In the fields of 5G communications, new energy vehicles, high-performance chips, etc., efficient heat dissipation has become a key bottleneck restricting technological development. The thermal conductivity of traditional polymer-based thermal conductive materials (such as silicone and epoxy resin) is only 0.1~0.3 W/(m·K), which is far from meeting the demand. When improving thermal conductivity by adding thermal conductive fillers, problems such as filler agglomeration, high interface thermal resistance, and oil seepage are often encountered. At this time, surface modification technology came into being and became the “golden key” to crack the performance bottleneck of thermal conductive materials!
Why do thermal conductive fillers need “surface modification”
The surface properties of thermal conductive fillers directly affect their dispersion and interfacial bonding in the matrix. For example, although alumina is cost-effective, its highly polar surface has poor compatibility with organic matrices (such as epoxy resins), resulting in particle agglomeration, increased interfacial voids, and ultimately reduced thermal conductivity.
How to modify the surface of thermal conductive fillers
There are many methods for filler modification, including physical modification and chemical modification, but the most widely used and effective modification method is chemical modification, which mainly includes coupling agent modification, esterification reaction modification and surface grafting modification.
1. Physical modification method
Physical methods mainly include mechanical force dispersion, ultrasonic dispersion and high-energy treatment. These methods can mechanically blend particles with polymers through mechanical grinding, ball milling, sand milling, high-speed stirring, etc. to form inorganic/organic composite materials.
2. Chemical modification method
Coupling agent modification is to bind organic molecules on the coupling agent to the surface of inorganic powder. The surface free energy of inorganic powder is reduced, the agglomeration phenomenon is reduced, and the compatibility with the organic matrix is increased. Generally, there are silane coupling agents, titanate coupling agents, and aluminate coupling agents.
The esterification reaction is a reaction between the hydroxyl groups on the surface of the inorganic powder and the carboxyl or alcohol hydroxyl groups in the modifier, so that the organic molecules are connected to the surface of the powder, thereby reducing the polarity of the powder surface.
Surface grafting modification refers to dispersing inorganic particles with active groups on the surface into the initiating monomer, and then the monomer is polymerized on the surface of the inorganic particles to form a coating layer through the action of the initiator. The surface grafted polymers include polymethacrylic acid, polyacrylamide, polymethacrylate glycidyl ester, hyperbranched polymers, etc.
With the rapid development of science and technology and the continuous improvement of material performance requirements in various fields, the technical development of thermal conductive fillers has shown a diversified trend, laying a solid foundation for meeting the needs of complex application scenarios in the future.
Intelligent design is an important direction for the development of thermal conductive filler technology. Traditional research and development of thermal conductive fillers often relies on a lot of experiments and experience, and the process is cumbersome and inefficient. By establishing a machine learning model, a large amount of experimental data and theoretical calculation results can be analyzed and learned to predict the relationship between thermal conductive fillers of different morphologies and thermal conductivity.
Multifunctional integration is also an inevitable trend in the development of thermal conductive filler technology. In modern electronic devices, such as smart phones and laptops, materials are required not only to have good thermal conductivity, but also to have multiple properties such as insulation and electromagnetic shielding. In order to meet these needs, researchers can achieve the integration of multiple functions by compounding thermal conductive fillers with insulating materials, electromagnetic shielding materials, etc.
The research on thermal conductive fillers is moving from single performance optimization to multifunctional composite and green direction. With the breakthrough of nanotechnology and preparation technology, thermal conductive materials will play a more critical role in 5G communications, new energy vehicles and other fields. In the future, it is necessary to further solve the problems of cost, performance balance and environmental compatibility to achieve large-scale industrial application.