作者：賈迪，左太森，sarah rogers，程賀，boualem hammouda，韓志超
關鍵字：共混不互溶，小角中子散射
論文來源：期刊
具體來源：Macromolecules，DOI: 10.1021/acs.macromol.6b00785
發表時間：2016年
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 profiles, and three Flory?Huggins interaction parameters (χPDEA?d?ethanol, χPDEA?D2O, and χd?ethanol?D2O) are obtained. When a small amount of d-ethanol is added to the system, it has a strong interaction with D2O, so it directly gets distributed into the water structure and makes a negative contribution to the dissolution of PDEA (χd?ethanol?D2O is much smaller than χPDEA?d?ethanol and χPDEA?D2O). With the addition of more d-ethanol, its interaction with water becomes weaker, but still stronger than those between PDEA?D2O and PDEA?d-ethanol. Neither d-ethanol nor D2O wants to help the dissolution of PDEA in the first place, until the structure of mixed solvents tends to be pure d-ethanol in the D2O-poor region.