Dhakal Subas, Sureshkumar Radhakrishna
Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, USA.
Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, USA and Department of Physics, Syracuse University, Syracuse, New York 13244, USA.
Phys Rev E. 2017 Jul;96(1-1):012605. doi: 10.1103/PhysRevE.96.012605. Epub 2017 Jul 24.
We investigate the mechanisms of anomalous diffusion in cationic surfactant micelles using molecular dynamics simulations in the presence of explicit salt and solvent-mediated interactions. Simulations show that when the counterion density increases, saddle-shaped branched interfaces manifest. In experiments, branched structures exhibit lower viscosity as compared to linear and wormlike micelles. This has long been attributed to stress relaxation arising from the sliding motion of branches along the main chain. Our simulations reveal a mechanism of branch motion resulting from an enhanced counterion condensation at the branched interfaces and provide quantitative evidence of stress relaxation facilitated by branched sliding. Furthermore, depending on the surfactant and salt concentrations, which in turn determine the microstructure, we observe normal, subdiffusive, and superdiffusive motions of surfactants. Specifically, superdiffusive behavior is associated with branch sliding, breakage and recombination of micelle fragments, as well as constraint release in entangled systems.
我们利用分子动力学模拟，在存在明确的盐和溶剂介导相互作用的情况下，研究阳离子表面活性剂胶束中反常扩散的机制。模拟结果表明，当抗衡离子密度增加时，会出现鞍形分支界面。在实验中，与线性和蠕虫状胶束相比，分支结构表现出较低的粘度。长期以来，这一直归因于分支沿主链滑动运动引起的应力松弛。我们的模拟揭示了一种由分支界面处增强的抗衡离子凝聚导致的分支运动机制，并提供了分支滑动促进应力松弛的定量证据。此外，根据表面活性剂和盐的浓度（这反过来又决定了微观结构），我们观察到表面活性剂的正常、亚扩散和超扩散运动。具体而言，超扩散行为与分支滑动、胶束片段的断裂和重组以及缠结系统中的约束释放有关。
