Novel highly hydrophilic organic/inorganic composites based on polyacrylamide and silica: synthesis strategy, structure and swelling behaviour

A series of novel hydrophilic organic-inorganic composites (OIC) with enhanced sorption properties were synthesized by one-pot synthesis technique - in situ radical polymerization of acrylamide (AM) and hydrolytic polycondensation of sodium silicate in aqueous solution. Formation of mixed organic-inorganic polyacrylamide (PAM)/SiO₂ phase has been detected by FTIR spectroscopy (appropriate changes in H-bonds network structure of PAM) and DSC analysis (dramatic decreasing glass temperature of PAM). Additive decreasing of mass loss of OIC with increasing of SiO₂ content is explained by the increasing of PAM-content in mixed PAM/SiO₂ phase on the interface of organic and inorganic phases. The formation of SiO₂ aggregates with different dispersity, which, in their turn, form submicron structures in composites with SiO₂ content more than 15 wt.% was observed from SEM data. Structurization of OIC resulted in the enhanced sorption characteristics (swelling capacity of the OIC reaches 2730%). Sorption kinetic curves obtained both in isothermic and isochoric regimes demonstrate that the swelling process of OIC is limited by relaxation of PAM chains and can be described by sorption mechanism of Type II.