Coldstream Jonathan G, Camp Philip J, Phillips Daniel J, Dowding Peter J
School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, Scotland, UK.
Infineum UK Ltd., P.O. Box 1, Milton Hill, Abingdon OX13 6BB, England, UK.
Soft Matter. 2022 Sep 14;18(35):6538-6549. doi: 10.1039/d2sm00741j.
The structures of amphiphilic block and gradient copolymers in solution and adsorbed onto surfaces are surveyed using molecular-dynamics simulations. A bead-spring model is used to identify the general effects of the different architectures: block and gradient copolymers have equal numbers of solvophilic and solvophobic beads, and the gradient copolymer is represented by a linear concentration profile along the chain. Each type of isolated copolymer forms a structure with a globular head of solvophobic beads, and a coil-like tail of solvophilic beads. The radius of gyration of a gradient copolymer is found to be much more sensitive to temperature than that of a block copolymer due to an unravelling mechanism. At finite concentrations, both gradient and block copolymers self-assemble into micelles, with the gradient copolymers again showing a larger temperature dependence. The micelles are characterised using simulated scattering profiles, which compare favourably to existing experimental data. The adsorption of copolymers onto structureless surfaces is modelled with an attractive potential that is selective for the solvophobic beads, and the surface structures are characterised using the average height of the molecules, and the proportion of beads adsorbed. Both types of copolymer form adsorbed films with persistent micelle-like structures, but the gradient copolymers show a stronger dependence on the strength of the surface interactions and the temperature. Coarse-grained, bead-spring models allow a rapid survey and comparison of the block and gradient architectures, and the results set the scene for future work with atomistic simulations. A superficial but favourable comparison is made between the results from the bead-spring models, and atomistic simulations of a butyl prop-2-enoate/prop-2-enoic acid (butyl acrylate/acrylic acid) copolymer in -dodecane at room temperature.
使用分子动力学模拟研究了两亲性嵌段共聚物和梯度共聚物在溶液中以及吸附到表面上的结构。采用珠簧模型来确定不同结构的一般影响：嵌段共聚物和梯度共聚物具有相等数量的亲溶剂珠和疏溶剂珠，梯度共聚物由沿链的线性浓度分布表示。每种类型的孤立共聚物都形成一种结构，其具有疏溶剂珠的球状头部和亲溶剂珠的线圈状尾部。由于一种解缠机制，发现梯度共聚物的回转半径比嵌段共聚物对温度更敏感。在有限浓度下，梯度共聚物和嵌段共聚物都会自组装成胶束，梯度共聚物再次表现出更大的温度依赖性。使用模拟散射曲线对胶束进行表征，其与现有的实验数据相比具有优势。用对疏溶剂珠具有选择性的吸引势对共聚物在无结构表面上的吸附进行建模，并使用分子的平均高度和吸附的珠的比例来表征表面结构。两种类型的共聚物都形成具有持久胶束状结构的吸附膜，但梯度共聚物对表面相互作用强度和温度的依赖性更强。粗粒化的珠簧模型允许对嵌段和梯度结构进行快速研究和比较，这些结果为未来的原子模拟工作奠定了基础。对珠簧模型的结果与室温下在正十二烷中的丁基丙烯酸酯/丙烯酸共聚物的原子模拟结果进行了表面但有利的比较。
