Journal of Sol-Gel Science and Technology 28, 81–86, 2003 c  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Hybrid Sol-Gel Coatings Produced from TEOS and γ -MPS S. PELLICE AND PABLO GALLIANO INTEMA-Conicet. Mar del Plata, Argentina Y. CASTRO AND A. DUR ´ AN ∗ Instituto de Cer ´ amica y Vidrio (CSIC), Campus de UAM, Cantoblanco, Madrid, Spain aduran@icv.csic.es Received September 19, 2002; Accepted March 18, 2003 Abstract. Hybrids sols from tetraetoxysilane (TEOS) and 3-(methacryloxypropyl) trimethoxysilane (γ -MPS) were prepared in acid medium for different TEOS/γ -MPS ratios and were modified by the addition of a colloidal silica suspension. The stability of the different sols was evaluated by viscosity measurements; the sols showed a Newtonian behaviour and the ageing effect was negligible even after two months from their preparation. Coatings were obtained by dipping at different withdrawal rates and heat-treated between 150 and 250 ◦ C. Transparent coatings with thickness higher than 4 μm were reached for most of the studied compositions. The surface microhardness of coatings for each composition and thermal treatment was evaluated by the pencil hardness test. The thermal stability was followed by simultaneous thermogravimetric and differential thermal analysis (TGA-DTA) determining the limit temperatures at which the coatings can be treated without losing its hybrid character. A structural analysis was made by deconvolution of Fourier transformed infrared spectra (FTIR) of self-supported films observing the influence of the organic groups on the silica network. Keywords: sol-gel, hybrid coatings, γ -MPS, structure, microhardness Introduction Sol-gel method is a simple technique used to pro- duce adherent and crack-free silica coatings, whose most important feature consists on the low sintering temperatures [1, 2]. In the last years, hybrid organic- inorganic coatings have been developed in order to im- prove mechanical, optical and abrasion properties [3– 5]. Trifunctional alkoxysilanes R ′ Si(OR) 3 , where R and R ′ are alkyl groups, have been used as starting materials to introduce organic groups in the coatings. Reactive or- ganic groups present in the alkyl chains, such as vinyl and methacryl groups, can react at low temperature producing crosslinked polymeric networks. One of the trialkoxysilanes usually employed for this purpose is ∗ To whom all correspondence should be addressed. the 3-(methacryloxypropyl)trimethoxisilane (γ -MPS). Recently, hybrid coatings and bulk materials have been obtained from the hydrolysis and condensation of γ - MPS, the microhardness of these coatings being lower than that of glass slides [6]. The silica porosity and Si O Si bond stresses were related to the longitudinal optical (LO) and transversal optical (TO) mode peaks in FTIR spectra [7–10]. In this sense, the effect of the organic content on the silica porosity and Si O Si bond tensile strain have a high importance on the coating properties, such as critical thickness and scratch resistance. The aim of this work was to obtain hybrid inorganic- organic coatings from TEOS and γ -MPS, modified by adding different molar ratios of a colloidal silica sus- pension in order to increase their hardness and scratch resistance.