Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. Part 2. Influence of surfactant chain length and surfactant/polymer ratio.
The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and a series of cationic surfactants, alkyltrimethylammonium bromide, CnTAB, n = 8-16, at the air-water interface has been studied by combining surface tension and ellipsometry measurements. We find that increasing the chain length of the surfactant from 8 to 10 carbons leads to a sharp increase in adsorption of PSS/CnTAB complexes. When the surfactant tail length is further increased to 12 and 14 carbons, surface adsorption becomes less favored than macroscopic phase separation, resulting in a partial surface depletion. Furthermore, we find that when surface tensions are plotted against surfactant/monomer molar concentration ratio, all data collapse to a single curve. This result shows that the surfactant-polymer molar ratio, s/p, is a key parameter for tuning the surface activity of the complexes formed.
Laboratoire de Physique, UMR 5672, Ecole Normale Supérieure de Lyon, 46, allée d'Italie, 69007 Lyon, France.
Cécile
C
Monteux
Claudine E
CE
Williams
Vance
V
Bergeron