Conductive adhesive

Abstract

This invention relates to an aqueous emulsion useful as a reversible, conductive (e.g. electrically and / or thermally conductive) adhesive. The invention also provides methods of making the aqueous emulsion and methods of using the aqueous emulsion.

Description

Conductive Adhesive

[0001] This invention relates to an aqueous emulsion useful as a reversible, conductive adhesive. The invention also provides methods of making the aqueous emulsion and methods of using the aqueous emulsion.BACKGROUND

[0002] Water-based adhesives are an example of organic solvent-free adhesives, and typically contain a polymer responsible for the cohesion (i.e., internal strength) of the adhesive. The required penetration is achieved by dissolving or dispersing the polymer in water, or by melting it into a liquid form, while the water-based adhesive is returned to a solid condition by removing the water by absorption or evaporation, or by cooling the melt. The demand for water-based adhesives had increased in recent years, as they are more eco-friendly than volatile organic compound (VOC) based solvents and facilitate the manufacture of products in an more environmentally friendly manner.

[0003] The high demand for electronic devices and their short lifespans contributes to the annual rise of electronic waste, with only 17% of global e-waste being properly recycled (Peng, P. & Shehabi, A., Nature Sustainability, vol. 6 (2022)). Electronic wastes contain substances that present a significant threat to human and environmental health. Thus, end-of-life management of e-waste requires complex consideration to minimise the impact on public health and the environment.

[0004] In addition to the environmental benefit, reusing and recycling electronic waste can have a positive economic impact by minimising the demand for virgin mining of vital metal supplies (e.g. the rare earth metals required to produce circuit boards). However, the recyclability of electronic waste is complicated by the difficulty in removing or separating different components from one another. For example, electronic waste may include components held together by an adhesive (which may be electrically and / or thermally conductive) that is difficult to remove. This is further complicated by the fact that many electrical components are highly temperature sensitive, negating the option of applying heat to remove / soften the adhesive.

[0005] Accordingly, there is a need in the art for a water-based, electrically and / or thermally conductive adhesive that is reversible.BRIEF SUMMARY OF THE DISCLOSURE

[0006] In accordance with a first aspect of the present invention, there is provided an aqueous emulsion selected from:an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase; wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged; and an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0007] The aqueous emulsions of the invention may be employed as adhesives, including as electrically conductive adhesives. The aqueous emulsions of the invention may also be employed as thermally conductive adhesives. The aqueous emulsions of the invention achieve several advantages over prior art adhesives.

[0008] The aqueous emulsion may be coated onto at least one of two opposing surfaces in order to reversibly adhere the surfaces to one another. In particular, the inventors have found that a first surface coated with an aqueous emulsion as defined in the first aspect, i.e. comprising a conductive filler and particles comprising hydrophobic polymer that are either positively charged or negatively charged, can adhere to a second surface to form a reversibly bonded interface. It may be that the first surface is coated with the aqueous emulsion and the second surface is not coated with the aqueous emulsion prior to adhering the two surfaces to one another. It may be that both the first surface and the second surface are coated with the aqueous emulsion prior to adhering the two surfaces to one another. Without wishing to be bound by theory, it is thought that the electrostatic attraction between the positively charged particles or the negatively charged particles and the first and second surfaces facilitates the adhesion. The two surfaces adhere to one another in water and remain adhered even after the adhesive has dried. The conductive filler remains part of the solid adhesive, meaning that the solid adhesive is electrically conductive. The solid adhesive may also be thermally conductive.

[0009] Typically, moisture does not compromise the adhesion between the two components. However, the adhesion can be reversed by altering the local pH at the bonded interface. Without wishing to be bound by theory, in the case of aqueous emulsions comprising particles which are negatively charged, it is thought that increasing the local pH at the bonded interface causes increased deprotonation of the negatively charged particle (e.g. due to an excess amount of hydroxide ions to form carboxylate ions), resulting in increased intraparticle electrostatic repulsion. Conversely, in the case of aqueous emulsions comprising particles which are positively charged, it is thought that decreasing the local pH at the bonded interface causes increased protonation of thepositively charged component, resulting in increased intraparticle electrostatic repulsion. As a result, in both circumstances where the pH is altered, electrostatic repulsion causes the hydrophobic polymer to expand, enhancing its solubility in water or polar solvents, thereby causing the interaction between the aqueous emulsion, and thus the adhesion of the first and second surfaces, to be reversed. Accordingly, the aqueous emulsion of the invention provides facile and effective reversibility under mild conditions. This is particularly advantageous in large scale recycling processes, including those in which relatively mild conditions are desirable so as to avoid damaging the recycled components, e.g. electronic waste.

[0010] Additionally, the adhesive solids formed from the aqueous emulsions of the invention are electrically conductive, enabling the flow of electrons between electrical components or between surfaces, e.g. where the surfaces form part of or are connected to electronic components. Thus, the aqueous emulsions of the invention may be employed to simultaneously adhere and electrically connect two components (e.g. two electrical components) to one another in a reversible manner.

[0011] Additionally, the adhesive solids formed from the aqueous emulsions of the invention may be thermally conductive, enabling the flow of heat between adhered surfaces.

[0012] Alternatively, the aqueous emulsions of the invention may be applied to at least one surface comprising two or more electrical components in order to electrically connect the two or more electrical components to one another in a reversible manner. For example, the aqueous emulsions may be applied to a printed circuit board to electrically connect two or more components of the printed circuit board, e.g. by using the aqueous emulsion to form an electrical bond between the two or more components.

[0013] Further, the aqueous emulsions of the invention are solvent-free, thereby providing a system that is scalable and environmentally friendly.

[0014] In a second aspect of the present invention, there is provided a method of making the aqueous emulsion of the first aspect, the method comprising: providing a suspension comprising conductive filler and water; and mixing the suspension with a precursor aqueous emulsion to provide the aqueous emulsion of the first aspect, wherein the precursor aqueous emulsion is:(i) a aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein theparticles comprise a hydrophobic polymer and wherein the particles are negatively charged; or(ii) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0015] In a third aspect of the invention, there is provided a method of making the aqueous emulsion of the invention, the method comprising adding a conductive filler to a precursor aqueous emulsion to provide the aqueous emulsion of the invention, wherein the precursor aqueous emulsion is: (i) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged; or (ii) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0016] In a fourth aspect of the present invention, there is provided an aqueous emulsion obtained or obtainable by the method of the second or third aspect.

[0017] In a fifth aspect of the present invention, there is provided a method of adhering two surfaces to one another, the method comprising: coating a first surface and / or a second surface with the aqueous emulsion of the first aspect or the fourth aspect; and contacting the first surface with the second surface to adhere the first and second surfaces to one another at a bonded interface.

[0018] In a sixth aspect of the present invention, there is provided a method of forming an electrically conductive pathway between two electrical components, the method comprising: applying the aqueous emulsion of the first aspect or the fourth aspect in a continuous line onto a surface between two electrical components in contact with said surface such that, once dried, the aqueous emulsion forms an electrically conductive pathway between the two electrical components.

[0019] In a seventh aspect, there is a provided a method of recovering electrical components that have previously been adhered via the method of the fifth aspect, the method comprising: detaching the first and second surfaces from one another by altering the pH of the first and second surfaces at the bonded interface.Aqueous emulsion

[0020] The hydrophobic polymer may be a polystyrene, a polyacrylate, a polymethacrylate, a polyvinyl, a polydiene, or a mixture / copolymer thereof. The hydrophobic polymer may be selected from: polystyrene, poly(butyl acrylate), poly(styrene-butyl acrylate) copolymer or polybutadiene. The hydrophobic polymer may be a polystyrene, a polyacrylate, a polymethacrylate, or a polyvinyl, or a mixture / copolymer thereof. The hydrophobic polymer may be selected from: polystyrene, poly(butyl acrylate), or poly(styrene-butyl acrylate) copolymer. The hydrophobic polymer may be a poly(styrene-butyl acrylate) copolymer.

[0021] Where the hydrophobic polymer is a poly(styrene-butyl acrylate) copolymer, the copolymer may comprise styrene and butyl acrylate in a weight ratio in the range of from 3: 1 to 0.01 : 1 , e.g. a weight ratio in the range of from 1.5: 1 to 1 : 1.5. It may be that the copolymer comprises styrene and butyl acrylate in a weight ratio of about 1 :1.5.

