PROCESS OF FABRICATING A BEADED PATH ON THE SURFACE OF A SUBSTRATE, A SYSTEM FOR FABRICATING SUCH A PATH, USE THEREOF, AND A KIT

Abstract

The invention relates to a process of fabricating a beaded path on the surface of a substrate, the process comprising: preparing a dispersion of particles in a liquid; supplying the prepared dispersion to at least one electrically conductive microcapillary in a continuous manner; forming and maintaining a convex meniscus of the dispersion at the outlet end of the microcapillary positioned above and/or below the surface of a substrate; applying alternating voltage to the microcapillary so that a beaded structure is formed between the dispersion meniscus and the surface of the substrate; and moving the microcapillary relative to the substrate and/or the substrate relative to the microcapillary so as to deposit the particles of the formed beaded structure on the surface of the substrate and simultaneously rebuild the beaded structure formed between the dispersion meniscus and the surface of a substrate. The invention also relates to a system for realizing this process and the use of the beaded path fabricated in accordance with the process of the invention for the production of electrodes in photovoltaic cells, new generation clothing, electronic components, including flexible electronics, artificial flagella, photonic and optomechanical materials, as well as for the regeneration of damaged paths on the surface of a substrate. The present invention also relates to a kit comprising a substrate and a beaded path fabricated on the surface of that substrate according to this process. The invented process is simple, efficient, hence economical, and enables fabricating beaded paths that retain their properties after turning off the voltage initially used to form a beaded structure. Moreover, the process occurs outside a liquid environment and enables fabricating of paths in a continuous manner, that is, through the formation of the beaded structure and its simultaneous depositing on the surface of a substrate allowing the fabrication of beaded paths of arbitrary length.

Claims

1. A process of fabricating a one-dimensional path of aligned one by one particles on the surface of a substrate, wherein a) a dispersion of electrically conductive particles in an electrically weakly-conductive liquid is prepared, and wherein the value of the dielectric constant of the particles is at least twice that of the dielectric constant of the dispersion liquid, whereas the value of the electrical conductivity of the particles is at least one order of magnitude larger than that of the dispersion liquid; b) the prepared dispersion is supplied in a continuous manner to at least one electrically conductive microcapillary; c) the convex meniscus of the dispersion is formed and maintained at the outlet end of the microcapillary positioned above and/or below the surface of a substrate; d) alternating voltage is provided to the microcapillary, so that a one-dimensional structure of aligned one by one particles is formed between the dispersion meniscus and the surface of the substrate; and e) the microcapillary is moved relative to the substrate and/or the substrate relative to the microcapillary so that the particles of the formed one-dimensional structure of aligned one by one particles are deposited on the surface of the substrate and the one-dimensional structure of aligned one by one particles formed between the dispersion meniscus and the surface of the substrate is rebuilt simultaneously, so that a one-dimensional path of aligned one by one particles is fabricated on the surface of that substrate.

2. A process according to claim 1, wherein particles of solid matter or soft matter are used.

3. (canceled)

4. A process according to claim 1, wherein particles with a size of 20 nm to 1 mm are used.

5. A process according to claim 4, wherein granular particles are used, preferably with a size of from approximately 1 μm to approximately 1 mm.

6. (canceled)

7. A process according to claim 1, wherein particles made of an electrically conductive material and/or a material with a high dielectric constant or the core-shell particle type, where the core is electrically non-conductive and the shell is made of an electrically conductive material, are used.

8. A process according to claim 7, wherein the particles are selected from the group consisting of i) steel particles, preferably with a size of from 25 μm to 300 μm, ii) glass particles coated with a layer of silver, preferably with a size of from 15 μm to 100 μm, iii) modified polystyrene particles, preferably with a size of 40 μm, and iv) copper particles, preferably with a size of from 1 μm to 25 μm.

9. (canceled)

10. (canceled)

11. (canceled)

12. A process according to claim 1, wherein spherical, oval, or cylindrical particles are used.

13. (canceled)

14. (canceled)

15. (canceled)

16. (canceled)

17. A process according to claim 1, wherein particles dispersed in a liquid of low dielectric constant having a viscosity in the range of 10 mPa.Math.s to 10000 mPa.Math.s or in a mixture of such liquids are used.

18. (canceled)

19. (canceled)

20. A process according to claim 17, wherein the particles are dispersed in a liquid selected from the group consisting of natural oil, synthetic oil, paraffin, and resin.

21. (canceled)

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. A process according to claim 1, wherein the concentration of particles in the dispersion is in the range of 10% to 50% by volume.

27. A process according to claim 1, wherein the distance between the dispersion meniscus and the surface of the substrate is at least three times the size of a single particle, and not less than 50 μm, and no more than fifty times the size of a single particle.

28. (canceled)

29. A process according to claim 1, wherein alternating voltage is applied with a magnitude such that the dielectrophoretic force acting on the particle overcomes the capillary force resulting from the capillary bridge formed between the surface of the dispersion liquid and the particle being pulled out from this dispersion.

