Preparation and thermal conductivity of dopamine and γ-aminopropyl triethoxysilane co-modified nano-diamond and silicone rubber composites

Abstract

"Elastomer thermal interface materials were mainly prepared by adding thermal conductive particles to silicone rubber(SiR). Nano-diamond (ND) had high thermal conductivity and insulation properties, making it an ideal thermal conductive filler. Nevertheless, ND was prone to agglomeration and difficult to disperse in SiR. In this work, ND was modified with polydopamine (PDA) and γ-aminopropyl triethoxysilane (KH 550) to improve its dispersion in SiR and its interfacial interaction with. Then the interfacial thermal resistance reduced and the thermal conductivity of the composite improved. Fig 1 showed the infrared spectra of ND, ND-KH 550 and ND-PDA-KH 550. The significant absorption peaks of unmodified ND at 3 200-3 600 cm-1 might be vibration absorption peaks of —OH and H—OH. At 1 624 cm-1, there was a bending vibration absorption peak of —OH or H—OH, indicating the presence of some hydroxyl groups on the ND surface or adsorbed water. The absorption peak position of ND-KH 550 was the same as that of ND, which meaned that KH 550 could not effectively modify ND without dopamine. After treatment with dopamine and KH 550, Si—O—Si ben-ding vibration absorption peak appeared at 463 cm-1, Si—O bond symmetric and asymmetric stretching vibration absorption peaks appeared at 763 cm-1 and 1 049 cm-1, Si—C stretching vibration absorption peak appeared at 695 cm-1, Si—H deformation vibration absorption peak appeared at 914 cm-1. The appearance of the new absorption peak indicated that PDA had successfully grafted silane coupling agent KH 550 onto the surface of ND as a “bridge”. ■ Fig 1 FTIR spectra of ND, ND-KH 550 and ND-PDA-KH 550 Fig 2 showed the thermal conductivity of SiR, ND/SiR, ND-KH 550/SiR and ND-PDA-KH 550/SiR at different temperatures. The thermal conductivities of SiR, ND/SiR and ND-KH 550/SiR composites were not sensitive to temperature. As the temperature increased, there were only a slight variation in the thermal conductivity. The thermal conductivity of ND-KH 550/SiR composite prepared by treating ND with only KH 550 was almost the same as that of ND/SiR at any temperature, indica-ting that there were no functional groups on the surface of ND that could react with KH 550. ■ Sample: ○—SiR; ●—ND/SiR; △—ND-KH 550/SiR; ▲—ND-PDA-KH 550/SiR Fig 2 Thermal conductivities of SiR, ND/SiR, ND-KH 550/SiR and ND-PDA-KH 550/SiR at different temperatures However, the thermal conductivity of ND-PDA-KH 550/SiR composite prepared by modifying ND with PDA and KH 550, and then adding it to silicone rubber, increased significantly with increasing temperature. The thermal conductivity of ND-PDA-KH 550/SiR was 0.340 W/(m·K) at 25 ℃ and 0.586 W/(m·K) at 100 ℃, which increased by 72.4%. Modifying ND with dopamine and KH 550 can improve the dispersion of ND in silicone rubber and the compatibility between ND and silicone rubber, reducing the interface thermal resistance and phonon scattering. The increase of temperature accelerated the movement of phonons and improved the efficiency of heat transfer, which showed that the thermal conductivity of the composite increased with the increase of temperature. At 25 ℃, 50 ℃, 75 ℃ and 100 ℃, the thermal conductivity of ND-PDA-KH 550/SiR composites with 6% ND increased by 94.3%, 118.7%, 161.6% and 211.7% respectively, compared with that of pure SiR."

Keywords

• silicone rubber， nano diamond，polydopamine， aminosilane， surface modification， thermal conductivity，