Surface and electrokinetic characterization of functional aldehyde polymer colloids

Abstract

Polymer colloids of aldehyde functionality were prepared by the emulsifier-free emulsion copolymerization of styrene and acrolein with potasium persulfate as initiator. Two aldehyde latexes were prepared, one of them with methanol (10% (w/w) of the monomers) charged into the reactor. By carrying out conductimetric and potentiometric titration experiments, together with 1H nuclear magnetic resonance and Fourier transform infrared analysis, the presence of aldehyde groups was detected with a surface concentration of approximately 1.2 × 10 −4 μeq cm −2 for the two latexes synthesized. Also, sulfate groups were detected which gave rise to a surface charge density of around 2.9 μC cm −2 for both latexes. The electrophoretic mobilities (μ e) of these functionalized latexes were studied versus the solution pH and in the presence of several electrolytes with different counterion valences. The μ e values were constant in the pH range 5–10, while exhibiting a maximum when plotted versus the electrolyte concentration. This maximum disappeared when the electrolyte was LaCl 3. The stability factors of the aldehyde latexes were measured at pH 6 and 9. The critical coagulation concentrations (CCCs) were very similar for both latexes at these pH values. The average CCC was 367 mM which is too high when considering the low surface charge density provided by the sulfate groups. The surface aldehyde groups seem to improve the colloidal stability of these latexes.