Creep and stress relaxation of hybrid organic-inorganic aerogels N. de la Rosa-Fox 1 , J. A. Toledo Fernández 1 , V. Morales-Flórez 2 , M. Piñero 3 , L. Esquivias 4 1 Dpto. Física de la Materia Condensada, Universidad de Cádiz. España 2 Física de Materiales. ICMSE-CSIC. Sevilla. España. 3 Dpto. Física Aplicada, CASEM, Universidad de Cádiz, España. 4 Dpto Física de la Materia Condensada, Universidad de Sevilla. España nicolas.rosafox@uca.es, Keywords: organic-inorganic hybrid aerogel, uniaxial compression, nanoindentation, creep compliance, stress relaxation. Abstract. Organic/inorganic hybrids silica aerogels were synthesized by the classical sol-gel method with application of high power ultrasounds to the liquid mixture. Precursors were tetraethoxysilane (TEOS), as inorganic phase, and polydimethyl siloxane (PDMS), as organic one. These hybrid organic-inorganic materials are known as ORMOSIL (ORganically MOdified SILicates). Monolithic aerogels were obtained by supercritical drying in ethanol. Failure tests by uniaxial compression shows an increase of the rupture modulus as well as a decrease of the Young’s modulus with the polymer content, tuning from a brittle solid to a rubbery-like one. These hybrid aerogels behave as elastomers showing a decrease in the relaxation viscoelastic modulus. Nanoindentation tests have been performed in these hybrid aerogels: load/unload cycles about 1.5 mN of maximum load have shown a decreasing value of the reduced modulus, as well as both plastic and elastic work with the organic content, while hardness remains almost constant. Elastic recovery parameter rised with the increasing organic content. Results from creep tests made with uniaxial compression configuration are discussed and compared with nanoindentation. Viscoelastic behavior of these hybrids materials can be described by a rheological model. Introduction Organic/inorganic hybrid silica aerogels are nanostructured materials that combine mechanical and texture properties of a nanoporous silica matrix with those from the organic polymer phase embedded into it [1]. These kinds of materials gather characteristics that make them very attractive from a practical point of view because they show optical transparency as well as high porosity. They also possess some characteristics from organic polymers, such as flexibility, low density and formability, while the inorganic fraction contributes for increasing surface hardness and strength, and improving transparency and good optical properties [2]. From a mechanical point of view, their behaviour can be tuned from fragile to rubber, depending on the content of the organic polymer and the copolymerization degree. This qualitative change can be explained in terms of the percolation of the organic phase [3]Their structural applications are restricted due to one of the main drawbacks of silica aerogels: its fragility. However, a kind of aerogels, tens times stronger than those of typical aerogels, have been prepared by Leventis´group by means crosslinking silica with some organic polymers on the original gel skeletons. For this, they used 3-aminopropyltriethoxysilane as a co-precursor to obtain wet gels with amino groups on their surfaces. The reinforced of the network was achieved by connecting the Key Engineering Materials Vol. 423 (2010) pp 167-172 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.423.167 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 83.46.15.231-05/09/09,07:34:22)