Mechanical properties of polyacrylic–titania hybrids—microhardness studies

Organic/inorganic (O/I) hybrid materials containing 4.6–19.5 wt% of titania have been prepared using poly(methylmethacrylate-co-butyl methacrylate-co-methacrylic acid) and acetic acid modified tetrabutyl titanate as the sol–gel precursor. The microhardness (MH) of the acrylic–titania hybrids was investigated. The influence of TiO2 content on MH is particularly discussed and compared with similar results obtained with other O/I composite materials. The hybrid material filled with 10.7 vol% of titania is more than twice harder than the polymer matrix. This strong hardening effect is ascribed to the homogeneous dispersion of the filler in the polymer matrix and to the strong filler–polymer interactions. Hardness was found to be related to the density of hybrids through a semi-logarithmic relationship. Besides, the glass transition temperature Tg of hybrids was determined from temperature dependence of hardness. The Tg evolution with titania content is discussed with reference to solvent extraction results. Finally, the time-dependence of MH reveals that the inorganic network more strongly affects the creep behavior of the polymer above Tg than below Tg.