Enhanced dielectric properties and thermal conductivity of sandwich-structured PVDF composites by spin coating

Polymeric dielectric composites with high thermal conductivity have played an important role in modern society because of their significant applications in the fields of sensing and energy storage. The combination of the use of various dimensions fillers and surface modification to prepare high thermal conductivity and high dielectric permittivity composite materials has attracted great attention. Poly(vinylidene fluoride) (PVDF), in general, has acted as basis materials to prepare dielectric materials due to its high permittivity and favorable flexibility. In this study, the modified BN (m-BN) was prepared by coating with polydopamine (PDA) to improve the compatibility and reduce the interfacial thermal resistance. Meanwhile, MWCNT grafted with PAAc named m-MWCNT was also used. The novel sandwich-structured PVDF nanocomposites with m-BN fillers in the outer PVDF layers and m-MWCNT in the middle PVDF layer were prepared by spin-coating. Results shown that the optimized sandwiched structure of PVDF composite with 20 wt% m-BN fillers in the outer layers and 2% m-MWCNT in the middle layer displays a high thermal conductivity of 3.5 W m
^-1
K
^-1
(three times of that of single layer). The dielectric constant of sandwiched structure PVDF composite is 17, which is about 190% times higher than that of PVDF/m-BN (single layer). These enhancements in dielectric properties may be attributed to m-MWCNT and Maxwell-Wagner interfacial polarization which was generated from the multi-layers structure. The mechanism is further explored.