Method for forming an article comprising a pathway of particles wherein a termination of the pathway of particles exposed

Abstract

The invention relates to a method for forming an article comprising a pathway of particles wherein a termination of the pathway of particles is exposed. The method comprises arranging the particles by applying an electric field and/or a magnetic field at an interface between a water soluble or a non-water soluble matrix and a matrix comprising a viscous material and particles. After fixating the viscous material, the termination is exposed by dissolving the water soluble or non-water soluble matrix. The invention also relates to articles obtainable by said method, and to the use of said method in various applications.

Claims

1. A method for arranging particles at an interface between a water soluble or non-water soluble matrix comprising particles and a matrix comprising a viscous material and particles, said method comprising the steps of: contacting the water soluble or non-water soluble matrix comprising particles and/or the matrix comprising a viscous material and particles with a support comprising at least one side, said at least one side of the support facing the water soluble or non-water soluble matrix comprising particles and/or the matrix comprising a viscous material and particles, placing the water soluble or non-water soluble matrix comprising particles in contact with the matrix comprising a viscous material and particles, thereby providing a structure comprising at least one interface between said water soluble or non-water soluble matrix comprising particles and said matrix comprising a viscous material and particles, subjecting the particles in said structure to an electric field thereby forming the particles into at least one pathway of particles in the water soluble or non-water soluble matrix comprising particles and in the matrix comprising a viscous material and particles, fixating the viscous material so as to fixate the at least one pathway of particles, and removing the water soluble or non-water soluble matrix comprising particles by dissolution, thereby exposing a termination of the at least one pathway of particles at the at least one interface, wherein the electric field has an electric field strength ranging from 5 to 100 kV/cm.

2. A method according to claim 1, wherein the water soluble or non-water soluble matrix comprises or consists of particles and a water soluble material.

3. A method according to claim 1, wherein said at least one pathway of particles forms part of a network of particles.

4. A method according to claim 1, further comprising the step of: subjecting the at least one side of the support to a surface modification technique selected from corona, plasma, or flame treatment.

5. A method according to claim 1, further comprising the step of: removing the support from the water soluble or non-water soluble matrix comprising particles and/or the matrix comprising a viscous material and particles.

6. A method according to claim 1, wherein the water soluble or non-water soluble matrix comprising particles is the water soluble matrix comprising particles, and wherein the water soluble matrix comprising particles is removed by rinsing with water or an aqueous solution.

7. A method according to claim 1, wherein the water soluble or non-water soluble matrix comprising particles is the non-water soluble matrix comprising particles, and wherein the non-water soluble matrix comprising particles is removed by rinsing with acids, bases, or organic solvents.

8. A method according to claim 1, wherein the water soluble or non-water soluble matrix comprising particles is the water soluble matrix comprising particles, and wherein the water soluble matrix comprises or consists of particles and one or more water soluble polymers selected from the group consisting of polyvinyl alcohol, cellulose ethers, polyethylene oxide, starch, polyvinylpyrrolidone, polyacrylamide, polyvinyl methylether-maleic anhydride, polymaleic anhydride, styrene maleic anhydride, hydroxyethyl cellulose, methylcellulose, polyethylene glycols, carboxymethylcellulose, polyacrylicacid salts, alginates, acrylamide copolymers, guar gum, casein, ethylene-maleic anhydride resin, polyethyleneimine, ethyl hydroxyethylcellulose, ethyl methylcellulose, and hydroxyetyl methylcellulose.

9. A method according to claim 1, wherein the viscous material of the matrix comprising a viscous material and particles comprises an adhesive and/or an elastomeric material.

10. A method according to claim 1, wherein the particles are conductive particles.

11. A method according to claim 1, wherein the at least one pathway of particles is an electrically conducting pathway of particles.

12. A method according to claim 7, wherein the organic solvent is selected from alcohols, esters, ketones, aldehydes, ethers, and hydrocarbons.

13. A method according to claim 10, wherein the conductive particles are particles of carbon, metal, and/or metal alloys.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be further described with reference to exemplary embodiments, with reference to the enclosed drawings, wherein:

(2) FIG. 1 shows a structure comprising a support 1, a soluble matrix 2 and a matrix 3 comprising a viscous material, particles 4, and an interface 5 between the matrix 2 and the matrix 3.

(3) FIG. 2 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4 being subjected to an electric field, and an interface 5 between the matrix 2 and the matrix 3.

(4) FIG. 3 shows a structure comprising a support 1, a soluble matrix 2 and a matrix 3 comprising a fixated viscous material, and particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination at an interface 5 between the soluble matrix 2 and the matrix 3.

