A visco-plastic interlayer material and its preparation method and application

Abstract

The present application relates to the technical field of flexible packaging, and particularly relates to a viscoplastic interposer material and a preparation method and application thereof, the preparation method of the viscoplastic interposer material comprises the following steps: mixing a carbon-based elastomer, a plasticizer and a polar grafted polymer to obtain a mixture; uniformly mixing the mixture by using an organic solvent dissolution method, a high-temperature melting method or a mechanical blending method to obtain the viscoplastic interposer material. The carbon-based elastomer is used as a matrix, a biocompatible small molecule is introduced as a plasticizer, and a polar grafted polymer is used as a confinement domain to construct a multiphase blending system; the plasticizer with a short chain increases the free volume and lubricates the carbon-based elastomer with a long chain to promote chain slipping, and the confinement domain forms an interpenetrating network with the matrix to spatially confine the slipping chain and achieve permanent disentanglement. The above-mentioned synergistic effect changes the viscoplastic interposer material from a traditional elasticity / viscoelasticity to a viscoplasticity, which exhibits significant residual strain, rapid stress relaxation and rate-dependent mechanical behavior.

Description

Technical Field

[0001] This invention relates to the field of flexible packaging technology, and in particular to a viscoplastic interlayer material, its preparation method, and its application. Background Technology

[0002] The fundamental reason why the encapsulation layer and the electrode are difficult to maintain stable shape is the elastic contact between heterogeneous interfaces. Implantable encapsulation materials mainly include polymer elastomers (such as styrene block copolymers, polyurethane, silicone, etc.) and plastic / ceramic films (such as polyimide, parylene, silicon nitride, etc.). Among them, non-planar electrodes are difficult to be compatible with film-type encapsulations due to geometric limitations, so elastomers are often used for encapsulation protection. The poor contact between the elastomer encapsulation and the electrode stems from the inherent high resilience and low loss properties of the elastomer. High resilience refers to the characteristic that the elastomer can quickly and almost completely recover its original shape and size after being deformed by force. This is due to the entropy elastic drive of polymer chains, that is, after the external force is removed, the molecular chains tend to return to the coiled state with the maximum entropy value. Low loss means that the elastomer has a weak energy dissipation ability during deformation. Most of the input energy is stored as elastic potential energy rather than dissipated through irreversible mechanisms such as internal friction and chain slippage. Therefore, the material exhibits small residual deformation after unloading.

[0003] Currently, the main methods for improving interface stability include covalent bonding and mechanical interlocking. Covalent bonding, by forming chemical bonds at the interface between the encapsulation layer and the electrode, enhances the bonding strength and is a common strategy for improving interface stability. For example, introducing maleic anhydride groups into the elastomer matrix can undergo an amidation reaction with the surface-grafted amino electrode under hot-pressing conditions, forming a strong covalent bond and thus enhancing the interfacial bonding force. Similar strategies include using siloxane bonds and epoxy ring-opening reactions to construct chemical anchoring between the elastomer and the metal electrode, which can improve the interfacial peel strength by several times. Mechanical interlocking expands the contact area and introduces mechanical interlocking forces by constructing interlocking structures at the nanometer to micrometer scale, thereby improving the interfacial peel resistance. For example, introducing microbridges or micropillar arrays between the elastomer encapsulation layer and the electrode, achieving solderless interconnection through physical interlocking, can improve shear bond strength. In addition, the use of micropillar array structures can effectively disperse interfacial stress and significantly improve the mechanical reliability of the encapsulation system under large deformation conditions. Although surface treatment methods can improve the adhesion strength between the electrode and the encapsulation layer, they do not change the intrinsic properties of the material. When two heterogeneous surfaces are joined, elastic recovery reduces the effective contact area, thereby decreasing bond density and uniformity. In summary, relying solely on covalent bonding or mechanical interlocking strategies is insufficient to completely eliminate all defect channels.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a viscoplastic interlayer material, its preparation method and application, in order to solve the problem of interface failure of non-planar electrodes in existing conventional elastomer encapsulation processes.

[0006] The technical solution of the present invention is as follows: A method for preparing a viscoplastic interlayer material includes the following steps: A mixture is obtained by mixing a carbon-based elastomer, a plasticizer, and a polar graft polymer. The mixture is homogenized by organic solvent dissolution, high-temperature melting, or mechanical blending to obtain a viscoplastic interlayer material.

[0007] The method for preparing the viscoplastic interlayer material, wherein the mass ratio of the carbon-based elastomer, the plasticizer, and the polar graft polymer is (1-10):(1-10):(1-10).

[0008] The method for preparing the viscoplastic interlayer material, wherein the carbon-based elastomer comprises one or more of high molecular weight polyisobutylene, styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-ethylene-butene-styrene, styrene-isobutylene-styrene, styrene-propylene-styrene, and styrene-ethylene-propylene-styrene; wherein the weight-average molecular weight of the high molecular weight polyisobutylene is 500,000-2,000,000.

[0009] The method for preparing the viscoplastic interlayer material, wherein the plasticizer includes one or more of low molecular weight polyisobutylene, tricresyl phosphate, and citrate; wherein the weight-average molecular weight of the low molecular weight polyisobutylene is 200-10,000.

