Patrick Koelsch

High-dielectric constant side-chain polymers that show reduced non-geminate recombination in heterojunction solar cells are reported. Active layer polymers with high dielectric side-chains show increased performance over alkyl side-chain polymers. The doubling in efficiency is attributed to suppressed recombination. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Abstract The photocatalytic activity of TiO 2 under sunlight irradiation depends on the bandgap energy. Due to the relatively low solar intensity in the UV region (<10%) and the fact that the bandgap of TiO 2 is usually greater than 3 eV (below 400 nm), many attempts have been made to shift the bandgap towards lower energies. Here, we investigate the structure, chemical composition, bandgap shift and charge transfer processes of Ag@TiO 2 core‐shell nanoparticle thin films by field emission scanning electron microscopy, atomic force microscopy, XPS, and UV‐Vis spectroscopy. As a solid support, Au‐coated Si wafers and Si surface covered with a native oxide were used and homogenously covered by Ag@TiO 2 core‐shell nanoparticles with overall film thicknesses of 80–100 nm and size distributions between 8 and 15 nm. The shell thickness of the adsorbed Ag@TiO 2 particles was estimated to be 1.5‐2.0 nm. The effect of the Ag core on the bandgap of TiO 2 and photoinduced charge separation of Ag@TiO 2 nanoparticle films was studied by UV‐Vis reflectance spectroscopy using the Kubelka‐Munk formalism. Films of Ag@TiO 2 core‐shell nanoparticles revealed a substantially reduced bandgap of 2.75 eV (corresponding to 450 nm), and an electron charge transfer to the Ag core occurring upon UV irradiation on nonconductive surfaces. These features make Ag@TiO 2 particulate films a promising candidate for photocatalytic surfaces under sunlight irradiation. Copyright © 2010 John Wiley & Sons, Ltd.

Nonfouling surfaces capable of reducing protein adsorption are highly desirable in a wide range of applications. Coating of surfaces with poly(ethylene oxide) (PEO), a water-soluble, nontoxic, and nonimmunogenic polymer, is most frequently used to reduce nonspecific protein adsorption. Here we show how to prepare dense PEO brushes on virtually any substrate by tethering PEO to polydopamine (PDA)-modified surfaces. The chain lengths of hetero-bifunctional PEOs were varied in the range of 45-500 oxyethylene units (M(n) = 2000-20,000). End-tethering of PEO chains was performed through amine and thiol headgroups from reactive polymer melts to minimize excluded volume effects. Surface plasmon resonance (SPR) was applied to investigate the adsorption of model protein solutions and complex biologic medium (human blood plasma) to the densely packed PEO brushes. The level of protein adsorption of human serum albumin and fibrinogen solutions was below the detection limit of the SPR measurements for all PEO chains end-tethered to PDA, thus exceeding the protein resistance of PEO layers tethered directly on gold. It was found that the surface resistance to adsorption of lysozyme and human blood plasma increased with increasing length and brush character of the PEO chains end-tethered to PDA with a similar or better resistance in comparison to PEO layers on gold. Furthermore, the chain density, thickness, swelling, and conformation of PEO layers were determined using spectroscopic ellipsometry (SE), dynamic water contact angle (DCA) measurements, infrared reflection-absorption spectroscopy (IRRAS), and vibrational sum-frequency-generation (VSFG) spectroscopy, the latter in air and water.

Due to their outstanding mechanical properties, spider silks have fascinated men for a long time. Silk is composed of proteins which can not only be processed into fibers, as found in nature, but also be cast to form films in vitro. Starting with a protein solution in hexafluoroisopropanol, we were able to cast films with different properties deviated from the two spider silk proteins employed. All as-cast films revealed an α-helixrich structure and were water soluble. However, the secondary structure of One-protein films (silk films cast from one spider silk protein) could be converted from an α-helical rich to a β-sheet rich secondary structure by post-cast treatment with methanol or potassium phosphate. The structural conversion was accompanied by a higher stability as seen by water-insolubility. Depending on the employed proteins, silk films were stable in protein denaturants such as urea and guanidinium hydrochloride. Strikingly, Two-protein films (silk films cast from a mixture of both spider silk proteins) showed properties derived from both proteins, indicating that the process of film casting based on silk proteins is closely related to film casting of traditional chemical polymers. Our results reveal novel possibilities to generate protein films for applications that demand stable biocompatible polymer films.