A Conductive Microsphere, a Stretchable Conductor and a Preparation Method Thereof

Abstract

The present invention relates to a conductive microsphere, a stretchable conductor and a preparation method thereof, belonging to the field of flexible electronics. The present invention provides a stretchable conductor, which comprises a packaging layer and conductive microspheres disposed inside the packaging layer; wherein, the conductive microspheres are microspheres with a core-shell structure formed by using polymer elastomer microspheres as the core and conductive fillers as the shell. The novel stretchable conductor provided by the present invention has high conductivity, high conductivity retention under large strain and soft mechanical characteristics; the prepared stretchable conductor with a close-packed structure has more excellent properties: the initial conductivity can reach 67185 S / cm, the elongation at break is 602%, and a high conductivity of >100 S / cm is maintained under a tensile strain of up to 445%; the elastic modulus at 1% strain is 0.53 MPa.

Description

Technical Field

[0001] The present invention relates to a conductive microsphere, a stretchable conductor and a preparation method thereof, belonging to the field of flexible electronics. Background Art

[0002] A stretchable conductor is a material that maintains high electrical conductivity under stretching conditions. Its most basic property lies in maintaining high electrical conductivity under strain conditions to ensure that the electronic components connected thereto can work without interference under complex deformation conditions. Therefore, stretchable conductors play an irreplaceable role in fields such as flexible displays, stretchable batteries, electronic skins, and soft robots.

[0003] Traditional methods for preparing stretchable conductors are to directly fill conductive components, such as metal nanoparticles or nanowires, into an elastic polymer matrix and further process them into different forms of stretchable conductors such as fibers, films, or inks. However, they all have certain drawbacks. For example, due to the high volume filling content required to reach the percolation value, the introduction of a large amount of conductive fillers will greatly reduce the stretchability of the material. Additionally, due to processing condition limitations during the blending process, the surface of the conductive components is always wrapped by an insulating polymer matrix layer. The polymer insulating layer inhibits the effective transmission of electrons, resulting in a reduction of several orders of magnitude in the electrical conductivity of the stretchable conductor compared to the filler itself. Finally, the high volume filling of rigid conductive components inevitably enhances the polymer matrix, making the final composite material exhibit a significant increase in modulus.

[0004] To solve the above problems, selecting "soft" conductive components to fill the polymer elastomer seems to endow the conductor with satisfactory properties. For example, currently, polymer composites filled with liquid metals are widely studied. Utilizing the fluidity and conductivity of liquid metals themselves, the final conductor can exhibit low modulus, high stretch ratio, and strain-enhanced electrical conductivity, etc. This "soft" solution is an important idea for solving the above problems. However, the fluid characteristics of liquid metals themselves make them prone to migration and leakage under dynamic strain, and it is also difficult to form a stable interface that is well compatible with other electronic components. Summary of the Invention

[0005] Based on the above defects, the purpose of the present invention is to provide a novel stretchable conductor (conductive soft filler), which is prepared by encapsulating conductive microspheres with a flexible material. The conductive microspheres are microspheres with a core-shell structure formed by a polymer elastomer and a conductive filler. The obtained stretchable conductor has high electrical conductivity, high electrical conductivity retention under large strain, and soft mechanical characteristics.

[0006] The technical solution of the present invention:

[0007] The first technical problem to be solved by the present invention is to provide a stretchable conductor, which includes a packaging layer and conductive microspheres disposed inside the packaging layer; wherein, the conductive microspheres are microspheres with a core-shell structure formed with a polymer elastomer microsphere as the core and a conductive filler as the shell.

[0008] Furthermore, the polymer elastomer includes: silicone rubber, natural rubber, polyurethane elastomer, styrene-butadiene-styrene rubber, or ethylene-octene rubber, etc.

[0009] Furthermore, the packaging layer material is a high-elasticity resin.

[0010] Even further, the high-elasticity resin includes: Ecoflex series elastomers, polyurethane elastomers, polybutadiene, polyisoprene, butyl rubber, ethylene-propylene copolymer elastomers, or styrene-butadiene rubber. The high-elasticity resin and the polymer elastomer can be the same.

