Fabrication And Propertiesstudy Of Temperature/Phresponsive Cholesteric Liquid Crystalcompositesbased On Hydrogen-Bonded Interaction

In this paper, four novel chiral hydrogen-bonded (H-bonded)complexes ISIN-AHBA, IMIN-AHBA, SPIN-AHBA and RPIN-AHBA were fabricated, which were derived from 4-(6-acryloyloxyhexyloxy) benzoic acid (AHBA) and four chiral pyridine derivatives. Their structures were characterized by fourier transform infrared (FT-IR) and the proton nuclear magnetic resonance spectrum. The thermal stability, phase behaviors and helical twisted power (HTP) characteristics of them were investigated by the measurement of variable-temperature FT-IR spectrum, the differential scanning calorimetry, the polarizing optical microscopy analysis and Cano wedge method. The result demonstrates that the HTP values of all the chiral H-bonded complexes decrease with an increase of the temperature. Based on the above results, two stimuli responsive materials able to respond to temperature and pH solutions were fabricated, including the H-bondedpolymer stabilized cholesteric liquid crystals (PSCLC)film and H-bonded cholesteric polymer film, both of which contains ISIN-AHBA as functional chiral dopant. The H-bondedPSCLCfilm was obtained by polymerizinga mixture of a PSCLC composite and ISIN-AHBA, and the film exhibits good temperature responsibitlity both before and after irradiation. Especially, SRB of the H-bonded PSCLC after irradiation presents a red shift of 200nm in visible region with the temperature increasing from 30to 75℃, as well as the film can be thermally switched to reflect green and red color from the initial state reflecting a blue/green color. The H-bonded cholesteric polymer film was obtained by UV-photopolymerizing a mixture of liquid crystal monomers and ISIN-AHBA, which is capable of responding to temperature and pH solutions by changing the color and shifting the selective reflection band (SRB). The H-bonded cholesteric polymer film exhibits different responsibilitywhen treated in diffrent solutions with different pH values for the same time. The SRB of the H-bonded cholesteric polymer film in solution with pH>7shows an obvious red shifts, while that with pH=7 and pH<7changes little. The temperature responsibilitiesof both two stimuli materials are due to the thermal sensitivity of H-bonds. The H-bonded interaction decreasing with temperature increasing contributes to the decreasing HTP of the films, as a result of red shift of SRB.The pH sensitivity of H-bonded cholesteric polymer film in solutionswith pH>7could be explained by the structral changes and the breakage of hydrogen bonds due to the reaction between -COOH groups in the H-bonded cholesteric polymer film and -OH- ions in the alkaline solutions.