[0010] The method for preparing the viscoplastic interlayer material, wherein the polar graft polymer includes one or more of maleic anhydride graft polymers, carboxyl graft polymers, amino graft polymers, and hydroxyl graft polymers.

[0011] The method for preparing the viscoplastic interlayer material, wherein the step of mixing the mixture using an organic solvent dissolution method to obtain the viscoplastic interlayer material specifically includes: The mixture is then mixed with an organic solvent to obtain a mixed solution; After heating and stirring the mixed solution at a first temperature, the temperature is lowered to a second temperature and stirred again to obtain a viscoplastic interlayer material.

[0012] The method for preparing the viscoplastic interlayer material, wherein the concentration of the mixed solution is 1 mg / mL-1000 mg / mL; Preferably, the organic solvent is selected from one or more of toluene, n-hexane, cyclohexane, dichloromethane, and tetrahydrofuran; Preferably, the first temperature is 120℃-160℃, and the heating and stirring treatment time is 4h-6h; Preferably, the second temperature is 40℃-60℃, and the stirring time is 2h-4h.

[0013] A viscoplastic interlayer material is prepared using the method for preparing the viscoplastic interlayer material.

[0014] Application of a viscoplastic interlayer material in electrode encapsulation.

[0015] The application described herein, wherein the electrode encapsulation includes the following steps: Functionalization treatment of electrode surface; The functionalized electrode is immersed in the viscoplastic interlayer material and subjected to heat treatment to form an interlayer film on the electrode surface. An electrode with an intermediate layer film formed on its surface is placed between two encapsulation films, and the electrode encapsulation is completed by hot pressing.

[0016] Beneficial Effects: This invention provides a viscoplastic interlayer material, its preparation method, and its applications. The preparation method of the viscoplastic interlayer material includes the following steps: mixing a carbon-based elastomer, a plasticizer, and a polar grafted polymer to obtain a mixture; and homogenizing the mixture using an organic solvent dissolution method, a high-temperature melting method, or a mechanical blending method to obtain the viscoplastic interlayer material. This invention uses a carbon-based elastomer as a matrix, introduces biocompatible small molecules as plasticizers, and polar grafted polymers as confinement domains to construct a multiphase blend system. The short-chain plasticizer increases free volume and lubricates the long-chain carbon-based elastomer to promote chain slip, while the confinement domains, by forming an interpenetrating network with the matrix, spatially confine the slip chains and achieve permanent unentanglement. These synergistic effects transform the viscoplastic interlayer material from a traditional elastic / viscoelastic material to a viscoplastic one, exhibiting significant residual strain, rapid stress relaxation, and rate-dependent mechanical behavior. Therefore, applying this viscoplastic interlayer material to electrode encapsulation can significantly improve the interfacial sealing and long-term reliability of non-planar electrodes, effectively solving the problem of poor long-term stability of neural electrodes caused by interfacial leakage in fields such as brain-computer interfaces. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow for preparing a viscoplastic interlayer material according to the present invention; Figure 2 A schematic diagram comparing the design of viscoplastic interlayer materials and the molecular chain motion behavior; Figure 3The graph shows the variation of the loss factor with temperature in the dynamic thermomechanical analysis of PIB and VPI. Figure 4 The melting peak curves of PP-g-MAH and VPI obtained by differential scanning calorimetry; Figure 5 Photos of VPI films after they have been stretched to preset strains (0%, 50%, and 100%). Figure 6 The uniaxial tensile stress-strain curves of VPI films at different strain rates are shown. Figure 7 The Fourier transform infrared spectrum of the VPI / electrode interface; Figure 8 This is a graph showing the water vapor transmission rate test data for VPI films. Detailed Implementation

[0018] This invention provides a viscoplastic interlayer material, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0020] Brain-computer interfaces (BCIs) establish a direct pathway between the brain and an external computer and controller, enabling the recording, analysis, and feedback of neural signals. One of the core technologies of BCIs is the neural electrodes used for signal acquisition; however, their long-term reliability still faces significant challenges. Structurally, neural electrodes involve several key interfaces, including the conductive layer-biological tissue interface, the conductive layer-encapsulation layer interface, the conductive layer-substrate polymer interface, and external interfaces. The stability of these interfaces collectively determines the device's lifespan and performance. Among these, the interface between the encapsulation layer and the conductive layer is particularly critical, as it directly affects the protective effect of the encapsulation on the internal structure, preventing biological fluids (such as cerebrospinal fluid) from seeping in along the interface, which could lead to a decrease in the device's signal-to-noise ratio or even functional failure.

