Molecular design of confined organic network hybrids with controlled deformation rate sensitivity and moisture resistance

Abstract

We demonstrate molecular design strategies for engineering the deformation rate sensitivity and fracture resistance of organic-inorganic hybrid films in moist environment. Hybrids with intimate mixing of inorganic and organic molecular networks were synthesized with an epoxy-functionalized silane, (3-glycidoxypropyl) trimethoxysilane and an acetate-stabilized zirconium alkoxide, tetra-n-propoxyzirconium. The highly confined non-hydrolysable organic molecular network connectivity was systematically manipulated by tuning the epoxy ring opening polymerization reaction and the incorporation of carbon bridges of selected lengths. By investigating the corresponding time-dependent crack growth in moist environments, new insights into the fundamental molecular-scale relaxation and cracking mechanisms of the hybrids are provided. These processes were found to be impacted by the confined organic network connectivity which results in significant changes in the deformation rate sensitivity and fracture resistance. With increasing non-hydrolysable organic network connectivity, mechanical behavior that varied from almost perfectly elastic to increasingly viscoelastic could be obtained in a controlled fashion. The related resistance to cracking in moist environments was found to be significantly improved. These findings provide a basis for the rational design of functional hybrids with precisely defined mechanical properties.