Imperio Alessandra, Reatto Luciano, Zapperi Stefano
Sezione dell'Università degli Studi di Milano, CNISM, Milano, Italy.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Aug;78(2 Pt 1):021402. doi: 10.1103/PhysRevE.78.021402. Epub 2008 Aug 4.
We study the rheological properties of colloidal microphases in two dimensions simulating a model of colloidal particles with competing interactions. Due to the competition between short-range attraction and long-range repulsion, as a function of the density the model exhibits a variety of microphases such as clusters, stripes, or crystals with bubbles. We prepare the system in a confined microphase employing Monte Carlo simulations and then shear the resulting configurations by applying a drag force profile. We integrate numerically the equation of motion for the particles and analyze the dynamics as a function of the density and the applied strain rate. We measure the stress-strain curves and characterize the yielding of the colloidal microphases. The results depend on the type of microphase. (i) Clusters are easily sheared along layers and the relative motion is assisted by rotations. (ii) Stripes shear easily when they are parallel to the flow and tend to jam when they are perpendicular to it. Under a sufficiently strong shear rate perpendicular stripes orient in the flow direction. (iii) Crystals with bubbles yield by fracturing along the bubbles and eventually forming stripes. We discuss the role of dislocations, emitted by the bubbles, in the yielding process. Finally, we analyze the effect of thermal fluctuations on the rheological properties.
我们通过模拟具有竞争相互作用的胶体粒子模型，研究二维胶体微相的流变特性。由于短程吸引和长程排斥之间的竞争，该模型随密度的变化呈现出多种微相，如团簇、条纹或带有气泡的晶体。我们采用蒙特卡罗模拟在受限微相中制备系统，然后通过施加拖曳力分布对所得构型进行剪切。我们对粒子的运动方程进行数值积分，并分析动力学随密度和外加应变率的变化。我们测量应力 - 应变曲线并表征胶体微相的屈服特性。结果取决于微相的类型。（i）团簇易于沿层状被剪切，相对运动由旋转辅助。（ii）条纹在平行于流动方向时易于剪切，而在垂直于流动方向时倾向于堵塞。在足够强的剪切速率下，垂直条纹会沿流动方向取向。（iii）带有气泡的晶体通过沿气泡破裂并最终形成条纹而屈服。我们讨论了气泡发射的位错在屈服过程中的作用。最后，我们分析了热涨落对流变特性的影响。