[0021] In planar electrodes, the continuous and flat surface minimizes the formation of interface defects between the encapsulation layer and the electrode layer, resulting in high encapsulation reliability. However, leakage is a particularly prominent issue in non-planar electrodes with complex three-dimensional structures. To adapt to the three-dimensional heterogeneous structure of brain tissue and achieve high-quality signal acquisition from deep or specific functional areas, non-planar electrodes have become an important development direction in the field of brain-computer interfaces. These electrodes often possess a three-dimensional configuration, enabling them to penetrate deep into brain tissue and achieve high spatiotemporal resolution neural signal recording and efficient electrical stimulation; their increased contact area and better interface conformation also contribute to improved signal-to-noise ratio and biocompatibility. Nevertheless, the undulating configuration of non-planar electrodes also presents significant challenges for encapsulation: the encapsulation layer struggles to achieve conformal conformation and strong interface bonding along its structure, easily generating microscopic gaps at the interface and further forming interconnected defect channels, leading to encapsulation failure.

[0022] Therefore, based on existing elastomer encapsulation methods, it is of great significance to further improve the interfacial sealing and long-term reliability between non-planar electrodes and encapsulation layers.

[0023] Based on this, such as Figure 1 As shown, the present invention provides a method for preparing a viscoplastic interlayer material, comprising the following steps: Step S10: Mix the carbon-based elastomer, plasticizer, and polar graft polymer to obtain a mixture; Step S20: The mixture is homogenized using an organic solvent dissolution method, a high-temperature melting method, or a mechanical blending method to obtain a viscoplastic interlayer material.

[0024] In this embodiment, such as Figure 2 As shown, a multiphase blend system is constructed using a carbon-based elastomer as the matrix, introducing biocompatible small molecules (oligomers) as plasticizers and polar graft polymers as confinement domains. The short-chain plasticizer increases free volume and lubricates the long-chain carbon-based elastomer to promote chain slip, while the confinement domains form an interpenetrating network with the matrix, spatially confining the slip chains and achieving permanent unentanglement. This synergistic effect transforms the viscoplastic interlayer material from traditional elastic / viscoelastic to viscoplastic, exhibiting significant residual strain, rapid stress relaxation, and rate-dependent mechanical behavior. Furthermore, after the interlayer is formed, the polar genes in the interlayer react with the surface-functionalized electrode to form covalent bonds. Finally, the viscoplastic interlayer is integrated between the non-planar electrode and the elastic encapsulation layer via a hot-pressing process, achieving defect-free integrated encapsulation. Therefore, applying this viscoplastic interlayer material to electrode encapsulation can significantly improve the interfacial sealing and long-term reliability of non-planar electrodes, effectively solving the problem of poor long-term stability of neural electrodes caused by interfacial leakage in fields such as brain-computer interfaces.

[0025] Specifically, the core of achieving leak-free sealing in this invention lies in transforming interface contact from elastic recovery to active conformal fitting, a goal that is highly compatible with the shape deformation characteristics of viscoplastic materials. The viscoplastic interlayer material prepared by the above-mentioned method can dissipate energy under external force through the slippage and permanent unentanglement of polymer chains, effectively suppressing elastic recovery. After unloading, it can still maintain significant residual strain, thereby adaptively fitting the three-dimensional micro-contour of non-planar electrodes.

[0026] In some embodiments, the mass ratio of the carbon-based elastomer, the plasticizer, and the polar graft polymer is (1-10):(1-10):(1-10). The carbon-based elastomer serves as the matrix, providing low water vapor permeability and mechanical strength. The plasticizer increases free volume and lubricates long chains to promote chain slip. The polar graft polymer acts as a confinement domain, forming an interpenetrating network with the carbon-based elastomer to spatially confine the slip chains and achieve permanent untangling. The three components work synergistically to achieve a transition from elastic / viscoelastic to viscoplastic behavior. Furthermore, the mass ratio of each component directly affects the viscoplastic behavior. If the plasticizer content is too low, chain slip is insufficient, and residual strain is small; if the content is too high, the material modulus decreases too quickly, and its strength and toughness are compromised. If the polar graft polymer content is too low, the spatial confinement effect is insufficient, and elastic recovery is still significant; if the content is too high, the phase separation scale increases, which may lead to local defects. Therefore, the mass ratio of the carbon-based elastomer, the plasticizer, and the polar graft polymer can be optimized according to the target application scenario.

[0027] In a preferred embodiment, the mass ratio of the carbon-based elastomer, the plasticizer, and the polar graft polymer is 5:1:1 or 6:2:1. Using a carbon-based elastomer as the matrix, the introduction of a plasticizer promotes molecular chain slippage, and the construction of polar confined microregions inhibits molecular chain springback to achieve permanent untangling. Both synergistically endow the material with viscoplastic properties.

[0028] In some embodiments, the carbon-based elastomer includes, but is not limited to, one or more of high molecular weight polyisobutylene (PIB), styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-ethylene-butene-styrene, styrene-isobutylene-styrene, styrene-propylene-styrene, and styrene-ethylene-propylene-styrene; wherein the high molecular weight polyisobutylene has a weight-average molecular weight of 500,000-2,000,000. Using the above-mentioned carbon-based elastomer as a matrix can provide low water vapor permeability and mechanical strength.

[0029] In a preferred embodiment, the carbon-based elastomer is a high molecular weight polyisobutylene with a weight-average molecular weight of 500,000-2,000,000. As a matrix material, the high molecular weight PIB has excellent water vapor barrier properties due to the steric hindrance effect of its methyl side groups and the resulting restriction of chain segment movement. If the molecular weight is less than 500,000, the molecular structure is loose, water molecules can easily pass through the polymer network, and the water vapor barrier properties will decrease significantly.

