Simultaneous Aggregation and Height Bifurcation of
Colloidal Particles near Electrodes in Oscillatory Electric Fields
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Abstract
Micrometer-scale particles suspended
in NaCl solutions aggregate
laterally near the electrode upon application of a low-frequency (∼100
Hz) field, but the same particles suspended in NaOH solutions are
instead observed to separate laterally. The underlying mechanism for
the electrolyte dependence remains obscure. Recent work by Woehl et
al. (PRX, 2015) revealed that, contrary to previous reports, particles
suspended in NaOH solutions indeed aggregate under some conditions
while simultaneously exhibiting a distinct bifurcation in average
height above the electrode. Here we elaborate on this observation
by demonstrating the existence of a critical frequency (∼25
Hz) below which particles in NaOH aggregate laterally and above which
they separate. The results indicate that the current demarcation of
electrolytes as either aggregating or separating is misleading and
that the key role of the electrolyte instead is to set the magnitude
of a critical frequency at which particles transition between the
two behaviors
