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 acryl ate) encapsulating nanoparticles of silica. Two kinds of silica have b een used for the preparation of the latexes: one of them has been func tionalized by treatment with methacryloylpropyltrimethoxysilane, and t he other has not. The molecular and colloidal properties of the latexe s were described previously. In both cases the resulting films are ful ly transparent up to a high silica content. Small-angle X-ray scatteri ng gives evidence that a good dispersion of the filler is obtained whe n encapsulated functionalized silica is involved in film formation. On the other hand, small agglomerates are present in the elastomeric mat erial when non-functionalized silica is employed; their size is estima ted from scanning electron microscopy. The mechanical properties of th e two series of films are strongly different, as shown by either stres s-strain experiments or from dynamic mechanical measurements. Very hig h elongations at break are obtained when the silica is functionalized, so that a part of the polymer is covalently bound to it as tight loop s. To account for these properties, a qualitative model is proposed an d some validation experiments are described.