Preparation And Application Of Azo-containing Stimulus Responsive Materials

Stimulation-responsive materials,whose physical and chemical properties/sizes can produce intelligent responses to external stimuli such as light,temperature,pH,etc.,thus realizing intelligent fine regulation of material properties,are widely used in intelligent sensors,optical devices,microfluidic and many other fields.Among them,light,as a clean external stimulus,can be easily,instantly,accurately remote control,to avoid the sample surface pollution damage.As a typical photosensitive molecular group,azobenzene has a thermodynamically stable trans configuration and a thermodynamically metastable cis configuration with obvious differences in molecular size and dipole moment.The two configurations can realize reversible transformation under the light induction of specific wavelengths.The introduction of azophenyl into the molecular structure and polymer structure is an effective strategy to construct light-responsive smart material systems.In this paper,using the excellent light response characteristics of azophenyl elements,combined with surface wrinkling and other technologies,a variety of azo-containing stimulus response materials have been prepared and their applications in information storage and sensing have been tentatively explored.It mainly includes:the construction and application exploration of azo-doped and azo-containing polymer blend membrane/base surface wrinkling system,the construction and application research of light/acid-base dual stimulation response membrane/base system,the design and synthesis of photoresponsive azobenzene small molecules and the application of intelligent emulsion system.Specific research contents are as follows:（1）The photoresponsive bilayer/base system was constructed by introducing azo components into the membrane layer,which mainly consisted of azo small molecule doping system and azo-containing polymer blend system.In the azobenzene small molecule doping system,three different kinds of azobenzene monomers（including azobenzene,aminoazobenzene and pseudoastragalus azobenzene）were doped with polymethyl methypropionate（PMMA）as the membrane layer,respectively.The photoresponsive film/base crease system materials（AZO-PMMA/PDMS,AAB-PMMA/PDMS,DO₃-PMMA/PDMS）were constructed with polydimethylsiloxane（PDMS）as elastic substrates.The photoinduced cis-trans isomerization reaction of azophenyl groups in the film was used to dynamically erase/regulate the wrinkle morphology of the system surface.The effects of azobenzene substituents,incident light wavelength,film thickness and wrinkle amplitude on the surface morphology of the materials were investigated systematically.The experimental results showed that only DO₃-PMMA/PDMS system showed excellent photoinduced regulation of the surface wrinkle morphology,while azobenzene and aminoazobenzene doping system did not show excellent photoregulation of the surface wrinkle morphology.The results showed that DO₃azobenzene with push-pull electron substituents exhibited rapid and reversible cis-trans isomerization,which gave excellent dynamic photoregulation/erase-removal properties to the wrinkle morphology of the doped membrane/substrate system.In the azobenzene-containing polymer blend system,based on the solution of small molecule azobenzene doping system phase separation problems,we synthesized side chain amorphous azo-containing polymers（PDO₃）with a single absorption peak andπ-π^*transition overlap with the absorption band of n-π^*transition,and then blended with polymer（PMMA）solution and spin-coated films to prepare the photoresponsive film/base system materials.Due to the reversible cis-trans isomerization of azophenyl groups induced by visible light irradiation,the intelligent response of non-light-responsive polymer PMMA was induced by the entanglement of polymer chain,and the surface wrinkle morphology regulation of membrane/substrate system was studied.The application of the photosensitive system in optical erasable information storage and other aspects was explored.（2）In the aspect of azobenzene material system with double stimulus response,this part uses azobenzene polymer PDO₃as the film layer and PDMS as the elastic substrate to construct the film/base system material with double light/pH response.The changes of chemical structure and spatial configuration of azophenyl groups in the surface membrane were induced by light stimulation and acid-base stimulation,which resulted in the dynamic evolution of surface morphology and color rendering of materials.On the one hand,when the thermally induced wrinkle morphology was exposed to visible light exposure,the wrinkle in the exposed region would disappear due to the stress perturbation caused by azobenzene cis-trans isomerism,while the wrinkle in the unexposed region would be oriented based on the boundary effect.On the other hand,the azobenzene material system showed obvious acid-base response,and the surface wrinkle morphology of the material completely disappeared when exposed to acid gas stimulation,accompanied by obvious visual color change.Wrinkles still existed in the covered area of the mask,and the orientation changed perpendicular to the junction of the two areas.The experimental results show that the color behavior of azobenzene is due to the protonation/deprotonation ofβ-nitrogen atoms under the stimulation of acid and base,and the erasement of wrinkles is caused by the balance of the compressive stress field of the surface wrinkling system,which is controlled by the expansion/contraction of acid and alkali.In addition,a series of fine and advanced patterns were prepared on the surface of the membrane/base system by simple selective exposure of the mask and stimulation of acid-base vapor,and their applications in environmental monitoring,information storage,anti-counterfeiting and other aspects were initially explored.Furthermore,the reversible visualization of the azo material was extended to filter paper,cotton fiber and other substrates,and the reversible fine regulation of the advanced patterns on the surface of a variety of substrates was successfully realized.（3）Stimulation-responsive surfactants have great application value in the field of material surface interface science,in which azobenzene containing surfactant systems have attracted much attention due to their photoregulatory molecular structure and surface properties.In this part of the study,azo surfactants with different substituents were synthesized by the mercaptoene click reaction containing azo acrylate and mercaptoacetic acid.The structure and light response characteristics of azo surfactants were characterized by NMR and UV-Vis absorption spectroscopy.System is investigated by synthetic azo surfactant for the stimulation of external light response performance,the results showed that all three azobenzene surfactants exhibit rapid trans/cis photoisomerization（within tens of seconds）,excellent reversible trans/cis/trans cycling stability（>20 cycles）,and optically adjustable surface properties.In addition,the surfactant can realize the reversible conversion of foaming and defoaming in the solution system,and it has a good application prospect in the intelligent emulsion system construction,sewage treatment,green dyeing and weaving,etc.,as a light-adjusting intelligent foam switch.