[0011] Furthermore, the conductive filler includes: conductive metals, carbon-based conductive materials, and conductive polymer materials.

[0012] Even further, the conductive metals include: silver, copper, or nickel; the carbon-based conductive materials include graphene or carbon nanotubes, etc.; the conductive polymer materials include: polypyrrole, polythiophene, or polyaniline.

[0013] Furthermore, the conductive microspheres are prepared by the following method: first, polymer elastomer microspheres are prepared, and then the conductive filler is firmly loaded on the surface of the polymer elastomer to form microspheres with a core-shell structure.

[0014] Furthermore, the preparation method of the conductive microspheres is: first, polymer elastomer microspheres are synthesized by suspension polymerization; then the polymer elastomer microspheres are placed in a solution of a conductive filler (such as a carbon-based conductive filler) or a solution containing a conductive filler precursor (such as a conductive metal or a conductive polymer material) to swell and fully absorb the conductive filler or its precursor; then a reducing agent is applied or the precursor is converted into a conductive filler through polymerization, and thus conductive microspheres with a core-shell structure can be prepared.

[0015] In order to improve the conductivity of the stretchable conductor, the following treatment can be further carried out before the encapsulation of the conductive microspheres: the conductive microspheres with a core-shell structure are made into microspheres with a closely packed three-dimensional network structure by the solvent evaporation method to make adjacent microspheres closely pull together.

[0016] Furthermore, the method for treating the conductive microspheres before encapsulation is: dispersing the conductive microspheres with a core-shell structure in a solvent, and then volatilizing the solvent at room temperature. Since the solvent volatilizes, a liquid bridge will be generated between adjacent microspheres. The local stress generated by the liquid bridge can reach the kilopascal or even megapascal level, which is sufficient to pull the adjacent microspheres together, thereby achieving the formation of conductive microspheres with a densely packed three-dimensional conductive network induced by solvent volatilization. The liquid bridge refers to a small liquid column between solids, that is, a section of liquid connecting two solid surfaces.

[0017] Furthermore, in the treatment process before encapsulating the conductive microspheres, the mass ratio of the conductive microspheres to the solvent is 1:2 to 1:10; for example, it can be 1:2, 1:4, 1:6, 1:8 and 1:10.

[0018] Furthermore, in the treatment process before encapsulation of the conductive microspheres, the solvent is at least one of methanol, ethanol, chloroform, water, acetone or n-heptane.

[0019] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned stretchable conductor, and the preparation method is: encapsulating the above-mentioned conductive microspheres with a packaging material.

[0020] Furthermore, the preparation method of the stretchable conductor is: firstly prepare polymer elastomer microspheres, then firmly cover the surface of the polymer elastomer with conductive fillers to form microspheres with core-shell structure; and finally encapsulate with encapsulation materials.

[0021] Furthermore, the preparation method of the stretchable conductor is: first prepare polymer elastomer microspheres, and then firmly cover the conductive filler on the surface of the polymer elastomer to form microspheres with a core-shell structure; then disperse the conductive microspheres with the core-shell structure in a solvent, and evaporate the solvent at room temperature. Since the evaporation of the solvent will generate liquid bridges between adjacent microspheres, the local stress generated by the liquid bridge can reach the kilopascal or even megapascal level, which is sufficient to pull the adjacent microspheres together, thereby realizing the solvent evaporation-induced formation of conductive microspheres with a tightly packed three-dimensional conductive network; finally, the conductive microspheres are encapsulated with a packaging material.

[0022] Furthermore, when the polymer elastomer and the packaging material are silicone rubber, and the conductive filler is a conductive metal, the method for preparing the stretchable conductor comprises the following steps:

[0023] 1) Synthesize polymer elastomer microspheres by suspension polymerization;

[0024] 2) activating the polymer elastomer microspheres and immersing them in a conductive metal precursor solution to allow the polymer elastomer to fully swell and adsorb the conductive metal precursor; then adding a reducing agent to reduce the metal ions to metal elements to obtain conductive microspheres with a core-shell structure;

[0025] 3) Disperse the obtained conductive microspheres in a solvent, pour them into a mold and dry. The volatilization of the solvent causes the conductive microspheres to form conductive microspheres with a close-packed three-dimensional conductive network; then pour in the encapsulating material for encapsulation and curing to obtain a stretchable conductor.