30. A process according to claim 29, wherein the minimum magnitude of the voltage applied to the microcapillary is 300 V, and the minimum frequency is 100 Hz, preferably the magnitude of the voltage is in the range of 500 V to 3 kV, and the frequency is from 100 Hz to 10 MHz, especially the voltage is 500 V, and the frequency is 1000 Hz or the voltage is 750 V, and the frequency is 5000 Hz or the voltage is 1000 V, and the frequency is 100 Hz.

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. A process according to claim 30, wherein the voltage used to initiate the formation of a one-dimensional structure of aligned one by one particles is approximately twice as high as the magnitude of the voltage used during the deposition of the particles of the formed one-dimensional structure of aligned one by one particles on the surface of a substrate.

36. A process according to claim 1, wherein a material with electrical conductivity below 10.sup.3 S.Math.m.sup.−1 or a material with electrical conductivity above 10.sup.3 S.Math.m.sup.−1 coated with a layer of a material with electrical conductivity below 10.sup.3 S.Math.m.sup.−1 is used as the substrate.

37. (canceled)

38. (canceled)

39. (canceled)

40. A process according to claim 1, wherein the one-dimensional structure of aligned one by one particles is deposited on the surface of a substrate partially or completely covered with a liquid immiscible with the dispersion liquid.

41. A process according to claim 1, wherein a one-dimensional path of aligned one by one particles in a form of a line or a non-linear pattern is fabricated.

42. A process according to claim 41, wherein the paths are fabricated so that they either cross or connect with the previously fabricated one-dimensional path of aligned one by one particles on the surface of a substrate.

43. A process according to claim 1, wherein the meniscus at stage c) of the process is made and maintained by means of a setup for controlling the amount of the dispersion supplied from the dosing unit to the microcapillary, preferably an optical system, more specifically a digital microscope connected to a computer.

44. A process according to claim 1, wherein a voltage generator, preferably with the possibility of adjusting the electric current, or a voltage generator with an external current limiter, is used as a source of the alternating voltage.

45. (canceled)

46. (canceled)

47. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0164] FIG. 1(a-e) is a schematic diagram illustrating the steps of the process of fabricating a beaded path on the surface of a substrate, at times t.sub.0 to t.sub.4, respectively.

[0165] FIG. 2(a-j) is a set of images illustrating the steps of the process of fabricating a beaded path on the surface of a substrate according to two embodiments of the present invention, in which particles of different sizes are used; two different modes of microcapillary movement relative to the substrates, according to Examples 1 and 2, are also presented.

[0166] FIG. 3(a-b) is a set of images illustrating the rate of fabrication of a beaded path on the surface of a substrate according to one embodiment of the present invention, according to Example 3.

[0167] FIG. 4(a-e) is a set of images of fabricated linear beaded paths composed of stainless-steel particles of different average sizes, (a) 5 μm, (b) 25 μm, (c) 45 μm, (d) 100 μm and (e) 200 μm, respectively, according to Example 4.

[0168] FIG. 5(a-c) is a set of images illustrating the steps of the process of fabricating a non-linear beaded path on the surface of a substrate forming a C-shaped letter according to one embodiment of the present invention, at times t=2 s, t=5 s, t=7 s, respectively. FIG. 5(d-f) presents microscope images taken from above and towards the substrate illustrating the fabricated non-linear beaded paths in the shape of (d) letter ‘C’, (e) sine wave, and (f) square wave, respectively, according to Example 5.

[0169] FIG. 6(a-f) illustrates linear beaded paths fabricated on different surface morphologies: (a) flat surface, (b) wavy surface, (c, d) surface with steps, (e) surface with cracks, and (f) curved surface, according to one embodiment of the present invention, according to Example 6.

[0170] FIG. 7(a-e) illustrates beaded paths fabricated according to one embodiment of the present invention on substrates made of different materials: (a) flexible polymer foil, (b) crystalline silicon wafer, (c) cotton fabric, and (d, e) cellulose paper, according to Example 7. Images in panels (d) and (e) were taken 1 min and 5 min, respectively, after the beaded path was formed on the paper surface, and they illustrate the absorption of liquid by the substrate.

[0171] FIG. 8(a-b) is a set of digital microscope images taken during the fabrication of beaded paths of core-shell particles with different average sizes of (a) 15 μm and (b) 100 μm, respectively, according to Example 8.

[0172] FIG. 9(a-e) presents (a) an image of a fabricated beaded path of modified polystyrene particles with an average size of 40 μm, and (b-e) four images illustrating a sintering process of the fabricated beaded path, according to Example 9.

[0173] FIG. 10(a-b) is a set of images illustrating fabricated beaded paths made of (a) copper particles and stainless-steel particles with an average size of 25 μm and 100 μm, respectively, and (b) copper particles and stainless-steel particles with an average size of 1 μm and 45 μm, respectively, according to Example 10.

