Khan Manas, Mason Thomas G
Department of Physics and Astronomy, University of California-Los Angeles, Los Angeles, CA 90095, USA.
Soft Matter. 2014 Dec 7;10(45):9073-81. doi: 10.1039/c4sm01795a.
We have developed a fast simulation that generates a random walk of an isolated probe sphere in a generalized linear viscoelastic complex fluid over a highly extended dynamic range. We introduce a coupled harmonically bound Brownian particle (c-HBBP) model, in which the relaxation modes of the viscoelastic medium are treated as harmonic wells. These wells are coupled to the probe sphere and perform Brownian motion in bound harmonic potentials corresponding to the next-longer relaxation mode, according to the relaxation spectrum of the viscoelastic material. We implement this c-HBBP model by generating variable temporal step sizes that have a uniform distribution in logarithmic time. We create and analyze trajectories for several different viscoelastic complex fluids: a polymer system at its gel point, a dense emulsion system, a blend of two monodisperse polystyrene polymers for which the relaxation spectrum has been measured, and a model anisotropic soft system that shows dense emulsion-like and gel-point behaviors along two orthogonal directions. Except for unusual viscoelastic materials, such as the polymer system at its gel point, the generated trajectories are neither self-similar nor self-affine. The resulting mean square displacements predicted by the c-HBBP model are consistent with the single-particle generalized Stokes-Einstein relation of linear passive microrheology.
我们开发了一种快速模拟方法，该方法能在高度扩展的动态范围内，生成孤立探测球体在广义线性粘弹性复合流体中的随机游走。我们引入了一种耦合谐波束缚布朗粒子（c-HBBP）模型，其中粘弹性介质的弛豫模式被视为谐波阱。这些阱与探测球体耦合，并根据粘弹性材料的弛豫谱，在对应于次长弛豫模式的束缚谐波势中进行布朗运动。我们通过生成在对数时间内具有均匀分布的可变时间步长来实现这个c-HBBP模型。我们为几种不同的粘弹性复合流体创建并分析了轨迹：处于凝胶点的聚合物体系、浓乳液体系、已测量其弛豫谱的两种单分散聚苯乙烯聚合物的混合物，以及一种模型各向异性软体系，该体系在两个正交方向上表现出浓乳液状和凝胶点行为。除了像处于凝胶点的聚合物体系这种特殊的粘弹性材料外，生成的轨迹既不是自相似的也不是自仿射的。c-HBBP模型预测的结果均方位移与线性被动微观流变学的单粒子广义斯托克斯 - 爱因斯坦关系一致。
