Chen Hongxu, Wen Gangyao, Chrysostomou Varvara, Pispas Stergios, Li Hongfei, Sun Zhaoyan
School of Material Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China.
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 11635, Greece.
Langmuir. 2021 Feb 23;37(7):2419-2425. doi: 10.1021/acs.langmuir.0c03424. Epub 2021 Feb 11.
The ion specificity effect on the water solubility of poly(-isopropylacrylamide)-containing copolymers complies with the Hofmeister series, which is applicable to other copolymers or not need to be explored. In this work, effects of ionic strength under acidic conditions and ion specificity under alkaline conditions on the air/water interface behavior of two amphiphilic diblock copolymers poly(dimethylaminoethyl methacrylate)-poly(lauryl methacrylate) (PDMAEMA-PLMA) were systematically studied. Under acidic conditions, the surface pressure-area isotherms of a predominantly hydrophilic copolymer are insensitive to ionic strength. In contrast, the isotherms of a predominantly hydrophobic copolymer successively shift to the large, small, and large molecular area with the increase of ionic strength. Under alkaline conditions, the interfacial stretch degrees of PDMAEMA chains of two copolymers change with salt species and concentrations, which do not comply with the Hofmeister series. All of the Langmuir-Blodgett films of the former copolymer exhibit separate circular micelles. Nevertheless, those of the latter copolymer obtained under alkaline conditions exhibit various distinctive morphologies such as separate circular micelles, large separate PLMA cores within large PDMAEMA domains, and large PLMA domains/aggregates surrounded by short PDMAEMA shells. It can be attributed to the high deformability of PLMA chains, the ion specificity effect on the stretch degree of PDMAEMA blocks, and their underwater solubility upon compression.
离子特异性对含聚（-异丙基丙烯酰胺）共聚物水溶性的影响符合霍夫迈斯特序列，该序列是否适用于其他共聚物有待探索。在本工作中，系统研究了酸性条件下的离子强度和碱性条件下的离子特异性对两亲性二嵌段共聚物聚（甲基丙烯酸二甲氨基乙酯）-聚（甲基丙烯酸月桂酯）（PDMAEMA-PLMA）气/水界面行为的影响。在酸性条件下，主要为亲水性共聚物的表面压力-面积等温线对离子强度不敏感。相反，主要为疏水性共聚物的等温线随着离子强度的增加依次向大分子面积、小分子面积和大分子面积移动。在碱性条件下，两种共聚物的PDMAEMA链的界面拉伸程度随盐种类和浓度而变化，这不符合霍夫迈斯特序列。前一种共聚物的所有朗缪尔-布洛杰特膜均呈现分离的圆形胶束。然而，在碱性条件下获得的后一种共聚物的膜呈现出各种独特的形态，如分离的圆形胶束、大PDMAEMA域内的大分离PLMA核以及由短PDMAEMA壳包围的大PLMA域/聚集体。这可归因于PLMA链的高可变形性、离子特异性对PDMAEMA嵌段拉伸程度的影响以及它们在压缩时的水下溶解性。