[0030] In some embodiments, the plasticizer includes, but is not limited to, one or more of low molecular weight polyisobutylene (PIB oligomer), tricresyl phosphate, and citrate; wherein the weight-average molecular weight of the low molecular weight polyisobutylene is 200-10,000. Introducing the above-mentioned plasticizer into the viscoplastic interlayer material can lower the exfoliation transition temperature of the matrix, increase the free volume of molecules, and lubricate long chains, thereby promoting chain slip under stress.

[0031] In some embodiments, the polar grafted polymer includes, but is not limited to, one or more of maleic anhydride grafted polymers, carboxyl grafted polymers, amino grafted polymers, and hydroxyl grafted polymers. These polar grafted polymers can serve as confinement domains, forming an interpenetrating network with the carbon-based elastomer to spatially confine slip chains and achieve permanent unentanglement.

[0032] In some embodiments, the maleic anhydride-grafted polymer includes, but is not limited to, one or more of maleic anhydride-grafted polypropylene (PP-g-MAH) and maleic anhydride-grafted acrylonitrile-butadiene-styrene copolymer. The polar grafted polymer has partial compatibility with carbon-based elastomers and can form nanoscale hard microdomains during phase separation.

[0033] In a preferred embodiment, the polar graft polymer is maleic anhydride-grafted polypropylene (PP-g-MAH).

[0034] In some embodiments, step S20, which involves homogenizing the mixture using an organic solvent to obtain a viscoplastic interlayer material, specifically includes: Step S21: Mix the mixture with an organic solvent to obtain a mixed solution; Step S22: After heating and stirring the mixed solution at a first temperature, the temperature is lowered to a second temperature and stirred to obtain a viscoplastic interlayer material.

[0035] In this embodiment, an organic solvent dissolution method is selected to ensure that the two materials can be fully mixed and form a homogeneous solution. This process reduces the crystallinity of the original polar graft polymer through chain segment rearrangement. Furthermore, during the dissolution process, high-temperature stirring ensures that the polar graft polymer is fully dissolved, and continued stirring after cooling can prevent the premature precipitation of the graft polymer, ensuring the uniformity of the blend. Finally, the viscoplastic interlayer material exists in the form of a mixed solution.

[0036] In some embodiments, the concentration of the mixed solution is 1 mg / mL to 1000 mg / mL.

[0037] In some embodiments, the organic solvent is selected from, but not limited to, one or more nonpolar or weakly polar organic solvents such as toluene, n-hexane, cyclohexane, dichloromethane, and tetrahydrofuran.

[0038] In some embodiments, the first temperature is 120℃-160℃, and the heating and stirring treatment time is 4h-6h; the second temperature is 40℃-60℃, and the stirring treatment time is 2h-4h.

[0039] Specifically, the mixed solution is heated and stirred in an oil bath at 120℃-160℃ while connected to a water-cooled reflux condenser for 4-6 hours until all components are completely dissolved. High-temperature heating and stirring ensure the polar graft polymer is fully dissolved in the organic solvent and promotes the interdiffusion and entanglement of its molecular chains with the matrix. The water-cooled reflux condenser effectively prevents solvent evaporation and maintains a stable concentration in the reaction system. Subsequently, the temperature is lowered to 40℃-60℃, and polar stirring is performed for 2-4 hours to ensure thorough mixing of all components. Continuous stirring ensures uniform dispersion of all components at the molecular scale, avoiding phase separation defects caused by localized concentration unevenness. This cooling process also inhibits premature precipitation or aggregation of the dissolved polar graft polymer and provides sufficient rearrangement time for polymer chains, which is beneficial for reducing the crystallinity of the polar graft polymer and forming a thermodynamically stable phase structure. After the solution is cooled to room temperature, a homogeneous, viscous precursor blend solution is obtained.

[0040] In addition, the present invention also provides a viscoplastic interlayer material, which is prepared by the method for preparing the viscoplastic interlayer material.

[0041] In this embodiment, the viscoplastic interlayer material prepared by the above preparation method can dissipate energy through the slippage and permanent untangling of polymer chains under external force, effectively suppressing elastic recovery; it can still maintain significant residual strain after unloading, thereby adaptively conforming to the three-dimensional micro-contour of the non-planar electrode.

[0042] In some embodiments, the viscoplastic interlayer material is used to form a film to prepare a viscoplastic interlayer film. For reaction systems based on organic solvents, a suitable substrate must first be selected, and then the viscoplastic interlayer material is uniformly poured onto the substrate. During this process, the various conditions for film formation must be strictly controlled. The specific film formation method can be solution casting or blade coating to ensure the uniformity of film thickness.

[0043] In some embodiments, a flat, clean peeling culture dish or glass plate is used as the substrate; the substrate is pretreated with plasma (argon-oxygen mixture, excitation frequency of 10-15MHz, treatment time of 5-15min) before use to enhance surface hydrophilicity, which is beneficial for uniform solution spreading and subsequent film peeling.

