On-off dissociation dynamics of colloidal doublets

Journal article, 2013

First-passage time theory is used to analyze the dissociation behavior of doublets of colloidal particles. The first-passage time distribution for particles interacting via a DLVO potential is determined numerically. For strongly attractive particles the distribution becomes broad such that the mean first-passage time becomes a poor measure of the dynamics. In spite of this, use can be made of the mean in a matching condition, which allows for reproducing distributions for strongly attractive doublets by a semi-analytical solution for particles interacting only through surface adhesion. The smallest eigenvalue in the analytical solution, which governs the long-time asymptotic behavior of the first-passage time distribution, is identified analytically for strongly attractive pairs of particles. In addition, in this limit the distribution is shown to asymptote to an exponential distribution, which means that the dissociation process can be simply captured by an on-off model, without sacrificing the effect of the surface chemistry, with a constant probability for dissociation. This probability is simply related to the surface-adhesive parameter and the separation distance at which the pair of particles ceases to be considered a doublet.