Unusual Excess Free Energies of Mixing in Mixtures of Partially Fluorinated and Hydrocarbon Surfactants at the Air–Water Interface: Correlation with the Structure of the Layer

Jackson, Andrew; Dong, Chu Chuan; Thomas, Robert K.; Penfold, J.

doi:10.1021/la5043074

Cited by 4 publications

(3 citation statements)

References 55 publications

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“…The use of the function ln( f 2 / f 1 ) reduces the degree of the polynomial to be solved by 1 (basically because x 1 + x 2 = 1) and makes the iteration easier. Thus, using eq gives , Iteration of can be done using the simplest iteration method, the sector method . The solutions are stable and the equation is easily extended to more complicated forms of G E .…”

Section: Resultsmentioning

confidence: 99%

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

Thomas

et al. 2016

J. Phys. Chem. B

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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.

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Section: Resultsmentioning

confidence: 99%

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

Thomas

et al. 2016

J. Phys. Chem. B

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“…Theoretical surface compositions of the surfactant systems were calculated, as mentioned previously, using the PPA approach in combination with the experimental NR measurements. ,, The process is defined here in several stages, starting with the calculation of x i μ values from CMC data, which forms the foundation of the approach. , Huang et al observed a shift in the monomer concentration above CMC large enough to invalidate PPA calculations: there is a significant change in the number of free surfactant molecules able to adsorb at the interface with changes in concentration above CMC Equation and the calculated x i μ values were used to obtain corrected monomer concentrations.…”

Section: Resultsmentioning

confidence: 99%

Temperature Resistant Binary SLES/Nonionic Surfactant Mixtures at the Air/Water Interface

Smith

Tucker

et al. 2018

Langmuir

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Surface compositions of adsorbed monolayers at the air/water interface, formed from binary surfactant mixtures in equilibrium, have been studied using neutron reflectivity at three discrete temperatures: 10, 25, and 40 °C. The binary compositions studied are sodium lauryl dodecyl ether sulfate (SLES EO3)/C12E n, where n = 6 and 8, at a fixed concentration of 2 mM with and without the addition of 0.1 M NaCl. Without NaCl, the nonionic surfactant dominates at the interface and nonideal mixing behavior is observed. This is modeled using the pseudophase approximation with a quadratic expansion of the free energy of mixing. The addition of 0.1 M NaCl screens the charge interaction between the surfactants and drives the surface composition of each system closer to that of the bulk composition. However, model fits to both the micelles and surface layers suggest that nonideal mixing is still taking place, although it is difficult to establish the extent of nonideality due to the limited data quality. The effect of temperature changes on the surface adsorption and composition of the surfactant mixtures is minimal and within error, with and without NaCl, but the critical micelle concentrations are significantly affected. This indicates the dominant influence of steric hindrances and surfactant charge interactions in determining interfacial behavior for these surfactants, relative to the temperature changes. The study also highlights the delicate effect of a relatively small change in the number of EO groups on mixing behavior.

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“…Modeling surface tension of solutions and surface adsorption of different components of solutions is an ongoing problem in surface science. − The major steps in the development of this field of science in historical perspective are shown in Figure . It is all based on the bulk thermodynamics of heterogeneous systems developed by Gibbs and also on his definition of surface tension …”

Section: Introductionmentioning

confidence: 99%

Partial Surface Tension of Components of a Solution

Kaptay

2015

Langmuir

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First, extending the boundaries of the thermodynamic framework of Gibbs, a definition of the partial surface tension of a component of a solution is provided. Second, a formal thermodynamic relationship is established between the partial surface tensions of different components of a solution and the surface tension of the same solution. Third, the partial surface tension of a component is derived as a function of bulk and surface concentrations of the given component, using general equations for the thermodynamics of solutions. The above equations are derived without an initial knowledge of the Gibbs adsorption equation and without imposing any restrictions on the thickness or structure of the surface region of the solution. Only surface tension and the composition of the surface region are used as independent thermodynamic parameters, similar to Gibbs, who used only the surface tension of the solution and the relative surface excesses of the components. The final result formally coincides with the historical Butler equation (1932), but without its theoretical restrictions. (Butler used too many unnecessary model restrictions during his work: he started from the Gibbs adsorption equation, and he assumed the existence of a surface monolayer.) Thus, the renovated Butler equation has gained general validity in this article. It was applied to derive both the Langmuir equation and the Gibbs adsorption equation, but the latter two equations do not follow from each other. Thus, it is shown that logically (not historically) the renovated Butler equation is a root equation for surface tension and the adsorption of solutions. It can be used to perform calculations for specific systems if the corresponding specific experimental data/models are loaded into it. In this case, both surface tension and surface composition can be calculated from the renovated Butler equation, which cannot be done using the Gibbs adsorption equation alone.

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Unusual Excess Free Energies of Mixing in Mixtures of Partially Fluorinated and Hydrocarbon Surfactants at the Air–Water Interface: Correlation with the Structure of the Layer

Cited by 4 publications

References 55 publications

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

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

Temperature Resistant Binary SLES/Nonionic Surfactant Mixtures at the Air/Water Interface

Partial Surface Tension of Components of a Solution

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