and that is commensurate with the object of the measurement and the accuracy of the measuring equipment used.

[0015] A range of numbers expressed by endpoints includes all numbers contained within that range, as well as endpoint values ​​(e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). The phrase "at most" for a number (e.g., at most 50) includes that number (e.g., 50).

[0016] The term "composite material" refers to a material in which two or more materials coexist without chemical interaction, and one or more phases can be discrete or continuous.

[0017] The above-described inventive summary is not intended to describe every disclosed embodiment or implementation. The following description provides more specific examples of exemplary embodiments. Attached Figure Description

[0018] Figure 1 This is an EMI performance curve of the composite material in Example 3A; and

[0019] Figure 2 This is an EMI performance curve of the composite material in Example 3B. Detailed Implementation

[0020] The composite materials disclosed herein typically comprise a polymer matrix and coated particles dispersed within the polymer matrix. The coated particles comprise hollow particles made of a resistive material and a coating comprising graphene flakes in direct contact with the outer surface of the hollow particles. As used herein, the term "direct contact" means that the coating is in physical contact with the surface of the hollow particles (i.e., without intermediate coatings or layers). These composite materials can be used as EMI mitigation materials in a variety of applications within the high-frequency range (e.g., 1–110 GHz). Each component of the composition is described in more detail below.

[0021] Coated Particles

[0022] The coated particles include hollow particles having a thin graphene coating in direct contact with the outer surface of the hollow particles. The hollow particles are typically made of resistive materials. As used herein, "resistive" means a resistivity of at least 10⁻⁶. 10 Ω The material is m. In some implementations, the resistivity is 10. 10 Up to 10 22 Ω m, or more specifically 10 10 Up to 10 18 Ω In some embodiments, the hollow particles have a void volume greater than 70%, 75%, 80%, 85%, or 90%. The void volume can be determined, for example, by the true density of the hollow particles and the bulk density of the material constituting the shell or casing of the hollow particles, i.e., void volume = (mass of hollow particle sample / true density) - (mass of hollow particle sample / bulk density). The “true density” of the hollow particles is obtained by dividing the mass of the hollow particle sample by the true volume of hollow glass microspheres measured through a gas specific gravity bottle. The “true volume” is the total volume of the aggregate of hollow glass microspheres, not the bulk volume. In some embodiments, the hollow particles have a void volume of 70%–95%, more specifically 80%–95%. Exemplary hollow particles include glass bulbs, nanotubes, or combinations thereof.

[0023] glass bulb

[0024] In some embodiments, the hollow particles are glass bubbles. As used herein, the term "glass bubble" refers to a hollow sphere made of glass, each sphere having a substantially single-chamber structure (i.e., each bubble is defined only by an outer wall, and there are no additional outer walls, partial spheres, concentric spheres, etc., in each individual bubble). The hollow spheres have a circular shape, such as oval, pearl-shaped, bead-shaped, elliptical, quasi-spherical, or spherical. Preferably, the hollow spheres have a spherical shape. The glass bubbles can have an aspect ratio ranging from 1:1 to 50:1, 1:1 to 40:1, 1:1 to 30:1, 1:1 to 20:1, 1:1 to 10:1, or 1:1 to 5:1. In some embodiments, the aspect ratio is 1:1.

[0025] There are no particular limitations on the size of glass bulbs; it will depend on their intended application. As used in this context, the term "size" refers to the maximum diameter of the glass bulb. In some embodiments, glass bulbs may have a median volume size in the range of 1 micrometer (μm) to 500 micrometers, 1 micrometer to 100 micrometers, 5 micrometers to 100 micrometers, or 10 micrometers to 60 micrometers (in some embodiments, in the range of 15 micrometers to 40 micrometers, 10 micrometers to 25 micrometers, 20 micrometers to 45 micrometers, 20 micrometers to 40 micrometers, 10 micrometers to 50 micrometers, or 10 micrometers to 30 micrometers). The median size is also referred to as d. 50 Sizes in which 50% by volume of the glass bulbs in the distribution are smaller than the size shown, and 50% by volume of the glass bulbs in the distribution are larger than the size shown.

