Fabrication Of Polyvinyl Alcohol Film Surface Wrinkles And Its Reversible Optical Properties

Preparation of surface wrinkles on a skin layer/elastomer substrate bilayer film has attracted extensive attention because of their unique structures and broad applications in flexible electronic devices,tunable diffraction gratings,smart windows,mechanical characterization of film and micro/nanofluidic templates.In this thesis,we developed a general strategy for fabricating mechanoresponsive surface wrinkles using various skin layer materials with wide tunability of wrinkles'wavelength and amplitude,large optical modulation range.rapid optical switching rate,and high stability.Furthermore.we reported a new strategy in developing moisture and temperature dual-responsive surface wrinkles on the polyvinyl alcohol/polydimethylsiloxane(PVA/PDMS)bilayer film by rationally designing the modulus changes of PVA skin layer upon moisture and temperature.These promising dual stimuli-responsive surface wrinkles on bilayer films motivate the invention of various optical devices triggered by moisture and temperature,such as smart windows and rewritable optical displays.The research contents are as follows:(1)Fabrication and optical properties of mechanoresponsive surface wrinkles on bilayer films.In order to develop a general method for fabricating skin layers/PDMS bilayer surface wrinkles with various skin layer materials,in this thesis,we treated the surface of PDMS with O2 plasma to enhance its hydrophilicity,then covered PDMS with various skin layer materials,through uniaxially stretching and subsequently releasing skin layer/elastomer substrate bilayer films,for producing highly ordered,crack-free,1D surface wrinkles on elastomeric PDMS substrates with various skin layer materials,including PVA,chitosan(CS),hydroxyethyl cellulose(HEC),and the mixtures of PVA and CS.The surface wrinkles on PVA/PDMS bilayer flm exhibit excellent mechanoresponsive optical switching properties,such as large transmittance modulation range(transmittance from?6%to 91%at visible region),high optical sensitivity with small mechanical strain(less than 20%),and long optical switching cycles(over 2000 times).A wide tunability of wrinkles'wavelength and amplitude are achieved on PVA/PDMS bilayer films controlled by simply increasing the thickness of PVA skin layers and pre-stretching.It is anticipated that this method will enable a new path to the fabrication of mechanoresponsive surface wrinkles with outstanding performance for applications in dynamic optical switching felds and beyond.(2)Design and properties of fast dual stimuli-responsive surface wrinkles on PVA/PDMS bilayer film.We show that it is possible to endow surface wrinkles on a PVA/PDMS bilayer film with the dual-stimuli response through rational design of PVA skin layer.By controlling the elastic modulus of the PVA layer via increasing/decreasing the molecule movement,the surface wrinkles can respond to both moisture and temperature.The as-prepared surface wrinkles on the bilayer film show long-awaited properties,such as fast response time,excellent reversibility without degradation of optical contrast,and high light transmittance modulation,which greatly outperforms the reported surface wrinkles.Moreover,the surface wrinkles on the bilayer film remain high bistability without additional energy consumption for more than four months in ambient room conditions both in the opaque and transparent states.These promising dual stimuli-responsive surface wrinkles on bilayer films motivate the invention of various optical devices triggered by moisture and temperature,such as smart windows and rewritable optical displays.