The Study On Photo-responsive Behavior Of Hydorgen-bonded Polymer Complex Containing Azobenzene Functional Group

Light-responsive material refers to a type of material that changes its color,physical properties,and shape when materials are illuminated by a specific wavelength.In recent years,photo-responsive materials have become one of the popular areas due to their high efficiency and simplicity.Hydrogen bonds are very common in organisms.For materials,introducing hydrogen bonds into the material can enhance the compatibility and stability of the material,and it can increase the sensitivity to external environmental stimuli,such as heat,humidity and p H etc.Poly(acrylic acid)(PAA)is a polymer with carboxyl side chains,which is a common hydrogen bond donor.Poly(ethylene oxide)(PEO)is a water-soluble crystalline polymer with oxygen atoms in the main chain,which can act as hydrogen bond acceptors to form a complex with PAA.Azobenzene and its derivatives because of the diversity of the substituent on the benzene ring and reversible reaction height is often applied in the field of optical response materials,and hydrogen bonds generally to the external environment such as temperature,humidity and solvent stimulus to respond quickly,so the azobenzene and its derivatives can be introduced into hydrogen bonding compounds,to achieve more functional material.This topic is the research point,and the specific research content is as follows:1.Disperse red 1(DR1)and 4-aminoazobenzene(Aazo),are linked to poly(acrylic acid)(PAA)side chainsThrough esterification reaction and amidation reaction,DR1 and Aazo are linked to the side chain of PAA separately(PAA-DR1 and PAA-Aazo).The graft degree was determined by ~1H NMR spectroscopy.The FT-IR spectra shows the stretching vibration peak of C=O moves towards the high-wave number region due to the carboxyl group becoming an ester group or an amido group.And UV-Vis spectra also shows that the functional group on the azobenzene has changed after DR1and Aazo were linked to PAA,which cause the blue shift of the absorption peak.The TGA and DSC test results show that comparing the azobenzene polymer before and after grafting with PAA,there is almost no change in stability and glass transition temperature,which indicates that the proportion of azobenzene polymer is relatively small.The group grafting on the PAA side chain does not significantly cause the thermal stability of the polymer.2.Study on the preparation and properties of PAA-DR1/PEO,PAA-Aazo/PEO and PAA/PEO complex filmThe preparation of hydrogen-bonded composites by layer-by-layer self-assembly technology is a basic method for studying the assembly structure of materials and lays the foundation for subsequent research.Therefore,PAA-DR1 and PAA-Aazo are used as hydrogen bond donors to prepare hydrogen bond composite films PAA-DR1/PEO and PAA-Aazo/PEO through layer-by-layer self-assembly with PEO.The FT-IR test explored the changes in functional groups between C=O in PAA and C-O-C in PEO caused by hydrogen bonds,effectively confirming the formation of hydrogen bonds in the film.The cis-trans isomerization of the azophenyl group of PAA-DR1 and PAA-Aazo were detected by UV-Vis spectra.It showed that the azophenyl group in PAA-DR1 is push-pull azobenzene and it has a very fast cis-trans isomerization speed,so it is impossible to capture the rich cis-azobenzene structure through UV spectra;while the cis-to-trans isomerization time of PAA-Aazo is relatively long,which can obtain rich trans or rich cis state.The isomerization stability test of PAA-Aazo also showed the excellent light stability and fatigue resistance of the azobenzene polymer.The cis-to-trans conversion can be effectively cycled more than ten times.Quartz crystal microbalance(QCM)is used to monitor the film thickness changes of the assembly in real time,and the film thickness simulation software finds that the film thickness of cis-PAA-Aazo/PEO increases exponentially compared to trans-PAA-Aazo/PEO,which shows that the state of azobenzene in the polymer will affect the assembly of the hydrogen-bonded complex film.The phenomenon indicates that it may affect the mechanical properties or other aspects of materials.3.Study on the preparation and properties of PAA-DR1/PEO,PAA-Aazo/PEO and PAA/PEO fibersChoosing a system with a molar ratio of[AA]:[EO]of 1:1,a hydrogen-bonded complex fiber was prepared by a method similar to wet spinning.The FT-IR spectra characterizes the formation of hydrogen bonds between PAA and PEO in the fiber.The DSC test shows that the glass transition temperature(T_g)of the fiber is between PAA and PEO,and the introduction of azobenzene in the fiber increases the steric hindrance of the molecular chain movement,making T_g increases,and the formation of hydrogen bonds also completely inhibits the crystallization of PEO.The mechanical performance test of a single fiber shows that the introduction of azobenzene will lead to a significant increase in the stress of the fiber,but the strain is reduced.After UV irradiation,PAA-Aazo/PEO fiber shows obvious mechanical properties change(initial modulus and yielding strength both increase tremendously)while PAA-DR1/PEO does not.When drawn and dried in vacuum,PAA-DR1/PEO and PAA-Aazo/PEO fiber both show quick contraction under UV irradiation,showing potential for photo-actuation.