Dielectric and flexoelectric oscillations in PDLC studied by flexoelectric spectroscopy and laser light diffraction

Nematic droplets of variable size of E7 were dispersed in a photopolymer NOA65 matrix by the method of UV photopolymerization-induced phase separation. Dielectric and flexoelectric oscillation of the director orientation in the droplets were excited by an ac driving voltage in the range 1 Hz to 3 kHz. Both thelinear and quadratic electro-optical response of the PDLC films were studied by the flexoelectric spectroscopy method and by laser light diffraction. The temperature and voltage dependence of the 1(st) and 2(nd) harmonic electro-optic spectra (amplitude and phase of the transmitted light vs frequency) were obtained, and strikingly deep minima in all spectra were found. These minima were interpreted as resulted from a spatial filtering (i.e. selective diffraction) of the time-modulated components of the transmitted light.