[0026] Further, in step 2), the conductive metal precursor solution can be selected from a tetrahydrofuran solution or an isopropyl alcohol solution containing silver trifluoroacetate.

[0027] Further, in step 2), the reducing agent is hydrazine hydrate, ascorbic acid, sodium citrate or sodium sulfite.

[0028] Further, in step 2), the method for activating the polymer elastomer microspheres before immersing them in the conductive metal precursor solution is: treating the polymer elastomer microspheres in a plasma environment for 10 - 30 min (30 min), with a power of 200 - 600 W (600 W).

[0029] Further, in step 3), the solvent is selected from at least one of methanol, ethanol, chloroform, water, acetone or n - heptane; preferably, the solvent is water. Here, a solvent that cannot swell the polymer elastomer and has a high surface tension is selected.

[0030] Further, in step 3), the mass ratio of the conductive microspheres to the solvent is 1:2 - 1:10; for example, it can be 1:2, 1:4, 1:6, 1:8 and 1:10; the final effects have no obvious difference.

[0031] The third technical problem to be solved by the present invention is to provide a preparation method of conductive microspheres. The preparation method is: first prepare polymer elastomer microspheres, and then firmly load conductive fillers on the surface of the polymer elastomer to form microspheres with a core - shell structure having a polymer elastomer microsphere as the core and conductive fillers as the shell (that is, the surface of the polymer elastomer microspheres is loaded with conductive fillers).

[0032] Further, the preparation method of the conductive microspheres is: first synthesize polymer elastomer microspheres by suspension polymerization; then place the polymer elastomer microspheres in a solution of conductive fillers (such as carbon - based conductive fillers) or a solution containing conductive filler precursors (such as conductive metals or conductive polymer materials) to allow them to swell and fully absorb the conductive fillers or their precursors; then apply a reducing agent or convert the precursor into conductive fillers by polymerization to obtain conductive microspheres with a core - shell structure.

[0033] Further, when the polymer elastomer is silicone rubber and the conductive filler is metal, the preparation method of the conductive microspheres is as follows: First, synthesize polymer elastomer microspheres by suspension polymerization, then activate the surface of the polymer elastomer microspheres, and then soak the activated polymer elastomer microspheres in a conductive metal precursor solution to allow the polymer elastomer to swell sufficiently and adsorb the conductive metal precursor; finally, reduce the conductive metal precursor to obtain the conductive microspheres.

[0034] Further, when the polymer elastomer is silicone rubber and the conductive filler is metal, the preparation method of the conductive microspheres includes the following steps:

[0035] (1) Add an organic solvent (diluent) to liquid silicone rubber (Sylgard 184) to obtain a liquid silicone rubber mixture; wherein, the content of the diluent is 0% - 20% (volume ratio) of the liquid silicone rubber.

[0036] (2) Slowly drop the silicone rubber mixture obtained in step (1) into a poor solvent under high-speed shear, then raise the temperature to 40 - 90 °C (preferably 70 °C), and reduce the shear rate to continue the reaction; wherein, the volume ratio of the poor solvent to the silicone rubber precursor mixture is 4:1 - 20:1 (preferably 10:1), the high-speed shear rate is 5000 - 18000 rpm (preferably 15000 rpm), and the high-speed shear time is 5 - 20 min (preferably 10 min); reduce the shear rate to 500 - 1000 rpm (preferably 1000 rpm), and the shear time is 10 - 60 min (preferably 30 min).

[0037] (3) Filter the solution obtained in step (2) by suction and dry it to obtain silicone rubber microspheres; treat the microspheres in a plasma environment for 5 - 30 min to activate their surfaces for later use.

