Exploration of the Nucleation-Growth Effect of Cetyltrimethylammonium Bromide for High β-Poly(Vinylidene Fluoride) Crystallization

Abstract

Poly(vinylidene fluoride) (PVDF, β-phase) exhibits excellent electrical properties because of its all-trans conformation in the crystalline phase, which has attracted much attention in electronic device applications. This paper describes our studies of the cetyltrimethylammonium bromide (CTAB)-induced PVDF crystallization in PVDF thin films via solution crystallization and melt crystallization by compression molding. In the solution crystallization process the relative crystal content of the polar crystals phase of PVDF reached 90% due to the solvent effect and low crystallization temperature. During the melt crystallization process the polar crystal nucleation effect of CTAB (powders) was pronounced. The strong "ion-dipole" interaction between the positive charges on the surface of CTAB and the -CF2 of PVDF promoted the formation of polar crystals. The incorporation of 1 wt% CTAB in PVDF led to the nucleation of polar crystallites up to 97.6%. Additionally, the tensile strength and elongation at break reached 39.8 MPa and 172.5%. The crystallinity of the PVDF increased with an increase in the content of CTAB. The electrostatic interaction between CTAB and the PVDF molecular chains induced and stabilized the all-trans conformation of the PVDF crystals, resulting in PVDF films with high polar phase content, which are expected to be applicable to industrially produced piezoelectric films.