The microrheology of colloidal dispersions: I. The microtube technique

Abstract

This paper describes a hydraulically-driven traveling microtube apparatus, designed and built with the aim of tracking the movements and interactions of individual colloidal particles and aggregates in Poiseuille flow through capillary tubes from 50 to 75 μm radius. The operation of the microtube device was tested using dilute dispersions of 2 μm diameter polyvinyl toluene latex spheres in water and biconcave, 8 μm diameter, human red cells in plasma. In the studies of aggregation phenomena, latex and coagulant were simultaneously infused into the flow tube, giving rise to a large variety of aggregate sizes and shapes. The formation and redistribution of aggregates with respect to size and geometry during flow down the tube was found to depend on the magnitude of the velocity gradient. In the case of blood, linear and branched chained rouleaux of red cells formed spontaneously during flow, but the number and size of aggregates decreased with increasing velocity gradient. The perturbation of the rotational orbits of individual latex aggregates by Brownian diffusion was also studied at velocity gradients from 2 to 30 sec −1 corresponding to rotary Péclet numbers from 6 to 90. The angular velocities of the axis of revolution of doublets and triplets of latex spheres fluctuated erratically, and over small time intervals the magnitude of the fluctuations correlated well with that measured in the absence of shear. The perturbation of the rotational orbit of single red cells and 2- and 3-cell rouleaux was much less pronounced than that of small latex aggregates.