Gjerde Natalie, Zhu Kaizheng, Nyström Bo, Knudsen Kenneth D
Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway.
Phys Chem Chem Phys. 2018 Jan 24;20(4):2585-2596. doi: 10.1039/c7cp07240f.
Understanding self-assembly of amphiphilic copolymers in aqueous solution is an important issue in many areas, e.g., in order to tailor-make carriers for drugs and genes. We have synthesized modified versions of the copolymer of type PEO-PPO-PEO (Pluronic, F127), with short (PCL(5)) or long (PCL(11)) PCL blocks at both ends. Turbidity, dynamic light scattering (DLS), small angle neutron scattering (SANS), and rheology measurements were carried out on dilute aqueous solutions of these polymers to investigate their self-assembly behavior. The DLS results clearly show that both micellization and inter-micellization can be controlled by polymer concentration, temperature, and length of the PCL block. The interplay between unimers, micelles, and clusters of micelles could be monitored and the size and size distribution of the species were determined. The SANS data could be portrayed by a spherical core-shell model at all considered conditions of temperature and concentration for F127 and PCL(5) apart from F127 at the lowest temperature measured. The SANS data for PCL(11) were described by a spherical core-shell model at low temperatures, whereas at elevated temperatures asymmetric sub-structures appeared and a cylindrical core-shell model was employed in the analysis of the data. The appearance of pronounced correlation peaks at elevated temperatures signalizes marked intermicellar interactions. The shear viscosity data revealed a minor shear thinning effect, suggesting that the interchain structures are rather stable and not easily disrupted. The work shows that PCL-modification of Pluronic has a large influence on the self-assembly process and on the final structure of the assemblies.
了解两亲性共聚物在水溶液中的自组装是许多领域的一个重要问题，例如，以便定制药物和基因载体。我们合成了PEO-PPO-PEO型共聚物（普朗尼克，F127）的改性版本，其两端带有短的（PCL(5)）或长的（PCL(11)）PCL嵌段。对这些聚合物的稀水溶液进行了浊度、动态光散射（DLS）、小角中子散射（SANS）和流变学测量，以研究它们的自组装行为。DLS结果清楚地表明，胶束化和胶束间相互作用都可以通过聚合物浓度、温度和PCL嵌段的长度来控制。可以监测单体、胶束和胶束簇之间的相互作用，并确定这些物种的尺寸和尺寸分布。除了在最低测量温度下的F127外，在所有考虑的温度和浓度条件下，F127和PCL(5)的SANS数据都可以用球形核壳模型来描述。PCL(11)在低温下的SANS数据用球形核壳模型描述，而在高温下出现不对称子结构，在数据分析中采用了圆柱形核壳模型。高温下明显相关峰的出现表明存在明显的胶束间相互作用。剪切粘度数据显示出轻微的剪切变稀效应，表明链间结构相当稳定，不易被破坏。这项工作表明，普朗尼克的PCL改性对自组装过程和组装体的最终结构有很大影响。
