Reaction-limited Colloidal Aggregation Induced by Salt and Inert Polymers

TL;DR

This study investigates how salt and inert polymers like PEG influence colloidal silica aggregation, revealing a stretched exponential kinetic pattern explained by DLVO theory and cluster-size scaling.

Contribution

It demonstrates the effect of salt and PEG on colloidal aggregation kinetics, introducing a model that aligns with experimental stretched exponential behavior.

Findings

Salt induces aggregation with a specific kinetic form.

PEG accelerates aggregation, especially with higher molecular weight.

Aggregation kinetics are consistent with a cluster-size dynamic scaling model.

Abstract

Salt-induced aggregation of 20 nm colloidal silica is followed by light transmission, which shows an a kinetic form exp[-(t/t_0)^{\alpha}], where \alpha = 2.6 and t_0 is an empirical time constant which reflects the colloidal stability. We found a power law dependence of t_0 on ionic strength, which can be explained by the classical DLVO theory. The neutral polymers polyethylene glycol (PEG) accelerate the aggregation rate, and those with higher molecular weight are more effective in inducing the aggregation with similar stretched exponential form of kinetics. Current theories of polymer-mediated interactions provide a reasonable interpretation of the effect of PEG. The stretched exponential kinetics of the light transmission is found to be consistent with a cluster-size dynamic scaling model of aggregation.