Investigation Of Controlled Surface Anti-Wrinkling And Surface Wrinkling On Film/Substrate Systems

As one common type of surface instabilities,surface wrinkling has attracted great attention in recent years.On one hand,surface wrinkling is undesired in some cases.Therefore,surface anti-wrinkling has become one of challenging subjects in fields such as cosmetic industry and material engineering.So far,the existing anti-wrinkling methods are limited.On the other hand,surface wrinkling mainly happens on non-planar film/substrate systems.Owing to geometric constraints,curved wrinkling behaviors can be quite different from planar ones.Although many theoretical researches have focused on non-planar systems,related experiments are extremely limited.The main challenging issues are how to construct non-planar film/substrate systems and employ matched external stimuli to induce curved wrinkling.This dissertation is based on surface wrinkling:developing a controllable surface wrinkling and anti-wrinkling strategy by introducing film size effect;microspheres as typical curved substrates,on which fabricating a series of curvature and overstress-sensitive wrinkle morphologies,revealing the curved wrinkling behavior;spherical wrinkling is further extended to non-spherical curved wrinkling,presenting a novel surface wrinkling induction way,achieving the surface wrinkling of highly ordered 2D functional polymer microspheres and non-spherical curved microstructure arrays.In order to fabricate desired wrinkle patterns or prevent wrinkling-related structure and performance failure,in the poly(dimethylsiloxane)(PDMS)-based film/substrate system fabricated by smart combination of mechanical straining and selective oxygen plasma(OP)exposure or solvent swelling and selective ultraviolet ozone(UVO)exposure through copper grids,we investigate the film size effect on surface wrinkling behavior in 1D,2D and 3D dimensions.The oxidized SiO_x film size effect on critical wrinkling strain is systematically studied by considering exposure duration,mesh number and geometry of copper grids.Simple quantitative relationship between film size and critical strain is well established in 1D and 3D dimensions,obtaining versatile critical wrinkling strain equations.Therefore,elaborately regulating the critical wrinkling condition could achieve controllable surface wrinkling and anti-wrinkling.In order to reveal curved wrinkling behavior,we develop a simple low-cost yet robust method to induce spherical wrinkling.Namely,the aqueous-phase-synthesized PDMS microspheres are exposed to OP,yielding the oxidized SiO_x layer and the corresponding stiff shell/compliant core system.The subsequ ent solvent swelling and evaporation induce the spontaneous formation of a series of curvature and overstress-sensitive spherical wrinkles such as dimples,short rod-like depressions,herringbone,and labyrinth patterns.The effects of experimental parameters,including radius and elastic modulus of microspheres,OP exposure duration and solvent species,on spherical wrinkling behaviors have been systematically studied,obtaining a spherical wrinkle morphology phase diagram determined by normalized substrate radius of curvature and over-swelling extent.Except spherical wrinkling,curved wrinkling on non-spherical substrates is more rarely involved.Here highly ordered 2D polyethylene glycol(PEG)microsphere arrays and non-spherical curved microstructure(e.g.,square/hemispherical/bowl-like)arrays have been successfully fabricated by template-directed confinement dewetting.After depositing Pt films,Pt/PEG curved film/substrate systems are correspondingly constructed.Subsequently,PEG microstructures wrinkle under thermal effect from the electronic beam processing.Finally,highly ordered 2D PEG microsphere and non-spherical curved microstructure surface wrinkle arrays have been obtained,promising in bringing about novel fuctional properties and application potentials.