title: DCl Transport through Dodecyl Sulfate Films on Salty Glycerol: Effects of Seawater Ions on Gas Entry.
abstract: Gas-liquid scattering experiments were employed to measure the entry and dissociation of the acidic gas DCl into salty glycerol coated with dodecyl sulfate ions (DS(-) = CH3(CH2)11OSO3(-)). Five sets of salty solutions were examined: 0.25 and 0.5 M NaCl, 0.25 M MgCl2, 0.25 M CaCl2, and artificial sea salt. DS(-) bulk concentrations were varied from 0 to 11 mM, generating DS(-) surface coverages of up to 34% of a compact monolayer, as determined by surface tension and argon scattering measurements. DS(-) surface segregation is enhanced by the dissolved salts in the order MgCl2 ≈ CaCl2 > sea salt > NaCl. We find that DCl penetration through the dodecyl chains decreases at first gradually and then sharply as more chains segregate to the surface, dropping from 70% entry on bare glycerol to 11% for DS(-) surface concentrations of 1.8 × 10(14) cm(-2). When plotted against DS(-) surface concentration, the DCl entry probabilities fall within a single band for all solutions. These observations imply that the monovalent Na(+) and divalent Ca(2+) and Mg(2+) ions do not bind differently enough to the ROSO3(-) headgroup to significantly alter the diffusive passage of DCl molecules through the dodecyl chains at the same DS(-) chain density. The chief difference among the salts is the greater propensity for the divalent salts to expel the soluble ionic surfactant to the surface.
authors: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors: Michael A
authors: MA
authors: Shaloski
authors: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors: Thomas B
authors: TB
authors: Sobyra
authors: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors: Gilbert M
authors: GM
authors: Nathanson