To achieve widespread industrial application, good thermal conductivity in thermal conductive silicone is crucial. Currently, research on enhancing the thermal conductivity of thermal conductive silicone focuses primarily on filler modification. The ultimate thermal capacity of thermal fillers depends on factors such as particle size, shape, surface properties, type of filler, and the filler’s thermal conductivity variations with temperature, humidity, and pressure. Here are five main ways to improve the thermal conductivity of thermal conductive silicone:

1. Ultrafine Particulation of Thermal Fillers

Reducing the particle size of thermal fillers enhances both the thermal conductivity and the physical and mechanical properties of thermal conductive silicone. For example, thermal conductive silicone filled with nano-scale alumina filler exhibits significantly better overall performance compared to silicone filled with micron-scale alumina. Studies have shown that ultrafine particulation of inorganic fillers can dramatically alter the inter-atomic distances and structures within the filler particles. When the particle size reaches the nano-scale, some properties of the fillers can even undergo qualitative changes. For instance, when covalent-bonded materials are reduced to the nano-scale, they can transform into materials with metallic bonds, significantly increasing their thermal conductivity. A Japanese company developed high-purity, ultrafine magnesium oxide with a thermal conductivity exceeding 50 W/m·K, which is three times that of alumina and four times that of silica. Moreover, conventional aluminum nitride has a thermal conductivity of about 36 W/m·K, but when reduced to the nano-scale, its thermal conductivity can soar to an impressive 320 W/m·K.

2. High Orientation of Thermal Fillers

The orientation of the thermal network chain formed between thermal filler particles greatly influences the material’s thermal conductivity. The key to enhancing the thermal conductivity of thermal conductive silicone is maximizing the alignment of these network chains with the direction of heat flow. High orientation of thermal fillers is thus a critical method for improving thermal conductivity. For example, ordinary silicon nitride has low thermal conductivity due to its random orientation in the sintered structure. However, adding seed particles with a diameter of 1 micron and a length of 3-4 microns to silicon nitride powder can induce high orientation, forming fibrous high-conductivity silicon nitride. This structured silicon nitride exhibits anisotropic thermal conductivity, with measured thermal conductivity three times higher than ordinary silicon nitride, reaching an impressive 120 W/m·K.

3.Surface Modification of Thermal Fillers

The thermal conductivity of thermal conductive silicone is closely related to the wettability of the filler particles’ surface. This is because the bonding degree between the filler and the matrix, the thermal barrier at the filler-matrix interface, and the filler’s dispersibility and loading amount are all influenced by the surface wettability of the fillers, which directly impacts the thermal conductivity. Surface treatment of thermal fillers significantly enhances their loading amount, thermal conductivity, and compatibility with silicone, especially for nano-scale fillers. For instance, treating alumina with substances like γ-aminopropyltriethoxysilane, hexamethyldisilazane, and dimethyldimethoxysilane before filling it into silicone can improve the thermal conductivity and reduce the viscosity of the resulting thermal conductive silicone.

4.Mixed Filler Loading

Many researchers have found that mixing different types, sizes, and shapes of thermal fillers in appropriate proportions is an effective way to enhance the thermal conductivity of thermal conductive silicone. For example, using a mixture of alumina particles with sizes of 0.5 microns, 3 microns, and 20 microns in a ratio of 10:30:15 significantly improves the thermal conductivity compared to using single-sized alumina particles. Additionally, combining spherical alumina particles of different volumes and sizes with non-spherical alumina can increase filler packing density while maintaining matrix flowability, greatly enhancing thermal conductivity while keeping hardness low.

5.Optimizing Processing Techniques

Once the thermal filler is determined, the processing technique becomes a key factor in determining the thermal conductivity of thermal conductive silicone. For example, silicone prepared by solution mixing has superior thermal conductivity compared to silicone prepared by direct compounding because different processing techniques result in different particle-matrix composite structures. Furthermore, the order of adding fillers and various additives during processing can significantly impact thermal conductivity. Studies have shown that mixing silicone with small-sized alumina first, followed by larger-sized alumina, yields better thermal conductivity than mixing all alumina particles simultaneously.

By employing these five methods, the thermal conductivity of thermal conductive silicone can be significantly enhanced in production and research. These methods work synergistically to determine the overall thermal performance, resulting in a stable, uniform, and well-formulated product with superior thermal properties, ready for application across various industries and fields.