[0038] (4) Place the silicone rubber microspheres obtained in step (3) in a conductive metal precursor solution to swell and adsorb the conductive metal precursor for 5 - 50 min; then dropwise add a reducing agent solution to fully reduce the metal ions.

[0039] (5) Filter the solution obtained in step (4) by suction and wash it with deionized water at least 3 times, and dry it to obtain polymer elastomer / conductive filler microspheres with a core-shell structure (such as silicone rubber@silver microspheres).

[0040] Further, in step (1), the organic solvent used for diluting the silicone rubber is selected from one of n-hexane, isopropanol, tetrahydrofuran, dichloromethane or xylene. Preferably, the diluent is isopropanol or tetrahydrofuran; more preferably, the diluent is n-hexane.

[0041] Further, in step (4), the time for the silicone rubber microspheres to adsorb the conductive metal precursor solution is 5 to 50 min; for example, it can be: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 min; preferably, the precursor adsorption time is 40 min.

[0042] Advantages of the present invention:

[0043] The present invention provides a novel stretchable conductor, which is prepared by encapsulating conductive microspheres with a flexible material. The conductive microspheres are microspheres with a core-shell structure formed by a polymer elastomer and a conductive filler; the obtained stretchable conductor has high electrical conductivity, high electrical conductivity retention under large strain, and soft mechanical characteristics. And the stretchable conductor with a close-packed structure prepared by the present invention has more excellent properties: the initial electrical conductivity can reach 67185 S / cm, the elongation at break is 602%, and a high electrical conductivity of >100 S / cm is maintained under a tensile strain of up to 445%; the elastic modulus at 1% strain is 0.53 MPa. Description of the drawings

[0044] Figure 1 It is the electron microscope and element distribution map of the conductive microspheres with a core-shell structure obtained in Example 4; from Figure 1 it can be seen that: the synthesized silicone rubber@silver microspheres have a regular spherical morphology, and a dense layer of silver nanoparticles is coated on the surface.

[0045] Figure 2 It is the microsphere conductive network morphology of the close-packed (Example 4) and loose-packed (Example 5) stretchable conductors ( Figure 2 on the left) and their corresponding electrical conductivity results ( Figure 2 on the right); from Figure 2 it can be seen that: in the close-packed conductive network, the microspheres are densely packed, forming a structure similar to hexagonal close packing; the microspheres are mainly in physical contact, and there is less polymer insulating layer. This structure is conducive to the conduction of electrons between the microspheres in an ohmic conduction manner, improving the electrical conductivity of the conductor; while in the loose-packed structure, the microspheres are far apart, and there is a polymer matrix insulating layer between the microspheres. The existence of the insulating layer will cause the transition of electron transport from ohmic conduction to tunneling transition, thereby reducing the electrical conductivity; from the electrical conductivity test results, the initial electrical conductivity of the stretchable conductor with a close-packed structure can reach 67185 S / cm, which is about one order of magnitude higher than that of the conductor with a non-close-packed structure.

[0046] Figure 3 It is the conductive network evolution diagram of the close-packed stretchable conductor obtained in Example 4 under tension (strain is 0 to 400%) (the tensile direction is the horizontal direction); from Figure 3It can be seen that: Since the volume of silicone rubber remains almost unchanged under tension (Poisson's ratio ~ 0.5), this closely packed conductive network can still be well maintained under high strain; the conductive network structure shows almost no obvious change at 200% strain, cracks and voids appear at 300% strain, but the conductive network formed by microspheres in the stretching direction is still continuous; the conductive network is significantly damaged only until 400% strain, and further stretching will cause the conductivity to decrease sharply.

[0047] Figure 4 are the initial conductivity and conductivity results under strain of the stretchable conductor. It can be seen from Figure 4 that: Example 4 can still maintain a high conductivity under tension, with a conductivity of 820 S / cm at 400% strain; the conductivity remains at 100 S / cm at 445% strain; among them, in Example 1, the activated silicone rubber microspheres were immersed in silver ink for 10 min, in Example 2, the activated silicone rubber microspheres were immersed in silver ink for 20 min, and so on up to Example 4; Example 5 is the change of the conductivity of a stretchable conductor with a loosely packed conductive network under strain.

