Normal- and Reverse-Mode Thermoresponsive Controllability in Optical Attenuation of Polymer Network Liquid Crystals

A simple nonuniform irradiation method for photopolymerization-induced phase separation (PPIPS) was developed to produce unconventional mesoscale domain structures composed of liquid crystal (LC) and reactive mesogen (RM) phases. The LC/RM phase formations and their molecular orientation ordering through PPIPS were comprehensively investigated as a function of LC/RM molar ratio, curing temperature, and the use of uniform or nonuniform irradiation. Then, two different optical-anisotropic structures that can cause normal- or reverse-mode thermoresponsive light attenuation were formed by nonuniform irradiation at different curing temperatures at the same molar ratios. These two structures consist of mesoscale domains organized with multiaxially orientation-ordered LCs and orientation-disordered RMs for normal-mode thermoresponse and uniaxially orientation-ordered LCs and RMs for reverse-mode thermoresponse. Phase-separation nuclei were generated by nonuniform irradiation at the incipient stage during the PPIPS process under nonuniform irradiation and subsequently coalesced to form mesoscale polymer networks while maintaining their molecular orientation order. This is a promising method to overcome the restraint of structural controllability due to intrinsic material properties and thus to provide unconventional optical and photonic devices, such as thermoresponsive smart windows and thermometric sheets.