| Liquid crystal-polymer composite materials possess both the various external-field responsive characteristics of liquid crystals and the excellent mechanical or machinable properties of polymers,exhibiting great application prospects in fields like large-size,flexible or ultra-thin displays,smart windows and intelligent sensors.At present,there are two mainly liquid crystal-polymer composite systems that have been widely studied,that is,polymer dispersed liquid crystal(PDLC)and polymer stabilized liquid crystal(PSLC).In a PDLC system,liquid crystal molecules are dispersed in the form of micro-droplets in the polymer matrix.The switching between light scattering state and light transmission state can be realized by applying electric field.Although the advantages in to the industrial preparation with large-area and flexible processing,the application of PDLC materials are somewhat limited due to the high driving voltage and inevitable energy consumption.In a PSBP system,the polymer network is used to stabilize the orientation of liquid crystal molecules.The optical states can be switched quickly under various external fields.However,the concentration of polymer network in the material system is usually low,resulting in poor mechanical properties and difficulties for flexible processing.Therefore,developing a new liquid crystal-polymer composite material that with proper electro-optic properties as well as high large-size machinability is of great scientific significance and commercial value.In this paper,a novel liquid crystal-polymer composite system with the micro polymer structures combined that of both PDLC and PSLC was fabricated by integrating the preparation methods of PDLC and PSLC.It was called a coexistent system of polymer-dispersed and polymer-stabilized liquid crystals(PD&SLC).Based on PD&SLC,electronic controllable dimming film,bistable film and temperature controllable dimming film were prepared,and their external field-regulated optical properties were studied.The main research content are listed as follows:(1)Research on the preparation of PD&SLC material system.The preparation method of PD&SLC material system was studied.By blending liquid crystalline polymerizable monomer and non-liquid crystalline polymerizable monomer with different kinds of liquid crystals,isotropic mixed material samples were obtained.The samples were photopolymerized with applying electric field.It is suggested that the polymerization rate of liquid crystalline polymerizable monomers is lower than the phase separation rate between liquid crystal molecules and non-liquid crystalline polymerizable monomers.Thus continuous porous polymer network structures are firstly formed during the polymerization process,and then oriented polymer fibrils in the liquid crystal droplets are formed by the liquid crystalline polymerizable monomers.Consequently,new polymer morphology with both PDLC and PSLC micro-network structure can be fabricated in the PD&SLC liquid crystal-polymer composites.(2)Research on the preparation and performance of PD&SLC based electronic controllable dimming film.The effects of chiral compound concentration,polymerization voltage and UV light intensity on the polymer network structure and electro-optic properties were investigated.The results show that the driving voltage of the films prepared by PD&SLC could be 50%lower than that of the films prepared by PDLC under the identical experimental conditions.The network microstructure and electro-optical properties can be improved by optimizing the experimental conditions.In this study,the electro-optic properties of the films were excellent when the chiral compound content was 6.0 wt%,the polymerization voltage was 80.0 V,and the light intensity was 2.0 mW/cm2.(3)Research on the preparation and properties of PD&SLC based bistable films.The effects of ionic liquid concentration,polymerization voltage and light intensity on the electro-optic properties of PD&SLC bistable films were investigated.The results show that the PD&SLC system could be used for the fabrication of smectic A liquid crystal based bistable films.The driving voltage can be effectively reduced and the transmission of field-on or field off state can be improved by optimizing the experimental conditions.In this study,the electro-optic properties of the bistable films were excellent when the ionic liquid concentration was 0.2 wt%,the applied voltage was 80.0 V and the illumination intensity was 0.1 mW/cm2.(4)Research on the preparation and properties of the PD&SLC based temperature controllable films made by materials.The effects of polymerization voltage and light intensity on the optical properties were studied.The results show that the PD&SLC based temperature controllable film has both good optical and mechanical properties when compared with PSLC system.In this study,the temperature controllable thin films exhibited excellent optical properties when the polymerization voltage wss 160.0 V and the illumination intensity was 0.1 mW/cm2.Remarkably,the flexible fabrication of the temperature-controlled thin film with an area of 2 m2 is realized by using the roll-to-roll technics. |
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