Investigation of Mixing in Binary Surfactant Solutions by Surface Tension and Neutron Reflection:  Anionic/Nonionic and Zwitterionic/Nonionic Mixtures

Abstract

Surface tension and neutron reflection measurements have been used to study the surface composition of aqueous solutions of mixtures of sodium dodecyl sulfate (SDS) and n-dodecyl--D-maltoside (C 12 maltoside) and C 12 maltoside and n-dodecyl-N,N′-dimethylamino betaine (C 12 betaine). From measurements of surface tension and mixed critical micelle concentrations (cmc) the pseudo-phase separation model has been used to calculate values of the interaction parameters in the micelle, M , and at the surface, σ . SDS/C 12 maltoside mixtures behave nonideally and both M are negative, indicating attractive interactions between the two surfactants, but the C 12 maltoside/C 12 betaine mixtures are closer to being ideal. Direct measurements of the surface excess using neutron reflection on isotopic mixtures of the surfactants are shown to be consistent with the surface tension measurements using the integrated form of the Gibbs equation. These direct values of the surface excess were found to agree with predictions from the partial phase separation model in the case of the nonideal pair, SDS/C 12 maltoside, but were different for the ideal pair, C 12 maltoside/C 12 betaine. It is suggested that this may result from the relatively large errors in the partial phase separation model when the mixture is very unsymmetrical (very different cmc's coupled with weak interaction). The C 12 maltoside/ C 12 betaine mixture was found to behave regularly in that σ showed negligible variation with either surface pressure or composition. On the other hand for the nonideal pair, SDS/C 12 maltoside, the magnitude of σ decreased with surface pressure, consistent with reduced interaction as the molecules are more widely spaced, and also decreased with higher SDS fraction in the layer, consistent with an increasing contribution from electrostatic repulsion.

The Interaction of Alkylglycosides with Other Surfactants

“…C 10 M has a considerably smaller maximum concentration at the air/water interface max , than C 10 G. This may be due to the inability of the planar air/water interface to accommodate the larger hydrophilic head in C 10 M. Since the reduction of the surface tension of the solvent is a function of the values of max and the CMC/C 20 ratio (as shown by Eq. [7]) (6d), [7] this accounts for the considerably lower γ cmc of C 10 G than C 10 M. An increase in the pH from 5.7 to 9 does not have much effect on the surface properties of C 10 M, C 10 G, and C 12 M. However, with change in pH, C 12 TMAC showed a decrease in the value of the CMC as well as in the area/molecule, which may be due to the compression of the electric double layer around the hydrophlic head with an increase in the electrolyte content at the higher pH. Table 2 shows the surface properties of the surfactant mixtures.…”

“…Although there are some papers that deal with surfactant mixtures containing alkylglycosides (7)(8)(9)(10) in terms of the surface properties, they only show the C 20 (surfactant concentration in the aqueous phase required to reduce the surface tension of the solvent by 20 mN m −1 ) and/or CMC values for the individual components and the mixtures, and in almost all cases the measurements were done in the absence of the swamping amount of electrolyte required to ensure that the β values are accurate.…”

Comparison of the Coadsorption of Benzyl Alcohol and Phenyl Ethanol with the Cationic Surfactant, Hexadecyl Trimethyl Ammonium Bromide, at the Air–Water Interface

“…The ± sign in Eqs. [8] and [9] reflects the phase uncertainty arising from Eq. [1], and in practice this does not present a problem for such systems.…”

Comparing Decyl-β-maltoside and Octaethyleneglycol Mono n-Decyl Ether in Mixed Micelles with Dodecyl Benzenesulfonate

“…For example, the surface composition and mixed micelle concentration has been investigated for ndodecyl-β-D-maltoside and sodium dodecyl sulfate (SDS) and n-dodecyl-N ,N -dimethylamino betaine respectively, using surface tension and neutron reflection measurements (7). It was shown that the maltoside surfactant interacts strongly with the SDS micelles rendering a net attraction between the surfactants.…”