Fabrication And Applications Of Blue Phase Liquid Crystalline Photonic Polymer Films

Blue phase liquid crystal(BPLC),that self-organize into three-dimensional(3D)periodic cubic lattices by nematic liquid crystal molecules and chiral liquid crystal molecules,can be regarded as 3D photonic crystals.Soft matter features of BPs render them intrinsically responsive to external stimuli,such as temperature,electricity,and light.Therefore,BPs show great potential in the field of stimuli-responsive materials.However,BPs are limited by some shortcomings:most of BPs are kept in the liquid crystal cell,can not be freestanding;BPs usually self-assemble into multi-domain structures,whose reflective intensity is low.For overcoming the drawbacks of BP materials,this thesis aims to develop a BP polymer film with stable structure and high reflectivity.Based on the BP polymer films,photonic shape memory polymers and inkjet printing polymer coatings are realized.The main research contents are listed as follows(1)A facile method is put forward to fabricate freestanding,large-domain BPLC polymer films based on self-assembly technology.This fabrication method enables the formation of large-scale BP domains,which exhibit sharp photonic bandgaps with high reflectivity.In addition,the large-domain BP structures with good optical performances can be preserved after photopolymerization.What is more,the long-range periodic nanostructures of double-twist cylinders can be directly visualized through transmission electron microscopy,providing a powerful tool to investigate BP structures at the nanoscale.Furthermore,dual-wavelength lasing is achieved by doping the large-domain BP films with fluorescent dyes,which is firstly observed in BP materials.(2)A generalized self-assembly approach for fabricating freestanding BP films which can be used as photonic shape memory polymers(SMPs).After being deformed by SM programming process,the films can memorize temporary shape accompanied with a blueshift reflection wavelength,where the degree of color change is corresponded to the magnitude of the mechanical pressures.The deformed BP film can recover to its original shape and structure color by heating of the polymer film to temperatures above the glass transition temperature.This facile,efficient,and low-cost strategy for fabricating freestanding BP materials not only enrich the photonic SMPs family,but also show great potential of these BP materials in a greater range of optical applications,such as battery-free optical sensors,rewritable photonic devices,and tunable lasers.(3)A printable photonic polymer coating has been fabricated from a monodomain liquid crystalline BP network.The BP polymer coating with high reflectivity is covalently linked to the glass substrate,which can be patterned by using a LC-ink to swell the network.The degree of swelling depends on the printed amount of LC-ink which can be controlled through adjusting the voltages of inkjet printer.Arbitrary multi-color patterns covering the visible spectrum from 451 to 618 nm can be printed and erased multiple times,making these BP polymer coatings promising to be rewritable photonic papers and responsive photonic materials.