Multiple Bragg Diffractions with Different Wavelengths and Polarizations Composed of Liquid Crystal/Polymer Periodic Phases

Abstract

We first fabricated holographic polymer-dispersed liquid crystals (HPDLCs) that produce multiple Bragg diffractions with different polarization states for every angle of incidence, through a photopolymerization-induced phase separation by one-time interferential exposure. The polarizations of the Bragg diffractions were well-controlled at individual wavelengths in the fabrication process by the compositional ratio of LCs to monomers. The raw mixtures of extremely low-functionality monomers having very different viscosities were used to reduce the domain size in phase separation and subsequently to form elaborate periodic structures of the LC and polymer phases. A cross-linker (1-vinyl-2-pyrrolidione) and a prepolymer with urethane groups were employed to strengthen the polymer network. Note that the diffractions of our HPDLCs are regarded as not purely but mostly Bragg type, according to the evaluation with the established criteria. The devices, which are monolithic but versatile in diffractive behaviors, have advantages of simple manufacturing and handling.

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

“…The textures and formation processes of the LC/polymer phase separation, which are important in soft matter physics to explore novel optical and photonic structures, have been extensively measured and calculated in the points of view of domain morphology, diffusion kinetics, the time-dependent Ginzburg-Landau model and Flory-Huggins theory. − However, elaborate meso (submicron- to micron-)-scale textures organized by domain shape and molecular orientation are still challenging to design and fabricate for optical and photonic applications because PPIPS processes are strongly affected by the physicochemical properties of the starting materials. Domain shape, or specifically domain size, which is a dominant factor for optical clarity of PNLCs, is mainly influenced by the curing temperature, LC/monomer molar ratio, and monomer functional number. ,− The larger (smaller) domain size can be achieved by photoexposure at higher (lower) curing temperatures from the raw mixtures of LCs and monomers with larger (smaller) functional numbers. , On the other hand, the orientation orders of LCs and reactive mesogens (RMs) are larger (smaller) at lower (higher) temperatures using monomers with smaller (larger) functional numbers. According to these intrinsic properties, large domains with a high orientation order are logically impossible for LC/RM systems to have because a high orientation order can be achieved by a low curing temperature for samples consisting of monomers with small functional monomers, whereas large domains can be achieved by a high curing temperature for samples consisting of monomers with large functional monomers.…”