A method for surface modification of thermally conductive fillers for high thermally conductive composites

Abstract

This invention discloses a method for surface modification of thermally conductive fillers for high thermal conductivity composite materials, belonging to the field of interface engineering for thermally conductive fillers. The method first constructs a dense anchoring layer of inorganic nanoparticles with a particle size of 5–30 nm on the surface of a plasma-activated thermally conductive filler through in-situ hydrolysis and condensation. Then, through surface-initiated atom transfer radical polymerization, a rigid molecular brush inner layer and a flexible molecular brush outer layer are sequentially grafted to form an "organic-inorganic hybrid nanobridge layer" with a thickness of 10–100 nm. This bridge layer achieves a gradient phonon modulus transition from the filler lattice to the polymer matrix, significantly reducing interfacial phonon scattering loss. Composite materials prepared using the filler modified by this invention, at a filler content of 5–15 wt%, achieve a thermal conductivity more than twice that of traditional silane coupling agent modification schemes, while simultaneously improving mechanical properties. The method of this invention is process-controllable, has a wide range of applications, and fundamentally overcomes the inherent limitations of low thermal conductivity and insufficient thickness of the interfacial layer in traditional small molecule coupling agents.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive filler surface treatment technology, specifically involving a surface modification method that reduces the thermal resistance of the filler-matrix interface and improves the macroscopic thermal conductivity of composite materials by constructing an "organic-inorganic hybrid nano-bridging layer" on the surface of a high thermally conductive filler. It falls under the category of functional composite material interface engineering. Background Technology

[0002] Polymer-based thermally conductive composites have broad application prospects in electronic packaging, 5G communication equipment, and thermal management of new energy vehicle batteries. However, the intrinsic thermal conductivity of polymers is extremely low, typically only 0.1–0.3 W / (m·K), far from meeting the requirements for efficient heat dissipation. Currently, the common practice in industry and academia is to fill the polymer matrix with high thermal conductivity fillers, such as alumina, aluminum nitride, boron nitride, carbon nanotubes, and graphene, forming thermally conductive pathways through the contact between the fillers.

[0003] However, existing thermally conductive composite material technologies face a core bottleneck—the interfacial thermal resistance between the filler and the polymer matrix. This manifests itself in the following ways: Phonon scattering at the interface is severe. Thermally conductive fillers are mostly inorganic crystalline materials, where heat is efficiently transferred via phonon vibrations, resulting in long mean free paths for phonons. In contrast, polymer matrices are organic polymers with disordered molecular chain movement, leading to extremely low phonon transport efficiency. When phonons travel from the filler to the filler-matrix interface, severe scattering occurs at the interface due to the significant differences in lattice structure, modulus, and density between the two phases, resulting in substantial energy dissipation. Theoretical calculations show that even with an intrinsic thermal conductivity of hundreds of W / (m·K), the thermal resistance of a single filler-matrix interface can be equivalent to the thermal resistance of a polymer layer several to tens of nanometers thick, becoming a bottleneck in the entire heat conduction pathway.

[0004] Limitations of Traditional Interface Modification Methods. To improve the interfacial compatibility between fillers and the matrix, the industry commonly uses small-molecule coupling agents such as silane coupling agents, titanate coupling agents, and aluminate coupling agents to treat the filler surface. These coupling agents undergo a condensation reaction with hydroxyl groups on the filler surface at one end, and possess organic functional groups that can react with the matrix at the other end, forming a monolayer "molecular bridge" between the filler and the matrix. However, these small-molecule coupling agent layers have inherent defects: First, the coupling agent molecular chain segments are extremely short (usually less than 2 nm), resulting in a limited interfacial layer thickness that cannot effectively buffer the modulus abrupt change between the filler and the matrix, and phonon scattering remains severe; second, the small-molecule coupling agents themselves have extremely low thermal conductivity, making this interfacial layer a "thermal insulation layer" encased on the filler surface, hindering heat from crossing the interface; third, the coupling agent is usually grafted onto the filler surface in isolated "point-like" patterns, failing to form a continuous, dense interfacial thermally conductive layer.

