Zhang Yu, Wen Gangyao, Giaouzi Despoina, Pispas Stergios, Li Jian
Department of Polymer Materials and Engineering, College of Material Science and Chemical Engineering, Harbin University of Science and Technology, 4 Linyuan Road, Harbin 150040, People's Republic of China.
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens 11635, Greece.
Langmuir. 2024 Apr 16;40(15):8284-8290. doi: 10.1021/acs.langmuir.4c00437. Epub 2024 Apr 3.
The aggregation behavior of amphiphilic block copolymers at the air-water interface has been extensively studied, but less attention was given to that of star copolymers. In this work, we studied the interfacial aggregation behavior of two double hydrophilic pH- and temperature-responsive miktoarm star copolymers of poly[di(ethylene glycol) methyl ether methacrylate]-poly[2-(dimethylamino)ethyl methacrylate] (PDEGMA-PDMAEMA and PDEGMA-PDMAEMA, the subscripts denote arm numbers) with different molecular weights. The effects of subphase pH and temperature on the monolayer isotherms and hysteresis curves of the two star copolymers and the morphologies of their Langmuir-Blodgett (LB) films were studied by the Langmuir film balance technique and atomic force microscopy, respectively. At the air-water interface, the two star copolymers tend to form closely packed micelles. These micelles exhibit a core-shell structure, where the small hydrophobic core consists of cross-linker of ethylene glycol dimethacrylate (EGDMA) and the carbon backbones of PDEGMA and PDMAEMA arms and the short hydrophilic shell is composed of di(ethylene glycol) and tertiary amine side groups. With increasing subphase pH, the surface pressure versus molecular area isotherms shift toward larger mean molecular areas as a result of the enhanced interface adsorption of nonprotonated tertiary amine groups. The isotherm shift of PDEGMA-PDMAEMA monolayers is primarily attributed to high density of tertiary amine groups in the shells, while that of PDEGMA-PDMAEMA is mainly attributed to high density of di(ethylene glycol) groups in the shells. The hysteresis degrees in the monolayers of the two copolymers under alkaline and neutral conditions are greater than those under acidic conditions due to the decreased protonation degree of the tertiary amine groups. At 10 °C, the mobility of the shells is poor and the isotherms are located on the right. Above the lower critical solution temperature, di(ethylene glycol) groups contract, which causes a slight shift of the isotherms toward smaller mean molecular areas.
两亲性嵌段共聚物在气-水界面的聚集行为已得到广泛研究，但星型共聚物的相关研究较少。在本工作中，我们研究了两种具有不同分子量的聚[二（乙二醇）甲基醚甲基丙烯酸酯]-聚[2-（二甲氨基）乙基甲基丙烯酸酯]（PDEGMA-PDMAEMA和PDEGMA-PDMAEMA，下标表示臂数）的双亲水pH和温度响应性米克托臂星型共聚物的界面聚集行为。分别采用朗缪尔膜天平技术和原子力显微镜研究了亚相pH和温度对两种星型共聚物的单分子层等温线和滞后曲线及其朗缪尔-布洛杰特（LB）膜形态的影响。在气-水界面，两种星型共聚物倾向于形成紧密堆积的胶束。这些胶束呈现核壳结构，其中小的疏水核由乙二醇二甲基丙烯酸酯（EGDMA）交联剂以及PDEGMA和PDMAEMA臂的碳主链组成，短的亲水壳由二乙二醇和叔胺侧基组成。随着亚相pH的增加，由于未质子化叔胺基团的界面吸附增强，表面压力对分子面积等温线向更大的平均分子面积移动。PDEGMA-PDMAEMA单分子层的等温线移动主要归因于壳层中叔胺基团的高密度，而PDEGMA-PDMAEMA的等温线移动主要归因于壳层中二乙二醇基团的高密度。由于叔胺基团的质子化程度降低，两种共聚物在碱性和中性条件下单分子层的滞后程度大于酸性条件下的滞后程度。在10℃时，壳层的流动性较差，等温线位于右侧。低于下临界溶液温度时，二乙二醇基团收缩，导致等温线向较小的平均分子面积略有移动。
