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Project B.2: Dense colloidal suspensions in microfluidic flow
We will set up a MPCD code to simulate hard disks
under pressure-driven flow in two dimensions. This restriction will
enable us to simulate larger systems.
We start with simulating binary mixtures of small and large colloids at moderate densities and vary the composition. Whereas at equal densities the larger particles accumulate in the center, this behavior is reversed when the smaller particles are in the majority. This result can be rationalized in terms of an entrance length, which a monodisperse dispersion needs to attain a stationary distribution. Our goal is to develop a deeper understanding of this behavior and identify the underlying principles.
For monodisperse suspensions we will then increase density and vary the ratio of channel width to colloid diameter to reproduce the oscillation regime in a sufficiently narrow channel. In contrast to experiments, in our simulations we are able to monitor both fluid and colloidal flow and thereby explore the role of permeation. A deeper understanding should give an estimate for the value of the oscillation frequencies.
In the transient jamming regime, where jammed regions resolve in stochastically occurring bursts, we will also monitor the size of the jammed regions and stress fluctuations, and, furthermore, look for force chains (similar to granular media). In addition, we have the idea to check if the system exhibits signatures of self-organized criticality. Finally, we will study channels with a constriction and investigate the possibility of crystallization upstream of the constriction.
Project leaders: Prof. Dr. H. Stark , Prof. Dr. R. Netz