Polymeric nanostructures with high aspect ratios, so-called nanopillars, are of interest for a wide range of applications. However, it remains a challenge to fabricate high-density, polymeric nanopillars using soft lithography when the feature size is decreased to hundreds of nanometers and the structures are close to each other. Here, we investigate the fidelity of replica molding technique to fabricate polymer nanopillar arrays with diameters ranging from 300 nm to 1 mum, and we compare the experimental results to the theoretical prediction to understand the nature of the instability of nanopillars. Nanopillars molded from soft materials, poly(dimethylsiloxane) (PDMS), mainly ground collapse due to the adhesive force when the aspect ratio is above 6, whereas those from stiffer materials, polyurethane and epoxy, collapse laterally at a much higher aspect ratio (>/=12), of which the critical value is dependent on the nanopillar's feature size, spacing, height, and shape. Further, we attempt to restore the collapsed high-aspect-ratio nanopillars using supercritical CO(2) drying.

We demonstrate a new light-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel nanocomposite incorporating glycidyl methacrylate functionalized graphene oxide (GO-GMA) instead of metallic nanoparticle fillers. GO-GMA is synthesized by esterification with glycidyl methacrylate. GO-GMA incorporated hydrogels are synthesized by photopolymerization of NIPAAm including 4-dimethylaminopyridine (DMAP) and N,N 0 -methylenebisacrylamide (NMBA) in GO-GMA dispersed dimethyl sulfoxide (DMSO) solution. Results show that such a nanocomposite hydrogel can undergo a large volumetric change in response to infrared (IR) light illumination, due to the highly efficient photothermal conversion of GO-GMA. It also exhibits significantly larger water uptake compared to conventional PNIPAAm hydrogel by 3 times. Based on the developed IRresponsive nanocomposite hydrogel, we have also realised a microvalve that controls the fluidic flow within a microfluidic channel through remote IR light actuation.

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The synthesis of an oriented liquid-crystalline photoresponsive polymer, prepared by polymerization of mono- and di-acrylates, both of which contain azobenzene chromophores, is reported. The prepared free-standing polymer film shows strong reversible photoinduced deformation upon exposure to unpolarized UV light at 366 nm, as a result of an optically induced isomeric change of the azobenzene moieties in the polymer network. The synthesis process is relatively simple and more efficient compared to conventional ones, and can be used to synthesize other liquid-crystalline photoresponsive polymers. The use of this photoresponsive polymer film as an optical high-pass/low-pass switch under UV or natural light irradiation for a laser beam is demonstrated. This photoresponsive polymer may have applications in robotic systems, artificial muscles, and actuators in microelectromechanical systems (MEMS) and labs on chips.

Harvesting and storing solar energy has become more and more important. Current solid-state photovoltaic cells and conventional photoelectrochemical cells are not capable of directly storing the converted energy, which has to be facilitated by connecting to external storing devices. We demonstrate a device architecture that can convert and store solar energy in the electrical form within an intrinsically single structure. Mobile charge is internally stored, based on the coupling between photoelectrochemical and ferroelectric effects. The tested device architecture can be photo-charged under 1000 W/m2 of white light to an open-circuit voltage of 0.47V with a capacity of 37.62 mC/cm2. After removal of the light source, the mobile charge stored lasts more than 8 hours, and the open-circuit output voltage lasts more than 24 hours