Biphenyl-Based High Thermal Conductivity Films with Intrinsic Self-Healing Properties

One kind of liquid crystal monomer (LM) based on a biphenyl mesomorphic unit was synthesized from 4,4′-biphenyldicarboxaldehyde and 4-amino-3-methylphenol. Then two films (LM/TPTMP and LM/PETMP) were prepared by reacting the two thiols (TPTMP and PETMP) with the liquid crystal monomer (LM), respectively. These two films simultaneously exhibit intrinsically high thermal conductivity and intrinsic self-healing properties. Due to the presence of biphenyl liquid crystal units in LM and its highly symmetrical structure, a distinct nematic liquid crystal phase can be observed through a polarized optical microscope when heated to the liquid crystal phase transition temperature. The crystallite size of LM was calculated as 37 nm by an X-ray diffractometer (XRD). The films exhibit outstanding thermal conductivity, with LM/TPTMP achieving a thermal conductivity in the horizontal direction (λ_∥) of 0.700 W/(m·K), which is significantly higher than that of epoxy resin-based intrinsic thermal conductivity materials in the range of 0.2–0.4 W/(m·K). The introduction of thiol flexible segments endowed the materials with good mechanical strength, with LM/PETMP demonstrating a tensile strength of 4.74 MPa and an elongation at break of 42.57%. Furthermore, the incorporation of dynamic imine bonds imparted excellent self-healing properties to the films. Specifically, LM/PETMP could retain 73% and 65.2% of its original tensile strength after one and three cycles of self-healing behavior, respectively. This type of high intrinsic thermal conductivity (λ) and excellent intrinsic self-healing performance film is expected to solve the problems of safety and service life of high-precision smart devices.