[0044] In some embodiments, the solution casting method includes the following steps: pouring a viscoplastic interlayer material cooled to room temperature into a treated glass petri dish; first, completely sealing the petri dish with aluminum foil; and allowing it to stand at room temperature for 1-24 hours to allow the polymer chains to undergo preliminary phase separation and conformational relaxation in the solution; then, piercing several micro-holes (approximately 0.1-0.5 mm in diameter) on the surface of the aluminum foil to control the evaporation rate of toluene; transferring the petri dish to a fume hood and allowing it to stand at room temperature for another 12-72 hours to allow the solvent to completely evaporate and form a solid film; finally, carefully peeling the film from the petri dish and drying it in a vacuum oven at 40-120°C for 6-24 hours to remove residual solvent, thereby obtaining a viscoplastic interlayer film with a thickness that can be controlled within the range of 0.1-1.0 mm.

[0045] In some embodiments, the steps of the blade coating method include: allowing the viscoplastic interlayer material to stand and seal for 1-24 hours, then pouring it onto a pretreated glass substrate, and uniformly coating the solution using a blade coater or scraper. During the coating process, the angle and pressure between the scraper and the substrate surface need to be precisely controlled to ensure the uniformity of the coating and the required thickness. The coating speed can be adjusted according to the viscosity of the solution and the required film thickness. After coating, the substrate is placed in a sealed container filled with saturated toluene vapor and left to stand for 1-6 hours to create a slow evaporation environment, promoting phase separation and forming a micro / nano-scale, uniform polar domain structure. It is then transferred to a fume hood to allow the solvent to evaporate naturally, and after drying, the film is peeled off and vacuum dried.

[0046] In some implementations, for the film-forming process of the blade coating method, if the settling time is too short, the polar components and the matrix will not separate sufficiently, making it difficult to form an effective confinement domain; if the settling time is too long, the polar components may completely settle and stratify, resulting in an uneven film composition. There are optimal values ​​for the concentration ratio of the viscoplastic interlayer material, the settling time, and the evaporation rate during the film-forming process. Selecting appropriate experimental parameters according to different film thickness requirements is crucial for the formation of bulk viscoplasticity.

[0047] In some embodiments, the method for preparing a viscoplastic interlayer film by forming a film using the viscoplastic interlayer material includes, but is not limited to, spin coating, dip coating, extrusion coating, etc.

[0048] In addition, the present invention also provides an application of the aforementioned viscoplastic interlayer material in electrode encapsulation.

[0049] In this embodiment, the viscoplastic interlayer constructed by chain slippage and permanent untangling control successfully integrates and unifies the interface conformability, adhesive strength and long-term sealing performance in flexible electronic packaging, achieving a systematic improvement in key performance.

[0050] Specifically, electrode encapsulation based on a bulk viscoplastic interlayer effectively bridges the contradiction between interface conformability, adhesive strength, and long-term sealing in flexible electronic packaging fields such as brain-computer interfaces, providing a widely applicable solution for packaging flexible electronic products with complex three-dimensional structures. Furthermore, the viscoplastic interlayer material is not only applicable to neural electrode encapsulation in the field of brain-computer interfaces, but also has broad development and application prospects in flexible wearable electronics, implantable medical devices, microelectromechanical systems (MEMS) packaging, and biosensors.

[0051] In some embodiments, the electrode packaging includes the steps of: Step S100: Functionalize the electrode surface; Step S200: Immerse the functionalized electrode in the viscoplastic interlayer material and perform heat treatment to form an interlayer film on the electrode surface. Step S300: Place the electrode with the intermediate layer film formed on its surface between two encapsulation films, and complete the electrode encapsulation by hot pressing.

[0052] In some embodiments, in step S100, to enable the electrode surface to form covalent bonds with the viscoplastic interlayer, active functional groups need to be introduced onto the electrode surface beforehand. Specifically, the organic functional molecules are thoroughly dissolved in a benign solvent such as ethanol at a concentration of 1-1000 mg / mL at a temperature ranging from room temperature to 80°C. Subsequently, the cleaned substrate is immersed in the solution containing the dissolved organic functional molecules for 10 min-48 h to allow for sufficient adsorption reaction at a temperature ranging from room temperature to 100°C. After immersion, the substrate is ultrasonically cleaned multiple times with anhydrous ethanol, acetone, etc., and finally dried with nitrogen gas for later use.

[0053] In this embodiment, the quality of the functionalization treatment of the electrode surface directly determines the density and uniformity of the interfacial covalent bonding; insufficient treatment time or low reagent concentration will lead to insufficient bonding sites and reduced adhesion strength; excessive treatment time or excessive concentration may result in multilayer molecular stacking, which will hinder effective bonding.

[0054] In some embodiments, the electrode is made of widely used electrode materials, including but not limited to inorganic materials, organic materials, and carbon-based materials; the selected electrode shape covers a variety of non-planar configurations, including but not limited to microfilaments, micropillars, serpentine, spiral, mesh, and island structures.