[0022] The conductive filler may be present in an amount of at least about 1 % by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 2% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 2.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 3% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 3.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 4% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 4.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 5.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 6% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 6.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 7% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 7.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 8% by weight of the aqueous emulsion.

[0023] The conductive filler may be present in an amount of at least about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 20% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 25% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 30% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 35% by weight of theaqueous emulsion. The conductive filler may be present in an amount of at least about 40% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 45% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 50% by weight of the aqueous emulsion. The conductive filler may be present in an amount of at least about 55% by weight of the aqueous emulsion.

[0024] The conductive filler may be present in an amount of no greater than about 75% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 70% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 65% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 60% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 55% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 50% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 45% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 40% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 35% by weight of the aqueous emulsion.

[0025] The conductive filler may be present in an amount of no greater than about 12% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 11% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 9.5% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 9% by weight of the aqueous emulsion. The conductive filler may be present in an amount of no greater than about 8.5% by weight of the aqueous emulsion.

[0026] The conductive filler may be present in an amount of from about 2% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 3% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 4% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 5% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 6% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 7% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about8% to about 10% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 8% to about 9% by weight of the aqueous emulsion.

[0027] The conductive filler may be present in an amount of from about 20% to about 75% by weight of the aqueous emulsion. The conductive filler may be present in an amount of from about 30% to about 70% by weight of the aqueous emulsion.

[0028] The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.25:1 to about 10:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 1 : 1 to about 8: 1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive.

[0029] The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.25:1 to about 4:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.5:1 to about 4:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.75: 1 to about 4: 1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 1:1 to about 4:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 1.5:1 to about 4: 1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive.

[0030] The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.25:1 to about 3.5:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.25:1 to about 3:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.25: 1 to about 2.5: 1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range offrom about 0.25:1 to about 2:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive.

[0031] The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.5:1 to about 3.5:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 0.75:1 to about 3:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 1:1 to about 2.5:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio in the range of from about 1:1 to about 2:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive.

[0032] The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio of about 1:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio of about 2:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive. The conductive filler and the particles comprising hydrophobic polymer may be present in a weight ratio of about 8:1 of conductive filler to particles comprising hydrophobic polymer by weight of the solid adhesive.

[0033] The conductive filler may be selected from: metal filler, carbon-based filler, ceramic filler, or metal-coated filler. The conductive filler may be selected from: metal filler, carbonbased filler, or metal-coated filler. The conductive filler may be a carbon-based filler. The conductive filler may be a metal-filler.

[0034] Exemplary metal fillers include: silver, gold, copper or nickel. The metal fillers may be metal nanoparticles, e.g. silver nanoparticles, gold nanoparticles, copper nanoparticles or nickel nanoparticles. The metal filler may be silver nanoparticles. Exemplary carbonbased fillers include: carbon nanotubes, carbon nanofiber, carbon black, and graphene. Exemplary ceramic fillers include titanium diboride. Exemplary metal-coated fillers include: metal core particles coated with metal (e.g. copper particles coated with silver) or non- metal core particles coated with metal (e.g. carbon, polymer, or glass coated with metal, such as silver or gold).

[0035] The conductive filler may comprise or may be a conductive nanofiller. For example, the conductive filler may comprise or may be metal nanoparticles or graphene nanoplatelets.

[0036] It may be that the conductive filler is graphene (e.g. graphene nanoplatelets) and is present in an amount of from about 20% to about 35% by weight of the aqueous emulsion. For example, it may be that the conductive filler is graphene (e.g. graphene nanoplatelets) and is present in an amount of about 33% by weight of the aqueous emulsion.

[0037] It may be that the conductive filler is a metal filler (e.g. metal nanoparticles) and is present in an amount of from about 55% to about 75% by weight of the aqueous emulsion. It may be that the conductive filler is a metal filler (e.g. metal nanoparticles) and is present in an amount of from about 60% to about 70% by weight of the aqueous emulsion. For example, it may be that the conductive filler is a metal filler (e.g. metal nanoparticles) and is present in an amount of about 66% by weight of the aqueous emulsion.

[0038] The conductive filler may have a size of no greater than about 4 pm. The conductive filler may have a size of no greater than about 3.5 pm. The conductive filler may have a size of no greater than about 3 pm. The conductive filler may have a size of no greater than about 2.5 pm.

[0039] The conductive filler may have a size of at least about 0.1 pm. The conductive filler may have a size of at least about 0.15 pm. The conductive filler may have a size of at least about 0.2 pm. The conductive filler may have a size of at least about 0.25 pm. The conductive filler may have a size of at least about 0.3 pm.

[0040] The conductive filler may have a size in the range of from about 0.1 pm to about 4 pm. The conductive filler may have a size in the range of from about 0.1 pm to about 3.5 pm. The conductive filler may have a size in the range of from about 0.1 pm to about 3 pm. The conductive filler may have a size in the range of from about 0.15 pm to about 4 pm. The conductive filler may have a size in the range of from about 0.2 pm to about 4 pm. The conductive filler may have a size in the range of from about 0.25 pm to about 4 pm.

[0041] The conductive filler may have a size in the range of from about 0.2 pm to about 3.5 pm. The conductive filler may have a size in the range of from about 0.25 pm to about 3 pm.

[0042] The conductive filler may be a carbon-based filler. The conductive filler may comprise graphene. The conductive filler may be graphene. The graphene may beselected from: graphene nanoplatelets, graphene oxide, reduced graphene oxide, mechanically exfoliated graphene, chemically exfoliated exfoliated graphene, and chemical vapour deposition (CVD) graphene. For example, the conductive filler may comprise or may be graphene nanoplatelets.

[0043] The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 2 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 1.5 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 1 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 0.9 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 0.8 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 0.7 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 0.6 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of no greater than about 0.5 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.1 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.15 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.2 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.25 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.3 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.35 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.4 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.45 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of at least about 0.5 pm.

[0044] The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 2 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 1.5 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 1.2 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 1 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 0.9 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 0.8 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 0.7 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 0.6 pm.

[0045] The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.1 pm to about 0.5 pm. The conductive filler (e.g. graphene nanoplatelets)may have a size in the range of from about 0.15 pm to about 0.45 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.2 pm to about 0.4 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size in the range of from about 0.25 pm to about 0.35 pm. The conductive filler (e.g. graphene nanoplatelets) may have a size of about 0.3 pm.

[0046] The conductive filler may comprise a metal filler. The conductive filler may be a metal filler. For example, the metal filler may be or may comprise metal nanoparticles, e.g. silver nanoparticles.

[0047] It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 4 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.75 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.5 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.4 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.3 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.2 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3.1 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of no greater than about 3 pm.

[0048] It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 0.5 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.25 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.5 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.6 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.7 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.8 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 1.9 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size of at least about 2 pm.

[0049] It may be that the conductive filler (e.g. metal nanoparticles) has a size in the range of from about 1 pm to about 4 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size in the range of from about 1.5 pm to about 3.5 pm. It may be that the conductive filler (e.g. metal nanoparticles) has a size in the range of from about 2 pm to about 3 pm.

[0050] Where the conductive filler is graphene (e.g. graphene nanoplatelets), the graphene may have a thickness of less than about 10 nm.

[0051] Where the conductive filler is graphene (e.g. graphene nanoplatelets), the graphene may be in the form of nanoplatelets of graphene which are from 2 to 10 molecular layers thick. These multilayer flakes are frequently referred to as “few-layer” nanoplatelets. Thus, the graphene (e.g. graphene nanoplatelets) may be present entirely as few-layer nanoplatelets. Alternatively, the graphene may be a single atomic layer thick, i.e. monolayer graphene.

[0052] The aqueous emulsion may be an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged.

[0053] In this embodiment, the particles comprising the hydrophobic polymer may further comprise a negatively charged polymer (e.g. a polyanion). The negatively charged polymer (e.g. the polyanion) may be associated with the hydrophobic polymer. For example, the negatively charged polymer (e.g. the polyanion) may be associated with the hydrophobic polymer via hydrophobic, electrostatic or covalent interactions.

[0054] The negatively charged polymer may be a polymeric species having one or more negatively charged groups. The negatively charged polymer may be a polymeric species having a plurality of negatively charged groups.