[0174] FIG. 11(a-b) is a set of SEM images that illustrate in high magnification fabricated beaded paths of particle size of ˜50 μm, wherein the particles were dispersed (a) in silicone oil, and (b) in liquid paraffin, according to Examples 11 and 12.

[0175] FIG. 12(a-c) is a set of images illustrating the mechanically strengthened beaded structure observed through (a-b) a digital microscope and (c) an electron microscope. A high magnification SEM image depicts the permanent bond between the particles after the sintering of the beaded structure, according to Example 13.

[0176] FIG. 13(a-c) is a set of images illustrating steps of the process of fabricating a beaded path on the surface of a substrate according to one embodiment of the present invention, in which non-spherical microparticles were used, according to Example 14.

[0177] FIG. 14(a-b) is a set of images from different perspectives illustrating two crossed beaded paths, according to Example 15.

[0178] FIG. 15(a-c) presents (a-b) a schematic diagram of two modes of microcapillary movement and (c) is a perspective image illustrating an exemplary embodiment of fabricating parallel beaded paths using a group of microcapillaries, according to Example 16.

[0179] FIG. 16(a-b) is a schematic diagram illustrating the fabrication of beaded paths in a liquid environment. FIG. 16 (c-d) is a set of images illustrating the fabricated beaded path on the surface of a substrate covered with a layer of liquid with thickness (c) greater and (d) smaller than particle size, according to Example 19.

[0180] FIG. 17 is an image illustrating the fabricated beaded path connecting two copper electrodes, according to Example 17.

[0181] FIG. 18(a-b) is a schematic diagram illustrating the system for fabricating beaded paths according to one embodiment (Example 18).

[0182] The images presented on FIG. 2(a-j), FIG. 3(a-b), FIG. 5(a-c), FIG. 6(a-d), FIG. 8(a-b), FIG. 13(a-c), FIG. 14(b) and FIG. 16(c-d) were taken at an angle of about 20° relative to the surface of a substrate (as a side view); therefore a mirror reflection of the particles from the surface of a substrate is shown on these images. The images presented on FIG. 4(a-e), FIG. 5(d-f), FIG. 7(a-e), FIG. 9(a), FIG. 10, FIG. 11(a-b), FIG. 12(a-c), FIG. 14(a), and FIG. 17 were taken from above, that is, perpendicular to the surface of a substrate.

EXAMPLES

[0183] A non-limiting embodiment of the present invention was schematically presented in FIG. 1(a-e), where at time t.sub.9 the microcapillary with the formed particle-dispersion meniscus is placed above the surface of a substrate. At time t.sub.1 (FIG. 1(b)) voltage is supplied to the microcapillary to initiate the process of formation of the beaded structure, which is formed from the dispersion meniscus towards the surface of the substrate. In this process, the particles first deform the dispersion meniscus, as presented in FIG. 1(b), and then the first particle is pulled out from the dispersion meniscus followed by other particles forming in this way a structure that resembles a bead necklace of particles in appearance (a beaded structure). The beaded structure reaches the surface of the substrate and is oriented roughly perpendicularly to that substrate (FIG. 1(c)). In the next step, the microcapillary is moved relative to the substrate (or the substrate is moved relative to the microcapillary). This results in sequential deposition of the particles of the formed beaded structure nearest to the surface, and the simultaneous pulling of other particles (sequentially) out of the dispersion, and thus, rebuilding the beaded structure at the side of the dispersion meniscus. That, in turn, enables continuous deposition of the particles of the beaded structure on the surface of the substrate. The subsequent steps of deposition of the beaded structure on the surface of the substrate at times t.sub.3 and t.sub.0 are presented in FIG. 1(d) and FIG. 1(e), where microcapillary movement above the surface of a substrate is indicated by the arrow. Voltage is continuously supplied during the deposition of the structure on the surface. After a path with the desired pattern is fabricated, voltage is turned off and the microcapillary is moved to a new place in order to initiate fabrication of the next path.

