Near-infrared signature reduction device

Abstract

The present invention provides a device for actively modifying NIR radiation, the device comprising: (i) a substrate; (ii) one or more permeable polymeric membranes comprising an ionic liquid electrolyte; (iii) one or more electrodes comprising carbon nanotubes and a transition metal oxide; and (iv) a protective encapsulating layer. The present invention further provides a method for making such a device.

Description

[Technical Field]

[0001] The present invention relates to devices containing carbon nanomaterials and transition metal oxides and having switchable near-infrared emissivity, methods for making such devices, and uses of the devices.

[0002] This invention was made with U.S. Government support under funds awarded by the U.S. Army. The U.S. Government has certain rights in this invention. [Background technology]

[0003] Active control of thermal radiation to and from objects, structures, and exterior surfaces is important for a variety of industrial applications that require management of thermal signatures to benefit overall thermal efficiency and heat loss. In some applications, such as building thermal conditioning, it is desirable to reduce or control near-infrared reflectance and absorption commensurate with solar radiation profiles to reduce heating and cooling energy costs. For example, passivation coatings made from materials whose properties, such as transparency, infrared / near-infrared (NIR) reflectivity and / or emissivity, can be tuned and useful in thermal windows and radiative temperature control.

[0004] Actively switchable electrochromic and thermochromic devices that transmit visible light but absorb or reflect near-infrared radiation are attractive for meeting the needs of modern heating, ventilation, and air conditioning (HVAC) systems. When integrated as large-area devices, these devices can be incorporated into glazing products. By applying an electric potential, the properties can be tuned so that transparency and reflectivity can be controlled. The performance of such devices can be greatly aided by the use of active coatings containing nanomaterials.

[0005] Carbon nanotubes are nano-sized tubes constructed from rolled sheets of graphite. The diameter of these tubes typically ranges from 1 nanometer to 50 nanometers, but their lengths can be in the micrometer range. Carbon nanotubes can be either single-walled (i.e., formed from a single rolled sheet of graphene) or multi-walled (i.e., formed from multiple concentric rolled sheets of graphene). Carbon nanotubes have attracted considerable interest due to their physical properties, namely, high tensile strength and high electrical conductivity.

[0006] 2D materials are known to possess many interesting and potentially useful properties that differ from those of their bulk 3D counterparts. For example, graphene is highly conductive, finding applications in conductive composites as well as electrode structures. The interesting functional properties of many materials are often only observed when the material is in its single-layer or few-layer (i.e., 2D) form. However, to harness these nanocarbon properties, a simple method for isolating these forms is required. To exfoliate bulk three-dimensional (3D) materials to form corresponding 2D materials, strong interlayer dispersion forces must be overcome. Liquid-phase exfoliation dispersions using high-shear mixing are a viable route to producing formulated inks containing 2D materials for use in many industrial applications.

[0007] Salihoglu et al., Nano Lett. (2018), 18, 4541-4548, describe a graphene-based adaptive thermal camouflage device that includes a layer of graphene, a layer of polyethylene film immersed in an ionic liquid, and a layer of gold electrodes to form a planar capacitor. The graphene was deposited using chemical vapor deposition, which is not as readily amenable to large-scale production as liquid-based printable nanocarbon layers are. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, there remains a need for devices for controlling NIR radiation, preferably devices for controlling NIR radiation that have improved properties, such as improved scalability (eg, area scalability). [Means for solving the problem]

[0009] Electrically switchable phase-change materials, particularly metal-insulator (MIT) materials, are suitable for incorporation into electrochemical capacitor structures. By combining these materials with nanocarbon electrodes, switchable devices can be fabricated that control the absorption of near-infrared radiation (NIR) from solar radiation sources.

[0010] Without wishing to be bound by theory, the inventors believe that NIR electrochromic devices containing nanoparticulate graphite / graphene and / or carbon nanotubes can modify the band structure of graphene to block state transitions by utilizing the Pauli blocking principle (see Figure 1). The band structure of graphene can be simplified and represented as a Dirac cone, where energy (E) is linear with momentum (k). In the ground state, the Fermi level, at absolute zero, is near the tip of the cone, with all lower states occupied. An incident photon can then cause the excitation of an electron to an empty state, resulting in an absorption event (left diagram in Figure 1). As the Fermi level is raised, more states can be occupied. When the same photon interacts with modified graphene, it cannot excite an electron because there are no available unoccupied states (right diagram in Figure 1).

[0011] This enables graphene-based or carbon nanotube-based devices in which the emissivity of NIR radiation can be tuned by tuning the Fermi level through application of a potential bias or by doping.

[0012] Large-area devices of this kind (constructed using nanocarbon electrodes in planar electrolytic capacitors and integrated onto a suitable substrate) act to reduce the apparent emissivity of a thermal body. It has been found that devices fabricated from nanocarbon materials can reduce emissivity when powered by their inherent electronic and resulting phonon effects.

[0013] For large-area devices, the fabrication method is preferably solution-based (e.g., rather than based on the transfer of ultrathin-film CVD-deposited graphene). The construction of electrolytic capacitor devices also requires the development of components such as porous thin-film separators and liquid ionic electrolytes to achieve fast switching times and large, observable differences. Nanocarbon materials also have a high surface area-to-volume ratio, which facilitates charge accumulation on localized surfaces. Therefore, the operating range and switching times of these devices are also driven by the physical properties of the electrolyte and its diffusion rate into the internal structure of the electrodes.

[0014] To enable low power consumption and large-area operation of the device, it is preferable to minimize the internal resistance losses of the electrode film as much as possible by using conductive carbon nanomaterials (e.g., carbon nanotubes and / or graphite nanoplatelets).

[0015] Some transition metal oxides exhibit a metal-insulator transition (MIT). While the inventors do not wish to be bound by theory, they note that metals are generally reflective to near-infrared (NIR) radiation because the nearly free electrons in the metal shield the electric field of impinging electromagnetic energy below the plasmon frequency. The plasmon frequency is determined by the carrier density, the number of electrons present, and the effective mass of the electrons, which are determined by band structure relationships. Insulators, in contrast, are transparent to NIR radiation due to a large band gap that prevents optical transitions in the visible and NIR portions of the spectrum. As a result, materials that exhibit MIT (such as some transition metal oxides) have variable emissivity of thermal radiation in the NIR region. Examples of such transition metal oxides include vanadium oxide (i.e., V) with variable stoichiometry. x O y where x and y are integers, typically selected from 1, 2, and 3.

[0016] The inventors have found that adding one or more transition metal oxides exhibiting MIT to the electrodes, in addition to carbon nanotubes, enhances the ability to modify the NIR emission of the device due to the strong "on / off" response of the transition metal oxide in the NIR region.

[0017] Thus, in a first aspect, the present invention provides a device for actively modifying NIR radiation, comprising: (i) a substrate; (ii) one or more polymeric membranes containing an ionic liquid electrolyte; (iii) one or more electrodes comprising carbon nanotubes and a transition metal oxide; (iv) a protective encapsulating layer.

[0018] One or more of the electrodes may include additional carbon nanomaterials in addition to carbon nanotubes. For example, an electrode may include carbon nanotubes along with graphite nanoplatelets (also known as few-layer graphene).

[0019] One or more electrodes may be adjacent to at least one of the one or more polymer membranes. For example, one or more electrodes may be deposited on at least one, or one or more, of the polymer membranes. In other embodiments, additional layers may be present between one or more permeable polymer membranes and one or more electrodes. For example, an additional electrode (e.g., an electrode containing carbon nanotubes but no transition metal oxide) may be present between one or more permeable polymer membranes and one or more electrodes (containing a transition metal oxide).

[0020] Preferably, the device includes a pair of electrodes. Both electrodes may include carbon nanotubes (and optionally additional carbon nanomaterials described herein). Both electrodes may include a transition metal oxide. Alternatively, if there is more than one electrode, the electrodes may be formed from different materials, and only one of the electrodes may include a transition metal oxide.

[0021] The device further comprises a protective encapsulating layer that protects the electrodes and polymer film from damage and / or degradation, and this layer is preferably NIR transparent so as not to interfere with the optical (e.g., emissivity) properties of the device.

[0022] The protective encapsulation layer may be flexible and polymeric in nature. The protective layer may prevent the diffusion of water vapor and / or oxygen molecules into the device, which may promote unwanted chemical reactions and shorten the device's lifespan. The layer is fixed onto the device and then encapsulated for operation.

