Complex Deformation Control Of Gradient Ionically Cross-linked Shape Memory Polymers

Shape memory polymers(SMP)are a class of stimuli-responsive polymers that have the ability to change their shape in response to external environmental stimuli.The initial shape of these materials can be altered and fixed into other temporary shapes under specific circumstances.These fixed temporary shapes are normally stable,only when an external stimulus is applied to them.and the material responds to this stimulus.To activate its segmental movement,the material eventually returns to its original shape under the elastic energy stored during the previous programming process.This material with the ability to "have different shapes in different environments" has great application value in many fields such as smart devices,information recording,sensors and the like.In recent years,the field of shape memory polymers has also developed tremendously,and many shape memory materials with different compositions and functions have been reported.However.the stimuli of shape memory materials have so far been limited to a few,such as light,heat,electricity.magnetic fields,pH,solvents,and the like.And the limitations of incentives are gradually becoming a bottleneck restricting their role in the broader field.On the other hand,designing complex three-dimensional shape memory polymers is also a hot topic in the field.The main purpose of this thesis is to realize the controllable complex deformation of SMP from two-dimensional(2D)to three-dimensional(3D)by mimicking the microscopic deformation structure of plants.The specific content will be discussed in two parts.In the first part,we selectively introduce a gradient ion-crosslinked structure into a strained SMP to make the SMP deformable deformation due to ion cross-linking in the thickness direction after heating,thereby achieving controllable complex deformation.In the second part,we first proposed stress as a stimulation method.After introducing gradient ion crosslinking into the plastic polymer,the complex 3D shape is directly realized by stretching.The first part of the work:to achieve complex programming shape transformation by suppressing strain relaxation under a certain strain.We prepared a blend film of polyethylene oxide(PEO)and poly(acrylic acid)(PAA)by blending and volatilizing solution.The material has excellent room temperature(RT)shape memoryperformance,based on the orientation and reconstruction of PEO crystals,and can be fixed by simple stretching at RT.The optimized fixation rate and recovery rate are both higher than 90%.Complex deformation can be achieved by surface treatment of the stretched SMP film using an iron ion solution.Due to the infiltration process of the solution,iron ions form a cross-linking density ion network in the thickness direction with the carboxyl group of the PAA.When the heating is restored,the strain recovery is limited to different degrees due to the difference in crosslink density,and the material is bent and deformed into a three-dimensional shape toward the non-treated surface.Through research,we found that the heating and bending behavior of the material is affected by factors such as SMP strain,iron ion solution concentration and SMP film thickness.In addition,based on the photochemical process of ultraviolet/visible light to reduce iron ions to ferrous ions and dissociate the crosslinked network,the three-dimensional deformation behavior of the light-controlled programmable material is realized by changing the ion cross-linking pattern of the material by local illumination.We further added polydopamine as a photothermal filler to the material,so that it can recover the shape induced by near-infrared light(NIR)stimulation,and then the three-dimensional complex deformation of the material can be performed under RT.Part ?:Inspired by the previous work,we propose stretching as a novel stimulus to directly achieve complex three-dimensional deformation of plastic polymers.A PEO/PAA/tannic acid(TA)three-component composite film was prepared by a similar method.The addition of TA can simultaneously form hydrogen bonds with PEO and PAA,which significantly improves the RT stretchability and plastic deformation ability of the material.After the surface patterning treatment of the film with an aqueous solution of copper chloride,a network of copper ion-carboxylate ions having a gradient of cross-linking density can be formed in the thickness direction,resulting in a significant increase in the yield strength of the plastic deformation of the crosslinked region.When the material is stretched,the uncrosslinked portion first undergoes plastic deformation,and the bending deformation faces one side of the pattern,thereby causing three-dimensional deformation of the entire material.In addition,by treating the pattermed region with a sodium metabisulfite solution,the copper ions can be reduced to cuprous ions,dissociating the ion-crosslinking network,and recovery of complex shapes can be achieved by heating.We believe that this tensile response complex deformation polymer has broad application prospects in the engineering field.