Rheological Behavior and Thermal Conductivities of Emulsion-Based Thermal Pastes

The role of thermal interface materials (TIMs) has become substantial due to their critical applications in electronic devices for effective heat dissipation. Dimethyl silicone oil-based thermal pastes are widely used as TIMs because they can provide an intimate bonding between the heat sink and the electronic chip; however, the thermal conductivities of typical silicone oil-based thermal pastes are low. In this study, we prepared thermally conductive emulsion-based thermal pastes with two kinds of boron nitride (BN) fillers and investigated their rheological behavior and thermal conductivities. The emulsion was composed of dimethyl silicone oil, n-butanol, and sorbitan monooleate (Span 80) as an emulsifier. The fillers were boron nitride fibers (BNFs) and boron nitride nanosheets (BNNSs). The viscosity, storage modulus, and loss modulus of the emulsion-based pastes were smaller than those of the corresponding silicone oil-based ones. The thermal conductivities of the emulsion based pastes were larger than those of the silicone oil-based ones because of their lower viscosity and higher baseline thermal conductivity. The pastes with BNNSs had larger thermal conductivities in comparison with the corresponding ones with BNFs. To further enhance the thermal conductivity, BNNSs were coated with two silane coupling agents, 3-aminopropyl-triethoxy silane (KH550) and 3-(Trimethoxysilyl)propyl methacrylate (KH570), and then introduced into the emulsion. The maximum thermal conductivity was 1.04 W m−1 K−1 for the emulsion-based paste with KH550-coated BNNSs at a filler loading of 39 vol.%, which was a ∼ 7-fold increase in comparison with that of neat silicone oil (0.13 W m−1 K−1).