Dependence of nanophase separated structure of epoxy hydrogels on swelling conditions investigated by SANS

A hydrophilic non-stoichiometric epoxy network was prepared by end-linking reaction of α,ω-diamino terminated poly(oxypropylene)-b-poly(oxyethylene)-b-poly(oxypropylene) (POP-POE-POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA) at the excess of amino groups. Series of epoxy hydrogels swollen to various degrees was prepared by swelling of the epoxy network in D₂O and solutions of inorganic salt (KNO₃) in D₂O, respectively, and investigated by small-angle neutron scattering (SANS). Degree of swelling was controlled in two ways: by partial evaporation of the solvent and by KNO₃ concentration in the swelling solution. Nanophase separated structure of all hydrogels was confirmed by SANS. Scattering data were fitted to the Teubner-Strey model assuming bicontinuous locally lamellar structure of the hydrogels. Changes in SANS profiles induced by the presence of KNO₃ in swelling solutions reflect a refinement of the nanophase separated structure of hydrogels caused by improvement of POE-D₂O interaction by means of breakage of deuterium-bonded structure of D₂O by nitrate anions.