Study On Photo-Thermal Storage And Room-temperature Release Of Azobenzene-based Polymer

Solar thermal fuels can convert sunlight into chemical energy stored in chemical bonds,and the energy will release in the form of heat when stimulated by appropriate light or heat.Thus realizing the photo-thermal recycling utilization.Azobenzene-based polymers are expected to be used as an ideal candidate self-supporting and stretchable photothermal-conversion films due to their various photoisomerizable chromophore,stretchability and bending properties.Azo-polymer films have some problems,such as low energy storage density,limited heat release,and poor film-forming property.In this paper,to solve this problem,Based on theoretical calculation,three azobenzene structures with different photoisomerization properties were obtained as the core molecules of photothermal storage materials.Polynorbornene template was synthesized by Ring-Opening Metathesis Polymerization,then azobenzene was grafted onto the side chain of the polynorbornene in the form of covalent bond to obtain Azobenzene-based side chain grafted polynorbornene(PNB-Azo).The results showed that the graft density of para-carboxyl substituted azobenzene(Azo-1)was 17.3%higher than that of Azobenzene with meta-methoxy and carboxyl substitutions(Azo-3,31%).The strain of PNB-Azo-1 film can reach 200%,which is 80%higher than that of PNB-Azo-3 film(120%).The photothermal storage performance of solar-thermal film under tension was studied.The results show that when the tensile strain of the film is 20%,the isomerization degree of the film increases from the initial 72%to 85%,and the energy density increases from43.0 Wh·kg^-1 to 49.0 Wh·kg^-1.The temperature changes of PNB-Azo films under different deformation(shape,strain,static/dynamic change),such as"heat charge"(light-induced trans-cis-isomerization)and"heat release"(cis-trans),were observed by infrared thermal imager.Dynamic stretching produces a higher temperature difference(1.5?),which is higher 0.25?than static release,and the film shows good cycle stability in 10 circles.The results showed that the self-supporting and stretchable PNB-Azo film is an ideal materials for solar thermal fuel.