Structure and Growth Kinetics of 3-Glycidoxypropyltrimethoxysilane-Derived Organic/Silica Hybrids at Different Temperatures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The structure and the growth kinetics of 3-glycidoxypropyltrimethoxysilane(GPTS)-derived organic/silica hybrids have been studied in situ by small-angle X-ray scattering (SAXS) at 298, 316, and 334 K. The SAXS data were compatible with the growth of silica-rich domains from a fixed number of primary particles, with polydispersity likely increasing with time. The isothermal growth of the average radius of gyration R-g of the domains occurs in a power law with time t as R-g proportional to (t - t(0))(alpha), with t(0) being a small offset time and alpha= 0.247 in the studied temperature range. The SAXS intensity I(0) extrapolated to q = 0 increases in a power law with time as 1(0) = B(t - t(0))(beta) where B is a function of temperature and beta a constant equal to 0.443 in the studied temperature range. The activation energy was evaluated as Delta E = 67.7 +/- 1.1 kJ/mol from an Arrhenius equation for the rate constant k = beta B-1/beta The extrapolated intensity I(0) scales with R-g as I(0) proportional to R-g(D) with D = 1.71 +/- 0.01 in the studied temperature range, in good agreement with the value beta/alpha = 1.79 +/- 0.07 from the kinetic study. This suggests that the macromolecules grow in a dimensionality similar to 1.7, typical of macromolecules in good solvent conditions in diluted or semidiluted solution. A time-independent function F(qR(g)) = 1(q,t)R-g(-D)/Q where Q is the invariant, was found to hold for every time and temperature within a domain limited by a primary particle size. This finding suggests that the system exhibits primary-particle-size-limited dynamic scaling properties.