The properties of ionized monolayers. Part 1.—Sodium dodecyl sulphate at the air/water interface

Abstract

In part 1 the experimental data on the surface tensions of sodium dodecyl sulphate (S.D.S.) solutions in a number of different sodium chloride concentrations at 20", 40" and 60°C are presented. The effect of salt on the force-area curves of S.D.S. is compared with that predicted from recent theories.

The effect of varying levels of surfactant on the reactive uptake of N<sub>2</sub>O<sub>5</sub> to aqueous aerosol

“…a factor of ∼5 greater coverage than that at which we observe the reduction. In order to produce a linear dependence of γ N 2 O 5 on , it is necessary to set the saturation surface coverage to 5×10 13 molecules cm −2 , a factor of 4 lower than the saturation coverages reported in the literature (Matijevic and Pethica, 1958;Persson et al, 2003). While we can't rule out a larger average footprint for SDS in the highly ionic aerosol used, it seems unlikely for the footprint to be ∼200Å 2 .…”

“…Following trends in the cmc of SDS as determined for dilute aqueous NaCl solutions, we expect the cmc to be much less than 10 −3 M SDS in our 9 M NaCl aerosol (Li et al, 1998;Matijevic and Pethica, 1958). But because of the small size and thus high surface area to volume ratio of our droplets, most SDS molecules present in the aerosol are partitioned to the surface, resulting in bulk monomer concentrations well below the cmc for all runs except that using 10 wt% SDS.…”

“…The sulfate head group of SDS is most similar to a carboxylic acid, although surfactants typically present in atmospheric aerosol can also have alcohol, aldehyde, ketone, ester, or amine head groups (Gill et al, 1983;Mochida et al, 2002;Peterson and Tyler, 2003;Tervahattu et al, 2002;Russell et al, 2002). Based on studies of dilute SDS-NaCl-H 2 O mixtures (Matijevic and Pethica, 1958;Persson et al, 2003), we can assume an SDS footprint of ∼50Å 2 , corresponding to a saturation surface coverage of 2×10 14 molecules cm −2 . At 3.5 wt% SDS, the concentration beyond which we did not observe additional suppression, we predict a surface coverage of ∼2×10 14 molecules cm −2 , assuming all SDS partitions to the aerosol surface, and a typical particle surface area of 2.5×10 −9 cm 2 .…”

“…Given the lack of direct kinetic studies of gas-aerosol interactions where surfactants are present, SDS was chosen as a proxy for natural organic surfactant molecules because it is readily soluble in water and because the SDS-NaCl-H 2 O system has been characterized in bulk solutions (Matijevic and Pethica, 1958;Rehfeld, 1967;Persson et al, 2003;Sorjamaa et al, 2004;Li et al, 1998). SDS is similar to fatty acids in that it contains a long aliphatic tail on a polar head group whose anionic character is likely pH dependent.…”

Thermodynamics of Amphiphilic Drug Imipramine Hydrochloride in Presence of Additives

“…The variable n is introduced to allow for the simultaneous adsorption of cations and anions. The expression used in the calculation of n was that proposed by Matejevic and Pethica (Matijevic & Pethica, 1958). n = 1+ m/(m+m s ), where m s is the concentration of the added electrolyte.…”