[0055] For the avoidance of doubt, where the negatively charged polymer has a plurality of negatively charged groups, this means that each molecule of the negatively charged polymer has a plurality of negatively charged groups. In other words, each molecule of the negatively charged polymer comprises more than one (e.g. more than two or three) negatively charged groups. It may be that each molecule of the negatively charged polymer comprises at least one negatively charged group in each repeating unit. For example, when the negatively charged polymer is poly(acrylic acid), the skilled person would appreciate that each repeating unit of the poly(acrylic acid) includes a carboxyl group (which is negatively charged in the aqueous emulsion of the invention) such that a single molecule of poly(acrylic acid) includes a plurality of carboxyl groups, and therefore has a plurality of negatively charged groups.

[0056] It may be that the components of the particle are arranged and selected such that the negatively charged groups (e.g. carboxylate groups) are situated at the surface of the particle. It may be that the components of the particle are arranged and selected such that there is a higher concentration of the negatively charged groups (e.g. carboxylate groups) at the surface of the particle than there is in the inner portions of the particle.Thus the hydrophobic polymer may be situated in the inner portions of the particle with the negatively charged polymer situated on the outer portions of the particle.

[0057] In certain embodiments, the aqueous emulsion has a pH in the range of from about 5 to about 9. The negatively charged polymer (e.g. the polyanion) may comprise one or more groups that are deprotonated at the pH of the aqueous emulsion, e.g. in the pH range of from about 5 to about 9, optionally from about 6 to about 8, to form an anion. The negatively charged polymer (e.g. the polyanion) may comprise a plurality of groups that are deprotonated at the pH of the aqueous emulsion, e.g. in the pH range of from about 5 to about 9, optionally from about 6 to about 8, to form an anion.

[0058] The negatively charged polymer (e.g. the polyanion) may comprise one or more groups selected from: carboxylate, sulfonate, phosphonate, and boronate. The negatively charged polymer (e.g. the polyanion) may comprise one or more carboxylate groups. The negatively charged polymer (e.g. the polyanion) may comprise a plurality of carboxylate groups.

[0059] The negatively charged polymer (e.g. the polyanion) may be selected from the group comprising: poly acrylic acids, acidic biopolymers, poly sulfonic acids and poly maleic acids. The negatively charged polymer (e.g. the polyanion) may be selected from poly(acrylic acid), alginate, carboxymethyl cellulose, xanthan gum, gum Arabic, carrageenan, poly(2-acrylamido-2-methylpropanesulfonic acid), poly(methacrylic acid), poly(maleic acid) and poly(vinyl sulfonic acid). The negatively charged polymer (e.g. the polyanion) may be poly(acrylic acid).

[0060] The particles of the aqueous emulsion may comprise the hydrophobic polymer and the negatively charged polymer (e.g. the polyanion) in ratio in the range from about 20:1 to about 60:1 by weight.

[0061] The aqueous emulsion may be an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0062] In this embodiment, the particles of comprising the hydrophobic polymer may further comprise a positively charged polymer (e.g. a polycation). The positively charged polymer (e.g. the polycation) may be associated with the hydrophobic polymer. For example, the positively charged polymer (e.g. the polycation) may be associated with the hydrophobic polymer via hydrophobic, electrostatic, or covalent interactions.

[0063] The positively charged polymer may be a polymeric species comprising one or more positively charged groups. The positively charged polymer may be a polymeric species comprising a plurality of positively charged groups.

[0064] For the avoidance of doubt, where the positively charged polymer has a plurality of positively charged groups, this means that each molecule of the positively charged polymer has a plurality of positively charged groups. In other words, each molecule of the positively charged polymer comprises more than one (e.g. more than two or three) positively charged groups. It may be that each molecule of the positively charged polymer comprises at least one positively charged group in each repeating unit. For example, when the positively charged polymer is chitosan, the skilled person would appreciate that each repeating unit of the chitosan includes an amino group (which is positively charged in the aqueous emulsion of the invention) such that a single molecule of chitosan includes a plurality of amino groups, and therefore has a plurality of positively charged groups.

[0065] It may be that the components of the particle are arranged and selected such that the positively charged groups (e.g. amino groups) are situated at the surface of the particle. It may be that the components of the particle are arranged and selected such that there is a higher concentration of the positively charged groups (e.g. amino groups) at the surface of the particle than there is in the inner portions of the particle. Thus, the hydrophobic polymer may be situated in the inner portions of the particle with the positively charged polymer situated on the outer portions of the particle.

[0066] In certain embodiments, the aqueous emulsion has a pH in the range of from about 5 to about 9, optionally from about 6 to about 8. The positively charged polymer (e.g. the polycation) may comprise one or more basic groups that are protonated at the pH of the aqueous emulsion, e.g. in the pH range from about 5 to about 9, optionally from about 6 to about 8, to form a cation. The positively charged polymer (e.g. the polycation) may comprise a plurality of basic groups that are protonated at the pH of the first aqueous emulsion, e.g. in the pH range from about 5 to about 9, optionally from about 6 to about 8, to form a cation. The positively charged polymer (e.g. the polycation) may comprise one or more amino groups. The positively charged polymer (e.g. the polycation) may comprise a plurality of amino groups. The amino groups may be primary, secondary or tertiary amino groups. The amino groups may be primary amino groups.

[0067] The positively charged polymer may be selected from the group comprising: chitosan, poly amino acrylates, poly amino methacrylates, poly allylamines and poly ethyleneimines. The positively charged polymer may be selected from chitosan, poly[2- (dimethylamino)ethyl acrylate], poly[2-(dimethylamino)ethyl methacrylate], and polyethylenimine. The positively charged polymer may be chitosan.

[0068] The particles of the aqueous emulsion may comprise the hydrophobic polymer and the positively charged polymer (e.g. the polycation) in a ratio in the range from about 20:1 to about 60:1 by weight.

[0069] The aqueous emulsion may have a low shear viscosity in the range from about 25 to about 100 Pa s. The aqueous emulsion may have a high shear viscosity in the range from about 50 to about 150 Pa s.

[0070] The hydrophobic polymer may have a glass transition temperature (Tg) of less than about 50 °C, less than about 25 °C, or less than about 20 °C. The hydrophobic polymer may have a glass transition temperature (Tg) of greater than about -50 °C. The hydrophobic polymer may have a glass transition temperature (Tg) of from about -50 °C to about 50 °C, from about -50 °C to about 25 °C, from about -50 °C to about 20 °C, from about -25 °C to about 20 °C, from about 0 °C to about 20 °C, or from about 10 °C to about 20 °C.

[0071] The particles comprising the hydrophobic polymer may be present in an amount in the range from about 0.25% to about 30% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 0.25% to about 25% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 2% to about 25% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 4% to about 20% by weight of the aqueous emulsion.

[0072] The particles comprising the hydrophobic polymer may be present in an amount in the range from about 2% to about 15% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 2% to about 10% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 2% to about 8% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 2% to about 6% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 3% to about 5% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount in the range from about 3.5% to about 4.5% by weight of the aqueous emulsion. The particles comprising the hydrophobic polymer may be present in an amount of about 4.5% by weight of the aqueous emulsion.

[0073] In embodiments in which the particles of the aqueous emulsion are negatively charged, the particles may further comprise one or more additives. The one or more additives may each comprise one or more sulfate groups. It may be that the particles each comprise one additive. It may be that the particles each comprise an additive comprising one or more sulfate groups.

[0074] Each additive may be an anionic surfactant or a cationic surfactant.

[0075] Each additive may be an anionic surfactant. For example, the additive may be an anionic surfactant selected from: an alkyl sulfate, an alkyl ether sulfate, and an alkyl sulfonate. Preferably, the additive is sodium dodecyl sulfate.

[0076] Each additive may be a cationic surfactant. For example, the additive may be a cationic surfactant selected from: an alkyl ammonium halide or other alkyl ammonium salt. Specific examples of cationic surfactants include triethylamine hydrochloride, octenidine dihydrochloride, adogen, cetrimonium bromide, cetyl pyridinium chloride, benzethonium chloride and dimethyldioctadecylammonium chloride.

[0077] The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 10 nm to about 20 pm.

[0078] The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 5 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 4 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 3 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 2.5 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 2 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 1.5 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 1 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 100 nm to about 900 nm.

[0079] The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 200 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 300 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 400 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 500 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 550 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 600 nm to about 10 pm. The particles of the aqueous emulsioncomprising hydrophobic polymer may have a size in the range of from about 650 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 700 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 750 nm to about 10 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 800 nm to about 10 pm.

