Purification of amphoteric polystyrene latex colloids

Abstract

A series of polystyrene-based zwitterionic (amphoteric) latex colloids were prepared with integral acid (carboxyl) and base (amine) surface groups, resulting in a range of isoelectric points (iep). Following a series of different cleaning procedures, the resulting dispersions were evaluated by techniques including conductometric/potentiometric titrations and microelectrophoresis. The cleaning was by one or more of the following procedures—dialysis, ion exchange, ultrafiltration, centrifugation-decantation, and activated charcoal cloth equilibration. The monodisperse latices cleaned by these methods showed little variation in iep or in the magnitude of the electrophoretic mobility at any pH relative to the iep. In contrast, the surface charge, as measured by both conductometric and potentiometric titrations, varied greatly with cleaning procedure. With dialysis, ion exchange, and/or activated charcoal cloth equilibration, the observed capacitance at the pze was greater than is theoretically possible, indicating that these techniques may not successfully clean a surface simultaneously charged with acid and base sites. The overall results of some seven different cleaning procedures for four different amphoteric latex materials are presented.