Composite Poly(vinylidene fluoride)/Polystyrene Latex Particles for Confined Crystallization in 180 nm Nanospheres via Emulsifier-Free Batch Seeded Emulsion Polymerization

Abstract

Recently, nanoconfined poly(vinylidene fluoride) (PVDF) and its random copolymers have attracted substantial attention in research. In addition to the drastic change in crystallization kinetics, major interest lies in crystal orientation and polymorphism in order to understand whether enhanced piezoelectric and ferroelectric properties can be achieved. For example, PVDF has been two-dimensionally (2D) confined in cylindrical nanopores of anodic aluminum oxide (AAO) with various pore diameters. The crystal c-axis becomes perpendicular to the cylinder axes, which favors dipole switching in the impregnated AAO membrane. However, no polar phases have been obtained from 2D confinement even down to 35 nm pores after melt recrystallization. In this work, we realized three-dimensionally (3D) confined crystallization of PVDF in 180 nm nanospheres by employing a facile emulsifier-free batch seeded emulsion polymerization to prepare PVDF@polystyrene (PS) core−shell particles. Influences of polymerization temperature, PVDF/styrene feed ratio, and polymerization time were systematically investigated to achieve completely wrapping of PS onto PVDF particles and avoid the formation of Janus particles. Exclusive confined PVDF crystallization was observed in these core−shell composite particles. Intriguingly, after melt recrystallization, polar β/γ phases, instead of the kinetically favored α phase, were resulted from 3D confinement in 180 nm nanospheres. We attributed this to the ultrafast crystallization rate during homogeneously nucleated PVDF crystallization. For the first time, we reported that 3D confinement was more effective than 2D confinement in producing polar crystalline phases for PVDF.

Primary and secondary crystallization of fast-cooled poly(vinylidene fluoride) studied by Flash DSC, wide-angle X-ray diffraction and Fourier transform infrared spectroscopy

“…In Fig. (a), PVDF prepared under slow cooling exhibits the characteristic (100), (020) and (110) reflections of α‐phase crystals at 17.7°, 18.5° and 20.0°, corresponding to interplanar spacing of 5.01, 4.80 and 4.44 Å, respectively . In Fig.…”

“…The semicrystalline PVDF forms five polymorphic crystalline phases with various features of conformations: monoclinic phase with alternating trans and gauche (TG + TG − ) conformation as α‐ and δ‐phases, orthorhombic phase with all‐ trans (TTTT) planar zigzag conformation as β‐phase, and hexagonal phase with mixtures of TT and TG conformations as γ‐ and ϵ‐phases. Although the β‐phase holds the thermodynamically most stable zigzag conformation with spontaneous alignment of C − F dipoles perpendicular to the c ‐axis in the crystalline region, PVDF commonly forms α‐phase crystals containing solidified antiparallel dipoles at ambient temperatures, which are bad for its ferroelectric performance. Such a situation can be changed by employing uniaxial stretching, an electric poling field, nucleation substrate, high pressure, nano‐droplets or nano‐clay composites to generate a high content of β‐phase for good ferroelectric performance.…”

Multiscale-structuring of polyvinylidene fluoride for energy harvesting: the impact of molecular-, micro- and macro-structure

“…A) WAXD profiles and (B) FTIR spectra for original latex, unconfined recrystallized (using original latex directly), and confined recrystallized (using PVDF@PS core-shell particles polymerized at 65 C for 10.5 h) PVDF samples. Reduced with permission 107. Copyright 2014 American Chemical Society.…”

Nanoconfinement-Induced β-Phase Formation Inside Poly(vinylidene fluoride)-Based Block Copolymers

“… 8 Recently, Pan et al have embedded PVDF nanoparticles in 180 nm polystyrene (PS) nanospheres followed by melt recrystallization. 9 Interestingly, the ferroelectric β-phase is obtained instead of the kinetically favorable α-phase. This is explained by a change of the crystallization mechanism from heterogeneous nucleation in zero, one, and two dimensions to homogeneous nucleation in three dimensions.…”