[0026] Glass bulbs according to this disclosure and / or applicable to the implementation of this disclosure can be prepared using techniques known in the art (see, for example, U.S. Patent No. 2,978,340 (Veatch et al.), U.S. Patent No. 3,030,215 (Veatch et al.), U.S. Patent No. 3,129,086 (Veatch et al.), U.S. Patent No. 3,230,064 (Veatch et al.), U.S. Patent No. 3,365,315 (Beck et al.), U.S. Patent No. 4,391,646 (Howell), U.S. Patent No. 4,767,726 (Marshall), and U.S. Patent Application Publication No. 2006 / 0122049 (Marshall et al.)). Techniques for preparing glass bulbs typically involve heating a ground glass charge, often referred to as the “feed,” which contains a foaming agent (e.g., sulfur or a compound of oxygen and sulfur). The product obtained from the heating step (i.e., the “crude product”) typically comprises a mixture of glass bubbles, broken glass bubbles, and solid glass beads, which are usually produced from ground glass frit particles that failed to form glass bubbles. The ground glass frit typically has a range of particle sizes that influence the size distribution of the crude product. During heating, larger particles tend to form more brittle glass bubbles than average, while smaller particles tend to increase the density of the glass bubble distribution. When preparing glass bubbles by grinding the glass frit and heating the resulting particles, the amount of sulfur in the glass particles (i.e., the feed) and the amount and duration of heat treatment (i.e., the rate at which the particles are fed through the flame) can typically be adjusted to change the density of the glass bubbles. As described in U.S. Patents 4,391,646 (Howell) and 4,767,726 (Marshall), a lower sulfur content in the feed and a faster heating rate result in higher density bubbles. Furthermore, grinding the glass frit to a smaller size can result in smaller, higher density glass bubbles.

[0027] Although the glass frit and / or feed can have any composition capable of forming glass, in some embodiments, the glass frit comprises 50% to 90% by weight of SiO2, 2% to 20% by weight of alkali metal oxides (e.g., Na2O or K2O), 1% to 30% by weight of B2O3, 0.005% to 0.5% by weight of sulfur (e.g., in the form of elemental sulfur, sulfate, or sulfite), and 0% to 25% by weight of divalent metal oxides (e.g., CaO, MgO, BaO). The glass composition may contain 0% to 10% by weight of tetravalent metal oxides other than SiO2 (e.g., TiO2, MnO2, or ZrO2), 0% to 20% by weight of trivalent metal oxides (e.g., Al2O3, Fe2O3, or Sb2O3), 0% to 10% by weight of pentavalent metal oxides (e.g., P2O5 or V2O5), and 0% to 5% by weight of fluorine (in fluoride form), which may act as a flux to promote melting of the glass composition. Additional components may be used in the glass composition and may be included in the glass feed, for example, to contribute specific properties or characteristics (e.g., hardness or color) to the resulting glass bulb.

[0028] In some implementations, the glass bulb comprises sodium calcium borosilicate glass.

[0029] In some embodiments, the glass bulb comprises 50% to 90% by weight of silicon dioxide (SiO2), 2% to 20% by weight of alkali metal oxide (R2O), and 1% to 30% by weight of boron oxide (B2O3) based on the total weight of the glass bulb. In the same or different embodiments, the glass bulb comprises no more than 25% by weight of divalent metal oxide (RO), more specifically calcium oxide (CaO). In the same or different embodiments, the glass bulb also comprises no more than 10% by weight of phosphorus oxide (P2O5). As used herein, “R” refers to a metal having the indicated valence, R2O is an alkali metal oxide, and RO is a divalent metal oxide, preferably an alkaline earth metal oxide.

[0030] Suitable glass bulbs are also commercially available, for example from 3M Company (Saint Paul, MN, USA) under the name 3M. ™ Glass bulbs of the K, S, iM, XLD, Floated, and HGS series (including glass bulbs iM16K, S60, K42HS, and S32HS) are commercially available. In some embodiments, the glass bulb is glass bulb iM16K, glass bulb S32HS, or combinations thereof. In some embodiments, the glass bulb is iM16K.

