On the importance of carrier fluid viscosity and particle-wall interactions in magnetic-guided assembly of quasi-2D systems

We demonstrate the influence of experimental conditions (carrier fluid viscosity and particle-wall interactions-friction) on the quasi-2D deterministic aggregation kinetics of carbonyl iron magnetic suspensions in rectangular microchannels. On the one hand, the carrier fluid viscosity determines the time scale for aggregation. On the other hand, friction strongly determines the aggregation rate and therefore the kinetic exponent (mean cluster size vs. time dependence). When particle-wall interactions are weak, the mean cluster size increases with a power of 0.65 +/- 0.06, for open cavities (>= 500 microns channel width), in very good agreement with theories and particle-level simulations. However, when the particle-wall interactions are strong, the kinetic exponent decreases and the aggregation is eventually arrested. This work suggests that particle-wall interactions may be one of the reasons for the discrepancies found in the experimental determination of the aggregation kinetic exponents in the literature.