Comparative methods for the characterization of core—shell latex particles

Abstract

Copolymer latices were prepared from both styrene and acrylamide and from styrene and N-methylolacrylamide, respectively, in a molar ratio of 4:1. Many characterization techniques were applied to these particles, and the results compared. The monodisperse particles were characterized using density measurements, flocculation tests and microelectrophoresis after purification of the latices by microfiltration. Also, solubility experiments in organic solvents and chemical analysis of the particles using pyrolysis/gas chromatography and X-ray photoelectron spectroscopy were performed after drying of the latex particles below the glass transition temperature. These measurements indicate that the particles contain only 2% of hydrophilic monomers, enriched at the surface. The latex particles are very colloidally stable and have a low negative surface potential. Contact angle measurements of octane drops and air bubbles on ‘films’ of latex particles under water show the particles to have a very hydrophilic surface. This hydrophilicity was also reflected in the absence of bovine serum albumin adsorption at pH 7.4 and the rather low adsorption of a nonionic surfactant (nonylphenol ether ethoxylated with 10 polyethylene oxide units), although differences were found between the acrylamide and methylolacrylamide latices with regard to adsorption of the latter. The sodium dodecyl sulphate adsorption was rather high and did not differ significantly for the various latices, which is indicative of hydrophobic spots lying close under the latex particle surfaces or caused by charge interactions between the equally charged surfactant molecules and the latex particle surface.