Giant reduction in thermal conductivity of single-chain polyvinylidene fluoride (PVDF) under external tensile strain

Polyvinylidene fluoride (PVDF) as a non-reactive thermoplastic polymer shows overwhelming prospects for pyroelectric and electrocaloric applications. In this work, first-principles calculations are performed to investigate the strain tunability of thermal transport in β-phase PVDF. Thermal conductivity of single-chain PVDF is found to decrease significantly as the tensile strain increases. Moreover, detailed spectral phonon analysis shows that the dominant phonon branch, which contributes most to the overall thermal conductivity, transits from the longitudinal acoustic (LA) branch to transverse acoustic (TA) branches as the tensile strain increases to 5%. This transition is attributed to the strain-induced flattening of the LA branch. We also find that, upon further stretching of the PVDF chain to 15%, its thermal conductivity decreases monotonically due to increased anharmonic scattering of TA modes.