Controlled Fabrication And Application Of Microstructured Surface Of Soft Materials Based On Unconventional Patterning Techniques

Smart soft materials with the characteristic of “weak stimuli and strong response” have gained considerable attention in recent years due to their huge potential in numerous fields.On the one hand,many applications of soft materials highly depend on their micro/nanoscale structures and functionalization.Currently,the development of new patterning technologies that adapt to specific soft materials still remains a challenging issue.On the other hand,the combination of smart soft materials and responsive surface patterns is becoming a new and promising research direction in the controlled fabrication of smart surface and devices.This dissertation was focused on the development of suitable unconventional patterning methods for two typical soft polymer materials,polydimethylsiloxane(PDMS)elastomers and photosensitive polymers: to achieve the controllable surface patterning of PDMS and its composite systems;to prepare photoresponsive surfaces and advanced wrinkle patterns on the basis of the photoresponses of soft materials combined with surface wrinkling.We demonstrated that the microstructured PDMS and photoresponsive systems can be used for microfluidics,micro/nano-fabrication,repeatable(confidential)information recording,multifunctional surfaces and well-regulated optical devices,and so on.Firstly,we reported a simple novel surface treatment-assisted switchable transfer printing(s TP)to pattern PDMS films of diverse thicknesses with prescribed microstructures.In the s TP,the PDMS decal inks were transferred from the “soft” side to the “hard” side,irrespective of the “soft” side coming from the PDMS stamp or the target PDMS substrate.Their “soft/hard” contrast can be finely induced and switched by a simple surface oxidation treatment,yielding the customized transfer patterns.In particular,multiple s TP with the smart combination of the additive/subtractive transfer mode can be easily realized for the controlled fabrication of the unprecedented hierarchical patterns.Systematical studies further provided insights into the involved cohesion-fracture mechanism.Next,based on surface wrinkling,controllable fabrication of photoresponsive wrinkle microstructures was obtained on film/substrate systems using PDMS as the soft substrate,photodegradable polymer and azobenzene polymer as the hard-film layers,respectively.In the photodegradable polymer/PDMS wrinkled systems,we presented a green method for the fabrication of photo-tunable wrinkling micropatterns.Photolysis of the photodegradable polymer with main-chain scission took place upon ultraviolet light irradiation,leading to stress release and finally the erasure of the wrinkles when they were incorporated into the wrinkled system.The wrinkles in the unexposed region were also dynamically tuned and oriented perpendicular to the exposed boundary during the selective exposure,yielding advanced wrinkle micropatterns.In the azopolymer-based film/substrate systems,we reported an all-optical strategy for fabricating reversible surface-wrinkled micropatterns via visible light illumination.These smart systems can be switched optically between flat and wrinkled states with diverse configurations by controlling the incident light intensity and exposure mode(e.g.,blanket exposure and selective exposure).For the first time,we achieved large-area fabrication of unexpected high-aspect-ratio wrinkles(up to 0.9)with controllable orientation.Systematic experiments combined with theoretical analysis deeply revealed the underlying physics.Different photoresponsive characteristics of azobenzene moieties(e.g.,photoisomerization,photosoftening and photothermal effect)were involved in driving the reversible wrinkling/dewrinkling cycle(e.g.,more than 20 times).This all-optical patterning strategy was further extended to other multi-functional azo-based wrinkling systems irrespective of planar,non-planar,or surface-patterned substrates employed.