Synthesis-Morphology-Mechanical Properties Relationships Of Polymer-Silica Nanocomposite Hybrid Materials
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, L. DAVID , J.F. GERARD 2 , H. KADDAMI 2,3 , J.P. PASCAULT 2 , G. VIGIER 1
I GEMPPM, UMR-CNRS 5510, INSA de Lyon, 69621 Villeurbanne cedex, France. 2 LMM, UMR-CNRS 5627, INSA de Lyon, 69621 Villeurbanne cedex France. 3 Universit6 Cadi Ayyad, F.S.T., D~partement de Chimie, BP 618, Marrakech 4000, Maroc.
ABSTRACT Two types of polymer-silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized Si0 2 nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol-gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis, morphology and mechanical properties are discussed mainly on the basis of solid state 29Si nuclear magnetic resonance spectroscopy (NMR), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA). INTRODUCTION A new class of materials based on organic and inorganic species combined at a nanoscale level has gained ever more attention during the last decade [1-6]. These new materials, so called nanocomposites or organic-inorganic hybrids, can be considered as composites which at least one phase is below 100 nm. Such a fine morphology is expected to lead to new interesting properties such as the possibility to obtain (i) optically transparent materials or (ii) an enhanced mechanical behavior, compared to classical microheterogeneous composites. These hybrid systems can be prepared by following various synthesis routes, thanks to the ability to combine different ways to introduce each phase. The organic one can be introduced as (i) a monomer, (ii) a polymer (in molten, solution, or emulsion states), or (iii) a preformed organic network. The mineral part can be introduced as (i) a monomer (e.g. a metal alkoxide), (ii) preformed nanoparticles, whiskers or platelets, and finally (iii) an existed porous structure (e.g. aerogel). In the present study, two different synthesis routes are considered to prepare two types of polymer-silica nanocomposite films (about 2 mm-thick) with the same chemical composition. The first route, denoted Type 1, consists in a bulk free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in the presence of HEMA-functionalized silica nanoparticles. The second route, denoted Type 2, is based on the in situ synthesis of a silicarich phase during the free radical polymerization of HEMA. In this case, silica results from a classical acid-catalyzed reaction, involving hydrolysis and condensation of tetraethoxysilane (TEOS). No addition of solvent was necessary because HEMA is a good cosolvent of TEOS and water, and the viscosity is low. The silica content of these hybrid films can be adjusted between 0 and 30 wt%. The aim of this paper is to establish relationships between the synthesis conditions, the resulting morphologies, and the mechanical properties of these polymer-silica nanocomposites. Practical applications will be d
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