[0031] The glass bulbs disclosed herein typically have a concentration of at least 0.2 g / cm³.3 ), 0.25g / cm 3 Or 0.3g / cm 3 The average true density. In some embodiments, the glass bulb has a maximum of 0.65 g / cm³. 3 0.6g / cm 3 or 0.55g / cm 3 The average true density. For example, the average true density of a glass bulb can be as low as 0.2 g / cm³. 3 Up to 0.65 g / cm 3 0.25g / cm 3 Up to 0.6 g / cm 3 0.3g / cm 3 Up to 0.60 g / cm 3 Or 0.3g / cm 3 Up to 0.55 g / cm 3 The "mean true density" or "true density" of a glass bulb is obtained by dividing the mass of the glass bulb sample by the true volume of that mass of the glass bulb. "True volume" refers to the total volume of the aggregate of the glass bulb, not its bulk volume. Mean true density can be measured using a hydrometer according to DIN EN ISO 1183-3. Hydrometers are available, for example, under the trade name "ACCUPYC II 1340 PYCNOMETER" from Micromeritics, Norcross, Georgia, or under the trade names "PENTAPYCNOMETER" or "ULTRAPYCNOMETER 1000" from Formanex, Inc., San Diego, CA. Mean true density is typically 0.001 g / cm³. 3 Precision measurement.

[0032] Nanotubes

[0033] In some embodiments, the hollow particles are nanotubes. Nanotubes are materials with a tubular structure in which the length of the tubular structure is typically greater than its diameter. In some embodiments, the average outer diameter of the nanotubes is from 2 nanometers (nm) to 200 nm, more specifically from 2 nm to 100 nm, or even more specifically from 50 nm to 70 nm. The average diameter can be determined by averaging the outer diameters of 20 nanotubes, which is measured by scanning electron microscopy (SEM). The required magnification of the SEM image depends on the size of the nanotubes. In some embodiments, the length of the nanotubes is from 3 nanometers to 5 micrometers, more specifically from 3 nanometers to 2 micrometers.

[0034] In some implementations, the nanotubes have an average aspect ratio in the range of 5:1 to 50:1, 5:1 to 40:1, 5:1 to 30:1, 5:1 to 20:1, or 10:1 to 20:1. The average aspect ratio can be determined by averaging the aspect ratios of 20 nanotubes obtained using SEM. The aspect ratio of a single nanotube is determined by measuring the length (longest dimension) and diameter of the nanotube and calculating the length-to-diameter ratio.

[0035] Nanotubes include inorganic nanotubes (e.g., BN, MoS2, WS2, and SnS2), clay nanotubes (e.g., halloysite and illomaitite), core-shell nanotubes (e.g., PbI2 / WS2, BiI3 / WS2, and SbI3 / WS2), and conventional ceramic nanotubes (e.g., TiO2, ZrO2, and ZnO). In some embodiments, the nanotubes comprise halloysite, illomaitite, or combinations thereof. In some embodiments, the nanotubes contain halloysite.

[0036] Coating

[0037] The coating comprises a sheet of graphene in direct contact with the outer surface of the hollow particles. The sheet can be derived from layered graphene precursors, which consist of individual layers held together by weak chemical forces (i.e., van der Waals forces). In contrast, the carbon atoms within each layer are held together by stronger chemical forces (i.e., sp... 2 Hybridized covalent bonds hold the layers together to form a two-dimensional honeycomb lattice. Layers can be exfoliated from the layered graphene precursor using mechanical exfoliation to form graphene flakes. These flakes are thinner than the layered graphene precursors from which they are derived and exhibit unique physical and chemical properties different from those of the bulk layered graphene precursors due to their smaller size. In some embodiments, the graphene flakes have no more than 100, 50, 25, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 layer. In some embodiments, the graphene flakes have 1 to 100 layers, 1 to 50 layers, 1 to 25 layers, 1 to 10 layers, 1 to 5 layers, or even 1 layer.

[0038] Graphene flakes typically have an average aspect ratio of at least 2:1, 15:1, 30:1, or 50:1. In some embodiments, the average aspect ratio of the graphene flakes is in the range of 2:1 to 50:1 or 2:1 to 30:1. The average aspect ratio can be determined by averaging the aspect ratios of 20 flakes obtained using SEM. The aspect ratio of a single graphene flake is determined by measuring the length (longest dimension) and thickness of the flake and calculating the length-to-thickness ratio.

[0039] In some embodiments, the average length of the graphene flakes is at least 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, or 50 micrometers. In some embodiments, the average length of the graphene flakes is in the range of 10 to 50 micrometers, 10 to 40 micrometers, 10 to 30 micrometers, or 10 to 20 micrometers. The average length can be determined by averaging the lengths of 20 flakes using SEM.