Example 1

[0184] In the present example, silicone oil (Rhodorsil Oils 47, purchased from VWR, catalogue number 83851.290, viscosity ˜350 mPa.Math.s, electrical conductivity ˜10.sup.−11 S/m and density ˜0.97 g/cm.sup.3; all measured at 25° C.) was used to prepare a dispersion of electrically conductive particles made of stainless steel (purchased from Cospheric, USA, average size ˜45 μm and density ˜7.8 g/cm.sup.3). Particle concentration was ˜50% by volume. The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter 0.6 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary using a dosing unit (syringe pump, neMESYS from CETONI) driven by a feedback loop system that included an optical system (digital microscope, Dino-lite AM7315) connected to a computer (DELL Latitude E 7470). The computer was used to record and analyze images from the microscope (i.e., the presence and shape of the dispersion meniscus at the outlet end of the microcapillary) with commercially available software (MATLAB, Image Processing Tolbox), so that the dosing unit received feedback information. The dispersion provided to one end of the microcapillary formed a convex meniscus at the second (outlet) end of that microcapillary. The second end of the microcapillary was positioned above the surface of a substrate (FIG. 2(a)) on which the particle structure was deposited to ultimately form a beaded path. The distance from the dispersion meniscus to the surface of the substrate was about 300 μm, that is about seven times the particle size. A voltage signal was provided to the microcapillary through an electrical wire with one end soldered to that microcapillary and the other end connected to the source of alternating field (voltage amplifier, Ultravolt HVA, model 5HVA24-BP1). In this example, square-wave voltage with frequency of 1 kHz and mean voltage (V.sub.rms) of 500 V was applied. The application of such voltage resulted first in meniscus deformation (FIG. 2(b)), followed by the formation of a beaded structure between the meniscus and the surface of a substrate. (FIG. 2(c)). The structure was formed in less than 0.5 s. In the next step, the microcapillary was moved relative to the substrate (with an average speed of about ˜0.25 mm/s), which resulted in sequential alignment of the particles of the formed beaded structure nearest to the surface, and simultaneous pulling of other particles (sequentially) out of the dispersion, and thus, rebuilding the beaded structure at the side of the dispersion meniscus, and that enabled the continuous deposition of the particles of the beaded structure on the surface of the substrate. FIG. 2(d) and FIG. 2(e) illustrate the successive steps of the deposition of the beaded structure on the surface of a substrate, at time t=5 s and t=10 s. Microcapillary movement above the surface of the substrate (to the left) is indicated by the arrow. Voltage was turned on during the formation of the beaded structure and its deposition on the surface of a substrate leading to the fabrication of the beaded path. After the path with the desired pattern was fabricated, the voltage was turned off and the microcapillary was moved to a new position in order to initiate fabrication of the next path. A microscope glass slide made of soda-lime glass was used as the substrate.

Example 2

[0185] In the present example, castor oil (Rhodorsil Oils 47, purchased from Sigma-Aldrich, catalogue number 83912, viscosity ˜700 mPa.Math.s, electrical conductivity ˜10.sup.−10 S/m and density ˜0.96 g/cm.sup.3; all measured at 25° C.) was used to prepare a dispersion of electrically conductive particles made of stainless steel (purchased from Cospheric, USA, with an average size ˜100 μm and density ˜7.8 g/cm.sup.3). Particle concentration was ˜40% by volume. The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter of 0.9 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1. The dispersion delivered to one end of the microcapillary formed the convex meniscus at the second (outlet) end of that microcapillary. The second end of the microcapillary was positioned above the surface of a substrate (FIG. 2(f)), on which the particle structure was deposited to ultimately form a beaded path. The distance from the dispersion meniscus to the surface of the substrate was about 500 μm, that is about five times the particle size. The voltage signal was provided to the microcapillary through an electrical wire with one end soldered to that microcapillary and the other end connected to the source of alternating field (voltage amplifier, Ultravolt HVA, model 5HVA24-BPI). In this example, square-wave voltage with frequency of 1 kHz and mean voltage (V.sub.rms) of 500 V was applied. Similarly, as in Example 1, the application of such voltage resulted first in meniscus deformation (FIG. 2(g)) followed by the formation of a beaded structure between the meniscus and the surface of the substrate. (FIG. 2(h)). The structure was formed in less than 0.1 s. In the next step, the microcapillary was moved relative to the substrate (with the average speed of about ˜1 mm/s), which resulted in sequential deposition of the particles of the formed beaded structure that were nearest to the surface, and simultaneous pulling of other particles (sequentially) out of the dispersion, and thus, rebuilding the beaded structure at the side of the dispersion meniscus, and that enabled the continuous deposition of the particles of the beaded structure on the surface of a substrate. FIG. 2(i) and FIG. 2(j) illustrate the successive steps of the deposition of the beaded structure on the surface of a substrate, at time t=2 s and t=2.1 s. The microcapillary was moved above the surface of the substrate to the right, as indicated by the arrow. Voltage was supplied all the time during the formation of the beaded structure and its deposition on the surface of a substrate leading to the fabrication of the beaded path. After the path with the desired pattern was fabricated, the voltage was turned off and the microcapillary was moved to a new position in order to initiate the fabrication of the next path. A microscope glass slide made of soda-lime glass was used as the substrate.

Example 3

[0186] In the present example, a beaded path was fabricated in the same manner and using the same materials as in Example 1, except that the microcapillary was moved relative to the substrate while the beaded structure was deposited on the surface of the substrate at an average speed of ˜5 mm/s (that is more than twenty times faster than in Example 1), and this is illustrated in FIG. 3(a) and FIG. 3(b). This example demonstrates well the efficiency of the process concerning the rate of path fabrication.