[0048] Figure 5 are the tensile stress-strain curves of pure Sylgard 184 silicone rubber and pure Ecoflex 0050 silicone rubber, as well as the closely packed stretchable conductors obtained in Examples 1 - 5. It can be seen from Figure 5 that: The elongation at break and tensile strength of the pure Ecoflex matrix are 940% and 2.9 MPa respectively; after introducing the closely packed silicone rubber@silver microspheres, the elongation at break decreases from 940% to 843%, and decreases to 602% with the extension of the silver precursor adsorption time; the elongation at break and tensile strength of the stretchable conductor obtained in Example 4 are 602% and 4.3 MPa respectively; the elongation at break and tensile strength of the stretchable conductor obtained in Example 5 are 698% and 3.6 MPa respectively.

[0049] Figure 6 are the tensile moduli of the stretchable conductors and silicone rubbers obtained in Examples 1 - 5. It can be seen from Figure 6 that: The stretchable conductors obtained in the present invention all exhibit "soft" mechanical behavior. Detailed implementation mode

[0050] The present invention provides a novel stretchable conductor, which is prepared by encapsulating conductive microspheres with a flexible material. The conductive microspheres are microspheres with a three-dimensional conductive network structure formed by a polymer elastomer and a conductive filler; the obtained stretchable conductor has high conductivity, high conductivity retention under large strain, and soft mechanical characteristics.

[0051] Preferably, the method of solvent evaporation-induced close packing of "soft" conductive microspheres can be adopted to construct a three-dimensional close-packed conductive network, and then an elastic matrix is cast. This close packing also shows the ability to maintain tight connection under strain, so that the conductor exhibits better conductivity and stability. The key to the highly conductive stretchable soft conductor lies in the preparation of silicone rubber@silver microspheres with a core-shell structure and the evaporation-induced close packing of conductive microspheres: in the first step, the synthesized silicone rubber microspheres are placed in silver ink for different times and reduced to prepare silver-plated microspheres; in the second step, the silver-plated microspheres are dispersed in a solvent, and the evaporation of the solvent causes the microspheres to be closely packed, and then Ecoflex 0050 silicone rubber with high stretchability is cast; among them, the polarities of the two silicone rubbers are similar, and the compatibility is good, and there is no interfacial compatibility problem, so as to obtain a soft conductor with a high elongation at break.

[0052] The embodiments of the present invention will be described in detail below in conjunction with the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0053] Examples 1-4 Preparation of Stretchable Conductors with Close-Packed Conductive Networks

[0054] I. Synthesis of Silicone Rubber Elastic Microspheres

[0055] 4 mL of n-hexane was added to dilute the precursor mixture in 22 mL of liquid silicone rubber precursor (grade: Sylgard 184, manufacturer: Dow Corning, including two components A and B (i.e., liquid matrix and curing agent), and the liquid matrix and curing agent were completely mixed at a weight ratio of 10:1 when in use); then the uniform mixture was slowly injected into 200 mL of warm water at 70 °C through a syringe needle (10G), and the warm water was maintained at high shear (15000 rpm) during the injection process; in a strong shear environment, the continuous silicone rubber precursor mixture was torn and broken into micron-sized particles, and accompanied by slow curing; after 15 min, the system was transferred to a mechanical stirrer at 1000 rpm and reacted for another 30 min; finally, the solution was filtered to obtain silicone rubber microspheres, which were washed with deionized water multiple times and stored dry at 60 °C.

