Wei Yuqing, Wen Gangyao, Balafouti Anastasia, Pispas Stergios, Li Hongfei
Department of Polymer Materials and Engineering, College of Material Science and Chemical Engineering, Harbin University of Science and Technology, Harbin 150040, China.
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 11635, Greece.
J Phys Chem B. 2024 Sep 5;128(35):8605-8612. doi: 10.1021/acs.jpcb.4c03557. Epub 2024 Aug 21.
The aggregation behavior of two amphiphilic hyperbranched copolymers of poly[oligo(ethylene glycol) methacrylate--lauryl methacrylate] (H-[P(OEGMA--LMA)]) at the air/water interface was investigated by using the Langmuir film balance technique and atomic force microscopy (AFM). At the air/water interface, H-[P(OEGMA--LMA)] copolymers spontaneously form the ultrafine network-like monolayer structures of micelles; each micelle consists of a tiny hydrophobic core of one or two carbon backbones and lauryl side groups and a short hydrophilic shell of oligo(ethylene glycol) (OEG) side groups, and the micellar cores are connected by the branching agent ethylene glycol dimethacrylate (EGDMA). These ultrafine micellar structures are successfully revealed by our relative aggregation number method presented in this work, which is based on our previous relative mass method and methylene number method. The surface pressure-molecular area isotherms of POEGMA29%-PLMA71% (weight percent) and POEGMA69%-PLMA31% are condensed and expanded, respectively, because the density/number of OEG side groups in the former shells is smaller than that in the latter case. Upon monolayer compression, the isotherms of the former are classified into regions I-IV, whereas those of the latter are classified into regions II and III based on their different variation trends of surface pressure. Subphase pH has little influence on the isotherms of the two copolymers because the stretching degrees of hydrophilic OEG side groups in the shells are probably limited by the connected cores, which is different from the large effects in our previous block copolymers containing POEGMA or poly[oligo(ethylene glycol) acrylate] blocks. Under neutral and alkaline conditions, in region III, the mean molecular area (mm) values of the isotherms of the two copolymers at 20 °C are smaller than those at 10 °C due to the collapse of the OEG side groups above 15 °C. Furthermore, the isotherms of POEGMA69%-PLMA31% move to larger mm values at 30 °C due to the increased thermal mobility and stretching degrees of more OEG side groups.
采用朗缪尔膜天平技术和原子力显微镜（AFM）研究了两种聚[甲基丙烯酸寡聚（乙二醇）酯 - 甲基丙烯酸月桂酯]两亲性超支化共聚物（H-[P（OEGMA-LMA）]）在空气/水界面的聚集行为。在空气/水界面，H-[P（OEGMA-LMA）]共聚物自发形成胶束的超细网络状单分子层结构；每个胶束由一两个碳主链和月桂基侧链组成的微小疏水核以及寡聚（乙二醇）（OEG）侧链组成的短亲水壳，并且胶束核通过支化剂乙二醇二甲基丙烯酸酯（EGDMA）相连。本文提出的相对聚集数方法成功揭示了这些超细胶束结构，该方法基于我们之前的相对质量法和亚甲基数法。POEGMA29%-PLMA71%（重量百分比）和POEGMA69%-PLMA31%的表面压力 - 分子面积等温线分别是凝聚型和膨胀型的，这是因为前者壳中OEG侧链的密度/数量小于后者。在单分子层压缩时，基于它们不同的表面压力变化趋势，前者的等温线分为I-IV区域，而后者的等温线分为II和III区域。亚相pH对两种共聚物的等温线影响很小，因为壳中亲水性OEG侧链的伸展程度可能受到相连核的限制，这与我们之前含POEGMA或聚[甲基丙烯酸寡聚（乙二醇）酯]嵌段的嵌段共聚物中的大影响不同。在中性和碱性条件下，在区域III中，由于OEG侧链在15℃以上坍塌，两种共聚物在20℃时等温线的平均分子面积（mm）值小于10℃时的值。此外，由于更多OEG侧链的热运动性和伸展程度增加，POEGMA69%-PLMA31%在30℃时等温线向更大的mm值移动。