[0040] Graphene sheets are generally conductive. Although the conductivity will depend on factors such as sheet size and coating thickness, in some embodiments, the conductivity of the graphene sheet in the planar direction is 10. 7 Up to 10 8 S / m.

[0041] Furthermore, graphene sheets are typically thermally conductive, which facilitates heat dissipation. In some embodiments, the thermal conductivity of the graphene sheet in the planar direction at room temperature is 3,000 W / m. K up to 3,300W / m K.

[0042] Graphene flakes are directly adhered to the surface of hollow particles to form a two-dimensional coating. "Adheded to the surface" means that the flakes are fixed to the surface of each hollow particle. When the coated particles, as disclosed herein, are composited with a polymer matrix material, the graphene flakes remain adhered to the surface of the hollow particles.

[0043] As disclosed herein, the coating of coated particles typically does not contain a binder. As used herein, "binder" means an organic or inorganic compound that has the function of adhering sheets to each other and / or to the surface of hollow particles, and has been added to the hollow particles and graphene sheets during the preparation of the coated particles.

[0044] The coated graphene flakes can be stacked layer by layer, or they can be placed irregularly on the surface of the hollow particles. Each graphene flake can be oriented parallel to the surface of the hollow particles, or it can be oriented in any direction not parallel to the surface of the hollow particles. Each graphene flake can also be oriented perpendicular to the surface of the hollow particles, i.e., radially oriented. In some embodiments, the majority of the graphene flakes, i.e., more than 50% of the graphene flakes, are oriented parallel to the surface of the hollow particles.

[0045] The coating on the outer surface of the hollow particles can be continuous or discontinuous. In some embodiments, the coating covers at least 50%, 60%, 70%, 80%, 90%, or 100% of the outer surface of the hollow particles. In some embodiments, the coating covers at least 90%, 95%, or 100% of the outer surface of the hollow particles. In a preferred embodiment, the coating covers 100% of the outer surface of the hollow particles.

[0046] The coating thickness can be up to 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, or 10 nm. Thinner coatings are preferred because they are more conductive and exhibit higher dielectric losses. Typically, the coating thickness is smaller than the minimum size of the hollow particle to which it is applied. In some embodiments, the coating thickness does not exceed 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, or 2 nm. In some embodiments, the coating thickness is in the range of 1 nm to 10 nm, 2 nm to 5 nm, or 3 nm to 5 nm. The coating thickness on the coated particles can be measured by scanning electron microscopy (SEM). For example, for coated glass bubbles, the coating thickness can be measured by crushing or breaking multiple coated glass bubbles uniaxially with a load of 10 kN and measuring the coating thickness on the resulting fragments of coated glass bubbles using SEM. The coating thickness of coated nanotubes can be measured in a similar manner.

[0047] In some embodiments, the graphene flakes comprise no more than 20%, 18%, 16%, 14%, or 12% by weight of the coated particles. In some embodiments, the flakes comprise 5% to 20% by weight or 10% to 20% by weight of the coated particles.

[0048] The coated hollow particles of this disclosure typically exhibit a higher dielectric constant (ε') and dielectric loss (tan δ) than uncoated hollow particles.

[0049] Preparation method

[0050] The coated particles of this disclosure can be prepared by mixing hollow particles with a layered graphene precursor, mechanically exfoliating the layered graphene precursor to produce flakes, and coating the hollow particles with graphene flakes. The weight ratio of hollow particles to the layered graphene precursor is at least 20:1, 25:1, 30:1, 35:1, or at least 40:1. Typically, the weight ratio of hollow particles to the layered graphene precursor is at most 50:1, 45:1, or 40:1. In some embodiments, the weight ratio of hollow particles to the layered graphene precursor is in the range of 20:1 to 50:1, 20:1 to 40:1, or 20:1 to 30:1. If the amount of layered graphene precursor is too high, sufficient exfoliation of the layers may not occur.

[0051] Mechanical exfoliation separates the layers in a layered graphene precursor to produce flakes. Exfoliation is typically performed on a ball mill roller using relatively low mixing speeds and long mixing times. In some embodiments, exfoliation is performed at mixing speeds of at least 20 rpm, 25 rpm, 30 rpm, or 40 rpm. In the same or alternative embodiments, exfoliation is performed at mixing speeds of up to 60 rpm, 55 rpm, 50 rpm, 45 rpm, or 40 rpm. In some embodiments, exfoliation is performed at mixing speeds ranging from 20 rpm to 60 rpm or from 20 rpm to 40 rpm. In some embodiments, the mixing time is at least 12 hours, 18 hours, or 24 hours. In the same or alternative embodiments, the mixing time is up to 60 hours, 50 hours, 40 hours, or 30 hours. In some embodiments, the mixing time is in the range of 12 hours to 60 hours, 12 hours to 50 hours, 12 hours to 40 hours, 12 hours to 30 hours, or 12 hours to 24 hours.