[0005] High filler content leads to performance degradation. To compensate for insufficient macroscopic thermal conductivity caused by interfacial thermal resistance, traditional methods have to significantly increase the filler content, typically above 50 wt%, to force filler particles into contact within the matrix to form a thermally conductive network. However, high filler content leads to increased composite material density, a surge in melt viscosity, and a sharp deterioration in mechanical properties (elongation at break can drop to below 5% of that of the pure matrix), severely limiting its practical applications.

[0006] There is a lack of proactive design for interfacial thermal conductivity channels. Existing filler surface modification techniques mostly focus on improving compatibility and dispersibility, aiming to make the filler "uniformly dispersed" in the matrix. However, uniformly dispersed filler particles separated from each other by a thin layer of polymer matrix actually increase the number of interfaces, and each interface introduces thermal resistance. Existing technologies lack a method to actively construct a "high thermal conductivity interfacial transition layer" on the filler surface. This transition layer must not only be firmly bonded to the filler surface, but also form a good phonon transport channel with the matrix, and have sufficient thickness to buffer modulus mismatch.

[0007] In summary, there is an urgent need to develop a novel surface modification method for thermally conductive fillers that can overcome the inherent limitations of small molecule coupling agents and construct an interfacial transition layer on the filler surface that combines high intrinsic thermal conductivity, good matrix compatibility, and appropriate thickness. This would fundamentally reduce the thermal resistance at the filler-matrix interface, enabling the composite material to achieve excellent thermal conductivity even with low filler content. Summary of the Invention

[0008] Technical problems to be solved The present invention aims to solve the following key technical problems existing in the prior art: First, the intrinsic thermal conductivity of the interfacial layer formed by traditional small molecule coupling agents is low, which hinders heat transfer across the interface; Second, the short molecular chain segments of the coupling agent result in insufficient interfacial layer thickness, which cannot effectively buffer the phonon modulus mismatch between the filler and the matrix; Third, the grafting of the coupling agent on the filler surface is discontinuous, which cannot form a dense interfacial thermally conductive layer; Fourth, there is a lack of methods to actively construct a high thermal conductivity interfacial transition layer on the filler surface, which means that the composite material can only obtain acceptable thermal conductivity by sacrificing mechanical and processing properties with high filler content. Technical solution

[0009] To address the aforementioned technical problems, this invention provides a method for surface modification of thermally conductive fillers for high thermal conductivity composite materials. Its core innovation lies in the sequential construction of an "inorganic nanoparticle anchoring layer" and an "organic molecular brush gradient layer" on the surface of the thermally conductive filler, forming an "organic-inorganic hybrid nanobridge layer" with a total thickness of 10–100 nm. This bridge layer achieves a gradient transition from "lattice structure → amorphous → polymer" from the filler surface to the matrix, significantly reducing the scattering loss of phonon transinterface transmission.

[0010] The method specifically includes the following steps: Step 1: Pretreatment and activation of filler surface High thermal conductivity inorganic fillers are selected as the matrix filler. The filler can be two-dimensional (e.g., hexagonal boron nitride nanosheets, graphene nanosheets), one-dimensional (e.g., carbon nanotubes, silicon carbide whiskers), or zero-dimensional (e.g., spherical alumina, aluminum nitride). The average particle size or sheet diameter of the filler is 1–20 μm. The filler is placed in a vacuum plasma treatment device and treated with a radio frequency power of 100–300 W for 5–20 minutes in an oxygen or air atmosphere, enriching the filler surface with active oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH). The advantage of plasma treatment is that it only acts on a very shallow layer (a few nanometers) of the filler surface, without destroying the internal crystal structure of the filler, thus maintaining the intrinsic high thermal conductivity of the filler.

[0011] Step 2: Construction of the Inorganic Nanoparticle Anchoring Layer This step involves constructing a dense, highly thermally conductive inorganic nanoparticle anchoring layer on the filler surface through in-situ growth or electrostatic self-assembly. The functions of this anchoring layer are: to provide a transition layer with a lattice structure similar to that of the filler bulk, reducing the first-stage scattering of phonons from the filler bulk to the interface layer; to increase the surface roughness and specific surface area of ​​the filler, providing abundant grafting anchor sites for subsequent organic molecular brushing; and to utilize the high thermal conductivity of the nanoparticles themselves to ensure that the intrinsic thermal conductivity of the interface layer remains high.

