Investigation of Polymer Hydrogels by Small-Angle Neutron Scattering

I. Krakovský

 (Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic)

Polymer hydrogel formation is a result of delicate interplay between elasticity of crosslinked polymer chains and thermodynamic compatibility of polymer network blocks with water. Therefore, polymer hydrogels respond very sensitively to changes of external parameters (temperature, pressure, chemical composition of surrounding medium, presence of species specifically interacting with chemical moieties attached to polymer network structure, etc.) by adaptation of its structure.

Epoxy networks are very versatile materials whose properties can be tuned by chemistry, functionality, and flexibility of the precursors used in their preparation. We have prepared hydrophilic epoxy networks by end-linking reactions of telechelic polyoxypropylene (POP), polyoxyethylene (POE) and their copolymers. Epoxy-based hydrogels were obtained by swelling of these networks to equilibrium in water.

Whereas POE remains hydrophilic within the temperature range 0 – 100 °C, POP is hydrophilic at temperatures below ca 15 °C. Moreover, POE and POP differ significantly in interaction with surfactants in water. Consequently, water in hydrogels is not distributed uniformly but gives rise to a temperature and surfactant sensitive structure consisting of water-rich and water-poor nanodomains. In this communication SANS study of structural changes in epoxy-based hydrogels induced by change of temperature and surfactant concentration will be discussed.