[0055] In a preferred embodiment, the inorganic materials include, but are not limited to, metals such as gold, copper, silver, and platinum and their alloys, as well as semiconductor materials such as silicon and indium tin oxide; the organic materials include, but are not limited to, conductive polymers such as polyacrylamide and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate; and the carbon-based materials include, but are not limited to, graphene and carbon nanotubes.

[0056] In some embodiments, the organic functional molecule used for surface functionalization is a compound containing an amino or thiol group, including but not limited to thio-undecamine hydrochloride, thioethylamine, 6-amino-1-hexanethiol hydrochloride, 4-aminobenzylthiophenol, 3-amino-1-propanethiol hydrochloride, γ-aminopropyltriethoxysilane, etc.

[0057] In some embodiments, step S200 specifically includes the following steps: immersing the surface-functionalized electrode in the viscoplastic interlayer material (concentration of 10 mg / mL-1000 mg / mL) and placing it in an oven at 50℃-70℃ for 2-12 hours for heat treatment; subsequently, forming a liquid film on its surface by dip coating, with the pulling speed controlled at 0.1 mm-10 mm; finally, allowing the solvent to completely evaporate at room temperature to form a continuous and dense interlayer film on the electrode surface, with a thickness controlled between 10 μm and 300 μm.

[0058] In some embodiments, step S300 specifically includes the following steps: placing an electrode coated with an interlayer film between two encapsulation films to form a sandwich-like stacked structure; subsequently performing hot pressing treatment at a pressure range of 0.1-10 MPa, a temperature range of 30-200°C, and a hot pressing time of 1-60 minutes. During the hot pressing process, the interlayer softens upon heating and undergoes viscous flow, fully filling the microscopic uneven structure of the substrate surface; simultaneously, the polar groups on the viscoplastic interlayer (VPI) molecular chain react with the activated functional groups pre-introduced on the substrate surface to form covalent bonds; after cooling, the plastic deformation of the interlayer is permanently locked, thereby achieving a conformal seal between the encapsulation layer and the substrate.

[0059] In some embodiments, the material of the encapsulating film includes, but is not limited to, polystyrene-isobutylene-styrene (SIBS), styrene-ethylene-butene-styrene block copolymer, styrene-butadiene-styrene block copolymer, polyurethane, polydimethylsiloxane, and other commonly used sealing materials.

[0060] In some implementations, in addition to dip coating, the intermediate layer can also be coated by spin coating, spray screen printing, and inkjet printing, among other methods.

[0061] In summary, the viscoplastic interlayer material and encapsulation process provided by this invention have the following advantages compared with existing elastomer encapsulation processes: 1) Bulk viscoplasticity of viscoplastic interlayer materials Existing elastomeric encapsulation materials (such as SIBS and polyurethane) rely on entropic elastic rebound after deformation under stress, resulting in microscopic voids at the interface with non-planar electrodes. This invention constructs a multiphase blend system of high molecular weight polyisobutylene, low molecular weight plasticizer, and polar grafted polymer. The plasticizer promotes chain slip, and the polar microdomains achieve permanent unentanglement, transforming the material from elastic / viscoelastic to bulk viscoplastic. This material retains significant residual strain after unloading and can adaptively conform to three-dimensional micro-contours, fundamentally eliminating interface defects caused by elastic rebound.

[0062] 2) Enhanced interfacial reliability through the synergistic effect of covalent bonding and viscoplastic conformality. Existing technologies often rely on covalent bonding or mechanical interlocking to improve interfacial adhesion strength, but fail to alter the inherent high resilience of elastomers. In this invention, the viscoplastic interlayer fills the electrode surface microstructure through irreversible plastic flow, and simultaneously utilizes polar groups such as maleic anhydride to react with activated functional groups on the electrode surface to form covalent bonds.

[0063] 3) The packaging process is suitable for a variety of non-planar substrate configurations and materials. Existing elastomeric encapsulation methods struggle to achieve conformal coverage on non-planar electrodes such as microfilaments, micropillars, and serpentine structures. In this invention, the selective coverage of the viscoplastic interlayer is driven by the material's inherent flowability and surface chemistry, rather than relying on geometric alignment. Therefore, high-quality encapsulation is achieved regardless of the electrode shape (microfilament, micropillar, serpentine, helical, mesh, or island), and regardless of the electrode material (metals such as gold, copper, silver, and platinum), or whether it is a conductive polymer or a carbon-based material.

[0064] 4) Compatible with various thin film coating and integration processes Existing elastomer encapsulation methods mostly employ hot pressing or lamination, which have limited adaptability to complex three-dimensional structures. The viscoplastic interlayer of this invention can be pre-formed using film-forming methods such as solution casting, blade coating, and spin coating, or directly coated onto the electrode surface using methods such as dip coating, spraying, and screen printing. It can also be mass-produced through extrusion coating. This process is highly compatible with existing semiconductor and flexible electronics manufacturing processes, demonstrating broad process adaptability.