[0080] The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 200 nm to about 2.5 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 500 nm to about 1.5 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 700 nm to about 1 pm. The particles of the aqueous emulsion comprising hydrophobic polymer may have a size in the range of from about 800 nm to about 900 nm.

[0081] The size of the particles may be determined by dynamic light scattering. This process involves measuring the Brownian motion of particles by illuminating the particles with a laser and analysing the intensity fluctuations in the scattered light to determine particle size. An instrument for measuring dynamic light scattering (e.g. a Zetasizer system) determines the average particle sizes and the polydispersity index from a sample, and typically produces these in a size distribution curve or histogram. To determine the particle size in the aqueous emulsion, a sample of the aqueous emulsion may be diluted with deionised water and placed in a dynamic light scattering instrument.Method of making the aqueous emulsion

[0082] In a second aspect, there is provided a method of making the aqueous emulsion of the invention, the method comprising: providing a suspension comprising conductive filler and water; and mixing the suspension with a precursor aqueous emulsion to provide the aqueous emulsion of the invention, wherein the precursor aqueous emulsion is: (i) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged; or (ii) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0083] The conductive filler may be present in an amount of from about 5% to about 15% by weight of the suspension. The conductive filler may be present in an amount of from about 5% to about 12.5% by weight of the suspension. The conductive filler may be present in an amount of from about 5% to about 10% by weight of the suspension.

[0084] The conductive filler may be present in an amount of from about 7.5% to about 12.5% by weight of the suspension. The conductive filler may be present in an amount of from about 9% to about 11% by weight of the suspension. The conductive filler may be present in an amount of about 10% by weight of the suspension.

[0085] The suspension may further comprise a surfactant. The surfactant may be an anionic surfactant, a cationic surfactant, or a nonionic surfactant. The surfactant may be an anionic surfactant or a cationic surfactant.

[0086] The surfactant may be an anionic surfactant. For example, the anionic surfactant may be selected from: an alkyl sulfate, an alkyl ether sulfate, and an alkyl sulfonate. Preferably, the anionic surfactant is sodium dodecyl sulfate.

[0087] The surfactant may be a cationic surfactant. For example, the cationic surfactant may be selected from: an alkyl ammonium halide or other alkyl ammonium salt. Specific examples of cationic surfactants include triethylamine hydrochloride, octenidine dihydrochloride, adogen, cetrimonium bromide, cetyl pyridinium chloride, benzethonium chloride and dimethyldioctadecylammonium chloride.

[0088] The surfactant may be an nonionic surfactant. For example, the nonionic surfactant may be selected from: a polyol ester (e.g. a polysorbate), an alkoxylate, an alkoxylated alcohol, an alkanolamide, a fatty acid alkyl ester, and a polyglucoside. Specific examples of nonionic surfactants include polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, sorbitan, sorbitan monolaurate, sorbitan monostearate, cetyl alcohol, decyl glucoside, Triton-X-100, poloxamer 407, isopropyl myristate, myristyl myristate and glyceryl monooleate. Preferably, the nonionic surfactant is poloxamer 407.

[0089] Without wishing to be bound by theory, it is thought that the conductive filler (e.g. graphene nanoplatelets) is stabilised by non-covalent functionalisation with the surfactant (e.g. the anionic surfactant). In particular, it is thought that the amphiphilic nature of the anionic surfactant (i.e. hydrophilic head and hydrophobic tail) helps to stabilise the graphene nanoplatelets due to the hydrophobic tails of the surfactant molecules interacting with the graphene surface, and while hydrophilic heads of the surfactant pointing outwards surrounding solvent. It is thought that this interaction creates steric hindrance and electrostatic stabilisation to prevent the nanoparticles from aggregating.

[0090] The surfactant may be present in the suspension in a weight ratio in the range of from 1:1 to 1:2 of surfactant to conductive filler.

[0091] The step of providing the suspension may further comprise sonicating the suspension. For example, the suspension may be sonicated at a temperature of less than 60 °C.

[0092] The step of mixing the suspension with the precursor aqueous emulsion may comprise stirring the mixture of the suspension and the precursor aqueous emulsion.

[0093] The mixture of the suspension and the precursor aqueous emulsion may be stirred at a speed in the range of from about 100 RPM to about 700 RPM.

[0094] The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for at least 5 minutes. The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for at least 10 minutes. The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for at least 15 minutes. The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for at least 20 minutes. The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for at least 25 minutes. The stirring of the mixture of the suspension and the precursor aqueous emulsion may be performed for no more than 30 minutes.

[0095] The conductive filler and particles comprising hydrophobic polymer in the formed aqueous emulsion may be in present in a ratio in the range of from 1 :1 to 2:1 of conductive filler to solid polymer.

[0096] The method may further comprise providing the precursor aqueous emulsion of option (i) or option (ii).

[0097] Where the precursor aqueous emulsion is the precursor aqueous emulsion of option (i), the method of providing the precursor aqueous emulsion may comprise stirring one or more hydrophobic monomers with an additive to form an emulsion; polymerising the emulsion in water to form an intermediate aqueous emulsion; adding a negatively charged monomer to the intermediate aqueous emulsion; and polymerising the mixture of intermediate aqueous emulsion and negatively charged monomer in water to form the precursor aqueous emulsion of option (i).

[0098] The step of stirring the one or more hydrophobic monomers with the additive to form an emulsion may be performed for at least 5 minutes.

[0099] The step of polymerising the emulsion to form the intermediate aqueous emulsion may involve a free-radical emulsion polymerisation. Thus, this step may include the addition of a free radical initiator. The free radical initiator may be a persulfate, a peroxide, or an aliphatic azo compound. For example, the free radical initiator may be selected from: potassium persulfate (KPS) and azobisisobutyronitrile (AIBN).

[0100] The step of polymerising the emulsion to form the intermediate aqueous emulsion may be performed at a temperature of at least 70 °C.

[0101] The step of polymerising the emulsion to form the intermediate aqueous emulsion may be performed for at least 2 hours.

[0102] The step of adding the negatively charged monomer to the intermediate aqueous emulsion may further comprise adding more of the free radical initiator.

[0103] The step of polymerising the mixture of intermediate aqueous emulsion and negatively charged monomer in water to form the precursor aqueous emulsion of option (i) may be performed at a temperature of at least 70 °C.

[0104] The step of polymerising the mixture of intermediate aqueous emulsion and negatively charged monomer in water to form the precursor aqueous emulsion of option (i) may be performed for at least 2 hours.

[0105] The one or more hydrophobic monomers may be selected from: styrenes (e.g. butyl styrene), acrylates (e.g. butyl acrylate), methacrylates (e.g. butyl methacrylate, ethylhexyl methacrylate), ethylhexyl methacrylate), vinyls (e.g. vinyl acetate, vinyl laurate), acrylated soybean oil, divinylbenzene. The one or more hydrophobic monomers may be selected from: styrene and butyl acrylate. It may be that the one or more hydrophobic monomers are styrene and butyl acrylate.

[0106] Where the one or more hydrophobic monomers are styrene and butyl acrylate, the styrene and butyl acrylate may be present in a weight ratio in the range of from 3:1 to 0.01 : 1 of styrene to butyl acrylate, e.g. a weight ratio in the range of from about 1.5:1 to about 1 : 1 .5 of styrene to butyl acrylate. It may be that the styrene and butyl acrylate are present in a weight ratio of about 1 :1.5 of styrene to butyl acrylate.

[0107] Where the precursor aqueous emulsion is the precursor aqueous emulsion of option (ii), the method of providing the precursor aqueous emulsion may comprise stirring one or more hydrophobic monomers with a positively charged polymer to form an emulsion; and polymerising the emulsion in water to form the precursor aqueous emulsion of option (ii).

[0108] The precursor aqueous emulsion may comprise the particles comprising the hydrophobic polymer in an amount in the range of from about 20% by weight to about 30% by weight of the precursor aqueous emulsion. The precursor aqueous emulsion may comprise the particles comprising the hydrophobic polymer in an amount in the range of from about 22.5% by weight to about 27.5% by weight of the precursor aqueous emulsion.

[0109] The precursor aqueous emulsion may comprise the particles comprising the hydrophobic polymer in an amount of about 25% by weight of the precursor aqueous emulsion.

[0110] The step of forming the emulsion from the one or more hydrophobic monomers and the positively charged polymer may be performed for at least 5 minutes, optionally for at least 10 minutes.