[0023] The electrodes are typically deposited on one or more polymeric films so that contact with the polymeric film(s) allows for the transport of ions / electrons from the polymeric film(s) to the electrodes. Such polymeric film(s) acts as a separator to prevent electrical shorting between the electrodes. When a potential difference is applied to a pair of electrodes, the electron occupancy at the Fermi level of the carbon nanotubes (or other carbon-containing materials) in the electrodes can be adjusted, thereby changing the NIR emissivity of the device. Applying a potential difference between the electrodes may also initiate MIT in the transition metal oxide in the electrodes, further changing the NIR emissivity of the device.

[0024] As mentioned above, the devices can be used to actively modify thermal emission, which can involve adjusting the transparency and / or reflectivity of the device, or the emissivity of the device.

[0025] Controlling the reflectivity and emissivity of a surface allows for thermal control by varying heat loss through radiation. Radiative heat loss is proportional to the surface's emissivity and the fourth power of the temperature difference. Thus, the present invention provides a means of controlling the temperature of computer components with minimal power consumption. This is particularly useful in environments where convection and conduction are not adequate.

[0026] Another example of this is the reduction of heat loss inside a glazing product. Glass exhibits high emissivity and therefore readily radiates heat. By reducing the external emissivity to the environment, heat loss can be reduced. Therefore, the device of the present invention can be integrated into the interior of a glazing laminate or fixed as an external laminate.

[0027] When the device of the present invention is located between a thermal emitter and a detector, the thermal radiation detected by the detector is reduced.Therefore, the device of the present invention can effectively block the thermal radiation in the NIR region from the heat source, and therefore can function as a thermal camouflage device.Therefore, the device for actively modifying thermal radiation can also be considered as a device for camouflaging / hiding / masking / blocking / suppressing thermal radiation.

[0028] Thus, the present invention further provides a method for actively modifying (e.g., camouflaging / hiding) thermal or NIR radiation from an object, comprising placing a device described herein between the object and a thermal / NIR radiation detector. The method may also include covering or surrounding the object with a device described herein. A further example of this is for protecting sensitive near-infrared detector devices used in astronomical observations.

[0029] The device can be formed by depositing (e.g., printing or spraying) an ink containing carbon nanomaterials and / or transition metal oxides onto one or a pair of polymeric membranes. The polymeric membrane(s) are typically infused with an ionic liquid. To accomplish this, the polymeric membrane may be formed as a porous membrane, and then, after formation, the ionic liquid may be applied (e.g., impregnated) to the porous membrane such that the ionic liquid penetrates the pores in the porous membrane. The polymeric membrane(s) can be infused with the ionic liquid before or after electrodes are deposited onto the membrane. Alternatively, the polymeric membrane may be co-cast with the ionic liquid to form an infused polymeric membrane.

[0030] Thus, the present invention provides a method of manufacturing a device as described herein, comprising the steps of: (a) optionally depositing a liquid composition comprising carbon nanotubes onto a first polymer film and / or a second polymer film; (b) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto at least one (e.g., both) of the first polymeric osmosis membrane and the second polymeric osmosis membrane and / or the liquid composition comprising carbon nanotubes to form a film comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) on the membrane; (c) impregnating the first polymer membrane and the second polymer membrane with an ionic liquid; (d) securing the first polymer membrane and the second polymer membrane to one another; The present invention further provides a method comprising:

[0031] Alternatively, a polymer film containing an ionic liquid may be formed before printing a liquid composition containing a carbon nanomaterial and a transition metal oxide onto the polymer film. Thus, the present invention provides a method of making a device as described herein, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) optionally depositing a liquid composition comprising carbon nanotubes onto the first and / or second permeable polymeric membranes; (c) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto at least one (e.g., both) of the first polymer film and the second polymer film and / or the liquid composition comprising carbon nanotubes to form a film comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets); (d) securing the first polymer membrane and the second polymer membrane to one another; The present invention further provides a method comprising:

[0032] Step (a) may involve impregnating a polymeric membrane with the ionic liquid, or co-casting a membrane made of polymer and the ionic liquid.

[0033] The present invention provides a method of manufacturing a device as described herein, comprising the steps of: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) optionally depositing a second liquid composition comprising carbon nanotubes onto the first electrode; (d) depositing a liquid comprising a polymer and an ionic liquid onto the first electrode or the second liquid composition to form a polymeric permeable membrane comprising the ionic liquid; (e) optionally depositing a second liquid composition comprising carbon nanotubes onto the polymeric membrane; (f) depositing a third liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto a polymeric membrane or a further second liquid composition to form a second electrode; Further provided is a method wherein the first liquid composition and / or the third liquid composition further comprises a transition metal oxide.

[0034] Alternatively, the carbon nanotubes and the transition metal oxide may be deposited in separate steps to form different sublayers, and thus references herein to depositing a liquid composition comprising carbon nanotubes and a transition metal oxide may be replaced with a two-step process comprising first depositing a liquid composition comprising carbon nanotubes and then depositing a liquid composition comprising a transition metal oxide, or vice versa, as appropriate.

[0035] The above method may further comprise the step of securing the first and second polymeric films to a substrate and / or applying a protective sealing layer to the polymeric films.

[0036] The present invention further provides a device obtainable according to the methods described herein. [Brief explanation of the drawings]

[0037] [Figure 1] Figure 1 illustrates the principle of Pauli blocking, which modifies the band structure of graphene to prevent state transitions. [Figure 2] FIG. 2 is a schematic diagram showing the width, length, and thickness of a layered nanoplatelet. [Figure 3] FIG. 3 shows a scanning electron microscope (SEM) image of the printed ink described in Example 2 below. [Figure 4] FIG. 4 shows a scanning electron microscope (SEM) image of the printed ink described in Example 2 below. [Figure 5A] FIG. 5A shows a schematic diagram of the structure of a device according to one embodiment of the present invention. [Figure 5B] FIG. 5B is a schematic diagram of a device structure according to a further embodiment of the present invention, showing the substrate and protective encapsulation layer. [Figure 6] 6A and 6B show two exemplary devices of the present invention. [Figure 7] 7A-7C show alternative structures of the device. [Figure 8] 8A and 8B show plots of current versus potential difference for a device containing a CNT electrode and a device in which electrical contact was made by spraying the electrode with VO 2 . DETAILED DESCRIPTION OF THE INVENTION

[0038] As used herein, the term "carbon nanomaterial" or "nanocarbon" refers to a nanomaterial (i.e., a material having an average size of 1 nm to 100 nm in at least one dimension) that contains or consists of carbon. Typically, carbon nanomaterials contain at least 90% by weight of carbon, preferably at least 95% by weight, e.g., 99% by weight or more. This term includes graphene, graphite nanoplatelets, single-walled carbon nanotubes, multi-walled carbon nanotubes, crystalline diamond, and diamond-like carbon (see the following ISO standard: ISO / TS80004-3:2020).

[0039] As described above, the electrodes comprise carbon nanotubes (preferably single-walled carbon nanotubes). At least one electrode comprises a transition metal oxide. One or more electrodes may further comprise graphite nanoplatelets.

[0040] For one or more electrodes containing both carbon nanotubes and transition metal oxide, the carbon nanotubes and transition metal oxide particles may be homogeneously mixed to form a uniform electrode containing both nanotubes and metal oxide. Alternatively, the electrode may have a layered structure with a sublayer containing nanotubes and a sublayer containing metal oxide. In other words, the electrode may have different sublayers, one containing a larger proportion of carbon nanotubes (or containing only carbon nanotubes) and the other containing a larger proportion of metal oxide (or containing only metal oxide). In this configuration, the deposition of a metal oxide layer on the carbon nanotube layer provides electrical contact between the metal oxide and the nanotubes without the need for homogeneous mixing of the components.

[0041] As used herein, the phrase "one or more electrodes comprising carbon nanotubes and a transition metal oxide" encompasses all such configurations, including those in which the carbon nanotubes and metal oxide are homogeneously mixed and those in which they are present in sublayers.