[0065] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0066] Example 1 First, a viscoplastic interlayer (VPI) film was prepared. High molecular weight polyisobutylene, PIB oligomer, and maleic anhydride-grafted polypropylene were added to 200 ml of toluene at a mass ratio of 5:1:1, resulting in concentrations of 107 mg / mL, 21.5 mg / mL, and 21.5 mg / mL, respectively. The mixture was stirred in an oil bath at 125 °C for 2 hours, with reflux condensation using circulating water. After complete dissolution, the mixture was cooled to 45 °C and stirred for another 3 hours to obtain a VPI precursor solution. The cooled precursor solution was poured into glass culture dishes pretreated with plasma (100 W, 5 min). The culture dishes were sealed with aluminum foil at room temperature and allowed to stand for 12 hours. Then, several tiny holes (approximately 0.2 mm in diameter) were pierced in the aluminum foil, and the culture dishes were placed horizontally in a fume hood to allow the toluene solvent to evaporate slowly. After the solvent has evaporated, the VPI film is gently peeled off from the petri dish and dried in a vacuum oven at 50°C for 12 hours to remove residual solvent, resulting in a VPI film with a thickness of approximately 400 μm.

[0067] Gold microwires (100 μm in diameter) were immersed in a 10 mM mercapto-undecylamine hydrochloride ethanol solution for 12 hours. After removal, they were ultrasonically cleaned three times with anhydrous ethanol and dried with nitrogen. Subsequently, the gold microwires were immersed in a VPI precursor solution, vertically pulled (pulling speed 0.5 mm / s), and heated in a 60 °C oven for 5 hours to evaporate the solvent, forming a VPI coating of approximately 50 μm thickness on the surface of the gold microwires. The VPI-coated gold microwires were placed between two layers of poly(styrene-block-isobutylene-block-styrene) (SIBS) films (300 μm thick) and hot-pressed at 180 °C and 0.5 MPa for 10 minutes to complete the electrode encapsulation.

[0068] The structure of the VPI film prepared in this embodiment was characterized as follows: The curves showing the change of loss factor with temperature in the dynamic thermomechanical analysis of PIB and VPI are shown below. Figure 3 As shown, the glass transition temperature of the viscoplastic interlayer (VPI) is significantly lower than that of pure PIB, indicating that the introduction of PIB oligomers increases the free volume of the molecular chains, thereby enhancing chain segment mobility and chain slippage. The melt peak curves of PP-g-MAH and VPI measured by differential scanning calorimetry are shown in the figure. Figure 4 As shown, differential scanning calorimetry results indicate that the crystallinity of maleic anhydride-grafted polypropylene (PP-g-MAH) in VPI decreased from 40.9% in the original powder to 26.8%. This is attributed to the formation of an interpenetrating network structure between PP-g-MAH and the PIB matrix. The PIB segments spatially confine the PP-g-MAH microdomains, disrupting their ordered arrangement. Photos of the VPI films stretched to preset strains (0%, 50%, and 100%) are shown below. Figure 5 As shown, the synergistic mechanism of chain slip and permanent untangling causes VPI to exhibit plastic deformation behavior similar to clay. Furthermore, the uniaxial tensile stress-strain curves of the VPI film at different strain rates are shown in the figure. Figure 6 As shown, mechanical tests indicate that VPI exhibits a significant rate dependence: it shows strain softening characteristics at low strain rates (0.5% s⁻¹) and strain hardening characteristics at high strain rates (50% s⁻¹), which further confirms its viscoplastic nature.

[0069] The interfacial chemical bonding properties of the sample with completed electrode encapsulation in this embodiment were characterized: Fourier transform infrared spectrum of VPI / electrode interface as follows Figure 7 As shown, after hot pressing the gold electrode, which has been surface-activated by mercapto-undecanine hydrochloride, with the VPI, the characteristic absorption peaks of amide I and amide II appeared in the Fourier transform infrared spectrum, confirming that a ring-opening amidation reaction occurred between the maleic anhydride group in the VPI and the amino group on the electrode surface, forming a stable covalent bond.

[0070] The water vapor barrier properties of the VPI film prepared in this embodiment were characterized: The water vapor transmission rate test data of VPI film is shown in the figure below. Figure 8 As shown in the illustration, the high-precision water vapor transmission rate testing equipment (Mocon Aquatran Model 3) is used; under conditions of 25℃ and 90% relative humidity, the water vapor transmission rate of a 400μm thick VPI film is only 0.28gm. -2 day -1 The temperature is significantly lower than that of conventional elastomer encapsulation materials such as silicone rubber and polyurethane, indicating that this viscoplastic interlayer has excellent airtightness.

[0071] Example 2 A VPI precursor solution with concentrations of 120 mg / mL, 40 mg / mL, and 20 mg / mL was obtained by using high molecular weight PIB, PIB oligomer, and PP-g-MAH in a mass ratio of 6:2:1. Toluene was used as the solvent. The VPI precursor solution was sealed and allowed to stand at room temperature for 6 hours, then poured onto a plasma-pretreated glass substrate. The solution was uniformly coated using a doctor blade with a blade-to-substrate gap of 200 μm and a coating speed of 0.05 m / s. After coating, the substrate was placed in a sealed container filled with saturated toluene vapor and allowed to stand for 2 hours. Then, it was removed and allowed to evaporate the solvent naturally in a fume hood. After drying, the film was peeled off and dried in a vacuum oven at 50 °C for 12 hours to obtain a VPI film with a thickness of approximately 150 μm.