[0111] The step of polymerising the emulsion to form the precursor aqueous emulsion of option (ii) may involve a free-radical emulsion polymerisation. Thus, this step may include the addition of a free radical initiator. The free radical initiator may be a persulfate, a peroxide, or an aliphatic azo compound. For example, the free radical initiator may be selected from: potassium persulfate (KPS) and azobisisobutyronitrile (AIBN).

[0112] The step of polymerising the emulsion to form the precursor aqueous emulsion of option (ii) may be performed at a temperature of at least 70 °C.

[0113] The step of polymerising the emulsion to form the precursor aqueous emulsion of option (ii) may be performed for at least 4 hours.

[0114] The one or more hydrophobic monomers may be selected from: styrenes (e.g. butyl styrene), acrylates (e.g. butyl acrylate), methacrylates (e.g. butyl methacrylate, ethylhexyl methacrylate), ethylhexyl methacrylate), vinyls (e.g. vinyl acetate, vinyl laurate), acrylated soybean oil, divinylbenzene. The one or more hydrophobic monomers may be selected from: styrene and butyl acrylate.

[0115] The positively charged polymer, negatively charged polymer and additive may be as described in any of the embodiments in this specification relating to the first aspect of the invention.

[0116] In another aspect, there is provided an aqueous emulsion obtained or obtainable by the method of the second aspect.

[0117] In a third aspect, there is provided a method of making the aqueous emulsion of the invention, the method comprising adding a conductive filler to a precursor aqueous emulsion to provide the aqueous emulsion of the invention, wherein the precursor aqueous emulsion is: (i) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged; or (ii) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

[0118] The method may comprise the following steps:(a) providing a suspension comprising conductive filler and water;(b) sonicating the suspension;(c) filtering the suspension to provide a solid; and(d) adding the solid to the precursor aqueous emulsion to provide the aqueous emulsion of the invention.

[0119] The suspension may be sonicated at a temperature of less than 60 °C.

[0120] The conductive filler may be as described in any of the embodiments in this specification relating to the first aspect of the invention.

[0121] The conductive filler may be present in the suspension in an amount of from about 0.5% to about 15% by weight of the suspension. The conductive filler may be present in the suspension in an amount of from about 1% to about 10% by weight of the suspension. The conductive filler may be present in the suspension in an amount of from about 5% to about 10% by weight of the suspension. The conductive filler may be present in the suspension in an amount of from about 1% to about 5% by weight of the suspension. The conductive filler may be present in the suspension in an amount of from about 1% to about 2% by weight of the suspension.

[0122] The suspension may further comprise a surfactant. The surfactant may be an anionic surfactant, a cationic surfactant, or a nonionic surfactant. The surfactant may be an anionic surfactant or a cationic surfactant.

[0123] The surfactant may be an anionic surfactant. This would particularly be the case where the conductive filler is graphene (e.g. graphene nanoplatelets). For example, the anionic surfactant may be selected from: an alkyl sulfate, an alkyl ether sulfate, and an alkyl sulfonate. Preferably, the anionic surfactant is sodium dodecyl sulfate.

[0124] The surfactant may be a cationic surfactant. For example, the cationic surfactant may be selected from: an alkyl ammonium halide or other alkyl ammonium salt. Specific examples of cationic surfactants include triethylamine hydrochloride, octenidine dihydrochloride, adogen, cetrimonium bromide, cetyl pyridinium chloride, benzethonium chloride and dimethyldioctadecylammonium chloride.

[0125] The surfactant may be an nonionic surfactant. This would particularly be the case where the conductive filler is metal filler (e.g. metal nanoparticles). For example, the nonionic surfactant may be selected from: a polyol ester (e.g. a polysorbate), an alkoxylate, an alkoxylated alcohol, an alkanolamide, a fatty acid alkyl ester, and a polyglucoside. Specific examples of nonionic surfactants include polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, sorbitan, sorbitan monolaurate, sorbitan monostearate, cetyl alcohol, decyl glucoside, Triton-X-100, poloxamer 407, isopropyl myristate, myristyl myristate and glyceryl monooleate. Preferably, the nonionic surfactant is poloxamer 407.

[0126] Without wishing to be bound by theory, it is thought that the conductive filler (e.g. graphene nanoplatelets or metal nanoparticles) is stabilised by non-covalent functionalisation with the surfactant (e.g. the anionic surfactant). In particular, it is thought that the amphiphilic nature of the anionic surfactant (i.e. hydrophilic head and hydrophobic tail) helps to stabilise the graphene nanoplatelets or metal nanoparticles due to the hydrophobic tails of the surfactant molecules interacting with the surface of the graphene nanoplatelets or metal nanoparticles, and while hydrophilic heads of the surfactant pointing outwards surrounding solvent. It is thought that this interaction creates steric hindrance and electrostatic stabilisation to prevent the nanoparticles from aggregating.

[0127] The surfactant may be present in the suspension in a weight ratio in the range of from 1:1 to 2.5:1 of surfactant to conductive filler. The surfactant may be present in the suspension in a weight ratio in the range of from 2:1 to 2.5:1 of surfactant to conductive filler.

[0128] Step (c) of filtering the suspension may comprise vacuum filtration of the suspension to remove water.

[0129] Step (c) may further comprise drying the solid obtained by the filtering of the suspension.

[0130] The solid may comprise conductive filler and surfactant. For example, the solid may comprise graphene (e.g. graphene nanoplatelets) and anionic surfactant (e.g. sodium dodecyl sulfate). Alternatively, the solid may comprise metal filler (e.g. metal nanoparticles) and surfactant (e.g. poloxamer 407).

[0131] It may be that the conductive filler and the surfactant in the solid are associated with one another. For example, the conductive filler and the surfactant in the solid may be associated with one another by non-covalent interactions, e.g. by van der Waals forces and / or other hydrophobic interactions.

[0132] Step (d) of adding the solid to the precursor aqueous emulsion may comprise adding the solid directly to the precursor aqueous emulsion to form the aqueous emulsion of the invention.

[0133] Alternatively, step (d) of adding the solid to the precursor aqueous emulsion may comprise: adding the solid to a liquid to form a second suspension; and mixing the second suspension with the precursor aqueous emulsion to form the aqueous emulsion of the invention.

[0134] Step (d) may further comprise stirring the mixture of the precursor aqueous emulsion and the solid.

[0135] The stirring of the mixture of the precursor aqueous emulsion and the solid may be performed for at least 5 minutes. The stirring of the mixture of the precursor aqueous emulsion and the solid may be performed for at least 10 minutes.

[0136] The conductive filler and particles comprising hydrophobic polymer in the formed aqueous emulsion may be in present in a ratio in the range of from about 0.25:1 to about 10:1 of conductive filler to solid polymer. The conductive filler and particles comprising hydrophobic polymer in the formed aqueous emulsion may be in present in a ratio in the range of from about 1 : 1 to about 8: 1 of conductive filler to solid polymer.

[0137] The method may further comprise providing the precursor aqueous emulsion of option (i) or option (ii), as described above in relation to the second aspect. Similarly, the positively charged polymer, negatively charged polymer and additive may be as described in any of the embodiments in this specification relating to the first aspect of the invention.

[0138] In another aspect, there is provided an aqueous emulsion obtained or obtainable by the method of the third aspect.Method of adhering two surfaces

[0139] In another aspect of the invention, there is provided a method of adhering two surfaces to one another, the method comprising: coating a first surface and / or a second surface with the aqueous emulsion of the invention; and contacting the first surface with the second surface to adhere the first and second surfaces to one another at a bonded interface.

[0140] As discussed above, the inventors have surprisingly found that the aqueous emulsions of the invention are strong, electrically and / or thermally conductive, reversible adhesives. In particular, these adhesives have been shown to be effective reversible adhesives on a range of substrates (including metals) and have been shown to be electrically conductive.

[0141] The method may further comprise detaching the first and second surfaces from one another by altering the pH of the first and second surfaces at the bonded interface. For example, the method may comprise increasing the pH of the first and second surfaces at the bonded interface to detach the first and second surfaces from one another. The step of increasing the pH may comprise increasing the pH to at least about 10, at least about 11, at least about 12, or at least about 13.

[0142] Alternatively, the method may comprise decreasing the pH of the first and second surfaces at the bonded interface to detach the first and second surfaces from one another. The step of decreasing the pH may comprise decreasing the pH to less than about 5, less than about 4, less than about 3, less than about 2, or less than about 1.

