UV-modulated Behavior On Self-supporting Liquid-crystalline Physical Gel And Its Electro-optical Properties

Liquid crystals have been widely used in the fields of sensor, transportation, electro-optical displays and catalyst, etc. due to their anisotropic molecular alignment and fluidity. The development of flexible liquid crystal devices with large area and fast stimuli response is currently one of the main research direction of liquid crystal materials. Introducing networks into the liquid crystal systems could obtain a class of stimuli-response soft materials---liquid crystal physical gel. The phase-separated structures between liquid crystals and networks are expected to enhance the electro-optical properties of liquid crystal or to induce new electro-optical properties. In addition, the mechanical properties of liquid crystal materials could be promoted once they are gelled.A kind of novel azobenzene-containing gelators(AG) that can gel the nematic liquid crystal P0616 A was designed and synthesized. The effect of content of AG on phase transition temperature, microstructure, mechanical strength and electro-optical properties of the liquid-crystalline physical gels(P0616A/AG) were systematically investigated. The results showed that the sol-gel transition temperature and the mechanical strength of the gels increased with increasing of the content of AG. The storage modulus G' of P0616A/AG was as high as 104 to 105 Pa with the gelator content above 4 wt%, showing good self-supporting ability. Moreover, the threshold voltage(Vth) remained almost the same while the saturation voltage(Vsat) increased when the content of AG increased. Based on the photoinduced trans-cis isomerization of the azobenzene group in gelator, the effect of UV and visible light irradiation on the electro-optical response speed and the mechanical strength of the liquid crystal physical gels were investigated in detail. It turned out that the switch-off time(?off) decreased sharply after UV irradiation and increased to close the initial value after visible light irradiation. This is because UV irradiation induced phase separation and the area of liquid crystal with low viscosity increased; therefore, the liquid crystal showed faster response to electric field after UV irradiation. Variable temperature FT-IR spectra indicated that one of the main driving force for the self-assembly of AG in nematic liquid crysal P0616 A was hydrogen bond from –CONH-.