[0056] II. Preparation of Core-Shell Silicone Rubber@Silver Microspheres

[0057] First, prepare Ag +AgCF3COO / THF solution (silver ink) with a concentration of 800 mg / mL; the pre-dried silicone rubber microspheres were treated in an air plasma environment for 30 min (600 W) to activate their surfaces (if the surface is not activated, the conductive silver layer cannot be firmly bonded to the microsphere surface and is likely to fall off); then, the activated silicone rubber microspheres were immersed in the silver ink for 10 min (Example 1), 20 min (Example 2), 30 min (Example 3), and 40 min (Example 4) respectively, to allow them to swell fully and adsorb the silver precursor; subsequently, an ethanol solution of hydrazine hydrate (diluted at a volume ratio of 1:1) was dropped into the microsphere solution adsorbed with the silver precursor to reduce the Ag + to elemental silver, obtaining silicone rubber@silver microspheres. The silicone rubber@silver microspheres were collected by suction filtration, washed multiple times with deionized water, and thoroughly dried at 60 °C to prepare silicone rubber@silver microspheres with a core-shell structure.

[0058] III. Preparation of a stretchable soft conductor with a close-packed structure

[0059] The silicone rubber@silver microspheres were dispersed in deionized water at a mass ratio of 1:10 (mass ratio of microspheres to deionized water), and then poured into a polytetrafluoroethylene mold (length × width × height, 100 mm × 100 mm × 10 mm); the solvent was volatilized at room temperature. Since the solvent volatilization would generate a liquid bridge between adjacent microspheres, the local stress (>13 KPa) caused by this liquid bridge was sufficient to pull adjacent particles together, thus realizing the formation of a three-dimensional close-packed conductive network of silicone rubber@silver microspheres induced by solvent volatilization; then, an Ecoflex 0050 silicone rubber mixture (manufacturer: Smooth-On) was mixed at room temperature to prepare a precursor solution, which was slowly poured into the mold deposited with the close-packed conductive microspheres to fully penetrate the voids between the microspheres and encapsulate the microspheres. Then, the mold was transferred to a vacuum condition and cured at 25 °C for 24 h to obtain a stretchable conductor.

[0060] Example 5 Preparation of a stretchable conductor with a loose-packed conductive network

[0061] I. Synthesis of silicone rubber elastic microspheres

[0062] In 22 mL of liquid silicone rubber precursor (grade: Sylgard 184, manufacturer: Dow Corning, including two components A and B (i.e., liquid matrix and curing agent), the liquid matrix and the curing agent are completely mixed at a weight ratio of 10:1 during use), 4 mL of n-hexane is added to dilute the precursor mixture; the uniform mixture is slowly injected into 200 mL of warm water at 70 °C through a syringe needle (10G), and high-speed shearing (15000 rpm) is maintained during the injection process; in a strong shearing environment, the continuous silicone rubber mixture is torn and broken into micron-sized particles, and accompanied by slow curing; after 15 min, the system is transferred to a mechanical stirrer at 1000 rpm and reacted for another 30 min; finally, the solution is filtered to collect the silicone rubber microspheres, which are washed several times with deionized water and dried and stored at 60 °C.

[0063] II. Preparation of core-shell silicone rubber@silver microspheres

[0064] First, prepare an Ag + CF3COO / THF solution (silver ink) with a concentration of 800 mg / mL; the pre-dried microspheres are treated in an air plasma environment for 30 min (600 W) to activate their surfaces; then, the activated silicone rubber microspheres are immersed in the silver ink for 40 min to allow them to swell fully and adsorb the silver precursor; subsequently, an ethanol solution of hydrazine hydrate (diluted 1:1, volume ratio) is dropped into the swollen microsphere solution adsorbed with the silver precursor to reduce the Ag + to elemental silver; the core-shell silicone rubber@silver microspheres are collected by filtration, washed several times with deionized water, and thoroughly dried at 60 °C.

[0065] III. Preparation of a stretchable soft conductor with a loose packing structure

[0066] The silicone rubber@silver microspheres are directly added to a polytetrafluoroethylene mold (length × width × height, 100 mm × 100 mm × 10 mm) in a certain mass; then, an Ecoflex 0050 silicone rubber mixture is mixed at room temperature to prepare a precursor solution, which is slowly poured into the mold deposited with closely packed conductive microspheres to allow it to fully penetrate the voids between the microspheres; the mold is transferred to a vacuum condition and cured at 25 °C for 24 h to obtain a stretchable conductor.