[0143] The step of detaching the first and second surfaces from one another at the bonded interface may comprise treating the first and second surfaces with an alkaline solution having a pH of greater than about 10, greater than about 11 , greater than about 12 or greater than about 13 at the bonded interface. Alternatively, the step of detaching the first and second surfaces from one another at the bonded interface may comprise treating the first and second surfaces with an acidic solution having a pH of less than about 5, less than about 4, less than about 3, less than about 2 or less than about 1 at the bonded interface. Detaching may be achieved by submerging or immersing the product containing the adhesive in the acidic or alkaline solution. The product containing the adhesive may be agitated when treating with the acidic or alkaline solution to facilitate said detaching.

[0144] The step of detaching the first and second surfaces from one another at the bonded interface may further comprise heating the acidic or alkaline solution to a temperature of no more than about 90 °C.

[0145] The method may comprise coating only the first surface with the aqueous emulsion. The method may comprise coating only the second surface with the aqueous emulsion. The method may comprise coating both the first surface and the second surface with the aqueous emulsion.

[0146] The step of coating the first and / or second surface may comprise applying the aqueous emulsion of the invention to the first and / or second surface in a weight / area ratio in the range of from about 1 mg / cm2to about 100 mg / cm2. The step of coating the first and / or second surface may comprise applying the aqueous emulsion of the invention to the first and / or second surface in a weight / area ratio in the range of from about 10 mg / cm2to about 100 mg / cm2. It may be that the step of coating the first and / or second surface may comprise applying the aqueous emulsion of the invention to the first and / or second surface in a weight / area ratio in the range of from about 20 mg / cm2to about 30 mg / cm2.

[0147] It may be that at least one of the first surface and second surface are independently selected from: metal (e.g. copper, steel, stainless steel, aluminium), glass, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE), and printed circuit board. It may be that the first surface and second surface are each independently selected from: metal (e.g. copper, steel, stainless steel, aluminium), glass, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE), and printed circuit board.

[0148] It may be that at least one of the first surface and second surface are independently selected from: metal (e.g. copper, steel, stainless steel, aluminium), glass, polypropylene (PP), high density polyethylene (HDPE), and low-density polyethylene(LDPE). It may be that the first surface and second surface are each independently selected from: metal (e.g. copper, steel, stainless steel, aluminium), glass, polypropylene (PP), high density polyethylene (HDPE), and low-density polyethylene (LDPE).

[0149] It may be that at least one the first surface and the second surface is or comprises a metal. For example, it may be that at least one of the first surface and second surface is selected from: copper, steel, stainless steel and aluminium. It may be that at least one of the first surface and second surface is selected from: copper, stainless steel and aluminium.

[0150] It may be that both the first surface and second surface is or comprises a metal.

[0151] It may be that one of the first surface and the second surface is a printed circuit board. For example, it may be that the first surface is a printed circuit board and the second surface is the surface of an electrical component. In these embodiments, the aqueous emulsion may both adhere and electrically connect the printed circuit board to the electrical component.

[0152] The steps of coating the surfaces may be achieved using a brush or applicator. The steps of coating the surfaces may comprise spray coating.

[0153] Following the step of detaching the first and second surfaces from one another, the method may further comprise cleaning the first surface and / or second surface to remove excess adhesive. Thus, after using the aqueous emulsions of the disclosure as adhesives, the components having the first surface and / or second surface may be recycled.

[0154] The step of cleaning the first surface and / or second surface may comprise treating the first surface and / or second surface with an organic solvent.

[0155] The organic solvent may be a paint thinner. For example, the organic solvent may be a paint thinner selected from acetone and turpentine.

[0156] The aqueous emulsion may be as described in any of the embodiments in this specification relating to the first aspect of the invention.Method of electrically connecting electrical components

[0157] In another aspect, there is provided a method of forming an electrically conductive pathway between two electrical components, the method comprising: applying the aqueous emulsion of the first aspect or the third aspect in a continuous line onto a surface between two electrical components in contact with said surface such that, once dried, the aqueous emulsion forms an electrically conductive pathway between the two electrical components.

[0158] For the avoidance of doubt, the continuous line above refers to an electrically uninterrupted path of aqueous emulsion from one of the two electrical components to the other of the two electrical components along the at least one surface such that, once the aqueous emulsion has dried, an electric current can flow between the two electrical components. The term ‘line’ in this context may refer to a straight line, a curved line or an angled line (i.e. comprising at least two straight line portions having different orientations).

[0159] The at least one surface may be a printed circuit board. Thus, the printed circuit board may comprise the two or more electrical components.

[0160] The aqueous emulsion may be as described in any of the embodiments in this specification relating to the first aspect of the invention.Method of recovering electrical components

[0161] In another aspect, there is provided a method of recovering electrical components that have been adhered to one another via the method of the fourth aspect, the method comprising: detaching the first and second surfaces from one another by altering the pH of the first and second surfaces at the bonded interface. For the avoidance of doubt, the first and second surfaces referred to in this aspect represent two components of an electrical system or device. For example, the two components may be electrical components on a printed circuit board assembly.

[0162] The method may comprise increasing the pH of the first and second surfaces at the bonded interface to detach the first and second surfaces from one another. The step of increasing the pH may comprise increasing the pH to at least about 10, at least about 11 , at least about 12, or at least about 13.

[0163] Alternatively, the method may comprise decreasing the pH of the first and second surfaces at the bonded interface to detach the first and second surfaces from one another. The step of decreasing the pH may comprise decreasing the pH to less than about 5, less than about 4, less than about 3, less than about 2, or less than about 1.

[0164] The step of detaching the first and second surfaces from one another at the bonded interface may comprise treating the first and second surfaces with an alkaline solution having a pH of greater than about 10, greater than about 11 , greater than about 12 or greater than about 13 at the bonded interface. Alternatively, the step of detaching the first and second surfaces from one another at the bonded interface may comprise treating the first and second surfaces with an acidic solution having a pH of less than about 5, less than about 4, less than about 3, less than about 2 or less than about 1 at the bonded interface. Detaching may be achieved by submerging or immersing the product containing the adhesive in the acidic or alkaline solution.

[0165] Following the step of detaching the first and second surfaces from one another, the method may further comprise cleaning the first surface and / or second surface to remove excess adhesive. Thus, after using the aqueous emulsions of the disclosure as adhesives, the electrical components may be recycled.

[0166] The step of cleaning the first surface and / or second surface may comprise treating the first surface and / or second surface with an organic solvent.

[0167] The organic solvent may be selected from acetone and turpentine.DETAILED DESCRIPTION

[0168] The term “polymer” used herein may refer to a single species of polymer or to a polymeric mixture comprising multiple species of polymer blended or bonded together to create a new material with different physical properties to each individual species of polymer.

[0169] The term “hydrophobic” used herein refers to a species that repels or is immiscible with water.

[0170] The term “emulsion” used herein may refer to a dispersion of particles in a liquid phase, the particles and liquid phase being immiscible with one another. The emulsion comprises both the particles comprising hydrophobic polymer and the conductive filler. The particles may be solid particles, semi-solid particles, or liquid particles. The liquid phase is typically an aqueous phase.

[0171] The term “glass transition” used herein refers to the gradual and reversible transition in amorphous materials from a hard and relatively brittle state into a viscous or rubbery state as temperature is increased.

[0172] The term “glass transition temperature” or “Tg" used herein refers to the temperature or range of temperatures at which the glass transition occurs. The glass transition temperature is lower than the melting temperature of the crystalline state of the material.

[0173] The terms “positively charged” and “negatively charged” as used herein refer to the charge state of the particles of the first and second aqueous emulsions at the pH of the respective emulsion, i.e. the pH of the respective aqueous phase. The terms may mean that the particles are positively or negatively charged at a pH in the range of from about 5 to about 9, e.g. about 7.

[0174] The term “organic solvent” may refer to a solvent system selected from: hydrocarbons (e.g. petrol ether, hexane, heptane) ethers (e.g. dimethylethylene glycol, diethyl ether, t-butylmethyl ether, tetrahydrofuran, dioxane), esters (e.g. ethyl acetate),ketones (e.g. acetone, t-butylmethylketone), amides (e.g. N-methylpyrrolidine, dimethylformamide, dimethylacetamide), sulfoxides (e.g. dimethylsulfoxide), aromatic solvents (e.g. benzene, toluene), chlorinated solvents (e.g. chloroform, dichloromethane, 1,2-dichloroethane), turpentine, or mixtures thereof.