[0012] The specific steps are as follows: (1) The filler activated in step one is dispersed in a solution or sol containing a metal salt precursor. The metal salt precursor is a precursor capable of generating highly thermally conductive inorganic nanoparticles, preferably at least one of aluminum isopropoxide, tetraethyl orthosilicate, tetrabutyl titanate, and zinc acetate. The generated nanoparticles correspond to alumina (thermal conductivity of about 30 W / (m·K)), silicon dioxide (thermal conductivity of about 1.4 W / (m·K)), titanium dioxide, zinc oxide, etc.

[0013] (2) By controlling the hydrolysis and condensation reaction conditions, the precursor is hydrolyzed and condensed in situ on the surface of the packing material to form inorganic nanoparticles with a particle size of 5-30 nm. The particles are uniformly and densely anchored on the surface of the packing material to form an inorganic nanoparticle anchoring layer with a thickness of 5-20 nm. The reaction conditions are: pH controlled at 4-10, temperature at 40-80℃, reaction time at 2-8 hours, and stirring speed at 300-600 rpm.

[0014] (3) After the reaction is completed, the mixture is centrifuged, washed three times alternately with anhydrous ethanol and deionized water, and dried under vacuum at 80°C for 6 hours to obtain a filler with surface-anchored inorganic nanoparticles.

[0015] Step 3: Grafting of the organic molecular brush gradient layer An organic molecular brush layer is grafted onto an inorganic nanoparticle anchoring layer using a surface-initiated polymerization method, forming a gradual transition from inorganic to organic. The organic molecular brush layer is characterized by a gradual decrease in segment rigidity and cross-linking density from the proximal end near the inorganic anchoring layer to the distal end extending into the matrix. Specifically, the molecular brushes near the filler side are denser and more rigid, while those near the matrix side are more porous and flexible, thus achieving a gradient transition in modulus.

[0016] The specific steps are as follows: (1) Introducing polymerization initiators onto the surface of the inorganic nanoparticle anchoring layer. The filler obtained in step two was dispersed in anhydrous toluene, and an aminosilane coupling agent (such as 3-aminopropyltriethoxysilane) was added. The mixture was refluxed at 80°C for 12 hours under nitrogen protection to introduce amino functional groups onto the surface of the inorganic nanoparticles. Subsequently, the filler containing amino groups on the surface was reacted with α-bromoisobutyryl bromide under ice bath conditions to introduce an atom transfer radical polymerization initiator.

[0017] (2) Grafting organic molecular brushes using a two-step sequential surface-initiated atom transfer radical polymerization method: Step 1: The anchoring initiator filler is polymerized in a solution containing rigid monomers. The rigid monomers are preferably at least one of glycidyl methacrylate, isobornyl methacrylate, and styrene. These monomers, after polymerization, form rigid molecular brush segments with a high glass transition temperature. The polymerization conditions are: using cuprous bromide / pentamethyldiethylenetriamine as the catalytic system, polymerization is carried out at 40–60°C for 2–6 hours. This step forms a dense, rigid molecular brush inner layer on the outside of the inorganic anchoring layer, with a thickness controlled at 5–20 nm.

[0018] Step 2: The product from Step 1 is removed, washed, and then placed in a solution containing flexible monomers for further polymerization. The flexible monomers are preferably at least one of butyl methacrylate, lauryl methacrylate, and polyethylene glycol methacrylate. These monomers, after polymerization, form flexible molecular brush segments with a low glass transition temperature. The polymerization conditions are: polymerization at 50–70°C for 1–4 hours. In this step, flexible molecular brushes continue to grow on the outer layer of the rigid molecular brush, with a thickness controlled at 10–50 nm, ultimately forming a gradient molecular brush layer from rigid to flexible, from the inside out.

[0019] (3) Optionally, reactive groups (such as epoxy, amino, acrylate, vinyl, etc.) that can participate in the matrix curing reaction are introduced at the end of the outermost flexible molecular brush, so that the molecular brush layer can be covalently bonded to the matrix during the subsequent composite material molding process, thereby further improving the interfacial bonding strength.

[0020] Step 4: Cleaning and drying of surface-modified fillers The surface-modified filler obtained in step three was thoroughly washed with tetrahydrofuran, ethanol and deionized water to remove unreacted catalyst and monomers. It was then vacuum dried at 60°C for 12 hours to obtain a modified thermally conductive filler with a core-shell structure of "inorganic nanoparticle anchoring layer + organic molecular brush gradient layer".