Example 4

[0187] In the present example, silicone oil (Rhodorsil Oils 47, purchased from VWR, catalogue number 6678.1000, viscosity ˜50 mPa.Math.s, electrical conductivity ˜10.sup.−11 S/m and density ˜0.96 g/cm.sup.3; all measured at 25° C.) was used to prepare a dispersion of electrically conductive particles made of stainless steel (purchased from Cospheric, USA). Particles of different average size, namely 5 μm, 25 μm, 45 μm, 100 μm and 200 μm, were used in each of the five experiments performed in this Example. Particle density was ˜7.8 g/cm.sup.3. The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter of 0.9 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1, so was microcapillary positioning and movement. As in Examples 1-3, square-wave voltage with frequency of 1 kHz and the mean value (V.sub.rms) of 500 V was applied to form the beaded structures. FIG. 4(a-e) presents five images of fabricated linear beaded paths made of stainless-steel particles of different average sizes, (a) 5 μm, (b) 25 μm, (c) 45 μm, (d) 100 μm and (e) 200 μm. A microscope glass slide made of soda-lime glass was used as a substrate.

Example 5

[0188] In the present example, non-linear beaded paths were fabricated by appropriately moving the microcapillary relative to the substrate. FIG. 5(a-c) illustrates images from the experiment, in which the microcapillary was initially moved from right to left (FIG. 5(a), the direction indicated by the arrow), subsequently it was moved towards the camera, indicated by the corresponding symbol in FIG. 5(b), and the direction was changed so that the microcapillary was moved from left to right, as shown in FIG. 5(c). As the result of this operation a beaded path in the form of a C-shaped pattern was fabricated, as shown on the microscope image taken from above, which is demonstrated in FIG. 5(d). In the subsequent experiments carried out as part of this embodiment of the invention, the microcapillary was moved along and across the substrate. FIG. 5(e) illustrates the image from the experiment, in which the microcapillary was moved so that a sine-wave pattern was formed, whereas FIG. 5(f) illustrates the image from the experiment, in which the microcapillary was moved so that a square-wave pattern was formed. The beaded paths, illustrated in FIG. 5(d-f), were fabricated using castor oil (Rhodorsil Oils 47, purchased from Sigma-Aldrich, catalogue number 83912) dispersion of electrically conductive particles made of stainless steel (purchased from Cospheric, USA with an average size ˜50 μm and density ˜7.8 g/cm.sup.3). The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter of 0.9 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1. Square-wave voltage with frequency of 5 kHz and the mean voltage value (V.sub.rms) of 750 V was applied to form beaded structures. The average translation rate of the microcapillary relative to the substrate was ˜0.2 mm/s, ˜1 mm/s, and ˜0.4 mm/s to fabricate paths in the form of a C-shaped pattern, sine-wave pattern, and square-wave pattern, respectively. A microscope glass slide made of soda-lime glass was used as the substrate.

Example 6

[0189] In the present example, beaded paths were fabricated on different surfaces of the substrate. FIG. 6(a) presents an image from the experiment illustrating the beaded path fabricated on a flat glass surface. A linear beaded path fabricated on a wavy surface is shown in FIG. 6(b). The height of the wave was approximately equal to particle size and the distance between the peaks of the wave was more than ten times the particle size. FIG. 6(c-d) presents a linear beaded path fabricated on surfaces with steps of a height up to five times the particle size. FIG. 6(e) shows a linear beaded path fabricated on surfaces with cracks with the separation distance about ten times the particle size. FIG. 6(f) presents a linear beaded path fabricated on a curved substrate. In the present example, the beaded paths were fabricated in the same manner and using the same materials as in Example 1, with a difference in depositing beaded structures on the surface of a substrate, that is, the microcapillary was not only moved along the substrate, but it also was lifted and lowered in order to maintain the same distance between the dispersion meniscus and the substrate, i.e., about 300 μm. The following materials were used as the substrates: (a) microscope glass slide made of soda-lime glass, (b) PVC polymer film, (c) microscope glass slide made of soda-lime glass with an insulating electric tape attached to the left side of the slide, (d) microscope glass slide made of soda-lime glass with an attached piece of plasticine, (e,f) plastic polymer.

Example 7

[0190] In the present example, beaded paths were fabricated on substrates made of different materials. FIG. 7(a-e) presents beaded paths fabricated on (a) flexible PVC (polyvinyl chloride) polymer film, (b) crystalline silicon n-type wafer with conductivity of approx. 4.5 S/cm from Siegert Wafer, (c) cotton fabric, and (d-e) cellulose paper with a basis weight of 200 g/m.sup.2. FIG. 7(d, e) illustrates images taken 1 min and 5 min after the beaded path was fabricated on the surface of a sheet of paper revealing liquid absorption by the substrate. The beaded paths were fabricated in the same manner and using the same materials as in Example 1, with a difference that the microcapillary was moved at an average speed of ˜1 cm/s, and particles with an average size of ˜100 μm were used.

Example 8

[0191] In the present example, the beaded paths were fabricated in the same manner and using the same materials as in Example 1, with a difference that particles made of glass microspheres coated by a thin (˜100 nm) silver layer were used instead of stainless-steel particles. Different average sized particles, i.e., ˜15 μm and ˜100 μm, were used in each of the two experiments performed within this example. Density of the particles was ˜2.5 g/cm.sup.3. The particles were electrically conductive and were purchased from Cospheric, USA. Digital microscope images taken during the fabrication of the beaded path on the substrate made of soda-lime glass are presented in FIG. 8(a-b).