[0042] In embodiments where there are two or more electrodes, one or more of the electrodes will comprise a transition metal oxide. For example, in embodiments where there are two electrodes, there may be one electrode comprising carbon nanotubes and a transition metal oxide, and a second electrode comprising carbon nanotubes but no transition metal oxide. In alternative embodiments where there are two electrodes, both electrodes may contain not only carbon nanotubes but also a transition metal oxide. In a preferred embodiment having two electrodes, one electrode comprises carbon nanotubes and a transition metal oxide, and the second electrode comprises carbon nanotubes but no transition metal oxide.

[0043] The carbon nanotubes may be single-walled or multi-walled carbon nanotubes, but preferably comprise or consist of single-walled carbon nanotubes. The carbon nanotubes may be metallic or semiconducting. The average outer diameter of the carbon nanotubes is typically 0.5 nm to 5 nm, e.g., 1 nm to 5 nm, and preferably 1 nm to 2 nm (determined by transmission electron microscopy), and their lengths may be greater than 3 μm, typically greater than 5 μm, e.g., greater than 10 μm or greater than 15 μm. While nanoplatelets, as described below, have two micron-sized dimensions, carbon nanotubes have only one micron-sized dimension (i.e., length).

[0044] Carbon nanotubes may be chirally selected so that they are semiconducting. The chirality of a carbon nanotube can be described using a pair of integers, m and n, as chiral indices. For chiral nanotubes, n ≠ m. For use in the present invention, the chiral indices, integers m and n, are typically such that nm ≠ k. *3, where k is an integer greater than 0. Because chirality confers semiconducting properties to nanotubes, it is preferred to combine chiralities within the carbon nanotubes used in the present invention.

[0045] The transition metal oxide may suitably be any transition metal oxide that exhibits a metal-insulator transition (MIT). Preferably, the transition metal oxide exhibits an MIT in the near-infrared region of the electromagnetic spectrum (i.e., the region from approximately 780 nm to 2500 nm). Suitable transition metal oxides include vanadium oxide (VOx), niobium oxide (NbOx), hafnium oxide (HfOx), cobalt oxide (CoOx), molybdenum oxide (MoOx), indium tin oxide (various compositions), and titanium oxide (TiOx), where x may be an integer or non-integer value between 1 and 5, preferably between 1 and 3. In a preferred embodiment, the transition metal oxide is vanadium oxide, e.g., selected from VO, VO, and VO.

[0046] The transition metal oxide may be doped as needed. For example, the transition metal oxide may be doped with Cr. The transition metal oxide may be alloyed as needed. For example, the transition metal oxide may be alloyed with La, Sr, or K. Doping and / or alloying the transition metal oxide may result in a shift in the potential difference required to initiate MIT.

[0047] The transition metal oxide may be added to the composition or present in the electrode as particles having a mass median diameter of 100 μm or less, typically 20 μm or less, for example, 10 μm or less or 1 μm or less. Preferably, the mass median diameter of the particles is 10 nm or more, 50 nm or more, or 80 nm or more, and 500 nm or less or 200 nm or less. For example, the mass median diameter of the particles may be 50 nm to 500 nm, for example, 80 nm to 200 nm. The particle size of the metal oxide can be measured by dynamic light scattering.

[0048] In some embodiments, more than one transition metal oxide is present in the liquid composition deposited in / to form the electrode. In embodiments in which more than one transition metal oxide is present, it is preferred that all transition metal oxides present exhibit MIT.

[0049] As used herein, the term "graphite nanoplatelets" (also referred to herein as "graphene nanoplatelets") refers to nanoparticles of graphite consisting of small stacks of graphene. The term graphite nanoplatelets refers to nanoplatelets having an average of 20 layers or less, typically 15 layers or less, and preferably 10 layers or less. The number of layers can be determined by UV-vis spectroscopy (see C. Backes et al., "Spectroscopic metrics allow in-situ measurement of mean size and thickness of liquid-exfoliated graphene nanosheets," Nanoscale, 2016, doi:10.1039 / C5NR08047A).

[0050] The average thickness of the nanoplatelets is typically less than 30 nm, e.g., less than 20 nm. As used herein, the term "thickness" refers to the dimension of the nanoplatelet along the axis along which the layers are stacked within the nanoplatelet. The terms "length" and "width" refer to the longer and shorter dimensions, respectively, of the nanoplatelet along orthogonal axes in the plane of the sheet of layered material (see Figure 2).

[0051] The average length and / or width of the nanoplatelets is typically 30 nm or more, preferably 50 nm or more or 100 nm or more. Typical average lengths and / or widths of the nanoplatelets are 10 μm or less, typically 3.0 μm or less, for example 2.0 μm or less, typically 1.5 μm or less, preferably 1 μm or less, for example 800 nm or less. In some instances, depending on the specific exfoliation process of these materials, graphite nanoplatelets have larger lateral dimensions, greater than 1 μm and less than 50 μm. The size distribution of these materials can be broad or narrow, depending on the exfoliation technique employed and / or any subsequent size selection process.

[0052] The dimensions of nanoplatelets can be measured using scanning electron microscopy or transmission electron microscopy. Nanoplatelets are typically micron-sized in only two dimensions (i.e., their length and width, and their thickness is significantly less than 1 μm, for example, less than 100 nm). These dimensions are preferably measured by transmission electron microscopy.

[0053] When present, graphite nanoplatelets are typically present in the electrode in an amount of 25% (w / w) or more, preferably 30% (w / w) or more, such as 35% (w / w) or more, and 50% (w / w) or less, preferably 45% (w / w) or less, such as 40% (w / w) or less.

[0054] When the electrode comprises a mixture of carbon nanotubes and graphite nanoplatelets, the carbon nanotubes may be present in the electrode described herein in a weight ratio relative to the amount of graphite nanoplatelets that is greater than 0.15:1 (carbon nanotubes:graphite nanoplatelets), preferably greater than 0.2:1, and less than or equal to 1:1, suitably less than or equal to 0.7:1, preferably less than or equal to 0.6:1.

[0055] For example, the carbon nanotubes are typically present in the electrode in a weight ratio relative to the amount of graphite nanoplatelets of 0.15:1 to 0.6:1 (carbon nanotubes:graphite nanoplatelets), preferably 0.4:1 to 0.5:1.

[0056] Alternatively, the amount of carbon nanotubes in the electrode may be defined relative to the weight of the total composition: carbon nanotubes are typically present in the electrode composition in an amount of 5% (w / w) or more, preferably 10% (w / w) or more, for example 15% (w / w) or more, and 30% (w / w) or less, preferably 25% (w / w) or less, for example 20% (w / w) or less.

[0057] When the electrode comprises carbon nanotubes as the only carbon nanomaterial, the carbon nanotubes may be present in the electrode in an amount of 50% by weight or more, preferably 75% by weight or more, such as 90% by weight or more, for example 95% by weight or more.

[0058] In embodiments containing a transition metal oxide in the electrode, the transition metal oxide is typically present in an amount of from 0.01% (w / w) to 40% (w / w) of the total liquid composition.

[0059] In the case of an electrode comprising a mixture of carbon nanotubes and a transition metal oxide, the carbon nanotubes may be present in the electrode in a weight ratio of 2:98 to 2:8 (carbon nanotubes:transition metal oxide) relative to the amount of transition metal oxide.

[0060] For electrodes containing both transition metal oxide and graphite nanoplatelets, the transition metal oxide may be present in the electrode in a weight ratio relative to the amount of graphite nanoplatelets of 2:8 to 1:1 (transition metal oxide:graphite nanoplatelets).

[0061] For an electrode containing a mixture of carbon nanotubes, transition metal oxide, and graphite nanoplatelets, the weight ratio of carbon nanotubes:transition metal oxide:graphite nanoplatelets is 1:94:5 to 1:8:1.

[0062] In the devices described herein, the electrodes typically have a thickness of from 10 nm to 750 nm, typically from 20 nm to 500 nm, for example from 50 nm to 250 nm.

[0063] Electrodes are typically deposited onto the polymer film from a liquid composition (or "ink"), such as a liquid composition containing carbon nanomaterial, transition metal oxide, and solvent (and optionally other thickeners, binders, and other additives described below) that can be sprayed or printed onto the polymer film.

