Chair of Polymer Sciences, Department of Chemistry, MV Lomonosov Moscow State University, Moscow 119991, Russia.
Langmuir. 2012 Aug 28;28(34):12663-70. doi: 10.1021/la302606a. Epub 2012 Aug 17.
Mixed polymer micelles with hydrophobic polystyrene (PS) core and ionic amphiphilic poly(4-vinylpyridine)/poly(N-ethyl-4-vinylpyridinium bromide) corona (P4VP/PEVP) spontaneously self-assembled from mixtures of PS-b-PEVP and PS-b-P4VP macromolecules in dimethylformamide/methanol/water selective solvent. The fraction of PEVP units in corona was β = [PEVP]/([PEVP] + [P4VP]) = 0.05-1.0. Micelles were transferred into pure water via dialysis technique and pH was adjusted to 9, where P4VP blocks are insoluble. Structural characteristics of micelles as a function of corona composition β were investigated. Methods of dynamic and static light scattering, electrophoretic mobility measurements, sedimentation velocity, transmission electron microscopy, and UV spectrophotometry were applied. Spherical morphology with core (PS)-shell (P4VP)-corona (PEVP) organization was postulated. Micelles demonstrated a remarkable inflection in structural characteristics near β ~ 0.5-0.7. Above this region, aggregation number (m), core and corona radii of mixed micelles coincided with those of individual PS-b-PEVP micelles. When β decreased below 0.5, dramatic growth of aggregation number was observed, accompanied by growth in micelle size and stretching PEVP chains. At β below 0.2, dispersions of mixed micelles were unstable and easily precipitated upon addition of NaCl. Scaling relationships between micelle characteristics and β were obtained via minimization the micelle free energy, taking into account electrostatic, osmotic, volume, and surface contributions. Theoretical estimations predicted dramatic influence of β on aggregation number, m ~ β(-3). This result is in general agreement with experimental data and confirms the correctness of the core-shell-corona model. The inflection in micelle characteristics entails drastic changes in micelle dispersion stability in the presence of oppositely charged polymeric (sodium polymethacrylate) or amphiphilic (sodium dodecyl sulfate) complexing agents.
具有疏水性聚苯乙烯 (PS) 核和离子两亲性聚 (4-乙烯基吡啶)/聚 (N-乙基-4-乙烯基溴化吡啶) 冠 (P4VP/PEVP) 的混合聚合物胶束由 PS-b-PEVP 和 PS-b-P4VP 大分子在二甲基甲酰胺/甲醇/水选择性溶剂中自组装而成。冠层中 PEVP 单元的分数β=[PEVP]/([PEVP]+[P4VP])=0.05-1.0。通过透析技术将胶束转移到纯水中，并将 pH 值调节到 9，此时 P4VP 嵌段不溶。研究了冠层组成β对胶束结构特征的影响。应用了动态和静态光散射、电泳迁移率测量、沉降速度、透射电子显微镜和紫外分光光度法。提出了具有核（PS）-壳（P4VP）-冠（PEVP）组织的球形形态。在β0.5-0.7 附近，胶束的结构特征出现了显著的拐点。在该区域之上，混合胶束的聚集数（m）、核和冠半径与单独的 PS-b-PEVP 胶束一致。当β降低到 0.5 以下时，观察到聚集数的急剧增长，伴随着胶束尺寸的增长和拉伸的 PEVP 链。当β低于 0.2 时，混合胶束的分散体不稳定，加入 NaCl 后容易沉淀。通过最小化胶束自由能，考虑静电、渗透、体积和表面贡献，获得了胶束特性和β之间的标度关系。理论估计预测β对聚集数的巨大影响，mβ^(-3)。这一结果与实验数据基本一致，证实了核壳冠模型的正确性。胶束特性的拐点导致在存在带相反电荷的聚合物（聚甲基丙烯酸钠）或两亲性（十二烷基硫酸钠）络合剂时，胶束分散体稳定性发生剧烈变化。
