Re-entrance of Poly(N,N-diethylacrylamide) in D2O/d-Ethanol Mixture at 27 °C

Abstract

The re-entrance of poly(N,N-diethylacrylamide) (PDEA) in D2O/d-ethanol mixtures (i.e., the coil-to-spherical aggregates-to-coil transition) has been observed at 27 °C by small-angle neutron scattering (SANS). PDEA has a lower critical solution temperature (LCST) phase diagram in the D2O-rich region and is soluble in the D2O-poor region for all of the observed temperature ranges. Its spinodal temperature decreases first from 33.5 °C in pure D2O to 26.7 °C in 80% D2O/20% d-ethanol and then increases to 283.1 °C in 50% D2O/50% d-ethanol. With the further decrease of D2O content, PDEA dissolves well, and its phase boundary can no longer be observed by SANS. Therefore, at 27 °C, PDEA dissolves as random coils when the D2O content is higher than 90% and then collapses and aggregates to form the globule phase in 20% D2O/80% d-ethanol; finally, it reswells and behaves as random coils again with excluded volume in the D2O-poor region. The ternary random phase approximation model (RPA) is used to analyze the SANS p...