Spatial Ordering of the Structure of Polymer-Capped Gold Nanorods under an External DC Electric Field.

We studied the alignment changes of polymer-capped gold nanorods (GNRs@PS) under an applied electric field by visible-near-infrared absorption and small-angle X-ray scattering (SAXS) measurements. Monodispersed GNRs with an aspect ratio of 4.0 were produced by the seed-mediated growth method using cetyltrimethylammonium bromide and sodium oleate binary surfactants. We investigated the phase transition between the ordered structure of GNRs@PS induced by the external electric field. At appropriate field strengths (>3 V/µm), the SAXS profiles of GNRs@PS showed a smectic ordered structure. Increasing the electric field strength densified the ordered structure and greatly increased the Raman signals (the 298 and 445 cm-1 bands) of the carbon tetrachloride (solvent) between the GNRs@PS. The insights gained are potentially applicable to catalysts, future displays, optical filters, and data storage devices.

Anion and cation effects on the size control of Au nanoparticles prepared by sputter deposition in imidazolium-based ionic liquids.

The sputter deposition of metals in an ionic liquid (IL) capture medium is a simple and elegant method for preparing nanoparticles without any chemical reaction. Although there have been some reports on the size determination factors for Au nanoparticles (AuNPs) prepared using this method, the effects with respect to the type of IL used have not been clearly elucidated. This is because there are some complicating factors, some of which have been revealed by our previous systematic studies. In the present study, we prepare AuNPs in nine types of imidazolium-based IL to examine the size determination effects of the type of anion involved, the length of the alkyl chain of the cation, and the preparation temperature for each IL, while keeping other factors constant. For most of the capture media ILs, the sizes of the AuNPs increase with an increase in temperature. The AuNPs prepared in ILs containing different types of anions exhibit distinctly different particle sizes and temperature dependences. Conversely, the alkyl chain is regarded as a secondary stabilizer that works only at higher preparation temperatures. We conclude that the sizes of AuNPs prepared by this method may be determined by the competition between the collision frequency of the ejected Au atoms and the stabilizing capability of the anions that form the first coordination shell around the AuNPs. The AuNP sizes are closely related to the volume of anions.

Anisotropic mechanical properties of collagen hydrogels induced by uniaxial-flow for ocular applications.

Engineering of well-organized tissue constructs is active in the field of material science for biomedical applications. Here, we propose a method for orienting collagen in transparent high-density collagen hydrogels using a simple rolling method. Structural organization and mechanical function were adjusted by regulating the thickness of the construct and the cross-linking reagent. Directionality of collagen alignment on the microscopic scale was achieved parallel to the extensional flow. The preferential alignment of collagen significantly affected the mechanical properties of the construct, with strong tensile strength in the direction parallel to the collagen, and high elastic strain in the perpendicular direction. The tensile strength in the parallel direction was effectively increased by 67% by increasing the cross-linking reagents by 33%, without affecting transparency which remained at 70-80% to visible light. The constructs exhibit good biocompatibility for as a substrate for the expansion of corneal epithelial cells isolated from human donor cornea, indicating the potential for tissue engineering and biomedical applications, particularly for ocular treatments.