Liquid Crystal-Engineered Polydimethylsiloxane: Enhancing Intrinsic Thermal Conductivity through High Grafting Density of Mesogens

Abstract

The increasing power and integration of electronic devices have intensified serious heat accumulation, driving the demand for higher intrinsic thermal conductivity in thermal interface materials, such as polydimethylsiloxane (PDMS). Grafting mesogens onto PDMS can enhance its intrinsic thermal conductivity. However, the high stability of the PDMS chain limits the grafting density of mesogens, restricting the improvement in thermal conductivity. This work proposes a new strategy to efficiently introduce mesogens onto PDMS through ring-opening copolymerization of liquid crystal cyclosiloxane and octamethylcyclotetrasiloxane, enhancing the grafting density. The relationship between the grafting density and intrinsic thermal conductivity of liquid crystal polydimethylsiloxane (LC-PDMS) is investigated by nonequilibrium molecular dynamics (NEMD) simulations. Based on the simulation results, LC-PDMS with enhanced intrinsic thermal conductivity is synthesized. When the grafting density of mesogens reaches 77.4%, its intrinsic thermal conductivity coefficient (λ) increases to 0.56 W/(m·K), showing a 180.0% improvement over ordinary PDMS (0.20 W/(m·K)). The LC-PDMS also exhibits the low dielectric constant (ε, 2.69), low dielectric loss tangent (tanδ, 0.0027), high insulation performance (volume resistivity, 3.51×1013 Ω·cm), excellent thermal stability (heat resistance index, 217.8℃) and excellent hydrophobicity (water contact angle, 137.4°), fulfilling the comprehensive requirements of advanced thermal interface materials.