Formation Mechanism of β-Phase in PVDF/CNT Composite Prepared by the Sonication Method

Two poly(vinylidene fluoride)(PVDF)/carbon nanotube (CNT) composites are prepared by solution sonication and mechanical mixture approaches. It is found that alpha-phase coexists with beta-phase in the composite prepared by sonicating the PVDF/CNT mixture solution, while no beta-phase can be observed in the composite prepared from the mechanical mixture route. With the help of the density functional theory calculations, it is explained that a large amount of energy is required for transforming transgauche-trans-gauche' (TGTG') into trans-trans (TT) conformations and the TT molecular chain can be bound on the CNT surface tightly. The emergence of beta-phases is independent of zigzag carbon atoms on the CNT surface. The formation mechanism of beta-phase is proposed based on the theoretical calculations and experimental results.