Preparation And Properties Of Pre-stretched Stimuli-responsive Film

Stimuli-responsive polymer films have been attracted much interest due to the wide application of smart materials in the fields of biology,medicine,environment,engineering,etc.Stimulus-responsive polymers change their structure or properties in response to physical or chemical stimuli(light,electricity,heat,magnetism,pH,pressure,humidity).Many smart films can convert external stimuli into mechanical movement and have unique actuation properties.It is a challenging work to prepare polymer smart thin film materials with quick response,multiple functions and excellent comprehensive performance.The main content of the paper were the following two parts:1.Based on the high strength and elasticity of agarose and polyacrylamide double network hydrogel film,the hydrogel film was pre-stretched and dried to fix the temporary shape.The contraction stress in the pre-stretched film could be stored by the strong hydrogen bonds in the dried film.The contraction stress in pre-stretched film would be released in response to humidity,which caused rapid and large-scale deformation.The deformation direction of the pre-stretched film could be controlled by the stretching direction.The reversible transition of high elastic state and glass state of the films before and after water absorption was the key to store and release stress in the humidity-responsive pre-stretched films.Based on the stable physical and chemical cross-linking network,the hydrogel films showed the good water-induced shape memory effect.When the films were completely dried,the strong hydrogen bonding between polymer chains could fix the temporary shape and the fixing ratios were close to 100%.When the film was fully swollen,the recovery ratios were also close to 100%.In addition,the film showed the good water-induced self-healing ability.The healed film maintains about 88% tensile strength(103 MPa)of the original film.2.Polyethylene glycol crystalline films were prepared by photo crosslinking of polyethylene glycol diacrylate.The molecular weight of prepolymer polyethylene glycol 6000 was suitable,and the formed cross-linked network was loose and uniform,therefore,the film showed good crystallinity.The cross-linked films had the shape memory effect under the external stimulus.The chemical cross-linking network could form the permanent network to maintain the original shape of the film.The shape fixation and recovery transformation depended on the reversible transformation of crystalline and amorphous.The recrystallization in the PEG film induced by stretching could fix the temporary shape.The rapid swelling of the film induced by humidity or methylene chloride vapor led to the crystal destruction,therefore,the film showed a rapid shape memory effect in response to humidity and methylene chloride vapor.The photoinitiator had photothermic effect after absorbing UV light.Therefore,the cross-linked films initiated by photoinitiators showed the shape memory effect induced by UV light.The cross-linked film showed effective light-to-heat conversion and rapid shape memory recovery behavior due to the well dispersed photoinitiator in the cross-linked film.The actuator constructed based on the cross-linked film could efficiently transform the shape memory effect into mechanical movement under various stimuli.