[0021] 3. Technical Effects Compared with the prior art, the present invention has the following significant advantages: (1) Significantly reduced interfacial thermal resistance. This invention achieves a gradient phonon modulus transition from the filler lattice to the polymer matrix by constructing a double-layer core-shell structure of "inorganic anchoring layer + organic gradient layer" on the filler surface. The high thermal conductivity inorganic nanoparticle anchoring layer has a similar lattice structure to the filler bulk, reducing the first-stage interfacial phonon scattering loss by more than 60%; the organic molecular brush gradient layer gradually transitions from rigid to flexible, reducing the second-stage interfacial phonon scattering loss by more than 40%. In summary, the composite material prepared using the surface-modified filler of this invention has an interfacial thermal resistance that is 60% to 80% lower than that of the traditional silane coupling agent modification scheme.

[0022] (2) Achieving high thermal conductivity with low filler content. Due to the significant reduction in interfacial thermal resistance, heat can be efficiently transferred across the filler-matrix interface. Even at low filler content, the efficiency of heat transfer between fillers through the matrix is ​​significantly improved. When the filler content is only 5-15 wt%, the thermal conductivity of the composite material can reach the level that can only be achieved with a filler content of 30-50 wt% by traditional methods, thus preserving the lightweight, mechanical and processing properties of the polymer matrix to the greatest extent.

[0023] (3) The intrinsic thermal conductivity of the interface layer is significantly higher than that of the traditional coupling agent layer. The traditional silane coupling agent layer is an organic small molecule with extremely low intrinsic thermal conductivity (about 0.1 to 0.2 W / (m·K)), which becomes an "insulating layer" when wrapped on the surface of the filler. The inorganic nanoparticle anchoring layer used in this invention (such as alumina with a thermal conductivity of about 30 W / (m·K)) has an intrinsic thermal conductivity that is 2 to 3 orders of magnitude higher than that of the coupling agent. When used as an interface layer, it does not introduce additional thermal resistance, but can instead participate in heat conduction.

[0024] (4) The surface function of the filler can be customized. By adjusting the type of inorganic nanoparticles (alumina, zinc oxide, silicon dioxide, etc.), particle size and coverage density, as well as the monomer combination, chain segment length and terminal functional group type of the organic molecular brush, the optimal interface structure can be customized for different polymer matrix systems (epoxy, acrylate, silicone, polyurethane, etc.), and the method has wide adaptability.

[0025] (5) The process is highly controllable and easy to scale up. The in-situ hydrolysis condensation and surface-initiated polymerization adopted in this invention are both mature industrial technology routes. The reaction conditions are mild, do not depend on expensive or rare reagents, and the process parameters are highly controllable, which has good prospects for industrial scale-up.

[0026] (6) Synergistic improvement of mechanical and thermal properties. The flexible outer layer of the gradient molecular brush is entangled with the matrix molecular chains and even covalently bonded, which can effectively transfer stress and dissipate energy when subjected to force. The composite material prepared by the modified filler of this invention has better tensile strength and elongation at break than the traditional coupling agent modification scheme, avoiding the brittle fracture problem caused by high filler content. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the surface modification method for thermally conductive fillers according to the present invention. The first step is to introduce hydroxyl / carboxyl groups through plasma treatment; the second step is to generate an alumina nanoparticle anchoring layer through in-situ hydrolysis and condensation; the third step is to introduce an initiator and graft rigid and flexible molecular brushes; and the fourth step is to obtain a core-shell structure modified filler.

[0028] Figure 2 The diagram shows a cross-sectional view of the core-shell structure of the surface-modified filler, where: (1) is the outer layer of the flexible molecular brush; (2) is the inner layer of the rigid molecular brush; (3) is the inorganic nanoparticle anchoring layer; (4) is the surface layer of the thermally conductive filler body; and (5) is the inorganic thermally conductive filler. The detailed structure of the inorganic nanoparticle anchoring layer and the organic molecular brush gradient layer is shown.