[0064] The solvent may be aqueous or non-aqueous. However, the solvent preferably is or contains water (necessary for hydrogel formation). Alternatively, the solvent may be a dipolar aprotic solvent. Examples of such dipolar aprotic solvents include cyclopentanone, cyclohexanone, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), sulfolane, dihydrolevoglucosenone (silene), and lactones such as γ-valerolactone. When γ-valerolactone is present, it may be present in the liquid composition in an amount of 1% (w / w) to 10% (w / w), for example, 5% (w / w) or less, or in an amount of 5% (w / w) to 10% (w / w), preferably 6% (w / w) to 10% (w / w).

[0065] The liquid composition (containing carbon nanotubes and optionally additional carbon nanomaterials) may further include a thickener (which may also act as a gelling agent) to increase the viscosity of the composition, which ensures that the composition is suitable for printing and also reduces the tendency of the carbon nanomaterials to agglomerate from suspension.

[0066] The thickener is preferably a hydrogel-forming thickener. A hydrogel matrix containing carbon nanotubes and additional carbon nanomaterials (e.g., graphite nanoplatelets) is formed, resulting in a highly electrically conductive ink. Hydrogel-forming thickeners are generally hydrophilic polymer chains that form colloidal gels in water via hydrogen bonding.

[0067] Examples of suitable thickeners include: cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, hydroxyethylcellulose, carboxyethylcellulose, and salts thereof (e.g., sodium salts thereof); polymers such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyaniline (PANI), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and poly N-isopropylacrylamide (PNIPAAm); cyclodextrin, -Natural gelling agents such as xanthan gum, gelatin, glycerol, alginate, chitosan, etc. inorganic silica and inorganic clays such as bentonite, montmorillonite, laponite, nanosilica, and titania, and - Fibrous or rod-like materials, for example those with an aspect ratio of more than 100 (for example carbon nanotubes), etc.

[0068] In a preferred embodiment, the thickening agent is a cellulose derivative, such as carboxymethylcellulose. The term cellulose derivative, as used herein, refers to a chemical derivative of cellulose formed by functionalizing some or all of the hydroxyl groups present in cellulose (e.g., by etherification or esterification). Derivatives can be formed by incorporating one or more, or all, of the following groups: carboxy, hydroxy, methyl, ethyl, and / or propyl. Examples of cellulose derivatives include cellulose itself, as well as hydroxypropylmethylcellulose, hydroxypropylcellulose, methylethylcellulose, methylcellulose, carboxymethylcellulose, and combinations thereof. CMC is available in several forms (e.g., varying by degree of substitution and functionality) and can be crosslinked with other agents using several chemicals through covalent or hydrogen-bonding networks to impart novel, tunable properties (Gels 2018, 4, 54; doi:10.3390 / gels4020054).

[0069] Cellulose derivatives readily form hydrogels, which are used in many industrial applications. These materials can also function as surfactants to stabilize nanocarbon materials in aqueous media. Hydrogels exhibit ideal thixotropic behavior due to their formation of extended hydrogen-bonded or supramolecular networks. These networks help provide long-range order, which improves rheological behavior.

[0070] The total concentration of thickener may be in the range of 0.5% to 2% by weight of the total liquid composition (including solvent), for example 1% to 1.75% by weight of the total liquid composition.

[0071] The thickener increases the viscosity of the composition, which is believed to further enable the carbon nanotubes to form a pre-ordered supramolecular network that increases the conductivity of electrodes printed from the composition.

[0072] The viscosity of the composition is important to ensure that it can be printed to form a film. Furthermore, the composition should be viscous enough to prevent agglomeration of the carbon nanomaterials within the composition. Naturally, the appropriate viscosity will depend on the intended use of the composition (and resulting film). The thickener also ensures that the ink viscosity is suitable for printing, e.g., screen printing. Inks suitable for screen printing are typically thixotropic, and therefore their viscosity depends on the shear rate. The viscosity of the liquid composition (containing the carbon nanotubes, transition metal oxide, and optionally additional carbon nanomaterials) may be between 100 Pa.s and 1000 Pa.s at a shear rate of 0.1 / s and / or between 1 and 10 at a shear rate of 100 / s.

[0073] The liquid composition may further contain one or more surfactants. The surfactant is typically a nonionic surfactant. Examples of suitable nonionic surfactants include polyethylene oxide (PEO) surfactants (e.g., Triton X-100), polypropylene oxide (PPO) surfactants, cyclodextrin, and polyvinylpyrrolidone (PVP) surfactants. However, ionic surfactants such as sulfate surfactants (e.g., sodium dodecyl sulfate) may also be used.

[0074] The total concentration of surfactant may be in the range of 0.01% to 1% by weight of the total composition (including solvent), or 0.01% to 0.1% by weight, for example 0.02% to 0.05% by weight of the total composition.

[0075] The composition may further comprise one or more solvents and / or adhesives to improve adhesion of the dry film (formed by printing the ink) to the substrate. The nature and combination of adhesives will, of course, depend on the substrate.

[0076] The composition may further include one or more crosslinkers to improve the rheological parameters of the ink and / or the properties of the resulting film. This may include a wide range of functional organic acids or bases, such as ascorbic acid. Examples of additional crosslinkers include dicarboxylic and tricarboxylic acids, such as glutaric acid and trimesic acid. This crosslinking helps stabilize the film against rapid redissolution and the effects of ambient humidity on conductivity.

[0077] The composition may further comprise one or more humectants to aid in the printability of the ink in industrial processes. In aqueous compositions, the addition of urea, glycerin, or glycols such as polypropylene glycol slows down the ink drying process, resulting in consistent and repeatable printing.

[0078] Additionally, the composition may further comprise a curing (crosslinking) agent, which is a material that cures upon exposure to heat or radiation, hardening the liquid ink composition into a solid film. These include photocurable monomers or infrared activators, for example, epoxides (which may undergo a ring-opening reaction), aldehydes, or acids such as citric acid (which may undergo an esterification reaction).

[0079] Alternatively, films formed with binders containing monovalent ions, such as sodium carboxymethylcellulose, may be treated with aqueous solutions of divalent, trivalent, or tetravalent ionic salts, such as calcium(II) chloride or iron(III) sulfate, to form ionically crosslinked insoluble films by an ion exchange process.

[0080] The carbon nanomaterial-containing liquid composition is deposited as an electrode on the polymer film to form the device of the present invention.

[0081] Preferably, the device includes a pair of electrodes. Both electrodes may include carbon nanotubes and a transition metal oxide (optionally with additional carbon nanomaterials). Alternatively, if more than one electrode is present, the electrodes may be formed from different materials. For example, a first electrode may include carbon nanotubes and a transition metal oxide, and a second electrode may be a metal electrode. In this configuration, the electrode adjacent to the substrate is typically a non-carbon nanomaterial-containing electrode. In further exemplary embodiments, the first electrode may include carbon nanotubes and a transition metal oxide, and the second electrode may include carbon nanotubes but not a transition metal oxide. In this configuration, the electrode adjacent to the substrate is typically a second electrode that includes carbon nanotubes but not a transition metal oxide.

[0082] The device preferably includes a pair of electrodes comprising carbon nanotubes (and optionally additional carbon nanomaterials such as graphite nanoplatelets), with at least one electrode comprising a transition metal oxide. However, the device may also include a first carbon-containing electrode and a second electrode having a different composition than the first electrode. For example, the second electrode may be a metal electrode, such as a gold electrode, a silver electrode, or a copper electrode.

[0083] In some embodiments where there are more than one electrode, there may be one electrode comprising carbon nanotubes and a transition metal oxide, and a second electrode comprising carbon nanotubes but no transition metal oxide. For example, the present invention provides a device for actively modifying NIR emissions, comprising: (i) a substrate; (ii) an electrode comprising carbon nanotubes and a transition metal oxide; (iii) a polymer membrane containing an ionic liquid electrolyte; (iv) an electrode comprising carbon nanotubes; (v) a protective encapsulating layer.

[0084] In another example, the present invention provides a device for actively modifying NIR emissions, comprising: (i) a substrate; (ii) an electrode comprising carbon nanotubes; (iii) a polymer membrane containing an ionic liquid electrolyte; (iv) an electrode comprising carbon nanotubes and a transition metal oxide; (v) a protective encapsulating layer.

[0085] In a further example, the present invention provides a device for actively modifying NIR radiation, comprising: (i) a substrate; (ii) an electrode comprising carbon nanotubes and a transition metal oxide; (iii) an electrode comprising carbon nanotubes; (iv) a polymeric membrane containing an ionic liquid electrolyte; (v) an electrode comprising carbon nanotubes; (vi) a protective encapsulating layer.

