Polyvinyl Alcohol-Few Layer Graphene Composite Films Prepared from Aqueous Colloids. Investigations of Mechanical, Conductive and Gas Barrier Properties.

Quasi all water soluble composites use graphene oxide (GO) or reduced graphene oxide (rGO) as graphene based additives despite the long and harsh conditions required for their preparation. Herein, polyvinyl alcohol (PVA) films containing few layer graphene (FLG) are prepared by the co-mixing of aqueous colloids and casting, where the FLG colloid is first obtained via an efficient, rapid, simple, and bio-compatible exfoliation method providing access to relatively large FLG flakes. The enhanced mechanical, electrical conductivity, and O2 barrier properties of the films are investigated and discussed together with the structure of the films. In four different series of the composites, the best Young's modulus is measured for the films containing around 1% of FLG. The most significant enhancement is obtained for the series with the largest FLG sheets contrary to the elongation at break which is well improved for the series with the lowest FLG sheets. Relatively high one-side electrical conductivity and low percolation threshold are achieved when compared to GO/rGO composites (almost 10-3 S/cm for 3% of FLG and transport at 0.5% FLG), while the conductivity is affected by the formation of a macroscopic branched FLG network. The composites demonstrate a reduction of O2 transmission rate up to 60%.

Slow Photons for Photocatalysis and Photovoltaics.

Solar light is widely recognized as one of the most valuable renewable energy sources for the future. However, the development of solar-energy technologies is severely hindered by poor energy-conversion efficiencies due to low optical-absorption coefficients and low quantum-conversion yield of current-generation materials. Huge efforts have been devoted to investigating new strategies to improve the utilization of solar energy. Different chemical and physical strategies have been used to extend the spectral range or increase the conversion efficiency of materials, leading to very promising results. However, these methods have now begun to reach their limits. What is therefore the next big concept that could efficiently be used to enhance light harvesting? Despite its discovery many years ago, with the potential for becoming a powerful tool for enhanced light harvesting, the slow-photon effect, a manifestation of light-propagation control due to photonic structures, has largely been overlooked. This review presents theoretical as well as experimental progress on this effect, revealing that the photoreactivity of materials can be dramatically enhanced by exploiting slow photons. It is predicted that successful implementation of this strategy may open a very promising avenue for a broad spectrum of light-energy-conversion technologies.

A comprehensive study of the reaction parameters involved in the synthesis of silica thin films with well-ordered uni-directional mesopores.

Ordered mesoporous thin films with well-orientated channels are an important feature in a series of applications including sensors, optics, photocatalysis, and solar cells. However, their preparation remains a great challenge. The structural optimization of highly organized mesoporous silica thin films, with channels perpendicularly orientated to the surface and prepared by a spin-coating technique, is reported. A large series of reaction parameters were revisited with a deep investigation such as the template, solvent, aging time, pH, rotation speed, and duration of spin-coating. The best conditions for each of these different parameters were subsequently used together to control the pore size and channel orientation of the well-organized films. Characterization of the films performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the films had homogeneous pores with a uni-directional orientation. Atomic force microscopy (AFM) and ellipsometric porosimetry analysis (EP) were employed to determine the orientation of the channels, pore size distribution, specific surface, thickness, and the accessible porosity. The present work constitutes an overall view of the different parameters which influence the formation of silica thin films, such as the thickness and the pore size distribution of a film which can be tailored to suit a potential application. The wettability properties of thin films have been studied by measuring the contact angle with different solvents such as water, isopropanol, and toluene.