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.