Example 9

[0192] In the present example, castor oil (purchased from Sigma-Aldrich, catalogue number 83912) was used to prepare a dispersion. Inorganic salt (TBAB, purchased from Sigma-Aldrich, catalogue number: 193119) in proportion of 50 mg to 100 mL was added to the oil, which resulted in the increase in the electrical conductivity of the oil from approximately ˜10.sup.−10 S/m to approximately −10.sup.−8 S/m. Modified polystyrene particles with an average size of 40 μm were used. The particles used for modification were purchased from Microbeads, Norway. Chemical modification was conducted according to the procedure described in A Mikkelsen et al., Electric field-driven assembly of sulfonated polystyrene microspheres, Materials 10(4), 329 (2017), in which the particles were sulfonated for 60 min. The chemical modification resulted in the increase in electrical conductivity by several orders of magnitude, i.e., from 10.sup.−11 S/m to 10.sup.−6 S/m, and the increase in the magnitude of the dielectric constant from approximately 2 to approximately 30. The density of the particles was ˜1.1 g/cm.sup.3. The dispersion was supplied to the microcapillary in the same manner as described in Example 1.

[0193] In this example, square-wave voltage with frequency of 100 Hz and the mean voltage value (V.sub.rms) of 1000 V was applied. In order to fabricate a beaded path on a soda-lime glass substrate, the microcapillary was moved relative to the substrate. The microcapillary was moved with an average speed of approximately 0.2 mm/s. A picture of the fabricated beaded path is presented in FIG. 9(a). After the beaded path was fabricated, the sintering of particles of the beaded path was initiated through heating on a hot plate at approximately 150° C. Four images illustrating particle sintering, taken before heating, after 5 min, 10 min and 12 min of heating, respectively, are presented in FIG. 9(b-e).

Example 10

[0194] In the present example, two experiments were performed, and in each of them castor oil (purchased from Sigma-Aldrich, catalogue number 83912, viscosity ˜700 mPa.Math.s, electrical conductivity ˜10.sup.−10 S/m and density ˜0.96 g/cm.sup.3; all measured at 25° C.) was used to prepare dispersions of two different types of particles, i.e., particles made of different materials and of different sizes, namely copper particles (density ˜8.9 g/cm.sup.3) with the average size of ˜25 μm and stainless-steel particles (density ˜7.8 g/cm.sup.3) with the average size of ˜100 μm (FIG. 10(a)), and in the second experiment copper particles with the average size of ˜1 μm and stainless-steel particles with the average size of ˜45 μm (FIG. 10(b)). The particles were purchased from Cospheric, USA. The fabricated beaded paths were made of larger particles connected by short sections made of smaller particles. Each beaded path was fabricated in the same way as described in Example 2. The images of the fabricated beaded paths are presented in FIG. 10.

Example 11

[0195] In the present example, the beaded path was fabricated in the same manner as in Example 1, with a difference that electrically conductive particles made of glass spheres coated with a thin (˜100 nm) layer of silver (purchased from Cospheric, USA) were used instead of stainless-steel particles, and the microcapillary was moved at an average speed of ˜0.01 mm/s. The average particle size was 55 μm and their density was ˜1.08 g/cm.sup.3. An SEM image of the fragment of the fabricated beaded path on a substrate is shown in FIG. 11(a). Silicone oil capillary bridges formed between particles are resolved on the image.

Example 12

[0196] In the present example, the beaded path was fabricated in the same manner and using the same materials as in Example 1, with a difference that paraffin was used instead of silicone oil. The paraffin was heated above the melting point, i.e., above 60 degrees, during path fabrication. Shortly after the structure was deposited on the surface of a substrate (after a few seconds), the paraffin constituting the capillary bridges between particles solidified thus fixing the structure, and additionally coated the particles preventing their degradation, for example oxidation, etc. An SEM image of a fragment of the fabricated path on a substrate is presented in FIG. 11(b).

Example 13

[0197] In the present example, the beaded path was fabricated in the same manner and using the same materials as in Example 2. After fabrication the path was sintered. A microscope glass, with the beaded path on it, was placed in a 750 W microwave oven and sintered for 30 seconds. The sintered particles of the beaded path adhered strongly to the surface of the substrate. Subsequently, using a pair of tweezers and gently touching the path it was examined whether the particles in the path were sintered, as presented on images in FIG. 12(a-b), where the arrow indicates the direction of tweezers motion. Then, residues of oil forming bridges between particles were removed using isopropanol, and the beaded structure, rigidified through the sintering, was moved onto a carbon substrate of the SEM stub to observe the connections formed between the particles. FIG. 12(c) is a SEM image illustrating the mechanically reinforced beaded structure. This high magnification SEM image reveals the permanent connection between particles after the beaded structure was sintered.