[0175] The term “nanoplatelets” may refer to single or few layered particles of two- dimensional layered material, e.g. graphene.

[0176] The term “few-layered” may refer to a species which is so thin that it exhibits different properties than the same compound when in bulk. Not all of the properties of the compound will differ between a few-layered particle and a bulk compound but one or more properties are likely to be different. A more convenient definition would be that the term ‘few layered’ refers to a thickness of from 2 to 9 molecular layers thick (e.g. 2 to 5 layers thick). A molecular layer is the minimum thickness chemically possible for that compound. In the case of graphene, one molecular layer is a single atom thick. Thus, few-layer particles are generally less than 10 nm thick, e.g. less than 5 nm thick.

[0177] The term ‘two-dimensional’ and ‘single or few layered’ are used interchangeably throughout this specification. Two-dimensional materials are not truly two dimensional, but they exist in the form of particles which have a thickness that is significantly smaller than their other dimensions. The term ‘two-dimensional1has become customary in the art.

[0178] The term ‘size’ as used herein may refer to the average particle size. In the case of nanoplatelets, the term ‘size’ may refer to the diameter of the nanoplatelets. The average particle size may be determined by measuring dynamic light scattering (e.g. using a Zetasizer system).

[0179] The term ‘solid adhesive’ as used herein may refer to the resulting composition of the aqueous emulsion of the invention having been allowed to dry and solidify.

[0180] The term ‘conductive filler’ as used herein may refer to an electrically and / or thermally conductive additive dispersed in the aqueous emulsion of the invention. When present, the conductive filler enables the flow of electrons and / or heat between adhered surfaces. Accordingly, the presence of the conductive filler renders the adhesive solid formed form the aqueous emulsion of the invention electrically and / or thermally conductive.

[0181] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article isused, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0182] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0183] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.EXAMPLESMaterials and Methods

[0184] Butyl acrylate (BA, Sigma Aldrich, 99%), styrene (ST, Sigma Aldrich, 99%), sodium dodecyl sulfate (SDS, Sigma Aldrich, >98.5%), potassium persulfate (KPS, Sigma Aldrich, ACS reagent, >99.0%), acrylic acid, graphene nanoplatelets (Fisher Scientific, sub-micron particles, S.A. 500 m2 / g), and distilled water were used. Silver nanoparticles (Thermo Scientific, 1-3 micron, S.A. min 0.25 m2 / g) were used and were stabilised using Pluronic F-127 (Sigma Aldrich). Sodium hydroxide (NaOH) (> 98%) was used to create alkaline solution for reversibility. Various surfaces such as copper, steel, stainless steel, aluminium, and glass were purchased (with 0.95 mm thickness) to examine the glue reversibility.Example 11. 1. Synthesis of precursor aqueous emulsion of poly(styrene-butyl acrylate) / poly(acrylic acid) (Pol(ST-BA / PAA))

[0185] Pol (St-BA / PAA) was synthesised following a free-radical emulsion polymerisation technique. It was carried out in a 100 mL three-neck flask in an oil bath into which 20 mL of deionised water was poured. After setting the stirrer at 350 rpm, 0.3 g of SDS (1.5 wt.%) was added and dissolved for around 15 min. It was then mixed with St and BA (25.7 wt.% monomer content at 2:3 ST:BA weight ratios) and added drop by drop for 10 minutes. At that point, the nitrogen flow was started. The emulsion was allowed to develop for a duration of about 15 minutes. Following this, 40 mg of potassium persulfate (KPS), which was previously dissolved in 1 mL of deionised water, was added. The heat was adjusted to 70°C and the nitrogen flow was subsequently reduced. The reaction was allowed to proceed for around 2 hours. After that time, 10 mg of KPS dissolved in 0.5 mL of deionised water were added dropwise, followed by 1 mL of acrylic acid in 1 mL of deionised water, dropwise over 10 min. Polymerisation proceeded for a further 3 h, and the resulting emulsion was collected and stored for analysis. The detailed formulations are shown in Table 1.Table 1Formulation ST:BA BA (g) ST (g) H2O (g) SDS (g) KPS (g) AA (g) ratioPol (ST- 2:3 4.96 3.31 22.5 0.3 0.05 1.05BA / PAA)1.2. Synthesis of pol(ST-BA / PAA) / graphene nanoplatelets (GNPs)

[0186] Graphene nanoplatelets (GNPs) were used as they possessed unique characteristics, such as a high aspect ratio, exceptional electrical conductivity, and thermal stability. Due to their hydrophobic nature, GNPs need to be dispersed in solvents such as water with the help of chemicals to minimise their surface tension. Due to their amphiphilic nature, sodium dodecyl sulfate (SDS) was used to disperse GNPs into water.

[0187] To disperse the GNPs, 40 ml of water was added to disperse GNPs in concentrations ranging from 5 to 10 wt.%. The stabilised GNP solution was obtained with in GNP to SDS ratio of about 2:1 with the help of high-power sonication (Qsonica-Q700) at a temperature of less than 60 °C for 60 mins. The solution was cooled by cooling bath to prevent heat build-up.

[0188] The particle size of the GNP solution was measured by Zetasizer to examine the dispersity of the particles in the solution. An average particle size of around 300 nm was achieved, with a polydispersity index (PDI) of around 0.3, which matched the size provided by the supplier. Also, the zetapotential of GNP solution was measured at around-42 mV, demonstrating that the GNP particles have good stability (Nazari, B. et al. Dispersing graphene in aqueous media: Investigating the effect of different surfactants. Colloids Surf A Physicochem Eng Asp 582, (2019)).

[0189] The conductive aqueous emulsion was prepared by mixing 2 mL of the precursor aqueous emulsion of (Pol(ST-BA / PAA) with 10 mL of the GNP solution (at 10 wt% GNP) under stirring at around 250 RPM for 30 min. A magnetic stirrer was preferred to a vertical mixer to achieve the required viscosity (not measured) for the glue to spread properly on a surface. The resulting loading of GNP in the conductive aqueous emulsion was 8.3% by weight of the emulsion. The resulting conductive aqueous emulsion comprised solid GNP : solid polymer in a weight ratio of about 2:1.1.3. Alternative synthesis of pol(ST-BA / PAA) / graphene nanoplatelets (GNPs)

[0190] Using the stabilised GNP solution obtained in the first step of 1.2, the stabilised GNP solution is filtered under vacuum to remove water and to produce a solid residue of stabilised GNP. The solid residue is washed with water and left overnight at room temperature to dry.

[0191] The dried residue of stabilised GNP is added to the 2 mL precursor aqueous emulsion of (Pol(ST-BA / PAA) under stirring with glass rod to produce the conductive aqueous emulsion.

[0192] The stabilised GNP was added to the precursor aqueous emulsion in an amount sufficient to obtain a GNP loading of 21%, 24%, 29% and 35% by weight of the emulsion.1.4. Synthesis of pol(ST-BA / PAA) / Silver nanoparticles (AgNPs) glue

[0193] Silver nanoparticles (AgNPs) were used as they possessed unique characteristics, such as exceptional electrical conductivity. Due to their hydrophobic nature, AgNPs need to be dispersed in solvents such as water with the help of chemicals to minimise their surface tension. Due to their amphiphilic nature, poloxamer 407 (Pluronic F-127) was used to disperse AgNPs into water.

[0194] To disperse the AgNPs, 200 mL of water was added to disperse AgNPs in concentrations ranging from 1 to 2 wt.%. The stabilised AgNPs solution was obtained with in AgNPs to Pluronic ratio of about 1 :2 with the help of high-power sonication (Qsonica- Q700) at a temperature of less than 60 °C for 60 mins. The solution was cooled by cooling bath to prevent heat build-up. The solution of AgNPs was then filtered under vacuum to produce a solid residue of stabilised AgNPs, which was subsequently left to dry overnight at room temperature.

[0195] The particle size of the AgNPs was measured by SEM to examine the dispersity of the particles in the dry film. An average particle size of around 2-3 pm was observed, which matched the size provided by the supplier.

[0196] The conductive aqueous emulsion was prepared by mixing 2 mL of the precursor aqueous emulsion of (Pol(ST-BA / PAA) with 4 g of the dried stabilised AgNPs under stirring for 10 min. The resulting loading of AgNPs in the conductive aqueous emulsion was 66% by weight of the emulsion. The resulting conductive aqueous emulsion comprised solid AgNPs: solid polymer in a weight ratio of about 2:1.

