Controlling Orientation Of Liquid Crystal Enabled By Polymer Brush Contained Azobenzene And Its Application In Responsive Smart Window

The preferred orientation of liquid crystal molecules along a specific direction plays a crucial role in preparing high-performance devices,such as,liquid crystal display,modulator,sensor,and smart window and so on.Therefore,it is of great significance to adopt appropriate methods to regulate the orientation of liquid crystal.In this thesis,we use azo polymer brush to realize the vertical orientation and photoalignment of liquid crystals,and further apply this method to the preparation of smart windows.1.We have prepared a kind of gold nanoparticle modified by side chain liquid crystalline polymer(SCLCP)with azobenzene(Au@TE-PAzo NPs),which has good solubility and film-forming ability.The influence of the Au@TE-PAzo NPs film thickness on the orientation effect of liquid crystal is investigated and verified by spin-coating the gold nanoparticles film.If the thickness of the gold nanoparticles film is too thin to cover the surface,orientation cannot occur.The results show that the synergistic effect of gold core and the SCLCP ligands induces the vertical orientation and light-controlled arrangement of liquid crystal molecules and the mechanism is similar to polymer brush.Furthermore,the gold nanoparticle film is used to prepare a smart window device with transparent and opaque transformation in response to UV light.The experimental results show that the UV light response of the smart window is derived from the photothermal effect of Au@TE-PAzo NPs.2.The photothermal effect of Au@TE-PAzo NPs may root in gold core or Azo polymer ligands,in order to eliminate the impact of the photothermal effect of gold core and strengthen the interaction between the polymer brush and the substrate through covalent bonds.A side chain copolymer(MAzo-co-GMA)has been synthesized from Azo monomer(MAzo)and glycidyl methacrylate(GMA)by atom transfer radical polymerization(ATRP).Due to the presence of GMA,MAzo-coGMA copolymer can form stable polymer brush on the surface of substrate after thermo-crosslinking.The obtained polymer brush within a certain concentration range can induce the vertical orientation of the chiral liquid crystal mixture.Moreover,due to the presence of azobenzene side groups,the polymer brush exhibits photothermal effect under UV light irradiation.Based on this,a responsive polymer stabilized liquid crystal(PSLC)smart window was prepared by using this polymer brush.The transparency of the smart window can be controlled by the concentration of the polymer brush.The transparent state of the smart window is induced by polymer brush to arrange PSLC(SmA* phase)vertically,and its opaque state(focal conic state)can be achieved by UV light irradiation or heating.The response time of PSLC smart window can be adjusted by adjusting the concentration of MAzo-co-GMA copolymer brush and UV light intensity.This kind of PSLC smart window with thermal response and UV response has good reversibility and stability,which shows enormous promise application in energy-saving smart window.