Wet Chemistry and Surface Functionalization

M. Langlet, O. Chaix, E. Pernot

PhD's and post-docs (2005-2010): S. Briche, M. Fallet, C. Holtzinger, M. Houmard, M. Messaoud, C. Millon, S. Permpoon, D. Riassetto, V.Gate
 

Objectives

This activity is a logical pursuit of previous works initiated in the early 90' in the field of functional coatings deposited through sol-gel routes. Over the past years, these studies have been widened  to new chemical methods in liquid solution, photochemical methods, and to their association with the sol-gel process. Thus, while surface functionalizations remain the main objectives of this work, synthesis efforts are essentially focused on liquid solution formulations through low cost procedures. Our goal is to set up original protocols giving access to a wide know-how, which enables us answering various needs. Over the past years, this skill has been concretised by several institutional or private contracts in association with different technological centres and industrial companies. Beside functionalities of interest, particular attention is given to the formulation of liquid solutions compatible with the deposition of homogeneous and optical grade coatings. Industrial criteria are also taken into consideration such as a prolonged lifetime of liquid solutions in bottle, which guarantees reproducible deposition conditions over a long period of time using a same solution, or again optimized coating adhesion and mechanical resistance, in order to fulfil durability criteria in practical application conditions.

Projects in progress are:

• Actiprotex project, in the frame of the Techtera pole of competitivity, including IFTH and a consortium of French textile industries as main partners.
• Contract with Ferrari Company for applications on outdoor technical textiles.
• Contract with Arcelor-Mittal Company, in collaboration with Simap laboratory (Grenoble Institute of Technology).
• Microsol-PV project, including CEA, INES, a consortium (PV Alliance) of French industries involved in new energy applications, and  LaHC laboratory (UJM, St Etienne) as partners.

Main activity topics

• Oxide coatings

All-oxide sols are formulated trough sol-gel routes in order to be deposited as single- or multi-layer coatings on various substrates. Over the past years, a particular importance has been given to TiO2 coatings deposited from polymeric sols or nano-crystallite liquid suspensions. These coatings are studied for their photo-induced properties under UV light (photocatalysis, photo-hydrophilicity) in the frame of self-cleaning applications. Crystalline suspensions are particularly adapted to a self-cleaning functionalization on low thermal stability substrates, such as polymers or textiles. TiO2 coatings are also studied for optical applications (high refractive index transparent coatings), and a direct photo-imprinting procedure has in particular been developed for the creation of TiO2-derived diffraction patterns, which are studied to enhance the light penetration in photovoltaic devices.

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• Nano-composite oxide coatings

Sol-gel routes are studied to formulate multi-component solutions from mixtures of polymeric and particulate sols. For instance, nano-composite SiO2-TiO2 coatings derived from such mixed sols are studied for their natural and persistent superhydrophilicity. This original property is characterized through static and dynamic wettability measurements. It  allows envisaging easy-cleaning surfaces, through simple water-rinsing without detergent, in indoor atmospheres where UV light cannot be permanently present. 

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• Functionalization from hybrid organic/inorganic sols

Sol-gel derived hybrid organic/inorganic sols are formulated to deposit silica-based hybrid coatings, which associate particular functionalities arising from the organic component to inherent properties of a silica matrix. Such approaches have, for instance, been developed to induce a hydrophobic functionalization on cotton-based textiles through long alkyl chains. So-functionalized textile fabrics exhibit a marked water repellence behavior. Such hybrid approaches are also studied for the direct photo-imprinting of micron-size patterns on epoxy-based photopolymerizable coatings, which are studied for integrated-optics or surface pixelisation applications..

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• Metal nano-particles

Photo-chemistry routes are developed to elaborate metal nano-particles which can be dispersed on various supports, for instance to form metal/oxide heterostructures. Photolytic reduction mechanisms have in particular been studied to prepare metal platinum nano-particles in liquid solutions. The dispersion of such particles is studied to enhance the photocatalytic activity of TiO2 coatings, through Schottky diode effects, while the dispersion of these particles on TiO2 pigments is studied to propose new cathode materials for PEMFC (Proton Exchange Membrane Fuel Cell) applications. Reductive photocatalytic mechanisms are also studied to form metal silver nano-particles. Such particles elaborated in TiO2 crystalline suspensions are, for instance, studied to induce an anti-bacterial functionality on textile fabrics. Silver particles dispersed on TiO2 coating supports are also studied for biosensor applications through a SERS (Surface Enhanced Raman Scattering) effect. The dispersion of such particles on photo-imprinted TiO2 motives can in particular allow envisaging an addressed detection of bio-molecules. 

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