Example 14

[0198] In the present example, castor oil (purchased from Sigma-Aldrich, catalogue number 83912) was used to prepare a dispersion. Inorganic salt (TBAB, purchased from Sigma-Aldrich, catalogue number: 193119) in proportion of 50 mg to 100 mL was added to the oil, which resulted in the increase in the electrical conductivity of the oil from approximately ˜10.sup.−10 S/m to approximately ˜10.sup.−8 S/m. Electrically conductive non-spherical (approximately oval in shape) stainless-steel particles with an average length of ˜300 μm, and density ˜7.8 g/cm.sup.3 (purchased from Cospheric, USA) were used. The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter of 0.9 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1. In the present example, square-wave voltage with frequency of 1 kHz and the mean voltage value (V.sub.rms) of 500 V was applied. In order to fabricate a beaded path on a soda-lime glass substrate, the microcapillary was moved relative to the substrate. The microcapillary was moved at an average speed of approximately 0.5 mm/s. FIG. 13(a-c) is a set of images illustrating steps of fabricating such a path, wherein FIG. 13(c) presents a fragment of the fabricated beaded path after the voltage was turned off.

Example 15

[0199] In the present example, castor oil (purchased from Sigma-Aldrich, catalogue number 83912) was used to prepare a dispersion. Inorganic salt (TBAB, purchased from Sigma-Aldrich, catalogue number: 193119) in proportion of 50 mg to 100 mL was added to the oil, which resulted in the increase in the electrical conductivity of the oil from approximately ˜10.sup.−10 S/m to approximately ˜10.sup.−8 S/m. Electrically conductive spherical stainless-steel particles with an average size of ˜100 μm, and density ˜7.8 g/cm.sup.3 (purchased from Cospheric, USA) were used. The dispersion was conveyed from the container (syringe, BD Discardit, 5 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter of 0.9 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1. In the present example, square-wave voltage with a frequency of 1 kHz and the mean voltage value (V.sub.rms) of 1000 V was applied to form the beaded structure, and then 500 V was applied during the fabrication of the beaded path at an average speed of 0.5 mm/s. Soon after one linear path was fabricated the voltage was turned off, the microcapillary was moved to another position, and the formation of a second beaded path was initiated, which then crossed with the first path. FIGS. 14(a) and (b) is a set of images illustrating the fabricated beaded paths, taken with different magnification and from two different perspectives. A silicon n-type wafer with conductivity of approximately 4.5 S/cm, purchased from Siegert Wafer, was used as a substrate.

Example 16

[0200] In the present example, five microcapillaries were used, mounted on one arm of the translation stage and thus enabling their simultaneous translation. The microcapillaries were connected to the dispersion container using microfluidic tubes, and one syringe pump was used for conveying the dispersion to the microcapillaries. After the dispersion menisci were created at each microcapillary, formation of the beaded structure below each microcapillary begun by turning on the voltage (500 V, 1 kHz). Subsequently, maintaining the same voltage parameters, the microcapillaries began moving simultaneously with an average speed of approximately 0.1 mm/s. After the beaded paths were fabricated, each with a length of around 1 cm, the voltage was turned off and the microcapillaries were moved away from the substrate. A perspective image of the fabricated beaded paths is shown in FIG. 15(c). In the present example, castor oil (purchased from Sigma-Aldrich, catalogue number 83912) was used to prepare a dispersion. Inorganic salt (TBAB, purchased from Sigma-Aldrich, catalogue number: 193119) in proportion of 50 mg to 100 mL was added to the oil. Electrically conductive spherical stainless-steel particles with an average size of ˜45 μm and density of ˜7.8 g/cm.sup.3 (purchased from Cospheric, USA) were used.

Example 17

[0201] In the present example, castor oil (purchased from Sigma-Aldrich, catalogue number 83912) was used to prepare a dispersion. Inorganic salt (TBAB, purchased from Sigma-Aldrich, catalogue number: 193119) in proportion of 50 mg to 100 mL was added to the oil. Electrically conductive spherical stainless-steel particles with an average size of ˜25 μm, and density of ˜7.8 g/cm.sup.3 (purchased from Cospheric, USA) were used. The dispersion was conveyed from the container (syringe, BD Discardit, 1 mL) to the conductive microcapillary (commercially available stainless-steel needle with the outer diameter 0.5 mm, TERUMO) through a polymer tube. The microcapillary also constituted an electrode. The dispersion was supplied to the microcapillary in the same way as in Example 1. In the present example, square-wave voltage with a frequency of 1 kHz and the mean voltage value (V.sub.rms) of 1000 V was applied to form the beaded structure, and then 500 V was applied during the fabrication of the beaded path at an average speed of 0.1 mm/s. The formation of the beaded path commenced at the copper tape (HB 720A, purchased from RS Components Ltd.) attached to the glass substrate. Subsequently, by moving the microcapillary the beaded path was formed at the glass substrate and then on the second piece of the copper tape, where the beaded path formation ended. An image of the fabricated beaded path is presented in FIG. 17. After the beaded path was fabricated, its electrical resistance was measured by placing multimeter probes to pieces of the copper tape attached to the glass substrate. The measured resistance was ˜5 S2.