[0029] Figure 3 The diagram shows the phonon transport at the filler-matrix interface for different surface modification methods, where: (1) is the interface of a traditional silane coupling agent, where phonon scattering is severe; (2) is the interface of an inorganic anchoring layer where phonon scattering is only partial; (3) is the gradient interface of the present invention, where phonon transport is smooth; (4) represents phonon scattering; and (5) represents phonon vibration.

[0030] Figure 4A bar chart comparing the thermal conductivity of composite materials modified by different methods is shown, where EG represents the experimental group and CG represents the control group. CG1 represents the thermal conductivity of unmodified alumina in the polymer; at a filler content of 15 wt%, the thermal conductivity of the composite material is only 1.2 W / (m·K). CG2 represents the thermal conductivity of alumina modified with a traditional silane coupling agent in the polymer; at a filler content of 15 wt%, the thermal conductivity of the composite material is 1.8 W / (m·K). CG3 represents the thermal conductivity of alumina in the polymer with only an inorganic anchoring layer and no organic molecular brush modification; at a filler content of 15 wt%, the thermal conductivity of the composite material is 2.5 W / (m·K). The EG1 alumina system is obtained by taking 5.0 g of spherical alumina powder with an average particle size of 10 μm, constructing an inorganic nanoparticle anchoring layer, and grafting an organic molecular brush gradient layer. The resulting composite material has a thermal conductivity of 3.8 W / (m·K), a tensile strength of 58 MPa, and an elongation at break of 4.2%. EG2 is a boron nitride nanosheet system, in which the filler is replaced with hexagonal boron nitride nanosheets with a diameter of 8 μm and a thickness of 10 nm. The inorganic nanoparticle anchoring layer uses zinc oxide nanoparticles (zinc acetate as a precursor) and an organic molecular brush system. With a filler content of 10 wt%, the composite material has an in-plane thermal conductivity of 6.5 W / (m·K) and a longitudinal thermal conductivity of 4.8 W / (m·K). EG3 is a carbon nanotube system, where the filler is replaced with multi-walled carbon nanotubes with a diameter of 15 nm and a length of 10 μm. The inorganic nanoparticle anchoring layer uses titanium dioxide nanoparticles (tetrabutyl titanate as a precursor), and the rigid monomer of the organic molecular brush is replaced with styrene. With a filler content of 5 wt%, the composite material has an axial thermal conductivity of 8.2 W / (m·K). EG4 is an organosilicon matrix system, where the polymer matrix is ​​replaced with addition-cured liquid silicone rubber, and the flexible monomer of the outer layer of the organic molecular brush is replaced with vinyl-containing polymethyl methacrylate, allowing the vinyl groups at the ends of the molecular brush to participate in the hydrosilylation curing reaction. With a filler content of 12 wt%, the composite material has a thermal conductivity of 2.9 W / (m·K), and the elongation at break remains above 75% of that of pure silicone rubber. Detailed Implementation

[0031] The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0032] Example 1

[0033] (1) Pretreatment of filler surface: Take 5.0g of spherical alumina powder with an average particle size of 10μm, place it in a vacuum plasma treatment device, and treat it for 10 minutes under oxygen atmosphere and radio frequency power of 200W to obtain activated alumina filler with hydroxyl-rich surface.

[0034] (2) Construction of inorganic nanoparticle anchoring layer: Activated alumina was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 20 minutes. A solution of 1.5 g aluminum isopropoxide dissolved in 20 mL of anhydrous ethanol was slowly added dropwise while stirring, followed by a 10 mL ethanol solution containing 0.5 mL of deionized water and 0.2 mL of concentrated hydrochloric acid. The reaction was stirred at 60 °C for 4 hours to allow aluminum isopropoxide to hydrolyze and condense in situ on the surface of the alumina filler to form the alumina filler.

[0035] (3) Construction of the inorganic nanoparticle anchoring layer: Activated alumina was dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 20 minutes. A solution of 1.5 g aluminum isopropoxide dissolved in 20 mL of anhydrous ethanol was slowly added dropwise while stirring, followed by a slow addition of 10 mL of ethanol solution containing 0.5 mL of deionized water and 0.2 mL of concentrated hydrochloric acid. The reaction was stirred at 60 °C for 4 hours, allowing aluminum isopropoxide to hydrolyze and condense in situ on the surface of the alumina filler to form an alumina nanoparticle anchoring layer. The mixture was centrifuged, washed alternately with ethanol and water, and dried at 80 °C for 6 hours. Transmission electron microscopy revealed a dense layer of alumina nanoparticles with a particle size of 10–20 nm, approximately 10 nm thick, covering the surface of the filler.

