In-Line and In Situ Monitoring of Ionic Surfactant Dynamics in Latex Reactors Using Conductivity Measurements and Ion-Selective Electrodes

Abstract

In an emulsion polymerization process, surfactant type and concentration play an important role in the stability, appearance, reaction kinetics, and particle size distribution of latexes. The possibility of carrying out in-line evaluation of the distribution of free surfactant molecules in the media is of interest in polymer reaction engineering, because this would provide information about the rates of nucleation and particle stabilization. Both ion-selective electrodes and conductimetry seem to be very promising techniques for this objective. Ion-specific electrodes are able to determine the concentration of several substances, in a quantitative and specific manner, and may also be a good way of monitoring ionic surfactant. Conductivity measurements offer a means of monitoring the evolution of concentrations of different species in the latex. The objective of this work is to evaluate the use of ion-selective electrodes as a tool for the on-line monitoring of an emulsion polymerization reaction and to compare this method to conductivity. Ion-selective electrodes were prepared for two ionic surfactant species: dodecyl sulfate and dodecyltrimethylammonium, coming from SDS (sodium dodecyl sulfate) and DTAB (dodecyl trimethylammonium bromide), respectively. To do so, a glass electrode was coated with polymeric membranes specific for each surfactant. It is demonstrated that ion-selective electrodes can provide insight into the evolution of the colloidal surface in the latex, even when temperature and composition drifts are present.