Example 18

[0202] FIG. 18 is a schematic diagram illustrating an example of the embodiment of the second object of the invention, namely the system for fabricating a beaded path on the surface of a substrate. The system for fabricating a beaded path on the surface of a substrate 9 comprises a container for a liquid dispersion of particles, placed in a dispersion dosing unit 2. The unit 2 is fluid connected to the electrically conductive microcapillary 1 through a microfluidic unit 3, and the unit 2 contains a setup for controlling the amount of the dispersion that includes an optical system 5 connected with a computer 6. The setup for controlling the amount of the dispersion is connected to the dosing unit 2. Moreover, to the electrically conductive microcapillary 1 a source of high voltage 7 with a current limiter is connected through an electrical wire 4 and the translation stage.

[0203] The system operates as follows: A particle dispersion is conveyed to the conductive microcapillary 1, through the polymer tube 3 used in microfluidic units, from a dispersion container being here a syringe that is placed in a syringe pump 2. The inner diameter of the microcapillary 1 is at least five times the particle size to prevent microcapillary clogging by the flowing particles through that microcapillary. The length of the microcapillary is such that it enables connecting it with the electrical wire 4, which provides voltage. The length of the microcapillary 1 is at least ten times as large as the size of particles.

[0204] The method for connecting the electrical wire 4 is optional: it can be soldered, glued using a conductive adhesive, or mechanically mounted to the top part of the microcapillary 1. Herein, the electrically conductive microcapillaries were made of stainless steel. Such microcapillaries with different inner diameters and lengths that are suitable for the invention embodiment are available commercially.

[0205] To dose an appropriate amount of the dispersion, that is, to avoid the excess dispersion flowing out of the microcapillary 1, which could then drip on the substrate 9, and to ensure that the dispersion does not run short for the embodiment of the invention an optical system is used that comprises a digital microscope 5 connected to the computer 6 with software used for both analyzing the amount of the dispersion (i.e., the shape of the dispersion meniscus) and controlling the operation of the syringe pump.

[0206] If a need arises for the use of particles with a density lower than the density of the liquid, a solution can be employed in which the surface of the substrate 9 is placed above the microcapillary 1 with its outlet end pointing upwards, meaning that the beaded structure is formed in the opposite direction to the gravity direction and the particles initially placed in the dispersion forming the convex meniscus at the outlet end of the microcapillary 1 will be transported upwards towards the surface of the substrate 9. The distance between the dispersion meniscus and the surface of the substrate 9 is at least three times the particle size, but not smaller than 50 μm and not greater than fifty-fold the size of a particle.

[0207] Both the substrate 9 and the microcapillary 1 are moved using the translation stages 8 along the xyz axes during the process of fabricating a beaded path in a form of a line or a non-linear pattern on the surface of the substrate 9. The translation stage enables translation with the step not greater than the order of magnitude of particle size.

Example 19

[0208] In the present example, the same silicone oil and conductive particles were used for preparing the dispersion as in Example 1. The dispersion was supplied to the microcapillary in the same way as in Example 1. Nonconductive flexible 50 μm thick polymer foil (DuPont Teijin Films U.S. Limited Partnership, USA) placed on a conductive stainless-steel grounded stage was used as a substrate. Two experiments were conducted. In the first experiment, the substrate was covered with a layer of photosensitive polymer resin (FLGPCL04, Formlabs, USA) with a thickness of approximately 100 μm (FIG. 16(c)), whereas in the second experiment the substrate was covered with a thinner layer of the same resin with a thickness of approximately 20 μm. The microcapillary was brought towards the surface of the liquid resin (approximately 200 μm), and then the fabrication of a beaded patch on the substrate was initiated. In the present example, square-wave voltage with a frequency of 1 kHz and the mean voltage value (V.sub.rms) of 500 V was applied to form the beaded structure, and then 300 V was applied during the fabrication of the beaded path at an average speed of 0.5 mm/s. Images marked as (2) in FIG. 16(c-d) demonstrate the process of fabricating the beaded path. In the first experiment, as well as in the second experiment, the resin was hardened by illuminating it with a UV light (time of exposure: 10 seconds, wavelength: 365 nm, irradiance: approximately 50 mW/cm.sup.2, the light source was purchased from ThorLabs, USA, model: CS2010) after the beaded path was fabricated. In such a way, a flexible composite material was made (the first experiment), in which the particles were completely embedded in the resin that protected the path against mechanical damage, that is, the attempted damaging mechanically the path by moving the metal part of a screwdriver against the hardened resin was unsuccessful (images (3-4) in FIG. 16(c)). Whereas, by hardening the thin layer of the resin (the second experiment, image (3) in FIG. 16(d)) and then by mechanically removing particles from that layer of resin (scrapping with a sponge), a porous material was obtained, with pores formed in the places where the beaded paths were fabricated, and the size of the pores corresponded to the size of the particles (image (4) in FIG. 16(d)).