Institute for Physical Chemistry, Bulgarian Academia of Sciences, 1113 Sofia, Bulgaria.
Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany and Department of Chemistry, University of Virginia, Charlottesville, VA 22901, USA.
Soft Matter. 2017 Mar 1;13(9):1888-1903. doi: 10.1039/c7sm00105c.
Semiflexible polymers under good solvent conditions interacting with attractive planar surfaces are investigated by Molecular Dynamics (MD) simulations and classical Density Functional Theory (DFT). A bead-spring type potential complemented by a bending potential is used, allowing variation of chain stiffness from completely flexible coils to rod-like polymers whose persistence length by far exceeds their contour length. Solvent is only implicitly included, monomer-monomer interactions being purely repulsive, while two types of attractive wall-monomer interactions are considered: (i) a strongly attractive Mie-type potential, appropriate for a strictly structureless wall, and (ii) a corrugated wall formed by Lennard-Jones particles arranged on a square lattice. It is found that in dilute solutions the former case leads to the formation of a strongly adsorbed surface layer, and the profile of density and orientational order in the z-direction perpendicular to the wall is predicted by DFT in nice agreement with MD. While for very low bulk densities a Kosterlitz-Thouless type transition from the isotropic phase to a phase with power-law decay of nematic correlations is suggested to occur in the strongly adsorbed layer, for larger densities a smectic-C phase in the surface layer is detected. No "capillary nematization" effect at higher bulk densities is found in this system, unlike systems with repulsive walls. This finding is attributed to the reduction of the bulk density (in the center of the slit pore) due to polymer adsorption on the attractive wall, for a system studied in the canonical ensemble. Consequently in a system with two attractive walls nematic order in the slit pore can occur only at a higher density than for a bulk system.
在良溶剂条件下，具有吸引力的平面与半柔性聚合物相互作用，通过分子动力学（MD）模拟和经典密度泛函理论（DFT）进行研究。使用珠-簧型势，补充弯曲势，允许链刚度从完全柔性线圈变化到棒状聚合物，其持久长度远远超过其轮廓长度。仅隐式包含溶剂，单体-单体相互作用纯粹是排斥的，而考虑了两种类型的吸引力壁-单体相互作用：（i）强烈吸引力 Mie 型势，适用于严格无结构的壁，以及（ii）由 Lennard-Jones 粒子排列在正方形晶格上形成的波纹壁。结果发现，在稀溶液中，前一种情况导致强烈吸附表面层的形成，并且 DFT 预测了垂直于壁的 z 方向上密度和取向有序的轮廓与 MD 非常吻合。虽然对于非常低的体密度，建议在强烈吸附层中发生从各向同性相到具有向列相关的幂律衰减的 Kosterlitz-Thouless 型转变，但是对于较大的密度，在表面层中检测到层状-C 相。在这个系统中，与具有排斥壁的系统不同，没有发现较高体密度下的“毛细向列化”效应。这一发现归因于聚合物在吸引力壁上的吸附导致体密度（在狭缝孔的中心）降低，对于在正则系综中研究的系统。因此，在具有两个吸引力壁的系统中，只有在比本体系统更高的密度下，才能在狭缝孔中发生向列有序。
