Synthesis of Surface-Reinforced Biodegradable Chitosan Nanoparticles and Their Application in Nanostructured Antireflective and Self-Cleaning Surfaces.

Surface-reinforced chitosan nanoparticles were used instead of polystyrene nanoparticles in the nanostructuring of antireflective, self-cleaning surfaces. Nanosphere lithography is a fascinating method to fabricate functional surfaces, but a large amount of nanoparticles are used and drained. Because synthetic polymer nanoparticles cause serious ecological and biological problems, the preparation of spherical nanoparticles was attempted with biodegradable, natural polymers, including chitosan and cellulose for application in nanosphere lithography. Chitosan nanospheres can be formed with a controlled size and surface charge, whereas cellulose spherical nanoparticles are hard to make. Therefore, chitosan nanoparticles were chosen and enclosed with trichloro(phenyl)silane to enhance their stability under plasma etching. A monolayer of the surface-reinforced chitosan nanoparticles was coated on a glass surface via a floating method for nanosphere lithography to act as a mask under reactive ion etching. After etching, the nanostructured glass showed a 2% increased transmittance compared with bare glass at 550 nm due to an antireflective effect. Moreover, the nanostructured glass with perfluoropolyether coating had a water contact angle of 152° and exhibited superhydrophobicity and a self-cleaning effect. This work addresses the issues of ecofriendly nanostructuring based on biodegradable, natural polymer nanoparticles for energy- and water-saving applications of nanostructured surfaces, by demonstrating the practical utilization of chitosan nanoparticles in nanosphere lithography.

Electrocatalytic activity of NiO on silicon nanowires with a carbon shell and its application in dye-sensitized solar cell counter electrodes.

To improve the catalytic activity of a material, it is critical to maximize the effective surface area by directly contacting the electrolyte. Nanowires are a promising building block for catalysts in electrochemical applications because of their large surface area. Nickel oxide (NiO) decoration was achieved by drop-casting a nickel-dissolved solution onto vertically aligned silicon nanowire arrays with a carbon shell (SiNW/C). Based on the hybridization of the NiO and silicon nanowire arrays with a carbon shell this study aimed to achieve a synergic effect for the catalytic activity performance. This study demonstrated that the resulting nanomaterial exhibits excellent electrocatalytic activity and performs well as a counter electrode for dye-sensitized solar cells (DSSCs). The compositions of the materials were examined using X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy. Their micro- and nano-structures were investigated using scanning electron microscopy and transmission electron microscopy. The electrochemical activity toward I(-)/I3(-) was examined using cyclic voltammetry and electrochemical impedance spectroscopy. The obtained peak power conversion efficiency of the DSSC based on the NiO@SiNW/C counter electrode was 9.49%, which was greater than that of the DSSC based on the Pt counter electrode.

A Sensitivity Enhanced MWCNT/PDMS Tactile Sensor Using Micropillars and Low Energy Ar⁺ Ion Beam Treatment.

High sensitive flexible and wearable devices which can detect delicate touches have attracted considerable attentions from researchers for various promising applications. This research was aimed at enhancing the sensitivity of a MWCNT/PDMS piezoresistive tactile sensor through modification of its surface texture in the form of micropillars on MWCNT/PDMS film and subsequent low energy Ar⁺ ion beam treatment of the micropillars. The introduction of straight micropillars on the MWCNT/PDMS surface increased the sensitivity under gentle touch. Low energy ion beam treatment was performed to induce a stiff layer on the exposed surface of the micropillar structured MWCNT/PDMS film. The low energy ion bombardment stabilized the electrical properties of the MWCNT/PDMS surface and tuned the curvature of micropillars according to the treatment conditions. The straight micropillars which were treated by Ar⁺ ion with an incident angle of 0° demonstrated the enhanced sensitivity under normal pressure and the curved micropillars which were treated with Ar⁺ ion with an incident angle of 60° differentiated the direction of an applied shear pressure. The ion beam treatment on micropillar structured MWCNT/PDMS tactile sensors can thus be applied to reliable sensing under gentle touch with directional discrimination.

Rapid double-dye-layer coating for dye-sensitized solar cells using a new method.

Intensive research with the specific aim of developing inexpensive renewable energy sources is currently being undertaken. In dye-sensitized solar cell (DSSC) production, the most time-consuming process is coating the dye on working electrodes: absorption of ruthenium-based dyes [e.g., N719=bis(trtrabutylammonium)-cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid-2,2'-bipyridine) ruthenium(II)] on a photoanode takes a long time. We report a simple dye-coating method using a mixed solvent of ethylene glycol (EG) and glycerol (Gly). According to our experiments, dye-coating time can be reduced to 5 min from several hours. Maximum performance was obtained with an EG/Gly ratio of 1:1. This mixture of solvents gave a performance of 9.1%. Furthermore, the viscous solvent system could control coating depth; positioning dye coatings to a specific depth was rapid and facile. A cell containing two different dyes (N719+black dye) had an efficiency of 9.4%.