[0052] The graphene flakes obtained by exfoliation are simultaneously milled and coated onto the outer surface of hollow particles in a ball milling roller. As used in this context, "simultaneously" means that the exfoliation and milling coating occur within the mixed time period mentioned above. Milling coating refers to an operation in which pressure is applied in a direction perpendicular to the object surface (e.g., the outer surface of the hollow particle) while the flake moves in a plane parallel to said surface (e.g., rotational motion, lateral motion, or combinations thereof).

[0053] The coating method can be performed at room temperature (i.e., the method does not require heat treatment). This provides a low-cost alternative to those coating processes that employ heat treatment and eliminates the need to soften the surface of the hollow particles.

[0054] In some implementations, the coating method is substantially free of added liquids (e.g., solvents). In this context, the term "substantially" means that no liquid is added to the mixture of hollow particles and layered graphene precursors during the coating process.

[0055] polymer matrix

[0056] The composite materials disclosed herein comprise a polymer matrix and coated particles dispersed therein. The polymer matrix may comprise thermoplastic polymers, thermosetting polymers, elastomeric polymers, or mixtures thereof. Those skilled in the art can select a suitable polymer for the composite material, at least in part, depending on the desired application.

[0057] In some embodiments, the polymer matrix comprises a thermoplastic polymer. Exemplary thermoplastic polymers include polyolefins, fluorinated polyolefins, polyimides, polyamide-imides, polyether-imides, polyetherketone resins, polystyrene, polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinyl chloride (PVC), liquid crystal polymers (LCP), polyphenylene sulfide (PPS), polysulfones, polyacetals, polycarbonates, polyphenylene oxide (PPO), polyphenylene ether (PPE), and blends thereof.

[0058] In some embodiments, the polymer matrix comprises a thermosetting polymer. Exemplary thermosetting polymers include epoxy resins, polyesters, polyurethanes, polyureas, silicones, polysulfides, phenolic resins, vulcanized rubbers, polyoxybenzylmethylene glycol anhydride, vinyl ester resins, and blends thereof.

[0059] In some embodiments, the polymer matrix comprises an elastomeric polymer. Exemplary available elastomeric polymers include polybutadiene, polyisobutylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, sulfonated ethylene-propylene-diene terpolymers, polychlorobutene, poly(2,3-dimethylbutadiene), butadiene-pentadiene copolymers, chlorosulfonated polyethylene, polysulfide elastomers, silicone elastomers, butadiene-nitrile copolymers, hydrogenated nitrile-butadiene copolymers, acrylic elastomers, ethylene-acrylate copolymers, fluorinated elastomers, fluorochlorinated elastomers, fluorobrominated elastomers, and combinations thereof. The elastomeric polymer may be a thermoplastic elastomer. Exemplary available thermoplastic elastomer polymer resins include block copolymers composed of glassy or crystalline blocks of, for example, polystyrene, poly(vinyl toluene), poly(tert-butylstyrene), and polyesters, and elastomeric blocks of, for example, polybutadiene, polyisoprene, ethylene-propylene copolymers, ethylene-butene copolymers, polyether esters, and combinations thereof. Some thermoplastic elastomers are commercially available, such as poly(styrene-butadiene-styrene) block copolymers marketed by Shell Chemical Company (Houston, TX) under the trade name "KRATON".

[0060] In some implementations, the polymer matrix comprises organosilicon.

[0061] Depending on the application, other additives may be incorporated into the polymer matrix according to this disclosure, such as preservatives, curing agents, mixing agents, colorants, dispersants, flotation agents or antisettling agents, flow agents or processing aids, wetting agents, air separation promoters, functional nanoparticles, acid / alkali or water scavengers, or combinations thereof.

[0062] In some embodiments, the polymer matrix comprises an impact modifier (e.g., an elastomeric resin or elastomeric filler). Exemplary impact modifiers include polybutadiene, butadiene copolymers, polybutene, waste rubber, block copolymers, ethylene terpolymers, core-shell particles, and functionalized elastomers, such as those available under the trade name “AMPLIFY GR-216” from Dow Chemical Company, Midland, MI.

