Research On Interpenetrating Polymer Network Optical Sensing Materials Based On Cholesteric Liquid Crystal

Cholesteric liquid crystal(CLC)is a material with an ordered helical structure that can selectively reflect incident light of a specific wavelength,forming a bright structural color when the wavelength of the reflected light is in the visible light region.Structural colors are insensitive to photobleaching,and the color response can be immediately observed by the naked eye.These advantages make cholesteric liquid crystals have good application prospects in the field of visual sensing and detection.Smart hydrogels can respond to small external stimuli and are easy to observe because they can undergo large volume and morphological changes.And smart hydrogels are environmentally friendly materials.Such stimuli-responsive hydrogel materials with certain functional properties have received extensive attention,and smart hydrogels that can respond to environmental stimuli such as temperature,ionic strength,p H,and certain biomolecules have been developed.Combining smart hydrogels with cholesteric liquid crystal polymer networks enables the preparation of novel interpenetrating polymers network(IPN).This interpenetrating polymer network has certain mechanical properties,so it can maintain a relatively stable structure,which increases its application range to a certain extent.In addition,due to its special optical properties,this interpenetrating polymer network can convert stimulus responses into optical signals,which can be measured or monitored by simple and convenient detection means.This paper combines the unique optical properties of cholesteric liquid crystals with the responsiveness of hydrogels to the environment.Through the intelligent response of the hydrogel to external stimuli,the network space in the cholesteric liquid crystal polymer changes,so the internal helical structure of the cholesteric liquid crystal changes.In this paper,two novel cholesteric liquid crystal-hydrogel interpenetrating polymer network optical sensing materials were prepared,and could be used for temperature response,information encryption and trace silver ion detection respectively.The specific research contents are as follows:In Chapter 2:CLC-PNIPAM interpenetrating polymer network was prepared by introducing poly(N-isopropylacrylamide)(PNIPAM)hydrogel into CLC polymer network using C6M,CB15 and E7 as monomers of liquid crystal mixture.The polymer film produces temperature-dependent optical changes in the range of 25°C to38°C.By adjusting the copolymerization ratio of N-isopropylacrylamide and acrylic acid,the IPN film responds at 26℃-47℃.The polymer film has good stability over 6temperature change cycles.In addition,the interpenetrating polymer network film was patterned by a step-by-step cross-linking method,and a polymer film with information encryption function was developed:In the non-responsive state,the interpenetrating polymer network film presented a transparent state,hiding information;In response to temperature or ethanol solution,the structural colors of the information area and the background area are inconsistent,so as to achieve the effect of information decryption.The information encryption and decryption process of the polymer film has good reversibility.In Chapter 3:CLC polymer networks were prepared using C6M,6OBA,undecylenic acid,E7,CB15.The DNA strand with a specific structure was mixed with polyacrylamide(PAM)prepolymer solution and penetrated into the CLC polymer network,and the CLC-DNA interpenetrating polymer network film was prepared by UV cross-linking.When the DNA-PAM hydrogel reacts with an aqueous solution or an acidic solution containing Ag~+,the DNA strand shrinks,the volume of the hydrogel decreases,and the helical pitch of the CLC polymer decreases.Therefore,the structural color of the CLC-DNA hydrogel interpenetrating polymer network film will be blue-shifted,and the optical signal will be changed.This CLC-DNA interpenetrating polymer network film has good selectivity and reusability,and can be used for the detection of Ag~+in the range of 10μM to 100μM.It maintains stable performance over three cycles.