High intrinsic thermal conductive polymer films by engineered interchain hydrogen bond interactions

A series of polyvinyl alcohol (PVA) composite films containing different hydrogen bond acceptors 4,4′-dihydroxydiphenyl (BP), 1,1′-biphenyl-4,4′-diyl dihexanoate (DHB) and benzene-1,3,5-triyl tribenzoate (TBB) were prepared by casting method. Due to the existence of strong intermolecular interaction, the highest in-plane thermal conductivity of the above films is 1.298 Wm⁻¹ K⁻¹, which is about 65% higher than pure PVA films. Fourier Transform infrared spectroscopy (FT-IR) and wide-angle X-ray diffraction (WXAD) demonstrated that the TBB acts as a thermal bridge to enhance the internal interaction force and make the internal structure more regular. Strong molecular contact forces were demonstrated by mechanical tensile testing. The thermal expansion rate of the system was explored through molecular dynamics. Thermal expansion experiments proved that hydrogen bond can effectively reduce the free volume. Molecular dynamics simulations were also performed in this work. The number and density of hydrogen bonds inside different polymers were calculated, and the phonon thermal transport was quantitatively analyzed. The thermal bridge and intermolecular contact force were discovered to effectively restrict the molecular chain's activity and reduce its free volume. The results of the experiments and molecular dynamics reveal that strong intermolecular interactions and thermal bridges can significantly improve polymer intrinsic thermal conductivity.