[0063] In some embodiments, the polymer matrix contains other density-modifying additives, such as plastic foam (e.g., those from Akzo Nobel, Amsterdam, The Netherlands, under the trade name "EXPANCEL"), foaming agents, or heavy fillers. In some embodiments, the polymer matrix may also contain at least one of glass fiber, wollastonite, talc, calcium carbonate, titanium dioxide (including nano-titanium dioxide), carbon black, wood flour, other natural fillers and fibers (e.g., walnut shells, hemp, and corn silk), silica (including nano-silica), and clay (including nano-clay).

[0064] Composite materials

[0065] The composite material described herein can be prepared by mixing coated particles with a curable polymer matrix material and curing the polymer matrix material to form a composite material.

[0066] In some embodiments, the composite material may contain up to 60 volume percentage (volume%), 55 volume%, 50 volume%, 45 volume%, 40 volume%, 35 volume%, 30 volume%, 25 volume%, 20 volume%, 15 volume%, or 10 volume% of coated particles based on the total volume of the composite material. In some embodiments, the composite material may contain 2 volume% to 60 volume%, 20 volume% to 50 volume%, or 30 volume% to 50 volume% of coated particles based on the total volume of the composite material.

[0067] In some embodiments, the composite material may contain up to 50 wt%, 45 wt%, 40 wt%, 35 wt%, 30 wt%, 25 wt%, or 20 wt% of coated particles based on the total weight of the composite material. In some embodiments, the composite material may contain 1 wt% to 50 wt%, 1 wt% to 40 wt%, 1 wt% to 30 wt%, or 1 wt% to 20 wt% of coated particles based on the total weight of the composite material.

[0068] When the coating particles are coated nanotubes, the higher aspect ratio of the hollow nanotubes allows for a reduction in the filler content of the coated particles in the composite material. Not wishing to be bound by theory, it is believed that nanotubes may align and contact with adjacent nanotubes during processing, thereby forming a network throughout the matrix that allows for a lower filler content. This reduced filler content can be advantageous because higher filler content composites may be more difficult to process, negatively impact the mechanical properties of the resulting composite, and / or increase manufacturing costs. Therefore, in some embodiments, it is preferred that the composite material contains coated nanotubes.

[0069] In some embodiments, the composite material may comprise up to 20%, 18%, 16%, 14%, 12%, 10%, 8%, 6%, 4%, or 2% of coated nanotubes based on the total volume of the composite material. In some embodiments, the composite material may comprise 1% to 20%, 2% to 20%, or 2% to 10% of coated nanotubes based on the total volume of the composite material.

[0070] In some embodiments, the composite material may comprise up to 20 wt%, 18 wt%, 16 wt%, 14 wt%, 12 wt%, 10 wt%, 8 wt%, 6 wt%, 4 wt%, or 2 wt% of coated nanotubes based on the total weight of the composite material. In some embodiments, the composite material may comprise from 1 wt% to 20 wt%, 2 wt% to 20 wt%, or 4 wt% to 15 wt% of coated nanotubes based on the total weight of the composite material.

[0071] The composite materials disclosed herein can be used in a variety of applications to reduce or eliminate unwanted EMI over a wide frequency range. Typically, these composite materials mitigate electromagnetic interference at frequencies from 1 GHz to 110 GHz. These composite materials can be used in telecommunications equipment (e.g., mobile phones, tablets, laptops, and computers), the automotive industry (e.g., automotive radar control and blind spot detection), and the medical industry (e.g., high-frequency scanners and tomography systems for diagnostics). In embodiments where these composite materials are used in telecommunications equipment, the composite materials can mitigate electromagnetic interference at frequencies from 1 GHz to 40 GHz, 5 GHz to 40 GHz, 10 GHz to 40 GHz, 15 GHz to 40 GHz, 20 GHz to 40 GHz, or 25 GHz to 40 GHz. In some embodiments, these composite materials mitigate electromagnetic interference at frequencies from 26 GHz to 40 GHz. In other embodiments where the composite materials are used in the automotive industry, the composite materials can mitigate electromagnetic interference at frequencies from 70 GHz to 110 GHz.

