Phase Transition and Preferential Alcohol Adsorption of Poly(N,N-diethylacrylamide) Gel in Water/Alcohol Mixtures
Phase Transition and Preferential Alcohol Adsorption of Poly(N,N-diethylacrylamide) Gel in Water/Alcohol Mixtures
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DOI：
10.1021/ma502393z
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发表时间：
2015-02-24
期刊：
影响因子：
5.5
通讯作者：
Feng, Jiwen
中科院分区：
文献类型：
--
作者：
Liu, Biaolan;Wang, Jian;Feng, Jiwen
通过变温高分辨率 H-1 MAS NMR 系统研究了水/醇（甲醇、乙醇、异丙醇和正丙醇）混合物中聚（N,N-二乙基丙烯酰胺）（PDEA）凝胶网络的相分离。 PDEA凝胶在具有较大醇疏水基团的水/异丙醇和水/正丙醇混合物中表现出融合效应和重入相变，但在具有较小醇疏水基团的水/甲醇和水/乙醇中则不表现出融合效应和重入相变，这与在所有水/醇溶液中观察到融合效应的聚(N-异丙基丙烯酰胺)的情况相反。在目前的PDEA凝胶中，相分离的特征是PDEA的疏水性烷基脱水，在低于临界溶液温度的情况下产生两种不同类型的水/醇溶液：凝胶网络内的受限二元溶剂（每个PDEA重复单元3-5个溶剂分子）和凝胶外的游离二元溶剂。受限混合溶剂中的醇浓度明显高于自由混合溶剂中的醇浓度，并且随着醇部分疏水性的增加而增加。有趣的是，收缩网络内的酒精富集不会导致 PDEA 网络进一步脱水。此外，收缩的PDEA凝胶网络的侧链迁移率因醇的出现而增强，并且随着醇部分的疏水性而增加。我们的结果表明，酒精和凝胶网络之间存在强烈的相互作用。
The phase separation of poly(N,N-diethylacrylamide) (PDEA) gel network in water/alcohol (methanol, ethanol, isopropanol, and n-propanol) mixtures has been systematically investigated by variable-temperature high-resolution H-1 MAS NMR. The PDEA gel exhibits the cononsolvency effect and reentrant phase transition in water/isopropanol and water/n-propanol mixtures with larger alcohol hydrophobic groups but not in the water/methanol and water/ethanol bearing smaller alcohol hydrophobic groups, in contrast to the case of poly(N-isopropylacrylamide) where the cononsolvency effect was observed in all water/alcohol solutions. In the present PDEA gel, the phase separation is characterized by dehydration of the hydrophobic alkyl groups of PDEA, resulting in two distinct types of water/alcohol solutions above the lower critical solution temperature: confined binary solvents (3-5 solvent molecules per PDEA repeating unit) inside the gel network and free binary solvents outside the gel. The alcohol concentration in confined mixture solvents is markedly higher than that in free mixture solvents and increases with increasing hydrophobicity of the alcohol moiety. Interestingly, the alcohol enrichment inside the shrunk network does not cause additional dehydration of the PDEA network. Besides, the side chain mobility of shrunk PDEA gel network is enhanced by the appearance of alcohol and increases with the hydrophobicity of alcohol moiety. Our results reveal that there exists a strong interaction between alcohol and gel network.