| Photoresponsive materials refer to compounds that can change their state or structure under the irradiation of light,thus affecting their physical and chemical properties.In recent years,azobenzene compounds of photoresponsive materials have received extensive attention.Two hydrogens in azobenzene compounds are substituted by benzene rings,azobenzene is one of the most studied photo-switching molecules.The thermodynamic stability of azobenzene is rod-like trans isomer and the metastable state is curved cis isomer.Some special azobenzene derivatives are solids whose melting point is higher than room temperature when they are in trans structure,while they are liquids whose melting point is lower than room temperature when they are in cis structure,so they have the property of photo-induced solid-liquid transition However,the lack of research on the effect of azobenzene compound structure of photo-induced reversible solid-liquid transition hinders the design of these novel compounds.In this thesis,the effects of flexible side chains on photo-isomerization and liquefaction behavior of azobenzene compounds were studied.The effects of different azobenzene compounds on photo-controlled adhesion behavior were also analyzed.1、Effect of flexible side chain on photo-isomerization and liquefaction behavior of azobenzene compounds.Firstly,the azobenzene compound 4-dihydroxy-3-methylazobenzene(Mazo)with an asymmetric methyl at the third position of the benzene ring was synthesized.Based on the Mazo monomer,four azobenzene compounds with different length flexible segments at both ends were synthesized.In solution,with the increase of the flexible segment,the movement ability of the molecule can be increased,and the photo-isomerization behavior can occur more easily.If the flexible segment contains electron donor atoms,the molecular packing will be closer to a certain extent.The photo-isomerization rate is lower than that of azobenzene molecules with similar flexible side chain length.In the solid state,because the molecular packing is more compact,the azobenzene compounds without flexible segments have no solid-liquid transition behavior,while the azobenzene compounds with flexible side chains at both ends have the phenomenon of photo-induced solid-liquid transition,with the increase of flexible segments,the liquefaction rate is faster.2、Photo-controlled adhesive based on solid-liquid transition of azobenzene compounds.Based on the study of photo-induced solid-liquid transition behavior of azobenzene compounds in flexible side chain,three kinds of azobenzene compounds with rapid photo-liquefaction were found.Based on the special properties of these three azobenzene compounds,a kind of photo-induced solid-liquid transition adhesive prepolymer coating was prepared.After UV irradiation,the solid coating was rapidly transformed into liquid,so it can be used for anaerobic bonding.It is found that increasing the flexible side connection length can accelerate the liquefaction rate of the adhesive prepolymer coating,but has no obvious effect on the bond strength;for azobenzene compounds with similar length flexible side chains,the enhancement of the electron supply capacity of the flexible side chain can provide more electron pairing with the interface,strengthen the force between the adhesive and the surface interface,and then improve the shear strength of the photo-controlled adhesive. |
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