[0036] (4) Grafting of organic molecular brush gradient layer: The product from the previous step was dispersed in 80 mL of anhydrous toluene, and 1.5 mL of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 80 °C for 12 hours under nitrogen protection, and then washed and dried. Then it was dispersed in 50 mL of anhydrous tetrahydrofuran, and 1.0 mL of triethylamine was added. 0.6 mL of α-bromoisobutyryl bromide was slowly added dropwise under ice bath conditions. The mixture was reacted at room temperature for 12 hours, and then washed and dried to obtain the initiator anchoring filler.

[0037] First step polymerization: The initiator anchoring filler was placed in a mixed solution containing 8 mL glycidyl methacrylate and 20 mL N,N-dimethylformamide, and 0.15 g of cuprous bromide catalyst and 0.22 mL of pentamethyldiethylenetriamine ligand were added. The mixture was polymerized at 50 °C for 4 hours under nitrogen protection to obtain the inner layer of the rigid molecular brush.

[0038] The second polymerization step: After washing the product from the previous step, it was placed in a mixed solution containing 10 mL of butyl methacrylate and 20 mL of N,N-dimethylformamide, and the same catalytic system was added. Polymerization was carried out at 60°C for 3 hours to obtain the outer layer of the flexible molecular brush. After washing and drying, the surface-modified alumina filler of this invention was obtained.

[0039] (5) Preparation of composite material: 4.5g of modified alumina filler was mixed with 25.0g of bisphenol A type epoxy resin E-51, 5.0g of methylhexahydrophthalic anhydride curing agent, and 0.1g of 2-ethyl-4-methylimidazolium accelerator. The mixture was planetarily stirred to remove bubbles, poured into a mold, cured at 100℃ for 2 hours, and then cured at 150℃ for 4 hours. The filler content was approximately 15wt%.

[0040] (6) Performance test: The obtained composite material has a thermal conductivity of 3.8 W / (m·K), a tensile strength of 58 MPa, and an elongation at break of 4.2%.

[0041] Comparative Example 1 (Unmodified raw alumina) The difference from Example 1 is that raw alumina powder without any surface treatment was used directly. At a filler content of 15 wt%, the composite material has a thermal conductivity of only 1.2 W / (m·K) and a tensile strength of 42 MPa.

[0042] Comparative Example 2 (Modification of Traditional Silane Coupling Agents) The difference from Example 1 is that only the conventional silane coupling agent KH-560 was used for surface treatment of alumina. With a filler content of 15 wt%, the composite material has a thermal conductivity of 1.8 W / (m·K) and a tensile strength of 50 MPa. Although the thermal conductivity is improved compared to Comparative Example 1, it is still only 47% of that of Example 1.

[0043] Comparative Example 3 (Inorganic anchoring layer only, no organic molecular brush) The difference from Example 1 is that only steps (1) and (2) are performed, and the organic molecular brush grafting in step (3) is not performed. At a filler content of 15 wt%, the thermal conductivity of the composite material is 2.5 W / (m·K), which is lower than that of Example 1, and the tensile strength is only 45 MPa due to insufficient compatibility between the filler and the matrix.

[0044] Example 2 (Boron nitride nanosheet system) The filler was replaced with hexagonal boron nitride nanosheets with a diameter of 8 μm and a thickness of 10 nm. Zinc oxide nanoparticles (zinc acetate as a precursor) were used as the inorganic nanoparticle anchoring layer, and the organic molecular brush system was the same as in Example 1. With a filler content of 10 wt%, the composite material had an in-plane thermal conductivity of 6.5 W / (m·K) and a longitudinal thermal conductivity of 4.8 W / (m·K).

[0045] Example 3 (Carbon Nanotube System) The filler was replaced with multi-walled carbon nanotubes with a diameter of 15 nm and a length of 10 μm. The inorganic nanoparticle anchoring layer used titanium dioxide nanoparticles (with tetrabutyl titanate as a precursor), and the rigid monomer of the organic molecular brush was replaced with styrene. With a filler content of 5 wt%, the axial thermal conductivity of the composite material was 8.2 W / (m·K).

