Programming And Fabrication Of Shape-shifting Structures Based On The Photopolymerization Process

Transforming planar sheets into desired 3D configurations has emerged as a promising design methodology,providing new means for the fabrication of the biotechnology,actuators,sensors,and engineering of complex metamaterials.In this paper,the polymer laminate cured under ultraviolet light was studied.Considering the shape morphing process driven by the uneven internal stress within the sheet structures,design schemes for shape-shifting directly from chip structures into specific 3D configurations have been established on basis of the frontal photopolymerization,which is spatially controlled by the geometry of photo patterning and photolithography process parameters.Our main contribution to this thesis is summarized as follows:(1)According to the characteristics of the front photopolymerization process,the existing photolithography experimental platform was first improved,and then the photomechanical model of the photocurable resin was established to verify the dependence between the polymerization of the cured polymer and its elastic modulus,volume shrinkage strain,crosslink density and solidification thickness.Accordingly,the experimental measurement were carried out to demonstrate our theoretical model.Finally,coupling the mechanical equilibrium conditions of polymerization,the space distribution of internal stress within polymer sheets illuminated under different effective exposure dose was obtained.Accordingly,the constitutive equation of volumetric contraction driven shape self-change was proposed,which was the theoretical basis of the shape-shifting among frontal photopolymerization.(2)In order to explore the bending deformation of quasi-one-dimensional structures,first of all,we analyzed the characteristics of the bending deformation within the quasi-one-dimensional structures and provided the measurement method for the deformation curvature.Besides,the evolution of bending rigidity and bending moment of polymer sheets cured by photopolymerization was revealed through the establishment of the composite beam model.Therefore,the function relationship between the exposure dose and the bending radius of the quasi-one-dimensional structure was acquired and its accuracy was verified experimentally.On basis of this,a design route of shape self-shifting structures through frontal photopolymerization was proposed.After obtaining the curvature information of desired 3D configurations,the corresponding photo patterning was generated according to the mapping relationship between the exposure dose and the radius of bending curvature.Ultimately,the influence of the aspect ratio on the bending deformation of the rectangular beam structure was investigated,and the preferred deformation shape of the quasi-one-dimensional structure under different process parameters was determined.Moreover,the self-folding grasper-like structure was taken as an example to illustrate how to control the deformation of self-assembly structures through the manipulation of the aspect ratio of slender structures.(3)Aiming at the bifurcation of the deformation curvature within the quasi-two-dimensional structures,the existence of the bifurcation during buckling deformation induced by the inconsistent internal stress and its variation characteristics were studied firstly.The buckling deformation equation of the disc-shaped structure was established next based on the energy potential function of nonEuclidean plane(NEP).Through coupling the thermal stress generated by photopolymerization with NEP function,the deformation curvature of disc-shaped structure was calculated.Accordingly,the transition law between the bending potential energy and the tensile potential energy in the frontal photopolymerization process was investigated.As a result,a finite element model based on thermal deformation of bilayer was established to realize the prediction and control of the buckling deformation of the quasi-two-dimensional structures.Combined with finite element analysis and physical experiments,the preferential deformation directions within different quasi-two-dimensional polymer sheets were determined.Additionally,the optically punched holes were introduced into the cured polymer sheets to eliminate the influence of the edge effect and the geometry of optical mask pattern on the buckling deformation of the quasi-two-dimensional structure.Eventually,some typical selffolding structures were fabricated based on the proposed design schemes and experimental models.