Following the growth process in macroporous methylsilsesquioxane films at the single macropore level by confocal correlation spectroscopy

Optical microscopy and in situ single pore confocal correlation spectroscopy (CCS) were used to study the evolution of macroporous methylsilsesquioxane (MSQ) films formed by the acid-catalyzed hydrolysis and condensation of methyltrimethoxysilane. Spinodal decomposition and gelation in the films were directly observed using these methods. Phase separation was found to occur 5 h 40 min after sol preparation, followed by gelation at 6 h 50 min. MSQ nanoparticles appeared in the films very early after sol preparation. These nanoparticles produced bursts of elastically scattered light as they passed through the detection volume. Detailed information on nanoparticle growth was obtained by recording single point time transients in the sol film and in individual pores of the phase-separated and gelled matrix. Apparent diffusion coefficients and average nanoparticle sizes were obtained by fitting autocorrelations of the time transient data to an appropriate expression. The nanoparticles were found to grow rapidly to a maximum diameter of similar to 30 nm and to remain in this size range until well after gelation of the matrix. Nanoparticle size stabilization was attributed to consumption of reactive species and to changes in nanoparticle surface reactivity brought about by the condensation process. Beginning soon after gelation, incorporation of the nanoparticles in/on the matrix was evidenced by a decrease in the number of particles present in the pores. After a delay of similar to 3 h, nanoparticle growth within the pores resumed, as exhibited by a decrease in their apparent diffusion coefficients. Nanoparticle growth in this later phase, was attributed to aggregation of nonpolar MSQ particles.