Surface characterisation of amine-containing latexes by charge titration and contact angle measurements

Surface properties of cationic amino-containing latexes, as obtained by emulsifier-free emulsion copolymerisation of styrene with vinyl benzyl amine hydrochloride using 2,2′-azobis (2-amidinopropane) dihydrochloride (V50) as initiator, were investigated. Surface charge density was first examined using 1H NMR, conductometry and two spectroscopic methods (UV, fluorescence). Whereas the first two methods only provide semi-quantitative information on the overall surface density, the latter two were more accurate and suitable for discriminating amidine (issued from the initiator) and amine (brought by the cationic monomer) surface groups. In addition, it was possible to show differences in the nature of surface groups according to the mode of polymerisation process (batch versus shot-growth). Latex surface polarity was examined through contact angle measurements which allowed one to determine surface tension using the mean harmonic approximation method. Such amino latexes were found to exhibit a much lower surface polarity than sulphate-charged ones.