[0086] A further example is a device for actively modifying NIR radiation, comprising: (i) a substrate; (ii) an electrode comprising carbon nanotubes; (iii) a polymer membrane containing an ionic liquid electrolyte; (iv) an electrode comprising carbon nanotubes; (v) an electrode comprising carbon nanotubes and a transition metal oxide; (vi) a protective encapsulating layer.

[0087] Preferably, the electrode adjacent to the substrate is an electrode that does not contain a transition metal oxide.

[0088] In alternative embodiments where there are two electrodes, both electrodes may contain not only carbon nanotubes but also transition metal oxides. For example, the present invention provides a device for actively modifying NIR radiation, comprising: (i) a substrate; (ii) an electrode comprising carbon nanotubes and a transition metal oxide; (iii) a polymer membrane containing an ionic liquid electrolyte; (iv) an electrode comprising carbon nanotubes and a transition metal oxide; (v) a protective encapsulating layer.

[0089] As noted above, in these examples, the electrode comprising carbon nanotubes and transition metal oxide may be a "single layer" electrode containing a homogeneous mixture of nanotubes and metal oxide forming a homogeneous layer, or the electrode may include separate and distinct carbon nanotube and transition metal oxide sublayers.

[0090] The polymer membrane is a dielectric and therefore electrically insulating. The polymer membrane can also retain ionic liquids (similar to a capacitor or battery device). For example, the polymer membrane may comprise polyethylene, polypropylene, polyvinylidene fluoride (PVDF), polyimide, cellulose, a cellulose derivative, or a mixture thereof. In a preferred embodiment, the polymer membrane is a polyethylene (PE) membrane, a polypropylene (PP) membrane, or a PE / PP membrane.

[0091] The ionic liquid is preferably a room temperature ionic liquid. Room temperature ionic liquids (RTILs) are a class of low melting point liquids whose conductivity is imparted by their ionic nature. The ionic liquid preferably has an electrochemical window of (+ / -) 4 V or greater, e.g., 4.5 V or greater.

[0092] As mentioned above, the ionic liquid may be introduced or infused into the polymer membrane either during or after its manufacture.

[0093] In some embodiments, the ionic liquid is infused into the polymer membrane by first forming a porous polymer membrane and then applying (eg, impregnating) the ionic liquid into the membrane.

[0094] Alternatively, ionic liquid-infused membranes comprise solid co-cast films of suitable polymers containing ionic liquids, commonly known as solid polymer electrolytes. To prepare such solid polymer electrolytes, the dielectric polymer and ionic liquid are dissolved in a suitable solvent in which they are both soluble (e.g., a polar aprotic solvent such as acetone, DMF, or NMP), and then the solvent is removed to form a polymeric layer infused with the ionic liquid.

[0095] When a polymer film is co-cast from a polymer and an ionic liquid, the polymer film may be cast onto a previously coated layer of an electrode containing carbon nanotubes. This approach has several advantages. First, it reduces the amount of liquid that can leak from the device. Second, the multi-step coating and encapsulation process allows for a more convenient method of device construction. Furthermore, mechanically, the device is less susceptible to dielectric breakdown due to localized stress-induced damage.

[0096] The devices described herein may be exposed to the environment during use and should therefore be fully operable under ambient conditions. Water present in the air is one potential source of harmful effects due to water's low potential window for electrolysis (1.23 V) and material interaction considerations. Therefore, the ionic liquid is preferably a hydrophobic ionic liquid.

[0097] Examples of suitable ionic liquids for use in the devices described herein include diethylmethyl(2-methoxyethyl)ammonium salts, including diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([DEME][TFSI]) and [DEME][BF4], and 1-ethyl-3-methylimidazulium salts, such as EMI-BF4 and [EMI][TFSI]. Alternatively, the ionic liquid may be a lithium-based ionic liquid (i.e., where the cation is Li + The ionic liquid may be, for example, LiClO4 or Li[TFSI].

[0098] In the devices described herein, the polymeric membrane typically has a thickness of from 100 nm to 100 μm, such as from 1 μm to 50 μm, for example from 1 μm to 30 μm.

[0099] The device may have a layered structure in which one or more sheets of polymer membrane are sandwiched between electrode films, and the combination of one or more polymer membranes and one or more electrodes is mounted on a substrate.

[0100] The substrate may be comprised of a rigid or flexible planar material, which may include a continuous organic polymer, a silicate-based glass, or a conductive metal sheet. The substrate may be further metallized by various means to facilitate efficient electrodes. The substrate may also be coated with nanocarbon materials to aid in industrial manufacturing.

[0101] The device may be protected from the ingress of environmental moisture using a top encapsulating substrate on top of the device. This barrier layer may comprise one or more layers of a continuous material. Such an encapsulating layer may be formed from a suitable barrier material with low absorption characteristics in the IR spectrum, such as poly(ethylene), flexible glass, quartz, sapphire, alkali metal halides, polycarbonate, and poly(methyl) methacrylate.

[0102] A typical thickness of the assembled layer structure consisting of one(s) polymer membrane(s) and one(s) electrode(s) is less than 1 cm, e.g., less than 500 microns, or less than 100 microns, or less than 50 microns. A typical thickness of the assembled layer structure is greater than 5 microns, e.g., greater than 10 microns. A typical surface area of ​​a layer of the layer structure is greater than 20 cm. 2 Over, typically 100 cm 2 It's super.

[0103] The device can be connected to or is connected to a power source, such as a battery. More specifically, the power source can be connected to or is connected to the electrodes of the device. A potential difference applied between the electrodes by the power source changes the Fermi level of the carbon nanomaterial (e.g., graphite nanoplatelets) in the electrodes, providing a thermal / NIR camouflage effect. The potential difference applied between the electrodes can also induce a metal-insulator transition in the transition metal oxide, thereby providing further thermal / NIR camouflage effects.

[0104] The device may further include one or more switches or control circuits for controlling the supply of power to the electrodes or for varying the potential difference supplied by the power source to the electrodes of the device.

[0105] The device preferably further comprises a pair of permeable polymeric membranes to facilitate device fabrication. When two polymeric membranes are used, a pair of identical polymeric membranes onto which carbon nanomaterials are printed can be symmetrically assembled to provide a device for actively modifying NIR radiation. For example, the device may include a pair of polymeric membranes, with electrodes deposited on the surface of each polymeric membrane. The polymeric membranes can be assembled together to form a symmetrical device having a structure similar to that of a battery or a capacitor.

[0106] As mentioned above, the device has a structure similar to a battery or a capacitor. As a result, it is envisioned that the devices described herein may be used as batteries or capacitors. Thus, the present invention provides (i) a substrate; (ii) one or more polymeric membranes containing an ionic liquid electrolyte; (iii) one or more electrodes comprising carbon nanotubes and a transition metal oxide; (iv) a protective encapsulating layer.

[0107] The device and layers within the device may have the structure or properties of the device or layers described above in connection with devices for actively modifying NIR emission.

[0108] In an exemplary embodiment, the invention provides a device for actively modifying (e.g., camouflaging) NIR radiation, comprising: (i) one or more polymeric membranes comprising polyethylene, polypropylene, or a mixture thereof, and containing an ionic liquid; (ii) one or more electrodes comprising carbon nanotubes and a transition metal oxide (optionally with graphite nanoplatelets).

[0109] In one embodiment, the present invention provides a device for actively modifying (e.g., camouflaging) NIR radiation, comprising: (i) a pair of polymeric membranes comprising polyethylene, polypropylene, or a mixture thereof, and containing an ionic liquid; (ii) optionally, an electrode comprising carbon nanotubes adjacent to one and / or both of the polymeric membranes; (iii) electrodes comprising carbon nanotubes (and optionally graphite nanoplatelets) deposited on one surface of each of the polymer films or electrodes comprising carbon nanotubes, wherein at least one of the electrodes additionally comprises a transition metal oxide.