[0072] Example

[0073] The following embodiments further illustrate the objects and advantages of the present invention, but the specific materials and quantities listed in these embodiments, as well as other conditions and details, should not be construed as undue limitation of the invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of the appended claims.

[0074]

[0075] Test methods

[0076] Electromagnetism of composite materials EM Characterization testing methods

[0077] Complex dielectric and complex magnetic properties were calculated using scattering (S) parameters obtained from a rectangular waveguide made of the composite material illustrated herein, in the frequency range of 18 GHz to 26.5 GHz (K-band), based on an Agilent E8363C network analyzer (Agilent Technologies, Santa Clara, CA). The composite sample (smooth and homogeneous) was cut to fit the transmission line, and its dimensions were set to have the smallest possible air gap within the transmission line.

[0078] Electromagnetic properties of coated particles EM Characterization testing methods

[0079] The samples with coated particles were measured using a TE01 delta-mode dielectric resonator at room temperature and 2.45 GHz using a vector network analyzer (Agilent E8363C network analyzer).

[0080] EMI Performance Analysis Testing Methods

[0081] The radar absorption or reflection loss model is a well-known model that assumes an electromagnetic wave is incident orthogonally on a single-layer composite absorber adhered to a highly conductive metal plate (which blocks transmission). EM wave absorption performance can be evaluated using reflection loss (RL), measured in decibels (dB). In this model, lower reflection loss indicates higher electromagnetic absorption performance.

[0082] The EM wave absorption performance is studied based on the following formula:

[0083] Where Z0 is the impedance in free space, t is the thickness of the absorber, and c is the speed of light. As indicated by equation (a), the input impedance of the absorber depends on six parameters: complex permeability (µF). r =µ'-jµ'') value and complex permittivity (ε rThe real and imaginary parts of =ε'-jε'', the thickness (t) of the absorber, and the operating frequency (f) are used. An industry-standard composite thickness (t) of 1.0 mm was used because space is precious for current microelectronic devices in many practical high-frequency EMI applications. A description of the radar absorption or reflection loss model can be found in "Structural and high GHz frequency EMI (Electromagnetic Interference) properties of carbonyl iron and boron nitride hybrid composites," *Materials Research Letters*. Materials Research Express )6(10), 106305, 2019 were found.

[0084] Example 1: Coated Clay Nanotubes

[0085] Based on the stoichiometry and time listed in Table 2, clay nanotubes and graphene sheets were combined in Nalgene. ® The mixture is stirred in a plastic bottle using a ball milling roller at a speed of 30 revolutions per minute (rpm).

[0086]

[0087] Example 2: Coated glass bubble

[0088] Based on the stoichiometric ratios and times listed in Table 3, the glass bulb and graphene sheet were placed together in Nalgene. ® The mixture is stirred in a plastic bottle using a ball mill roller at a speed of 30 rpm.

[0089]

[0090] Example 3: Composite Materials

[0091] The composite material was prepared using coated nanotubes and coated glass bubbles as described in Examples 1 and 2. The required amount of SYLGARD silicone A portion was added to a plastic cup. Then, the required amount of SYLGARD silicone B portion was added to the SYLGARD silicone A portion in the plastic cup. The coated particles were then added to the mixture in the amounts listed in Table 4. The plastic cup was covered with a lid configured to allow rapid mixing under vacuum (100 mbar) for 2 minutes and 15 seconds. The mixture was then poured onto a stainless steel plate. A second stainless steel plate was placed on top of the mixture. Teflon sheets were placed between the mixture and each steel plate to prepare a composite material with a smooth surface. Spacers were used between the two plates to separate them to a desired thickness of 1.0 mm. The plates with the mixture were hot-pressed at 118°C and 3 tons of pressure for 45 to 60 minutes. The plates were allowed to cool for 30 to 45 minutes, after which the cured composite sheet was removed.

[0092] Dielectric and magnetic properties of the composite material were obtained using electromagnetic (EM) characterization methods. The results are reported in Tables 5 and 6.

[0093]

[0094] Example 4: EMI performance of composite materials

[0095] The EMI performance of the composite material in Example 3 was analyzed using the radar absorption or reflection loss model described in the EMI performance analysis test method. The EMI performance curve of composite material 3A is provided below. Figure 1 The EMI performance curves of the 3B composite material are provided in [the relevant source]. Figure 2 middle.

