Two-Stage Evolution of Gamma-Phase Spherulites of Poly (Vinylidene Fluoride) Induced by Alkylammonium Salt.

We investigated the evolution of the γ-phase spherulites of poly(vinylidene fluoride) (PVDF) added to 1 wt% of tetrabutylammonium hydrogen sulfate during the isothermal crystallization at 165 °C through polarized optical microscopy and light scattering measurements. Optically isotropic domains grew, and then optical anisotropy started to increase in the domain to yield spherulite. Double peaks were seen in the time variation of the Vv light scattering intensity caused by the density fluctuation and optical anisotropy, and the Hv light scattering intensity caused by the optical anisotropy started to increase during the second increase in the Vv light scattering intensity. These results suggest the two-stage evolution of the γ-phase spherulites, i.e., the disordered domain grows in the first stage and ordering in the spherulite increases due to the increase in the fraction of the lamellar stacks in the spherulite without a change in the spherulite size in the second stage. Owing to the characteristic crystallization behavior, the birefringence in the γ-phase spherulites of the PVDF/TBAHS was much smaller than that in the α-phase spherulites of the neat PVDF.

Dynamic photoswitching of helical inversion in liquid crystals containing photoresponsive axially chiral dopants.

Chirality switching is intriguing for the dynamic control of the electronic and optical properties in nanoscale materials. The ability to photochemically switch the chirality in liquid crystals (LCs) is especially attractive given their potential applications in electro-optic displays, optical data storage, and the asymmetric synthesis of organic molecules and polymers. Here, we present a dynamic photoswitching of the helical inversion in chiral nematic LCs (N*-LCs) that contain photoresponsive axially chiral dopants. Novel photoresponsive chiral dithienylethene derivatives bearing two axially chiral binaphthyl moieties are synthesized. The dihedral angle of the binaphthyl rings changes via the photoisomerization between the open and closed forms of the dithienylethene moiety. The N*-LCs induced by the dithienylethene derivatives that are used as chiral dopants exhibit reversible photoswitching behaviors, including a helical inversion in the N*-LC and a phase transition between the N*-LC and the nematic LC. The present compounds are the first chiral dopants that induce a helical inversion in N*-LC via the photoisomerization between open and closed forms of the dithienylethene moiety.