Pryamitsyn Victor, Ganesan Venkat
Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2008 Apr 7;128(13):134901. doi: 10.1063/1.2842075.
We present the details and results of a simulation study addressing the dynamics and rheology of rod suspensions over a wide regime of concentrations ranging from dilute to concentrated systems. Our study compares the results of two complementary simulation methods. The first method adapts a recently proposed explicit solvent simulation strategy and incorporates both hydrodynamical effects and steric interactions between the rod units. We compare the results of such a method with those obtained from a Brownian dynamics simulation approach which retains the steric interactions but neglects the effects of hydrodynamic interactions. Overall, our results in the context of the translational and rotational diffusivities are in agreement with the hydrodynamical predictions in the dilute regime and the corresponding results of the tube model and its extensions thereof in the semidilute regimes. The latter results suggest that effects of hydrodynamic interactions on the translational and rotational diffusivities are secondary relative to the steric interactions and at best lead only to a small correction to the results of the classical tube model. Our results in the context of linear viscoelasticity also broadly confirms the predictions of the tube model for the storage and loss moduli and allows us to extract for the first time the independent hydrodynamic and Brownian contributions to the zero shear viscosity. While the relative magnitudes of these contributions are consistent with the theoretical predictions, the quantitative magnitudes are quite different from the theoretical predictions. Overall, these results confirm the validity of the hydrodynamic "screening" hypothesis and ratify the neglect of hydrodynamical stresses in quantifying the linear rheology of Brownian rod suspensions.
我们展示了一项模拟研究的细节和结果，该研究探讨了从稀溶液到浓溶液的广泛浓度范围内棒状悬浮液的动力学和流变学。我们的研究比较了两种互补模拟方法的结果。第一种方法采用了最近提出的显式溶剂模拟策略，并纳入了流体动力学效应和棒状单元之间的空间相互作用。我们将这种方法的结果与从布朗动力学模拟方法获得的结果进行比较，后者保留了空间相互作用，但忽略了流体动力学相互作用的影响。总体而言，我们在平动和转动扩散系数方面的结果与稀溶液区域的流体动力学预测以及半稀溶液区域的管模型及其扩展的相应结果一致。后者的结果表明，相对于空间相互作用，流体动力学相互作用对平动和转动扩散系数的影响是次要的，充其量只会对经典管模型的结果产生微小的修正。我们在线性粘弹性方面的结果也大致证实了管模型对储能模量和损耗模量的预测，并使我们首次能够提取出对零剪切粘度的独立流体动力学贡献和布朗贡献。虽然这些贡献的相对大小与理论预测一致，但定量大小与理论预测有很大不同。总体而言，这些结果证实了流体动力学“屏蔽”假设的有效性，并认可了在量化布朗棒状悬浮液的线性流变学时忽略流体动力学应力的做法。