(5) FIG. 4 shows a structure comprising a soluble matrix 2 and a matrix 3 comprising a fixated viscous material, and particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination at an interface 5 between the soluble matrix 2 and the matrix 3.

(6) FIG. 5 shows a structure comprising a matrix 3 comprising a viscous material and particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination at a surface 6.

(7) FIG. 6 shows a structure comprising a support 1, a matrix 3 comprising a fixated viscous material, particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination and a soluble matrix 2. The termination of said at least one pathway of particles is arranged at the interface 5 between the soluble matrix 2 and the matrix 3.

(8) FIG. 7 shows a structure comprising a support 1, a matrix 3 comprising a fixated viscous material and particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination arranged at a surface 6.

(9) FIG. 8 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4, at least some of which as in the form of at least one pathway of particles comprising a termination at interfaces 5 and 6, respectively, a further soluble matrix 7, and a further support 8.

(10) FIG. 9 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4, a further soluble matrix 7, and a further support 8. At least some of the particles 4 that are contained within the matrix 3 have a linear dimension that is larger than the thickness 9 of the matrix 3.

(11) FIG. 10 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4, at least some of which as in the form of at least one pathway of particles comprising a termination at both interfaces 5 and 6, wherein said at least one pathway of particles is a single particle that has been arranged by the electric field, a further soluble matrix 7, and a further support 8.

(12) It should be noted that the drawings have not been drawn to scale and that the dimensions of certain features have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIG. 1 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material and particles 4. The soluble matrix 2, the matrix 3 comprising a viscous material and the particles 4 may be as described herein. The particles 4 are contained within the matrix 3. Due to immiscibility or very limited miscibility of the soluble matrix 2 and the matrix 3 an interface 5 is formed between the soluble matrix 2 and the matrix 3. The structure may be formed by coating the support 1 with the soluble matrix 2, optionally followed by drying. Thereafter the matrix 3 containing the particles 4 and a viscous material is deposited onto the soluble matrix 2.

(14) FIG. 2 shows the application of an electric field to the structure illustrated in FIG. 1. Upon application of the electric field the particles 4 will form at least one pathway of particles comprising a termination, wherein the termination is arranged at the interface 5 between the soluble matrix 2 and the matrix 3. At least part of the pathway of particles may form a network of particles. The termination of the at least one pathway of particles may be arranged in the plane of the interface and/or may protrude from the matrix 3 into the soluble matrix 2 through the interface 5. Advantageously, the electric field is applied until no visible movement of the particles is observed. In cases where the alignment is either too fast or too slow to be easily observed, or where the nature of the particles makes in situ observation of alignment difficult, response of the particles to the electric field can be verified by other means, or verified by observation after the electric field is removed.

(15) Subsequent to application of an electric field the viscous material of the matrix 3 is fixated so as to fixate said at least one pathway of particles comprising a termination at the interface 5. FIG. 3 shows the resulting structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a fixated viscous material, the particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination, and the interface 5. At least part of the particles and/or the at least one pathway of particles may form a network of particles. The termination of said at least one pathway of particles is located in the plane of the interface 5 between the matrix 3 without being embedded within or covered by the viscous material of the matrix 3 thereby allowing them to be exposed upon subsequent removal of the soluble matrix 2. Moreover, some of the particles and/or the termination of said at least one pathway of particles and/or network of particles may protrude from the matrix 3 into the soluble matrix 2.

(16) FIG. 4 shows a structure resulting from removal of the support 1 from the structure shown in FIG. 3. The resulting structure comprises the soluble matrix 2, the matrix 3, the particles 4 at least some of which are in the form of at least one pathway of particles comprising a termination, and the interface 5. The termination of said at least one pathway of particles is arranged at the interface 5. The termination may be located in the plane of the interface 5 and/or protrude from the matrix 3 into the soluble matrix 3.

(17) Exposure of the soluble matrix 2 to appropriate chemical means, such as rinsing or washing with a solvent, makes it dissolve thereby exposing the termination of said at least one pathway of particles at a surface 6. The termination may be in the plane of the surface 6 and/or protrude from the surface 6. The resulting structure is shown in FIG. 5. External electrical means may be connected to the network of particles within the matrix 3 via connection with the exposed termination of said at least one pathway of particles.

(18) A support 1 may be deposited on the matrix 3 of the structure illustrated in FIG. 4. The support 1 may be deposited on the side of the matrix 3 opposite to the side facing the soluble matrix 2. The resulting structure is shown in FIG. 6.