[0067] The surface morphology of the silicone rubber@silver microspheres and the distribution of the microspheres in the stretchable conductor were observed using a scanning electron microscope (FEI-SEM, Quanta 650 ESEM) and an optical microscope (OLYMPUS BX51). The initial conductivity of the conductor was measured using a low-resistance tester (JK2512BDC). The stress-strain curve of the conductor was recorded using a universal tensile testing machine (SANS CMT 40000). The conductivity of the conductor under different tensile strains was measured by combining the universal tensile testing machine and a comprehensive IV performance tester (JCY3100).

[0068] The test results of the structures and properties of the stretchable conductors prepared in Examples 1-5 of the present invention are as shown in the appendix Figures 1 to 6 as follows.

[0069] It can be seen from Figure 2 the above that the optimal initial conductivity (the conductivity of the stretchable conductor when the strain is 0) of the stretchable conductor with a close-packed structure is 67185 S / cm (Example 4), while the initial conductivity of the stretchable conductor with a loose packing obtained without adding a solvent (Example 5) is only 3043 S / cm; the elongation at break and modulus of the close-packed stretchable conductor obtained in Example 4 are 602% and 0.79 MPa respectively, and the conductivity under stretching is 820 S / cm (at 400% strain).

[0070] From the above results, it can be seen that the present invention can prepare conductive microspheres with a closely packed network structure by means of solvent evaporation; solvent evaporation will generate liquid bridges between adjacent particles, and the tension of the liquid bridges can reach the level of kilopascals or even megapascals, thereby tightly pulling adjacent particles with a certain distance together; then the obtained conductive microspheres are encapsulated with a packaging material (liquid Ecoflex silicone rubber). Since the re-poured liquid Ecoflex silicone rubber has a high elongation at break and a low elastic modulus, and has good compatibility with the conductive microspheres, a soft conductor with high stretchability and ultra-high conductivity is obtained.

Claims

1. A preparation method of a stretchable conductor, characterized in that, The method for preparing the stretchable conductor comprises the following steps: 1) Synthesize polymer elastomer microspheres by suspension polymerization; 2) activating the polymer elastomer microspheres and immersing them in a conductive metal precursor solution to allow the polymer elastomer to fully swell and adsorb the conductive metal precursor; then adding a reducing agent to reduce the metal ions to metal elements to obtain conductive microspheres with a core-shell structure; wherein the conductive metal precursor solution is selected from a tetrahydrofuran solution or an isopropanol solution containing silver trifluoroacetate; and the reducing agent is hydrazine hydrate, ascorbic acid, sodium citrate or sodium sulfite; 3) The obtained conductive microspheres are dispersed in a solvent, poured into a mold for drying, and the solvent evaporates, causing the conductive microspheres to form conductive microspheres with a densely packed three-dimensional conductive network; then, a packaging material is poured for packaging and solidification to obtain a stretchable conductor; The polymer elastomer and the material used for packaging are silicone rubber; In addition, the obtained stretchable conductor includes a packaging layer and conductive microspheres disposed inside the packaging layer; the conductive microspheres are conductive microspheres with a core-shell structure formed by using polymer elastomer microspheres as cores and conductive fillers as shells.

2. The preparation method of a stretchable conductor according to claim 1, characterized in that, The mass ratio of the conductive microspheres to the solvent is 1:2 to 1:

10.

3. The preparation method of a stretchable conductor according to claim 2, characterized in that, The mass ratio of the conductive microspheres to the solvent is 1:2, 1:4, 1:6, 1:8 or 1:

10.

4. The preparation method of a stretchable conductor according to claim 1 or 2, characterized in that, The solvent is at least one of methanol, ethanol, chloroform, water, acetone or n-heptane.

5. The preparation method of the stretchable conductor according to claim 1, wherein, In step 2), the method for activating the polymer elastomer microspheres before immersing them in the conductive metal precursor solution is as follows: treating the polymer elastomer microspheres in a plasma environment for 10 to 30 minutes at a power of 200 to 600 W.

6. A stretchable conductor obtained by the method for preparing a stretchable conductor according to any one of claims 1 to 5.

Images