Investigation Of Light-responsive Behaviors Of Azobenzene Film Via Surface Wrinkling

Composition and functionalization is an important research field of modern material science.How to effectively solve and make good use of the stress-relaxation-related material defects is a great challenge.In this thesis,light-responsive azobenzene-containing materials are incorporated into surface film to construct responsive film/substrate wrinkling systems.Surface wrinkling can be dynamically formed,prevented and/or erased by light irradiation.Based on the film composition,the main contents of this thesis are focused on two film/substrate systems,i.e.,azobenzene film/elastic substrate bilayer system and azobenzene film/liquid-based substrate bilayer system.In the azobenzene film/elastic substrate bilayer system,side-chain poly?p-aminoazobenzene??PAAB?,PAAB-PMMA mixure?PMMA:polymethyl methacrylate?and supramolecule P4VP?OH-DMA?_x?P4VP:poly?4-vinylpyridine?;OH-DMA:4-hydroxy-4'-dimethylaminoazobenzene?films are coated on a poly?dimethylsiloxane??PDMS?elastic substrate,respectively.First,we systematically investigate the photo-induced mechanical changes of PAAB film through mechanical straining-induced surface wrinkling.In-situ optical observations reveal that surface wrinkling can be controlled and suppressed by visible light irradiation.In particular,the influences of physical and geometrical parameters including light intensity I,strain release rate V,light dose,prestrain and film thickness on the surface wrinkling morphologies have been investigated.Our experimental results show that the photosoftening behavior of PAAB film strongly depends on I and V.Dimensional analysis reveals that the Young's modulus?E_f?of the PAAB film depends on the ratio of I/V.Besides,the degree of photosoftening has also been systematically studied as a function of chromophore concentration and the molecular weight in PAAB-PMMA mixure and supramolecule P4VP?OH-DMA?_x by using the same method.Similarly,Young's moduli of these two films are controlled by I/V.By comparing PAAB,PAAB/PMAA and P4VP?OH-DMA?_x,the influence of the interaction between azobenzene group and polymer chain on the surface wrinkling behavior is also studied.Taking advantage of the low modus of water and the free state of PAAB floating film,we use deionized water,instead of PDMS,as a liquid base for fabrication of a more sensitive PAAB/H₂O bilayer system.First,capillary wrinkling is formed when placing a drop of glycerol on the PAAB floating film.Both unpolarized and polarized lights are applied to illuminate the winkled film.It is seen that unpolarized light can erase the as-formed wrinkles while polarized light can only erase parts of them and surface wrinkles in some specific directions evolve but not disappear.Second,we investigate light-responsive behaviors of the PAAB floating film without introducing the glycerol drop.Hierarchical winkles are formed during the irradiation of a polarized light.In the exposed area,an initial disordered deformation of the PAAB film is induced immediately.With the increase of the light duration,a subsequent surface wrinkling with good orientation is observed in the irradiated region.As for the film out of the illuminated area,surface wrinkling gradually occurs with the wrinkles'orientation perpendicular to the edge of the light spot.Here we investigate systematically the influences of the parameters?e.g.,incident lights,polarization direction,light intensity,light spot area?on the wrinkle evolution and the light-controlled surface wrinkling/anti-wrinkling/wrinkle eliminating effects.In conclusion,a simple and new approach of light modulation is developed for the large-scale surface wrinkling/anti-wrinkling/wrinkle eliminating as well as fine tailoring of the wrinkled microstructures.This key solution offers us a wrinkling-based technique which can be regarded as a fundamental and efficient method to study the photoinduced mechanical properties of azo-containing materials.Additionally,our work also provides a quantitative light-control strategy to prevent materials from the undesired surface wrinkling while keeping their desired structural integrity and functionality,which is crucially important for some advanced microelectronic circuits and optical devices.