[0197] In alternative syntheses, the dried stabilised AgNPs were added to the precursor aqueous emulsion in an amount sufficient to obtain an AgNP loading of 56%, 61% and 72% by weight of the emulsion.

[0198] Table 2 summarises the measured particle size, polydispersity index (PDI) and zetapotential of the precursor aqueous emulsion Pol(ST-BA / PAA, the stabilised GNP solution, and the aqueous emulsion of the invention (Pol(ST-BA / PAA) / GNP.Table 2Formulation Avg. particle size PDI Zeta potential (nm) (mV)Pol (ST-BA / PAA) 845 0.21 -36.5GNP solution (10 wt.% of 300 0.3 -42GNP in water)Pol (ST-BA / PAA) / GNP (Sg1) 1120 0.36 -42.6Example 2: Reversibility and Conductivity of Adhesive2. 1. Adhesion reversibility

[0199] The reversibility of the adhesion using pol(ST-BA / PAA) / graphene was evaluated by first attaching two surfaces of the same material together using the aqueous emulsion (Sg1). Once dried, the attached samples were then placed in an alkaline solution (pH=14). After two days, surface detachment was observed, as shown in Table 3.Table 3Surface used Surface area Filler loading Reversibility (cm2) (mg) durationCopper 4 60 2 daysSteel 4 99 No separationStainless steel 4 75 2 daysAluminium 4 82 2 daysGlass 5 70 2 days

[0200] The reversibility of the adhesion using pol(ST-BA / PAA) / Silver nanoparticles was evaluated by first attaching two surfaces of the same material together using the Ag aqueous emulsion. Once dried, the attached samples were then placed in an alkaline solution at 500 rpm and 85 °C. surface detachment was observed, as shown in Table 4.Table 4Surface used Surface area Filler loading Reversibility (cm2) (wt.%) durationCopper 1 66 10 minAluminium 1 66 20 min2.2 Conductivity measurements

[0201] The electrical conductivity of the Pol (ST-BA / PAA) / GNP was measured using a four-point probe (Ossila Four-Point Probe). The dried adhesive (0.04 mm thickness) on a glass surface was placed on a four-point probe device to measure its sheet resistance. The film's resistivity was obtained once the film thickness was measured, where the conductivity is a reciprocal of the resistivity, as shown in Table 5.

[0202] For pol(ST-BA / PAA) / Silver nanoparticles (AgNPs) with 66 wt.% silver loading, the dried film with a thickness around 0.5 mm was placed on a four-point probe device to measure its sheet resistance. The film's resistivity was obtained once the film thickness was measured, where the conductivity is a reciprocal of the resistivity, as shown in Table 5.Table 5Sample Sheet Resistivity Conductivity Filler loading resistance (mQ.m) (S / m) (wt.%) (Q / square)Pol (ST- BA / PAA) / 73.91 2.95 339 8.3GNP (Sg1)Pol (ST-BA / PAA) / 0.009 0.0034 294.1x10366AgNPs

[0203] The minimum electrical conductivity required for electrical applications should be > 10'1S / m (Fadil, Y. Synthesis of Waterborne Graphene / Polymer Nanocomposites.(2020) doi:10.26190 / unsworks / 22169). Thus, the aqueous emulsions of the invention achieve the necessary electrical conductive properties to render them suitable for use in electrical applications.

[0204] Table 6 provides a comparison of the resistivity of some known conductive materials with an aqueous emulsion of the invention (Sg1).Table 6Materials Resistivity p (Q m)Silver 1. 59 x 1CT8Copper 1. 72 x 1CT8Gold 2.44x 10’8Aluminium 2.65 x 1CT8Lead 22 x 10’8Sg1 2.95x 10’3Silicon 0.1-2300Carbon (Pure) 3.5 x 105

Claims

CLAIMS1. An aqueous emulsion selected from: an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and a negatively charged polymer; and an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and a positively charged polymer.

2. The aqueous emulsion of claim 1, wherein the conductive filler is present in an amount of at least about 5% by weight of the aqueous emulsion.

3. The aqueous emulsion of claim 1 or claim 2, wherein the conductive filler is present in an amount of no greater than about 75% by weight of the aqueous emulsion.

4. The aqueous emulsion of any preceding claim, wherein the conductive filler is selected from: metal filler, carbon-based filler, ceramic filler, or metal-coated filler.

5. The aqueous emulsion of claim any preceding claim, wherein the conductive filler comprises metal nanoparticles or graphene nanoplatelets.

6. The aqueous emulsion of claim 5, wherein the metal nanoparticles or graphene nanoplatelets have a size of no greater than about 4 pm.

7. The aqueous emulsion of claim 5 or claim 6, wherein the graphene nanoplatelets have a thickness of less than about 10 nm.

8. The aqueous emulsion of any preceding claim, wherein the aqueous emulsion is an aqueous emulsion comprising particles dispersed in an aqueous phase and further comprising a conductive filler dispersed in the aqueous phase, wherein the particles comprise a hydrophobic polymer and a negatively charged polymer.

9. The aqueous emulsion of claim 8, wherein the negatively charged polymer comprises one or more groups that are deprotonated at the pH of the aqueous emulsion to form an anion.

10. The aqueous emulsion of claim 8 or claim 9, wherein the negatively charged polymer comprises one or more groups selected from: carboxylate, sulfonate, phosphonate and boronate groups.

11. The aqueous emulsion of any of claims 8 to 10, wherein the negatively charged polymer is selected from: poly(acrylic acid), alginate, carboxymethyl cellulose, xanthan gum, gum Arabic, carrageenan, poly(2-acrylamido-2-methylpropanesulfonic acid), poly(methacrylic acid), poly(maleic acid) and poly(vinyl sulfonic acid), optionally wherein the negatively charged polymer is poly(acrylic acid).

12. The aqueous emulsion of any of claims 8 to 11, wherein the particles comprising the hydrophobic polymer further comprise an additive comprising one or more sulfate groups.

13. The aqueous emulsion of claim 12, wherein the additive is sodium dodecyl sulfate.

14. The aqueous emulsion of any preceding claim, wherein the particles comprising the hydrophobic polymer are present in an amount of from about 0.25% to about 25% by weight of the aqueous emulsion.

15. The aqueous emulsion of any preceding claim, wherein the hydrophobic polymer is poly(styrene-butyl acrylate) copolymer.

16. The aqueous emulsion of any preceding claim, wherein the aqueous emulsion has a pH in the range of from about 5 to about 9.

17. The aqueous emulsion of any preceding claim, wherein the particles comprising the hydrophobic polymer have a size of from about 20 nm to about 10 pm.

18. A method of making the aqueous emulsion of claim 1, the method comprising adding a conductive filler to a precursor aqueous emulsion to provide the aqueous emulsion of the invention, wherein the precursor aqueous emulsion is: (i) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are negatively charged; or (ii) an aqueous emulsion comprising particles dispersed in an aqueous phase, wherein the particles comprise a hydrophobic polymer, wherein the particles comprise a hydrophobic polymer and wherein the particles are positively charged.

19. The method of claim 18, wherein the method comprises the following steps:(a) providing a suspension comprising conductive filler and water;(b) sonicating the suspension;(c) filtering the suspension to provide a solid; and(d) adding the solid to the precursor aqueous emulsion to provide the aqueous emulsion of claim 1.

20. The method of claim 19, wherein the solid comprises conductive filler and surfactant.

21. The method of claim 19 or claim 20, wherein the conductive filler is present in the suspension in an amount of from about 0.5% to about 15% by weight.

22. An aqueous emulsion obtained or obtainable by the method of any of claims 18 to 21.

23. A method of adhering two surfaces to one another, the method comprising: coating a first surface and / or a second surface with the aqueous emulsion of any of claims 1 to 17 or claim 21; and contacting the first surface with the second surface to adhere the first and second surfaces to one another at a bonded interface.

24. The method of claim 23, further comprising increasing the pH of the first and second surfaces at the bonded interface to detach the first and second surfaces from one another.

25. The method of claim 24, wherein the step of increasing the pH comprises increasing the pH to at least about 12.

26. The method of any one of claims 23 to 25, wherein at least one of the first surface and second surface are selected from: copper, steel, stainless steel, aluminium, glass, polypropylene, HDPE, and LDPE.