Analysis of the Asymmetric Synergy in the Adsorption of Zwitterionic–Ionic Surfactant Mixtures at the Air–Water Interface below and above the Critical Micelle Concentration

Abstract

Surface tension (ST) and neutron reflection (NR) measurements have been made on a series of mixtures of two ionic surfactants, one anionic (SDS) and one cationic (C12TAB), with the two zwitterionic surfactants dodecyldimethylammonium propanesulfonate (C12SB) and dodecyldimethylammonium acetate C12CB. The anionic surfactant SDS interacts equally strongly with both zwitterionics and the C12TAB less strongly. For the SDS-C12SB mixtures simultaneous fitting of ST and NR data made it possible to use the pseudophase approximation with an expansion of the excess free energy, GE, up to and including the quartic term. GE is asymmetric for the adsorbed layer and the minimum occurs at a surface mole fraction, xSDS, of 0.38 with a depth of -2.8RT. NR was also used to follow the adsorption above the CMC, and the changes showed that the intramicellar interaction is more asymmetric, but weaker than the surface interaction with a depth of GE of -2.2RT at the minimum of xSDS = 0.23. A strong synergy in the total surface excess was observed above the mixed CMC with an enhancement over the adsorption of the pure components of about 45%, which appears to result from a sharp variation of the packing with surface composition coupled with the effects of the strongly asymmetric micellization. NR data on SDS-C12CB showed that GE for both surface and micelles was similarly asymmetric to those for SDS-C12SB, but there is no strong synergy in adsorption. This is attributed to the more rigid headgroup. C12TAB-C12SB has an asymmetric GE for both surface and micelle similar to those for SDS-C12SB but the depths are smaller at -0.6RT and -0.5RT, respectively, and there is no synergy in the total adsorption.

Self-assembly and surface behaviour of pure and mixed zwitterionic amphiphiles in a deep eutectic solvent

“…The thicknesses of the surfactant layers in DES were found to be thinner than those in water, where, at the CMC, a C 12 -PC monolayer fits to a total thickness of 20 AE 2 Å and a SB3-12 monolayer shows a total thickness of 14 AE 3 Å. 29,54 Whereas the thickness of the headgroup layer in DES in both cases is comparable to that in water, 40,55 thicker monolayers in water may indicate the presence of a stronger lyophobic interaction in water than in DES. The interfaces between different layers appear to be diffuse, potentially due to thermal-induced capillary waves.…”

“…Neutron reflectivity results have shown that these surfactants on water, at the CMC, present a surface excess concentration of 3.35 Â 10 À6 mol m À2 and 3.70 Â 10 À6 mol m À2 for C 12 -PC and SB3-12 respectively. 29,54 The higher values found in water are again indicative of the greater affinity of the DES for solvated surfactant free monomers, which thus leads to reduced surface excess concentrations. Finally, the calculated values indicate that the area per surfactant monomer at the air-DES interface is larger in the case of SB3-12 than C 12 -PC.…”

Surface Adsorption in Ternary Surfactant Mixtures above the Critical Micelle Concentration: Effects of Asymmetry on the Composition Dependence of the Excess Free Energy

“…Apart from the more direct relevance to applications, such measurements above the CMC have the potential to probe deviations of G E for both micelles and surface from the symmetry of the regular solution assumption, and hence to explore possible contributions from factors such as differences in size and charge between the components of a mixture. 18 The properties of a wide range of different binary surfactant mixtures have been studied. 1,3,19 Bearing in mind the limitations described above, the results are usually consistent with the pseudophase-regular solution model.…”

Investigation on Foam Self‐Generation Using In Situ Carbon Dioxide (CO2) for Enhancing Oil Recovery

“…Most likely, simultaneous adsorption may be taking place at the water/gas interface in the mixed system (SDS and LHSB) due to the strong interaction between the cationic group (i.e., amino [N + ]) of LHSB and anionic group (i.e., sulfonate [SO 3− ]) of SDS. The mixture of SDS and LHSB possesses a higher activity at the surface in comparison to the single surfactant or other mixtures, which favors the foaming performance (Li, Ma, & Thomas, ; Wang, Fang, & Gong, ; Wei et al, ). Therefore, mixtures of SDS and LHSB were selected for further investigations.…”