Re-entrance of Poly(N,N-diethylacrylamide) in D2O/d-Ethanol Mixture at 27 °C
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- 作者：Di Jia ; Taisen Zuo ; Sarah Rogers ; He Cheng ; Boualem Hammouda ; Charles C. Han
- 刊名：Macromolecules
- 出版年：2016
- 出版时间：July 26, 2016
- 年：2016
- 卷：49
- 期：14
- 页码：5152-5159
- 全文大小：501K
- 年卷期：0
- ISSN：1520-5835
文摘
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.