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

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.