[0110] In a further aspect, the present invention provides a method of manufacturing a device as described herein, comprising the steps of: (a) optionally depositing a liquid composition comprising carbon nanotubes onto a first permeable polymer membrane and / or a second permeable polymer membrane; (b) depositing a liquid composition comprising carbon nanotubes and transition metal oxides (and optionally graphite nanoplatelets) onto (i) at least one of the first and / or second permeable polymeric membranes, or (ii) the layer formed in step (a); (c) impregnating the first polymer membrane and the second polymer membrane with an ionic liquid; (d) securing the first polymer membrane and the second polymer membrane to one another; The present invention provides a method comprising:

[0111] Alternatively, a polymer film containing an ionic liquid may be formed before printing a liquid composition containing a carbon nanomaterial and a transition metal oxide onto the polymer film. Thus, the present invention provides a method of making a device as described herein, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) optionally depositing a liquid composition comprising carbon nanotubes onto the first and / or second permeable polymeric membranes; (c) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto (i) at least one of the polymer films or (ii) the latter formed in step (a) to form a film comprising carbon nanotubes and a transition metal oxide; (d) securing the first polymer membrane and the second polymer membrane to one another; The present invention further provides a method comprising:

[0112] As noted above, in devices where there are more than one electrode, there may be one electrode comprising carbon nanotubes and a transition metal oxide, and a second electrode comprising carbon nanotubes but no transition metal oxide. Thus, in one embodiment of the present invention, there is provided a method of making a device as described herein, comprising the steps of: (a) depositing a liquid composition containing carbon nanotubes onto a first permeable polymer membrane and / or a second permeable polymer membrane; (b) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto (i) at least one of the first and / or second permeable polymeric membranes, or (ii) the layer formed in step (a), to form a film comprising carbon nanotubes on the membrane; (c) impregnating the first polymer membrane and the second polymer membrane with an ionic liquid; (d) securing the first polymer membrane and the second polymer membrane to one another; A method is provided, comprising:

[0113] A further exemplary method of the present invention is a method of manufacturing a device described herein, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) depositing a liquid composition comprising carbon nanotubes onto the first polymeric permeable membrane and / or the second polymeric permeable membrane; (c) depositing a liquid composition comprising carbon nanotubes and transition metal oxides (and optionally graphite nanoplatelets) onto (i) at least one of the polymeric films or (ii) the layer formed in step (b) to form a film comprising carbon nanotubes and transition metal oxides; (d) securing the first polymer membrane and the second polymer membrane to one another; The present invention provides a method comprising:

[0114] In alternative embodiments where a pair of electrodes is present, both electrodes may comprise carbon nanotubes and a transition metal oxide. Thus, the present invention provides a method of making a device as described herein, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto both the first polymer film and the second polymer film to form a film comprising carbon nanotubes and a transition metal oxide; (c) securing the first polymer membrane and the second polymer membrane to one another; The present invention provides a method comprising:

[0115] Instead of preparing pre-coated first and second polymeric films and fixing them together, the devices of the invention can be prepared by subsequent deposition of layers onto a substrate. Thus, in a further aspect, the invention provides a method of making a device as described herein, comprising: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) optionally depositing a second liquid composition comprising carbon nanotubes onto the first electrode; (d) depositing a liquid comprising a polymer and an ionic liquid onto the first electrode or the layer formed in step (c) to form a polymeric permeable membrane comprising the ionic liquid; (e) optionally depositing a second liquid composition comprising carbon nanotubes onto the polymeric membrane; (f) depositing a third liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto the polymeric membrane or layer formed in step (e) to form a second electrode; The method further comprises the first liquid composition and / or the third liquid composition further comprising a transition metal oxide.

[0116] As noted above, in embodiments where there are more than one electrode, there may be one electrode comprising carbon nanotubes and a transition metal oxide, and a second electrode comprising carbon nanotubes but no transition metal oxide. Thus, the present invention provides a method of making a device as described herein, comprising: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) depositing a liquid comprising a polymer and an ionic liquid on the first electrode to form a polymeric permeable membrane comprising the ionic liquid; (d) depositing a second liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto the polymeric membrane to form a second electrode; The present invention provides a method comprising:

[0117] In a further example, the present invention provides a method of manufacturing a device described herein, comprising: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) depositing a liquid comprising a polymer and an ionic liquid on the first electrode to form a polymeric permeable membrane comprising the ionic liquid; (d) depositing a second liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto the polymeric membrane to form a second electrode; The present invention provides a method comprising:

[0118] In a further exemplary embodiment, the present invention provides a method of manufacturing a device described herein, comprising: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) depositing a liquid comprising a polymer and an ionic liquid on the first electrode to form a polymeric permeable membrane comprising the ionic liquid; (d) depositing a second liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto the polymeric membrane; (e) depositing a third liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto the polymeric membrane to form a second electrode; The present invention provides a method comprising:

[0119] A further embodiment of the present invention is a method of manufacturing a device as described herein, comprising the steps of: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) depositing a second liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto the first electrode; (d) depositing a liquid comprising a polymer and an ionic liquid on the first electrode to form a polymeric permeable membrane comprising the ionic liquid; (e) depositing a third liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) onto the polymeric membrane to form a second electrode; The present invention provides a method comprising:

[0120] In alternative embodiments where a pair of electrodes is present, both electrodes may comprise carbon nanotubes and a transition metal oxide. Thus, the present invention provides a method of making a device as described herein, comprising the steps of: (a) providing a substrate; (b) depositing a first liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto a substrate to form a first electrode; (c) depositing a liquid comprising a polymer and an ionic liquid on the first electrode to form a polymeric permeable membrane comprising the ionic liquid; (d) depositing a third liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto the polymeric membrane to form a second electrode; The present invention provides a method comprising:

[0121] The liquid compositions in steps b) to f) typically further comprise a solvent (as described above), and therefore the method may further comprise evaporating the solvent after depositing one liquid composition and before depositing the next liquid composition.

[0122] It will be appreciated that this method is suitable for devices in which the polymeric permeable layer is formed by co-casting the polymer with the ionic liquid (rather than impregnating the ionic liquid into a polymer once formed into a membrane).

[0123] As mentioned above, the carbon nanotubes and the transition metal oxide may be present in an electrode that is a separate, distinct layer, rather than an electrode formed from a single liquid composition containing both. Thus, in the above-described method embodiments, "depositing a liquid composition containing carbon nanotubes and a transition metal oxide" may be replaced with performing the following steps: i) "depositing a liquid composition containing carbon nanotubes," and ii) "depositing a liquid composition containing a transition metal oxide," or vice versa.

[0124] The liquid compositions containing carbon nanomaterials and polymeric films used in these methods may have the properties and characteristics of the compositions and films described in connection with the devices described herein.

[0125] Preferably, the liquid composition containing the carbon nanomaterial is deposited (eg, printed) onto both the polymer film or substrate.

[0126] When the method includes fixing the first and second polymer films to each other, the polymer films are typically fixed to each other so that the uncoated surfaces of the two polymer films (i.e., the film surfaces on which the carbon nanomaterial-containing liquid composition has not been deposited) are in contact with each other.

[0127] The deposition process may be carried out by spraying or printing the liquid composition onto the polymer film. A wide variety of printing techniques can be used, such as screen printing, flexography, offset lithography, slot die coating, doctor blade coating, or inkjet printing.

[0128] The impregnation step may be carried out by applying the ionic liquid to the surface of the polymer membrane and applying a vacuum.

[0129] The above method may further comprise the step of securing the first and second polymeric films to a substrate and / or applying a protective sealing layer to the polymeric films.

[0130] The method may comprise the step of obtaining a liquid composition comprising single-walled carbon nanotubes, a transition metal oxide and, optionally, graphite nanoplatelets. Thus, prior to step a) above, the method may comprise the following steps: (i) optionally obtaining exfoliated graphite nanoplatelets; (ii) obtaining exfoliated single-walled carbon nanotubes; (iii) obtaining a transition metal oxide; (iv) dispersing the exfoliated single-walled carbon nanotubes, the transition metal oxide, the thickener, optionally a surfactant, and optionally the exfoliated graphite nanoplatelets in a solvent.

[0131] To ensure homogeneous mixing of the components, the mixture in step iii) may be subjected to a high shear mixing stage. Furthermore, a further step of compressing the ink (e.g., roll milling) may be performed to degas the ink, which facilitates printing of the ink onto a membrane.

[0132] The present invention further provides a device obtainable according to the methods described herein.The present invention further provides a method of camouflaging / hiding NIR / thermal radiation from an object, comprising the step of placing a device described herein between the object and an NIR / thermal radiation detector.