[0046] Example 4 (Organosilicon matrix system) By replacing the polymer matrix with addition-type liquid silicone rubber and replacing the flexible monomer of the outer layer of the organic molecular brush with vinyl-containing polymethyl methacrylate, the vinyl groups at the ends of the molecular brush participate in the hydrosilylation curing reaction. With a filler content of 12 wt%, the composite material exhibits a thermal conductivity of 2.9 W / (m·K) and retains more than 75% of the elongation at break of pure silicone rubber.

Claims

1. A method for surface modification of thermally conductive fillers for high thermal conductivity composite materials, characterized in that, Includes the following steps: (1) Constructing an inorganic nanoparticle anchoring layer on the surface of thermally conductive filler: The surface-activated thermally conductive filler is dispersed in a solution containing a metal salt precursor, and a dense inorganic nanoparticle anchoring layer with a particle size of 5-30 nm is formed on the surface of the filler through in-situ hydrolysis and condensation reaction. (2) Construct an organic molecular brush gradient layer on the inorganic nanoparticle anchoring layer: First, introduce a polymerization initiator on the surface of the inorganic nanoparticle anchoring layer, and then graft the rigid molecular brush inner layer and the flexible molecular brush outer layer in sequence through surface-initiated polymerization to form a gradient molecular brush layer from the inside to the outside and from rigid to flexible.

2. The method according to claim 1, characterized in that, In step (1), the thermally conductive filler is at least one of spherical alumina, aluminum nitride, hexagonal boron nitride nanosheets, graphene nanosheets, carbon nanotubes, and silicon carbide whiskers; the average particle size or sheet size of the filler is 1 to 20 μm.

3. The method according to claim 1, characterized in that, In step (1), the surface activation treatment is a vacuum plasma treatment, which is performed in an oxygen or air atmosphere with a radio frequency power of 100-300W for 5-20 minutes to enrich the filler surface with hydroxyl and / or carboxyl active functional groups.

4. The method according to claim 1, characterized in that, In step (1), the metal salt precursor is at least one of aluminum isopropoxide, tetraethyl orthosilicate, tetrabutyl titanate, and zinc acetate; the generated inorganic nanoparticles are at least one of aluminum oxide, silicon dioxide, titanium dioxide, and zinc oxide; and the anchoring layer thickness is 5–20 nm.

5. The method according to claim 1, characterized in that, In step (2), the polymerization initiator is an atom transfer radical polymerization initiator, which is introduced by grafting an aminosilane coupling agent onto the surface of the inorganic nanoparticle anchoring layer and then reacting it with α-bromoisobutyryl bromide.

6. The method according to claim 1, characterized in that, In step (2), the rigid molecular brush is polymerized from at least one monomer selected from glycidyl methacrylate, isobornyl methacrylate, and styrene; the flexible molecular brush is polymerized from at least one monomer selected from butyl methacrylate, lauryl methacrylate, and polyethylene glycol methacrylate.

7. The method according to claim 1, characterized in that, In step (2), the inner layer thickness of the rigid molecular brush is 5-20 nm, and the outer layer thickness of the flexible molecular brush is 10-50 nm.

8. The method according to any one of claims 1 to 7, characterized in that, In step (2), a reactive group that can participate in the matrix curing reaction is introduced at the end of the outer layer of the flexible molecular brush. The reactive group is at least one of epoxy, amino, acrylate, and vinyl groups.

9. A surface-modified thermally conductive filler prepared according to any one of claims 1 to 8, characterized in that, The packing material has a core-shell structure, consisting of, from the inside out: a thermally conductive packing body, an inorganic nanoparticle anchoring layer, a rigid molecular brush inner layer, and a flexible molecular brush outer layer, with a total shell thickness of 10–100 nm.

10. A polymer composite material containing the surface-modified thermally conductive filler of claim 9, characterized in that, The thermal conductivity of this composite material at a filler content of 5–15 wt% is at least twice that of the filler modified with traditional silane coupling agents at the same filler content.

11. The application of the polymer composite material of claim 10 in thermal interface materials, electronic packaging heat dissipation substrates, 5G communication equipment heat dissipation components, or new energy vehicle power battery thermal management components.

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