Padding J T, Boek E S, Briels W J
Computational Biophysics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
J Chem Phys. 2008 Aug 21;129(7):074903. doi: 10.1063/1.2970934.
We perform coarse-grained computer simulations of solutions of semidilute wormlike micelles and study their dynamic and rheological properties, both in equilibrium and under shear flow. The simulation model is tailored to the study of relatively large time and length scales (micrometers and several milliseconds), while it still retains the specific mechanical properties of the individual wormlike micelles. The majority of the mechanical properties (persistence length, diameter, and elastic modulus of a single worm) is determined from more detailed atomistic molecular dynamics simulations, providing the link with the chemistry of the surfactants. The method is applied to the case of a solution containing 8% (by weight) erucyl bis(hydroxymethyl)methylammonium chloride (EHAC). Different scission energies ranging from 15.5k(b)T to 19.1k(B)T are studied, leading to both unentangled and entangled wormlike micelles. We find a decrease in the average contour length and an increase in the average breaking rate with increasing shear rate. In equilibrium, the decay of the shear relaxation modulus of the unentangled samples agrees with predictions based on a theory of breakable Rouse chains. Under shear flow, transient over- and undershoots are measured in the stress tensor components. At high shear rates we observe a steady-state shear stress proportional to gamma(1/3), where gamma is the shear rate. This is confirmed by our high shear rate experiments of real EHAC in a parallel-plate geometry.
我们对半稀溶液中蠕虫状胶束进行了粗粒度计算机模拟，并研究了它们在平衡态和剪切流作用下的动力学和流变学性质。该模拟模型适用于研究相对较大的时间和长度尺度（微米和几毫秒），同时仍保留了单个蠕虫状胶束的特定力学性质。大多数力学性质（单个蠕虫的持久长度、直径和弹性模量）由更详细的原子分子动力学模拟确定，从而建立了与表面活性剂化学性质的联系。该方法应用于含有8%（重量）芥酸双（羟甲基）甲基氯化铵（EHAC）的溶液情况。研究了范围从15.5k(b)T到19.1k(B)T的不同断裂能，得到了非缠结和缠结的蠕虫状胶束。我们发现，随着剪切速率的增加，平均轮廓长度减小，平均断裂速率增加。在平衡态下，非缠结样品的剪切松弛模量的衰减与基于可断裂Rouse链理论的预测相符。在剪切流作用下，应力张量分量中测量到了瞬态过冲和下冲。在高剪切速率下，我们观察到稳态剪切应力与γ(1/3)成正比，其中γ是剪切速率。这在我们对真实EHAC在平行板几何结构中的高剪切速率实验中得到了证实。
