Self-organization, structure, dynamic properties, and surface morphology of silica/epoxy films as seen by solid-state NMR, SAXS, and AFM

The high degree of self-assembling of epoxide-based products made from functionalized organosilica building blocks, functionalized oligo(oxypropylene)-diamine and/or -triamine, and colloidal silica nanoparticles was evidenced by solid-state NMR spectroscopy, small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM). Under optimized conditions of preparation, isolated siloxane cagelike clusters arise in the reaction mixture. No cleavage of oxirane rings occurs before thermal curing, and thus the whole process is well controlled. The presence of silica nanoparticles accelerates the kinetics of polycondensation and affects the condensation rate of siloxane units in final products. Two-dimensional solid-state NMR experiments (2D CRAMPS, 2D H-1-C-13 and H-1-Si-29 HETCOR, WISE) revealed differences in structure and segmental dynamics of final films as well as in self-organization and homogeneity degree depending on reaction conditions. Ideally, siloxane cagelike clusters are regularly dispersed within the bulk and oxypropylene chains form phase which separates organic tails of siloxane clusters. The SAXS determined distance between clusters (1.8 nm) well corresponds to the constraints determined by NMR spin-diffusion experiments. Polymer interaction with silica nanoparticles is confirmed by two-dimensional H-1-Si-29 HETCOR experiments.