[0133] The present invention can be used in a wide range of applications where modulation of IR radiation is required. This includes thermal management of objects where conventional and / or conductive methods are not feasible, such as in space electronics. Additionally, as noted above, the device of the present invention may be useful in thermal windows and radiative temperature control. [Example]

[0134] Example 1 - Exfoliation of Graphite to Form Nanoparticulate Graphite The graphite flakes were exfoliated using the apparatus and process described in International Patent Application No. WO2020 / 074698 (PCT / EP2019 / 077579) to yield nanoparticulate graphite with a lateral size distribution averaging approximately 1 μm and an average thickness of approximately 10 layers.

[0135] Briefly, fine graphite powder (air classification of the milled powder to produce flake sizes of 1-50 μm) was dispersed in a surfactant-water system and added to the injection vessel of a high-pressure homogenizer (e.g., International Patent Application No. WO2020 / 074698 (PCT / EP2019 / 077579)). The fluid was then pressurized and accelerated under reduced pressure before exiting the homogenizer's processing cell and entering a heat exchanger. Once the fluid had cooled to a temperature maintained by an external cooling system, it was recovered or recycled, depending on the system configuration.

[0136] Once the graphite was processed, the exfoliated mixture was centrifuged at 5,000 g for 20 minutes to remove all unexfoliated crystallites and larger debris. These parameters resulted in the precipitation of all but a few layered nanosheets (i.e., nanoparticulate graphite). The lateral size and thickness distributions of the resulting nanoparticulate graphite were 50 nm to 2,000 nm and approximately 20 nm or less, respectively.

[0137] Example 2 - Electrode Ink Formulation with Carbon Nanotubes The composition of one batch of ink prepared is shown in the table below: The total solids content of the prepared ink (including binder etc.) was approximately 3.7% by weight.

[0138] [Table 1]

[0139] To prepare the ink, the ingredients were weighed into a suitable container. The mixture was heated (60°C hot plate) while mixing using a Silverson L5M-A Laboratory High Shear Mixer operating at 5000 rpm to sufficiently reduce the viscosity and blend the ingredients. The mixture was then mixed for 5 minutes.

[0140] The lateral size distribution of the graphite nanoplatelets is 50-800 nm, and the thickness is approximately 20 nm or less. Viscosity measurements of the ink at shear rates ranging from 0.1 / s to 100 / s show that the ink is thixotropic.

[0141] Structural characterization was performed by SEM, which shows that there is a dense network of carbon nanotubes present in the interstitial spaces between the packed carbon nanoplatelets (see Figures 3 and 4).

[0142] The ink was successfully printed on a variety of substrates, including several grades of polyethylene terephthalate (PET) substrates (DuPont Tejin ST504 and Felix Scholler F40100) and paper substrates.

[0143] Example 3 - Electrode Ink Formulation with Carbon Nanotubes and Transition Metal Oxides The composition of one batch of ink is shown in the table below: The total solids content of the ink (including binder etc.) is approximately 3.7% by weight.

[0144] [Table 2]

[0145] To prepare the ink, weigh the ingredients into a suitable container. The mixture is heated (60°C hot plate) while mixing using a Silverson L5M-A Laboratory High Shear Mixer operating at 5000 rpm to sufficiently reduce the viscosity and blend the ingredients. The mixture is then mixed for 5 minutes.

[0146] The lateral size distribution of the graphite nanoplatelets is between 50 nm and 800 nm, and the thickness is approximately 20 nm or less.

[0147] Vanadium oxide was obtained from Sigma Aldrich and is a typical D50 The nanoparticles are processed by liquid-phase exfoliation to produce a population of nanomaterials that are less than 10 microns in size.

[0148] Example 4 - Film Deposition and Device Assembly To enable spray deposition, the carbon nanotube-containing ink of Example 2 is diluted 20 times. The diluted ink is sprayed onto a PE / PP Celgard membrane (2340) that has been infiltrated with an ionic liquid.

[0149] The ionic liquid, diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([DEME][TFSI]), was pipetted onto the surface of the Celgard membrane and left at 100 bar for 30 minutes, resulting in a concentration of 200 μL / cm 2 permeate the membrane.

[0150] Alternatively, [DEME][TSFI] at 100 μL / cm 2 The ionic liquid was then added to the polyethylene film at a temperature of 100°C and allowed to soak for 10 minutes. The film was then subjected to rolling compression to remove excess ionic liquid. The single-walled carbon nanotube dispersion (described in Example 2) was then sprayed at 3 bar using an airbrush through a suitable stencil at a distance of 15 cm to form an electrode approximately 20 nm thick. This was done on a hot plate at 90°C.

[0151] The same process is repeated using the ink containing carbon nanotubes and vanadium oxide of Example 3 to form a polyethylene film coated with an electrode containing carbon nanotubes and vanadium oxide.

[0152] Film thickness is measured by SEM cross-section analysis or scanning probe profilometry, and the conductivity and thickness are used to calculate the specific conductivity. The conductivity of printed films is measured using a four-point probe according to International Electrotechnical Commission standard IEC TS 62607-2-1:2012.

[0153] The device is then assembled by laminating the two films (one with an electrode containing carbon nanotubes and the other with an electrode containing carbon nanotubes and vanadium oxide) such that a pair of ionic liquid-permeated Celgard membranes separate the two electrodes by the printed carbon-containing film.

[0154] The device structure is shown schematically in Figures 5A and 6A. The device includes a pair of ionic liquid-permeated Celgard membranes (10). One side of each membrane is printed with a film (12) from the ink described in Example 2 or Example 3. These printed films function as the electrodes of the device. Electrical contact with the electrodes was made using copper tape (14), which was connected to a voltage source by electrical wires (16).

[0155] Another device structure, including a substrate and an IR-transparent protective layer made of LDPE, is shown in Figure 5B. The device structure in Figure 5B is substantially as shown in Figure 5A. However, the device further includes a PET substrate (18) and a protective encapsulating layer (20) formed from LDPE (low-density polyethylene). Copper connectors (14) penetrate the substrate (18) and protective layer (20) to allow connection of the electrodes (12) to an external voltage / power source via electrical wires (16).

[0156] FIG. 6B shows an alternative embodiment comprising three electrodes, with an electrode printed from an ink containing carbon nanotubes adjacent to each side of the polymeric membrane structure, and an additional electrode printed on one of these electrodes from an ink comprising carbon nanotubes and a transition metal oxide (e.g., the ink described in Example 3).

[0157] Example 5 - Devices Fabricated from Co-cast Ionic Liquid-Infused Polymer Membranes In a further example, a carbon nanotube-containing ink is prepared as described in Example 2. The carbon nanotube dispersion is diluted 10 times with deionized water and sonicated in a treatment bath for 10 minutes to form a sprayable ink.

[0158] The ink is then sprayed using an airbrush at 3 bar through a suitable stencil from a distance of 15 cm on a hotplate at 90°C to form the carbon nanotube-containing electrode layer.

[0159] A polymer membrane was formed on the carbon nanotube-containing electrode layer by co-casting poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with the ionic liquid [EMI][TFSI] to form a 30 μm thick membrane. To achieve this, a solid electrolyte precursor solution containing 1.94% (w / w) PVDF-HFP, 2.91% (w / w) [EMI][TFSI], and 95.15% (w / w) acetone was applied at a concentration of 200 μL / cm. 2 The solution is then drop-cast onto the carbon nanotube-containing electrode. The solvent is evaporated, leaving a film containing 60% [EMI][TSFI] and 40% PVDF-HDP.

[0160] A second ink is prepared from 0.4 wt.% single-walled carbon nanotubes and 3.6% vanadium oxide (e.g., VO2) in water containing 0.8 wt.% sodium carboxymethylcellulose according to Example 3 or as purchased from OCSiAl. The carbon nanotube and vanadium oxide dispersion is diluted 10 times with deionized water and sonicated in a processing bath for 10 minutes to form a sprayable ink. The second ink is then sprayed using an airbrush at 3 bar from a distance of 15 cm through an appropriate stencil to form a carbon nanotube-containing electrode layer, forming an electrode layer containing carbon nanotubes and vanadium oxide. This is done on a hot plate at 90°C.

[0161] A device is then constructed in a manner similar to that described in Example 4 above.

