Analysis of chaining structures in colloidal suspensions subjected to an electric field

Abstract

Structures formed by a colloidal suspension of silica particles in 4-methyl cyclohexanol have been analyzed in the presence of an electric field. The formation of chains of particles was detected using an elliptical mirror to collect scattered light and a nearly matched refractive index between particles and solvent. A numerical method has been developed to obtain the size distribution of chains and their kinetics of formation from the record of a two-dimensional map of scattered light. We have compared the experimental size distribution to the prediction of a statistical theory based on a minimization of the free energy of a gas of chains. This theory quite well reproduced the experimental results for small chains but overestimates the tail of the distribution at high field. A saturation of the average size of chains versus the electric field was observed experimentally instead of a continuous growth as would be expected from aggregation under dipolar forces. A kinetic model, taking into account both capture and escape rates of a particle at the extremity of a chain, was shown to reproduce well the experimental growth of the average size of chains with time.

Two-stage kinetics of field-induced aggregation of medium-sized magnetic nanoparticles

“…The physics of particle aggregation is rather different for micron-sized particles (with >>1) and for nanoparticles (with1).  Kinetics of field-induced aggregation of micron or sub-micron-sized particles (typically d>100 nm) has been studied experimentally by either direct visualization [22][23][24] or light scattering [25][26][27][28] . The common feature shared between most of the studied systems is that these particles exhibit a rapid field-induced aggregation in linear chains aligned with the direction of applied magnetic field, and the average chain length 2a grows with time as 2at   , with 0.45 0.8…”

Kinetics of internal structures growth in magnetic suspensions

“…A model of aggregation of Brownian magnetic particles in linear chains has been developed in Ref. [7] on the basis of the Smoluchowski equations for the distribution function of the number of particles in the chain. The results of this model are in good agreement with experiments.…”

Structure evolution in electrorheological fluids flowing through microchannels

“…These three stages correspond to the three previously observed periods of stress response and the duration of each stage of structure growth was found to be comparable to the corresponding stages observed in stress measurements. In addition to these experimental observations, a number of simulation studies have been carried out to advance understanding of the rheology and kinetics of structure formation in ER fluids [25][26][27][28][29] .…”