How does the nature of the steric stabilizer affect the pickering emulsifier performance of lightly cross-linked, acid-swellable poly(2-vinylpyridine) latexes?

A near-monodisperse styrene-functionalized poly[2-(dimethylamino)ethyl methacrylate] (PDMA) macromonomer was evaluated as a reactive steric stabilizer for the preparation of poly(2-vinylpyridine (P2VP) latexes via emulsion polymerization. The solution pH was shown to be a critical parameter for successful syntheses: stable latexes with minimal coagulum were only obtained at (or above) neutral pH. The presence of the grafted PDMA stabilizer in a near-monodisperse P2VP latex of 280 nm diameter was indicated by FT-IR spectroscopy and quantified at 6.0 wt % using 1H NMR spectroscopy. XPS studies confirmed that this stabilizer was located at the latex surface, as expected. Combined DLS and electrophoretic data indicated that these PDMA-P2VP particles exist in three states depending on the solution pH: swollen cationic microgels were obtained below pH 4.1, nonsolvated latex particles with a cationic stabilizer layer were obtained at intermediate pH, and flocculated latex particles with neutral PDMA stabilizer chains were obtained at around pH 8.5. Finally, this PDMA-P2VP latex was shown to be a superior Pickering emulsifier for stabilizing water-in-1-undecanol emulsions than either a poly(ethylene glycol)-stabilized P2VP latex or a charge-stabilized P2VP latex. This serves to illustrate the important role played by the steric stabilizer in determining particle wettability.