[0162] Example 6 - Exemplary Device of the Invention FIG. 6A shows a device according to the present invention having a first electrode layer 25 comprising a composite of carbon nanotubes and vanadium oxide adjacent to an electrolyte 26 adjacent to a second electrode layer 27 comprising carbon nanotubes but no vanadium oxide.

[0163] FIG. 6B shows a further device according to the invention having a first electrode layer 25 comprising a composite of carbon nanotubes and vanadium oxide adjacent to a second electrode layer 27 comprising carbon nanotubes but not vanadium oxide, which is adjacent to an electrolyte 26 adjacent to a second electrode layer 27 comprising carbon nanotubes but not vanadium oxide.

[0164] The exemplary device shown in Figures 6A and 6B is expected to control NIR signature levels in real time.

[0165] Figures 7A-7C show further devices according to the invention. The device in Figure 7A comprises a first electrode layer 25 comprising a homogeneously mixed composite of carbon nanotubes and vanadium oxide adjacent to an electrolyte 26 adjacent to a second electrode layer 27 comprising carbon nanotubes but no vanadium oxide.

[0166] In Figures 7B and 7C, the electrode containing both carbon nanotubes and vanadium oxide includes sublayers of each material. Thus, in the devices shown in Figures 7B and 7C, there is a first electrode layer including a layer of carbon nanotubes 25A and a separate layer of vanadium oxide 25B, which together form the electrode. This electrode is adjacent to an electrolyte 26, which is adjacent to a second electrode layer 27, which includes carbon nanotubes but no vanadium oxide. In Figure 7B, the vanadium oxide sublayer 25B of the electrode is adjacent to the electrolyte 26, while in Figure 7C, the carbon nanotube sublayer 25A is adjacent to the electrolyte 26.

[0167] Figure 8A shows a plot of current versus potential difference for a device containing CNT-only electrodes and a device in which electrical contact was made by spraying VO onto the surface of one of the electrodes (corresponding to the device shown schematically in Figure 7C). In this device, the ionic liquid used comprised [EMIM][TFSI] and PVDF-co-HFP in a 1:1 ratio. The plot shows electrochemical charge accumulation between -2 V and 2 V.

Claims

1. 1. A device for actively modifying NIR radiation, comprising: (i) a substrate; (ii) one or more polymeric membranes comprising an ionic liquid electrolyte; (iii) one or more electrodes comprising carbon nanotubes and a transition metal oxide; (iv) a protective sealing layer; and Including, the device.

2. The device of claim 1 , wherein the one or more electrodes comprise a first sublayer comprising the carbon nanotubes and a second sublayer comprising the transition metal oxide.

3. 3. The device of claim 1 or claim 2, wherein the one or more electrodes further comprise graphite nanoplatelets.

4. 4. The device of claim 3, wherein the carbon nanotubes and graphite nanoplatelets are present in the electrode in a weight ratio of 0.15:1 to 0.6:1 (carbon nanotubes:graphite nanoplatelets).

5. 10. A device according to any preceding claim, wherein the carbon nanotubes and transition metal oxide are present in the electrode in a weight ratio of from 2:98 to 2:8 (carbon nanotubes:transition metal oxide).

6. 10. The device of claim 1, wherein the one or more electrodes comprising carbon nanotubes and a transition metal oxide are adjacent to a surface of at least one of the one or more polymeric films (e.g., the one or more electrodes are vapor-deposited on a surface of at least one of the one or more polymeric films).

7. 6. The device of claim 1, further comprising one or more electrodes comprising carbon nanotubes adjacent at least one of the one or more permeable polymeric membranes.

8. 10. A device according to any preceding claim, wherein the polymer membrane(s) is / are disposed between a pair of electrodes.

9. 9. The device of claim 8, wherein one of the electrodes comprises carbon nanotubes and a transition metal oxide, and the other electrode comprises carbon nanotubes but no transition metal oxide.

10. 10. A device according to any preceding claim, optionally comprising single-walled carbon nanotubes having an average diameter of between 1 nm and 5 nm and / or a length greater than 3 μm.

11. 10. A device according to any preceding claim, wherein the electrode further comprises a thickening agent, such as carboxymethyl cellulose.

12. 10. The device of any preceding claim, wherein the polymeric membrane comprises polyethylene, polypropylene, or a mixture thereof.

13. 10. The device of any preceding claim, wherein the ionic liquid has an electrochemical window of 4 V or greater.

14. 10. A device according to any preceding claim, connectable or connected to a power source.

15. (i) one or more polymeric membranes comprising polyethylene, polypropylene, or a mixture thereof, and containing an ionic liquid; (ii) one or more electrodes comprising a mixture of carbon nanotubes and a transition metal oxide; The device of claim 1 , comprising:

16. (i) one or more polymeric membranes comprising polyethylene, polypropylene, or a mixture thereof, and containing an ionic liquid; (ii) a pair of electrodes comprising a mixture of carbon nanotubes, transition metal oxides, and graphite nanoplatelets; The device of claim 1 , comprising:

17. 17. The device of claim 15 or 16, wherein the one or more electrodes comprising a mixture of carbon nanotubes, transition metal oxide, and graphite nanoplatelets are adjacent to a surface of at least one of the one or more polymeric films (e.g., the one or more electrodes are vapor-deposited on a surface of at least one of the one or more polymeric films).

18. 17. The device of claim 15 or 16, comprising one or more electrodes comprising carbon nanotubes (and optionally graphite nanoplatelets) adjacent to at least one of the one or more permeable polymeric membranes.

19. 10. A method for manufacturing a device according to any of the preceding claims, comprising the steps of: (a) optionally depositing a liquid composition comprising carbon nanotubes onto a first polymer film and / or a second polymer film; (b) depositing a liquid composition comprising carbon nanotubes and transition metal oxides (and optionally graphite nanoplatelets) onto at least one of the first and second polymeric membranes and / or the layer formed in step (a); (c) impregnating the first polymer membrane and the second polymer membrane with an ionic liquid; (d) securing the first polymer membrane and the second polymer membrane to one another; A method comprising:

20. 20. The method of claim 19, wherein step b) comprises depositing (e.g., printing) a liquid composition comprising a carbon nanomaterial and a transition metal oxide onto both the first polymer film and the second polymer film.

21. 19. A method for manufacturing a device according to any one of claims 1 to 18, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) optionally depositing a liquid composition comprising carbon nanotubes onto the first polymeric permeable membrane and / or the second polymeric permeable membrane; (c) depositing a liquid composition comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets) onto at least one (e.g., both) of the polymer films and / or the layer formed in step (a) to form a film comprising carbon nanotubes and a transition metal oxide (and optionally graphite nanoplatelets); (d) securing the first polymer membrane and the second polymer membrane to one another; A method comprising:

22. 10. A method for manufacturing a device according to any one of the preceding claims, comprising the steps of: (a) optionally depositing a liquid composition comprising carbon nanotubes onto a first polymer film and / or a second polymer film; (b) depositing a liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) and a liquid composition comprising a transition metal oxide onto at least one of the first and second polymeric permeable membranes and / or the layer formed in step (a), or vice versa; (c) impregnating the first polymer membrane and the second polymer membrane with an ionic liquid; (d) securing the first polymer membrane and the second polymer membrane to one another; A method comprising:

23. 23. The method of claim 22, wherein step b) comprises depositing (e.g., printing) a liquid composition comprising a carbon nanomaterial and a transition metal oxide onto both the first polymer film and the second polymer film.

24. 19. A method for manufacturing a device according to any one of claims 1 to 18, comprising the steps of: (a) forming a first polymer permeable membrane and a second polymer permeable membrane comprising an ionic liquid; (b) optionally depositing a liquid composition comprising carbon nanotubes onto the first polymeric permeable membrane and / or the second polymeric permeable membrane; (c) depositing a liquid composition comprising carbon nanotubes (and optionally graphite nanoplatelets) and a liquid composition comprising a transition metal oxide, or vice versa, onto at least one (e.g., both) of the polymer films and / or the layer formed in step (a) to form a sublayer comprising carbon nanotube oxide and (optionally graphite nanoplatelets) a transition metal; (d) securing the first polymer membrane and the second polymer membrane to one another; A method comprising:

25. 20. A method of camouflaging / hiding NIR radiation from an object, comprising the step of placing a device according to any one of claims 1 to 18 between the object and an NIR detector.

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