(19) The soluble matrix 2 may then be removed from the structure illustrated in FIG. 6. The removal may take place by chemical means such as rinsing or washing with a solvent thereby exposing the termination of the at least one pathway of particles at the surface 6 and/or protruding from the matrix 3. The resulting structure is shown in FIG. 7.

(20) FIG. 8 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4, at least some of which are in the form of at least one pathway of particles comprising a termination at interfaces 5 and 6, respectively, a further soluble matrix 7, and a further support 8. The particles 4 have been exposed to an electric field, causing them to arrange into at least one pathway of particles extending from interface 5 to interface 6. The terminations of the at least one pathway of particles may be arranged in the plane of said interfaces and/or may protrude from the matrix 3 into the soluble matrices 2 and 7 through the interfaces 5 and 6. This structure allows for removal of the soluble matrices 2 and 7 and external electrical means may be connected to said terminations allowing electrical current to be passed through said at least one pathway of particles.

(21) FIG. 9 shows a structure comprising a support 1, a soluble matrix 2, a matrix 3 comprising a viscous material, particles 4, a further soluble matrix 7, and a further support 8. At least some of the particles 4 that are contained within the matrix 3 have a linear dimension that is larger than the thickness 9 of the matrix 3.

(22) FIG. 10 shows the application of an electric field to the structure illustrated in FIG. 9. Upon application of the electric field the particles 4 will be arranged and/or rotated by the electric field and form at least one pathway of particles comprising terminations at interfaces 5 and 6, respectively. It will be appreciated that in this embodiment, said at least one pathway of particles comprises a single particle. The terminations of the at least one pathway of particles protrude from the matrix 3 into the soluble matrices 2 and 7 through the interfaces 5 and 6. Alternatively, the at least one pathway of particles may be arranged in the planes of said interfaces. This structure allows for removal of the soluble matrices 2 and 7 and external electrical means may be connected to said terminations allowing electrical current to be passed through said at least one pathway of particles.

(23) The invention is further illustrated by the following non-limitative examples.

EXAMPLES

Example 1

(24) A polyethylene terephthalate (PET) substrate purchased from Dupont Teijin Melinex 453 was subjected to corona treatment on one of its sides. Then, polyvinylalcohol (PVA) in the form of a 1% by weight aqueous solution of 50/40 Elvanol, PVA, with 0.2% (by weight) polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, (Triton X100) purchased from Du Pont was applied as a thin film onto the side of the PET substrate having been subjected to corona treatment using a metered coating rod applicator. The coated film was dried in a convection oven in order to remove the water and harden the film resulting in a PVA coating thickness from 0.15 micrometers to 0.60 micrometers on the PET substrate.

(25) Silver particles having a size from 2 to 3.5 micrometers and at a concentration of 0.5% by volume purchased from Sigma-Aldrich were mixed with the UV curable adhesive Dymax 3094 purchased from Dymax Corporation. The resulting adhesive mixture was coated as a film onto the PVA coating using a rod applicator. Due to the incompatibility of the matrix polymers and their relative viscosities the materials did not intermix. The layers were discrete with a defined interface between the layers. The particle-rich adhesive layer had a thickness of about 80 micrometers.

(26) The PET substrate with the PVA coating and the particle-adhesive coating was placed over an electrode with the PVA and adhesive facing away from the electrode. An electric field was created using an interdigitated electrode design with a voltage of 350 volts and a frequency of 10 kHz. The electric field induces electrical dipoles in the silver particles causing them to move towards the regions with highest electrical field gradient, i.e. 5 through the adhesive layer toward the PVA-adhesive interface. Furthermore the silver particles interact with each other through dipole-dipole interactions, thus forming a connective, continuous network with the highest network density being near the adhesive-PVA interface. Some of the connected particles remained at the surface of the adhesive and some connected particles penetrated the interface. For both circumstances, the adhesive polymer does not cover or shield the silver particles. When the particles did not appear to move under magnification and appeared to be connected the network of particles were fixed to prevent further movement which ensures the continuity of the particle connected network. Particle immobilization for network connectivity was accomplished by exposing (crosslinking) the adhesive to a UV light source which cures the adhesive and increases the viscosity of the matrix, thereby rendering the particles immobile, inhibiting particle movement or drift which could otherwise break the particle network. The adhesive matrix with the assembled conductive particles was UV cured using an Omnicure S2000 with a 200-watt mercury short arc lamp delivering an UV spectral output of 350-600 nm.

(27) The film was separated by manually peeling the PET from the PVA and aligned particle-rich adhesive structure. Thereby, providing a two layer structure comprising of a PVA layer, and an adhesive layer with a continuous, connected network of silver particles in which the highest organized network density occurred at the interface.