[0072] A copper pillar array electrode (200 μm in height, 200 μm in diameter, and 500 μm in spacing) was immersed in a 5 mM mercaptoethylamine ethanol solution for 12 hours. After removal, it was cleaned with acetone and dried. A VPI precursor solution was uniformly sprayed onto the surface of the copper pillar array using a spraying method at a distance of 8 cm and a spraying time of 30 seconds. It was then dried at 60 °C for 2 hours to form a VPI coating with a thickness of approximately 30 μm. The VPI-coated copper pillar array was placed between two SEBS films (500 μm thick) and hot-pressed at 130 °C and 0.8 MPa for 15 minutes to complete the electrode encapsulation.

[0073] In summary, this invention provides a viscoplastic interlayer material, its preparation method, and its application. The preparation method of the viscoplastic interlayer material includes the following steps: mixing a carbon-based elastomer, a plasticizer, and a polar grafted polymer to obtain a mixture; and homogenizing the mixture using an organic solvent dissolution method, a high-temperature melting method, or a mechanical blending method to obtain the viscoplastic interlayer material. This invention uses a carbon-based elastomer as a matrix, introduces biocompatible small molecules as plasticizers, and polar grafted polymers as confinement domains to construct a multiphase blend system. The short-chain plasticizer increases free volume and lubricates the long-chain carbon-based elastomer to promote chain slip, while the confinement domains, by forming an interpenetrating network with the matrix, spatially confine the slip chains and achieve permanent unentanglement. These synergistic effects transform the viscoplastic interlayer material from a traditional elastic / viscoelastic material to a viscoplastic one, exhibiting significant residual strain, rapid stress relaxation, and rate-dependent mechanical behavior. Therefore, applying this viscoplastic interlayer material to electrode encapsulation can significantly improve the interfacial sealing and long-term reliability of non-planar electrodes, effectively solving the problem of poor long-term stability of neural electrodes caused by interfacial leakage in fields such as brain-computer interfaces.

[0074] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a viscoplastic interlayer material, characterized in that, Including the following steps: A mixture is obtained by mixing a carbon-based elastomer, a plasticizer, and a polar grafted polymer. The mixture is homogenized by organic solvent dissolution, high-temperature melting, or mechanical blending to obtain a viscoplastic interlayer material.

2. The method for preparing the viscoplastic interlayer material according to claim 1, characterized in that, The mass ratio of the carbon-based elastomer, the plasticizer, and the polar graft polymer is (1-10):(1-10):(1-10).

3. The method for preparing the viscoplastic interlayer material according to claim 1, characterized in that, The carbon-based elastomer includes one or more of high molecular weight polyisobutylene, styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-ethylene-butene-styrene, styrene-isobutylene-styrene, styrene-propylene-styrene, and styrene-ethylene-propylene-styrene; wherein the weight-average molecular weight of the high molecular weight polyisobutylene is 500,000-2,000,000.

4. The method for preparing the viscoplastic interlayer material according to claim 1, characterized in that, The plasticizer includes one or more of low molecular weight polyisobutylene, tricresyl phosphate, and citrate; wherein the weight average molecular weight of the low molecular weight polyisobutylene is 200-10,000.

5. The method for preparing the viscoplastic interlayer material according to claim 1, characterized in that, The polar grafted polymer includes one or more of maleic anhydride grafted polymers, carboxyl grafted polymers, amino grafted polymers, and hydroxyl grafted polymers.

6. The method for preparing the viscoplastic interlayer material according to claim 1, characterized in that, The step of homogenizing the mixture using an organic solvent dissolution method to obtain a viscoplastic interlayer material specifically includes: The mixture is then mixed with an organic solvent to obtain a mixed solution; After heating and stirring the mixed solution at a first temperature, the temperature is lowered to a second temperature and stirred again to obtain a viscoplastic interlayer material.

7. The method for preparing the viscoplastic interlayer material according to claim 6, characterized in that, The concentration of the mixed solution is 1 mg / mL to 1000 mg / mL; Preferably, the organic solvent is selected from one or more of toluene, n-hexane, cyclohexane, dichloromethane, and tetrahydrofuran; Preferably, the first temperature is 120℃-160℃, and the heating and stirring treatment time is 4h-6h; Preferably, the second temperature is 40℃-60℃, and the stirring time is 2h-4h.

8. A viscoplastic interlayer material, characterized in that, It is prepared using the method for preparing the viscoplastic interlayer material as described in any one of claims 1-7.

9. The application of the viscoplastic interlayer material as described in claim 8 in electrode encapsulation.

10. The application according to claim 9, characterized in that, The electrode encapsulation includes the following steps: Functionalization treatment of electrode surface; The functionalized electrode is immersed in the viscoplastic interlayer material and subjected to heat treatment to form an interlayer film on the electrode surface. An electrode with an intermediate layer film formed on its surface is placed between two encapsulation films, and the electrode encapsulation is completed by hot pressing.

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