Phase separation photonic crystals

For PIPS, polymerization of the monomer or pre-polymer component in die initial mixture of liquid crystal, monomer, or pre-polymer, and photo-initiator induces fdiase separation. The conversion of monomer to polymer with thermal or photon initiated polymerization destabilizes the homogeneous mixture and induces phase separation. Photon-initiation affords the flexibility of multi-wavelen processing that has resulted in H-PDLCs and other spatially tailored LCPD morphologies (12). The morphology depends primarily on the choice of liquid crystal and monomer/pre-polymer, the weight fraction of liquid crystal in... 

Another important method for photonic crystal fabrication employs colloidal particle self-assembly. A colloidal system consists of two separate phases a dispersed phase and a continuous phase (dispersion medium). The dispersed phase particles are small solid nanoparticles with a typical size of 1-1000 nanometers. Colloidal crystals are three-dimensional periodic lattices assembled from monodispersed spherical colloids. The opals are a natural example of colloidal photonic crystals that diffract light in the visible and near-infrared (IR) spectral regions due to periodic modulation of the refractive index between the ordered monodispersed silica spheres and the surrounding matrix. 

Block copolymers have a number of interesting properties, in particular, when they are made up of incompatible units. Such materials show extremely interesting morphologies, it is possible to obtain phase separation, with each unit forming separate domains. The potential for self-assembly of such units is now attracting considerable interest, particularly in the area of photonic crystals. As the following procedures show, the methods by which... 

Polymer-dispersed liquid crystals were introduced many years ago. There are now several techniques for preparing such composite liquid crystalline materials, including the phase separation and the encapsulation methods.More recently, optical holographic interference methods have been employed successfully in making polymer-dispersed liquid crystal photonic crystals (regular array of materials of different refractive indices). Caputo et al. and Strangi et al. have also demonstrated one-dimensional (ID) polymer/liquid crystal layered structures that exhibit high diffraction efficiency as well as laser emission capabilities. 

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