Simple-structure thermoresponsive PNLCs for smart windows

Abstract

We have developed reverse- and normal-mode thermoresponsive polymer network liquid crystals (PNLCs) that are applicable to switchable windows and other devices. Our nonuniform photoirradiation is an easy technique to produce meso- (submicron- to micron-) scale phase separation of orientation-ordered liquid crystals (LCs) with (an)isotropicpolymerized reactive mesogens (RMs) and achieve various thermoresponsive light attenuators. The PNLCs were fabricated in a simple self-assembling process through photopolymerization induced phase separation (PPIPS) by nonuniform irradiation. The size of phase-separation domains and the orientation order of LC molecules in the domains are intrinsic factors to produce high transparence at low temperatures and intense light scattering at high temperatures. Their factors are controlled by size of laser speckle patterns projected on the samples during PPIPS in nonuniform irradiations. Optical polarization property of the transmittance spectrum is also controlled by speckle patterns projected on the sample in the nonuniform irradiation. Different microscopic structures of PNLCs were formed depending on the size of speckle patterns but not simply in proportion to the size. The results suggest that the dynamics of domain formation through PPIPS is connected to the competition between intrinsic nature of phase separation and extrinsic influence by nonuniform light intensity in the irradiated area.