POLY(ETHYL ACRYLATE) LATEXES ENCAPSULATING NANOPARTICLES OF SILICA .3. MORPHOLOGY AND MECHANICAL-PROPERTIES OF REINFORCED FILMS

Films were prepared through coalescence of latexes of poly(ethyl acrylate) encapsulating nanoparticles of silica. Two kinds of silica have been used for the preparation of the latexes: one of them has been functionalized by treatment with methacryloylpropyltrimethoxysilane, and the other has not. The molecular and colloidal properties of the latexes were described previously. In both cases the resulting films are fully transparent up to a high silica content. Small-angle X-ray scattering gives evidence that a good dispersion of the filler is obtained when encapsulated functionalized silica is involved in film formation. On the other hand, small agglomerates are present in the elastomeric material when non-functionalized silica is employed; their size is estimated from scanning electron microscopy. The mechanical properties of the two series of films are strongly different, as shown by either stress-strain experiments or from dynamic mechanical measurements. Very high elongations at break are obtained when the silica is functionalized, so that a part of the polymer is covalently bound to it as tight loops. To account for these properties, a qualitative model is proposed and some validation experiments are described.