Surface characterization of latexes with different interfacial properties

In this paper we have studied the effect of copolymerization of a non-ionic but hydrophilic monomer on the interfacial properties of the latex surface. Hydrophilic polymer colloids were prepared by the emulsifier-free emulsion copolymerization of styrene and 2-hydroxyethyl methacrylate (HEMA) with potassium persulfate as initiator. The copolymer compositions were evaluated by 1H nuclear magnetic resonance and compared with the initial concentration of each monomer. Results show very good agreement which is an indication of the absence of secondary nucleation. Also, the presence of the carbonyl group (i.e. a weak acid group) was detected by Fourier transform-infrared and 13C nuclear magnetic resonance analysis, together with conductometric and potentiometric titration experiments. In all cases, a conventional hydrophobic polystyrene latex was used as a reference. The hydrophobic character of the latexes was estimated by using contact angle and viscosity measurements, and adsorption of a non-ionic surfactant. These three methods are compared. As expected, the results showed that as the amount of hydrophilic monomer in the synthesis increases, so does the hydrophilic character of the latex surface.