Fabrication of a hierarchical structure by oxygen plasma etching of a photocured microstructure containing a silicon moiety

We present a simple and straightforward method for creating a hierarchical structure in which the nanoscale roughness is derived from a microstructure. This hierarchical structure is at the backbone of almost all biomimetic functions. A liquid blend of a photocurable prepolymer and a functionalized polysiloxane is moulded by photocuring, and then the moulded film is simply exposed to a blanket oxygen plasma to produce the hierarchical structure. The nanoscale roughness is controlled by varying the weight ratio of acrylate-functionalized polysiloxane to acrylated prepolymer. To demonstrate the efficacy of the fabrication method, a superhydrophobic surface was produced by coating the hierarchical structure with a self-assembled monolayer (SAM)

Surface energy-tunable iso decyl acrylate based molds for low pressure-nanoimprint lithography

We presented surface energy-tunable nanoscale molds for unconventional lithography. The mold is highly robust, transparent, has a minimized haze, does not contain additives, and is a non-fluorinated isodecyl acrylate and trimethylolpropane triacrylate based polymer. By changing the mixing ratio of the polymer components, the cross-linking density, mechanical modulus, and surface energy (crucial factors in low pressure ((1-2) x 10(5) N m(-2)) low pressure-nanoimprint lithography (LP-NIL)), can be controlled. To verify these properties of the molds, we also characterized the surface energy by measuring the contact angles and calculating the work of adhesion among the wafer, polymer film, and mold for successful demolding in nanoscale structures. Moreover, the molds showed high optical clarity and precisely tunable mechanical and surface properties, capable of replicating sub-100 nm patterns by thermal LP-NIL and UV-NIL. © 2017 IOP Publishing Ltd Printed in the UK

Fabrication of Antireflection and Antifogging Polymer Sheet by Partial Photo polymerization and Dry Etching

We present a simple method to fabricate I polymer optical sheet with antireflection and antifogging properties. The method consists of two consecutive steps: photocross-linking of UV-curable polyurethane acrylate (PUA) resin and reactive ion etching (RIE). During photopolymerization, the cured PUA film is divided into two domains of randomly distributed macromers and oligomers due to a relatively short exposure time of 20 s at ambient conditions. Using the macromer domain as an etch-mask, dry etching was Subsequently carried out to remove the oligomer domain, leaving behind a nanoturf surface with tunable roughness. UV-vis spectroscopy measurements demonstrate that transmittance of a nanoturf surface is enhanced up to 92.5% as compared to a flat PUA surface (89.5%). In addition, measurements of contact angle (CA) reveal that the etched surface shows superhydrophilicity with a CA as small as 5 degrees. To seek potential applications, I-V characteristics of I thin film organic solar cell were measured under various testing conditions. It is shown that the efficiency call be increased to 2.9% when a nanoturf film with the surface roughness of 34.73 nm is attached to indium tin oxide (ITO) glass. More importantly, the performance is maintained even in the presence of water Owing to superhydrophilic nature of the film

Efficiency Improvement of Organic Solar Cells by Tuning Hole Transport Layer with Germanium Oxide

Improving optical property is critical for optimizing the power conversion efficiency of organic solar cells. In the present research, we show that modification of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layer with GeO2 leads to 15% improvement of power conversion efficiency in a polymer solar cells through enhancement of short circuit currents. Modified PEDOT:PSS layer with optimized concentration of GeO2 assists active layer absorbing much light by playing a role of optical spacer. Using AFM and grazing incidence X-ray diffraction (GIXD) data, we also present the evidence that an addition of GeO2 does not affect crystallinity of active layer

Adhesion hysteresis of Janus nanopillars fabricated by nanomolding and oblique metal deposition

We present a simple method to fabricate Janus-faced nanopillars showing the direction-sensitive behavior as a dry adhesive. Polymeric nanopillars were first molded from an etched SiO2 substrate containing high aspect ratio nanoholes, followed by the oblique metal deposition on polymer nanopillars such that metal layers in different thicknesses were selectively deposited only on one side of the nanopillars. We found that the Janus nanopillars show the asymmetric adhesion behavior: it exhibits the strong shear attachment when pulled from a polymer contact (???20 N/cm2) compared with the relatively weak adhesion when pulled from a metal layer in contact with a glass substrate (???10 N/cm2). The difference in the shear adhesion strength is believed to originate from different interfacial adhesions between different sides of the Janus nanopillars and a target substrate. In addition, the Janus nanopillars could be further allowed to bend by thermal annealing or E-beam irradiation. The bending mechanism for nanopillars bending toward the metal layer by thermal annealing can be explained by the mismatch in thermal expansion coefficients between metal and polymer, followed by the plastic deformation of polymeric pillars. What is strikingly interesting is the fact that these bent Janus nanopillars show even greater adhesion hysteresis: the strong shear attachment when pulled from the bent direction (???31 N/cm2) in contrast to the easy detachment from the opposite direction (???4.1 N/cm2) just like gecko-like adhesives. We also demonstrate that this type of relatively simple bending process to produce Janus-faced nanopillars has a distinct advantage for large-area fabrication.close434

Magnetic Nanoparticle-Embedded Hydrogel Sheet with a Groove Pattern for Wound Healing Application

Endothelial progenitor cells (EPCs) can induce a pro-angiogenic response during tissue repair. Recently, EPC transplantations have been widely investigated in wound healing applications. To maximize the healing efficacy by EPCs, a unique scaffold design that allows cell retention and function would be desirable for in situ delivery. Herein, we fabricated an alginate/poly-l-ornithine/gelatin (alginate-PLO-gelatin) hydrogel sheet with a groove pattern for use as a cell delivery platform. In addition, we demonstrate the topographical modification of the hydrogel sheet surface with a groove pattern to modulate cell proliferation, alignment, and elongation. We report that the patterned substrate prompted morphological changes of endothelial cells, increased cell–cell interaction, and resulted in the active secretion of growth factors such as PDGF-BB. Additionally, we incorporated magnetic nanoparticles (MNPs) into the patterned hydrogel sheet for the magnetic field-induced transfer of cell-seeded hydrogel sheets. As a result, enhanced wound healing was observed via efficient transplantation of the EPCs with an MNP-embedded patterned hydrogel sheet (MPS). Finally, enhanced vascularization and dermal wound repair were observed with EPC seeded MPS

Continuous and Scalable Fabrication of Bioinspired Dry Adhesives via a Roll-to-Roll Process with Modulated Ultraviolet-Curable Resin

A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly­(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly­(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ∼38.7 N cm^–2 on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10 000 repeating cycles with high accuracy

Continuous and scalable fabrication of bioinspired dry adhesives via a roll-to-roll process with modulated ultraviolet-curable resin

A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ???38.7 N cm -2 on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10 000 repeating cycles with high accuracy.open0