(28) A second PET support film was attached to the exposed adhesive layer of the two layer structure (opposite to the side facing the PVA coating). Thereafter, the PVA coating was rinsed with water to expose a portion of the network of particles and network nodes at the interfacial surface of the adhesive coating. Once the PVA was completely removed, the film was dried using a forced hot air hand-held heater.

(29) After washing and drying as described above, the resulting structure was subjected to analysis using a Scanning Electron Microscope (SEM) and X-ray elemental analysis. SEM analysis was completed at a magnification of 1500× using a field voltage of 20 kV and the X-ray elemental analysis used an electron beam volume which created a penetrating surface of approximately 0.5-1.0 μm. The results confirmed the formation of a network of silver particles and its exposure at the polymer surface.

Example 2

(30) PVA in the form of a 2% by weight aqueous solution of 50/40 Elvanol PVA purchased from Du Pont was applied using a metered coating rod applicator as a 50 μm thick film onto a PET substrate purchased from Goodfellow. The coated film was dried in a convection oven in order to remove the water and harden the film resulting in a PVA coating thickness of about 1 micrometer on the PET substrate. The PET substrate with the PVA coating was then cut into smaller pieces and two pieces of the substrate was placed on two separate flat transparent electrodes with the PVA facing away from the electrode.

(31) Nickel Graphite particles having a size from 25 to 90 micrometers and at a concentration of 0.5% by volume purchased from Sultzer Metco were mixed with the UV curable adhesive Norland NOA81 purchased from Edmund Optics. The resulting adhesive mixture was deposited with a wooden applicator stick as a drop onto the PVA coated substrate on top of one of the electrodes. Spacers with a defined thickness of 150 μm were placed on top of said electrode, separated from the adhesive mixture. The other electrode was then pressed on top of the mixture, with the PVA coating facing the adhesive, compressing the mixture drop into a circular film with a controlled thickness equal to the thickness of the spacers.

(32) Due to the incompatibility of the PVA and the adhesive and their relative viscosities the materials did not intermix. The resulting sandwich consisted of a series of layers, comprising from one end to another: electrode, substrate, PVA, particle rich adhesive mixture, PVA, substrate, electrode. All layers were discrete with a defined interface between the layers.

(33) An electric field was set up between the electrodes by applying a voltage of 350 volts and a frequency of 10 kHz. The electric field induces electrical dipoles in the silver particles causing them to align into assembled and connected chains. The particle chains extend perpendicular to the plane of the adhesive mixture, creating stacked particle columns which span the gap between the PVA-adhesive interfaces on either side of the mixture. Because of the finite size of the electrodes the electric field is somewhat stronger closer to the electrode than in the center of the gap between them. This causes a dielectrophoretic force on the nickel graphite particles that attracts the ends of the particle chains to the adhesive-PVA interfaces. Some of the connected particles remained at the surface of the adhesive and some connected particles penetrated the interface. For both circumstances, the adhesive polymer does not cover or shield the nickel graphite particles at the PVA-adhesive interface.

(34) After 1 minute, when the particles showed no further movement, as viewed under magnification, the network of particles were fixed to prevent further movement and to ensure the continuity of the particle connected network by curing (crosslinking) the adhesive using a UV light source. The UV-light is directed through the transparent electrodes, substrate and PVA, penetrating and curing the adhesive in the center of the sandwich. Exposing the adhesive with the aligned conductive particles to the UV light cures the adhesive and increases the viscosity of the matrix, thereby, inhibiting the particle movement. The matrix (adhesive) with the aligned and connected particle chains was UV cured using a Dymax BlueWave200 spot light system.

(35) The film was separated by first manually separating the electrodes from the PET, and then peeling the PET from the PVA and aligned particle-rich adhesive structure. Thereby, providing a three layer structure comprising of a PVA layer, an adhesive layer with a continuous, connected network of nickel graphite particles aligned parallel to the layer normal, and a PVA layer on the opposite side of the first PVA layer.

(36) Thereafter, the PVA coating was rinsed with water to expose the network nodes at the interfacial surfaces on both sides of the adhesive layer. Once the PVA was completely removed, the film was air dried in ambient conditions for 15 minutes.

(37) After washing and drying as described above, the conductive nature of the adhesive layer was confirmed by sandwiching the layer between two pieces of copper, each with a surface area of approximately 1 square centimetre, and measuring the resistance between the copper pieces with a multimeter. The measured resistance was on the order of 10 Ohm.