[0096] Example 5: Dielectric properties of coated glass bulbs

[0097] Electromagnetic (EM) characterization of powder was used to compare the dielectric properties of coated and uncoated glass bulbs at a frequency of 2.54 GHz. The results are presented in Table 7.

[0098]

[0099] Therefore, this disclosure particularly provides composite materials containing graphene-coated hollow particles that can be used in high-frequency EMI applications. The following claims set forth various features and advantages of this disclosure.

Claims

1. A composite material, the composite material comprising: Polymer matrix; and Coated particles dispersed within the polymer matrix, the coated particles comprising: Hollow particles made of resistive material, each hollow particle having an outer surface; and A coating comprising a graphene sheet in direct contact with the outer surface.

2. The composite material according to claim 1, wherein the coating covers at least 50% of the outer surface of the hollow particles.

3. The composite material according to claim 1 or claim 2, wherein the coated particles comprise 5% to 20% by weight of graphene flakes.

4. The composite material according to claim 1 or claim 2, wherein the coating has a thickness of less than 5 nanometers.

5. The composite material according to any one of the preceding claims, wherein the coating does not contain an adhesive.

6. The composite material according to any one of the preceding claims, wherein the composite material comprises at most 50% by weight of the coated particles based on the total weight of the composite material.

7. The composite material according to any one of the preceding claims, wherein the hollow particles are glass bubbles, nanotubes, or combinations thereof.

8. The composite material according to any one of the preceding claims, wherein the hollow particles are nanotubes.

9. The composite material according to any one of the preceding claims, wherein the coated particles are coated nanotubes, and the composite material comprises no more than 20% by weight of the coated nanotubes.

10. The composite material according to any one of claims 7 to 9, wherein the nanotubes comprise inorganic nanotubes, clay nanotubes, core-shell nanotubes, ceramic nanotubes, or combinations thereof.

11. The composite material according to any one of claims 7 to 10, wherein the nanotubes comprise halloysite, epigealite, or a combination thereof.

12. The composite material according to any one of claims 7 to 11, wherein the nanotubes have an aspect ratio of 5:1 to 50:

1.

13. The composite material according to any one of claims 1 to 7, wherein the hollow particles are glass bubbles.

14. The composite material of claim 13, wherein the glass bubble has a median volume size in the range of 1 micrometer to 500 micrometers.

15. The composite material according to any one of the preceding claims, wherein the polymer matrix comprises a thermoplastic polymer selected from the group consisting of: polyolefins, fluorinated polyolefins, polyimides, polyamide-imides, polyether-imides, polyetherketone resins, polystyrene, polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinyl chloride (PVC), liquid crystal polymers (LCP), polyphenylene sulfide (PPS), polysulfones, polyacetals, polycarbonates, polyphenylene oxide (PPO), polyphenylene ether (PPE), and blends thereof.

16. The composite material according to any one of claims 1 to 14, wherein the polymer matrix comprises a thermosetting polymer selected from the group consisting of: epoxy resin, polyester, polyurethane, polyurea, silicone, polysulfide, phenolic resin, vulcanized rubber, polyoxybenzylmethylene glycol anhydride, vinyl ester resin, and blends thereof.

17. The composite material according to any one of the preceding claims, wherein the polymer matrix further comprises a preservative, a curing agent, a mixing agent, a colorant, a dispersant, a flotation agent or an antisettling agent, a flow agent or a processing aid, a wetting agent, an air separation promoter, functional nanoparticles, an acid / alkali or water scavenger, or a combination thereof.

18. An article comprising a composite material according to any one of the preceding claims.

19. The article of manufacture according to claim 18, wherein the article of manufacture is an electronic mobile device.

20. A method for preparing a composite material, the method comprising: The coated particles are mixed with a curable polymer matrix material; as well as The curable polymer matrix material is cured to form the composite material. The coated particles comprise: Hollow particles made of resistive material, each hollow particle having an outer surface; and A coating comprising a graphene sheet in direct contact with the outer surface.

21. Coated particles, the coated particles comprising: Hollow particles made of resistive material, each hollow particle having an outer surface; and A coating comprising a graphene sheet in direct contact with the outer surface.

22. A method for preparing the coated particles according to claim 21, the method comprising: The hollow particles are mixed with layered graphene; The layered graphene is mechanically exfoliated to produce graphene sheets; as well as The hollow particles are coated with the graphene sheets.

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