6149-03-7Relevant academic research and scientific papers
Micelle Formation of Ionic Surfactants. Tracer Self-Diffusion Studies and Theoretical Calcualtions for Sodium p-Octylbenzenesulfonate
Lindman, Bjoern,Puyal, Marie-Claude,Kamenka, Nicole,Brun, Bernard,Gunnarsson, Gudmundur
, p. 1702 - 1711 (1982)
An investigation of association phenomena in aqueous solutions of a surfactant, sodium p-octylbenzenesulfonate (SOBS), was performed by self-diffusion measurements.Self-diffusion coefficients were obtained for amphiphile ions, sodium counterions, solubilized decanol molecules, water molecules, and chloride co-ions as a function of surfactant concentration by using the open-ended capillary tube method employing radioactive labeling.Decanol self-diffusion provides information on micellar translation and size.Surfactant ion self-diffusion gives the concentration of free surfactant ions.It is found that, at higher concentrations, free-surfactant concentration falls well below the critical micelle concentration.Counterion self-diffusion provides information on the concentration of free counterions and on β, the ratio of counterions and surfactant ions in the micelles. β is invariant over wide concentration ranges corresponding to an ion condensation type behavior; however, at low concentrations β decreases with increasing micelle concentration.The co-ion self-diffusion coefficients are used to deduce an effective excluded volume; teh excluded volume per micelle decreases with increaseng surfactant concentration.The water self-diffusion coefficients give information on micelle hydration; although hydration numbers are difficult to obtain (and to define), it may be shown that they are small and that there is no marked water penetration deep into the micelles.The various types of information obtained give an overall view of micellar solutions which is compared with current studies by other approaches, experimental and theoretical.Furthermore, various methodological problems and advantages of self-diffusion investigations of micelle formation are considered.Using a recently developed theory, which treats the electrostatic effects according to the Poisson-Boltsmann equation, we calculated the concentrations of free and micellized amphiphile ions and counterions.All of the features of the experimental observations were displayed also by the theoretical results, and for the amphiphile concentrations good quantitative agreement was found.For β, quantitative differences between experiment and theory were found which can be referred to the somewhat ambiguous division into free and micellar counterions.
Krafft Points of Anionic Surfactants and Their Mixtures with Special Attention to Their Applicability in Hard Water
Tsujii, Kaoru,Saito, Naoyuki,Takeuchi, Takashi
, p. 2287 - 2291 (2007/10/02)
The Krafft points of the sodium and calcium salts of typical anionic surfactants and their mixtures have been measured to examine their applicability in hard water.The pure model compounds of the linear alkylbenzene sulfonates, α-olefin sulfonates, and alkylpoly(oxyethylene) sulfates were synthesized and used for Krafft-point measurements.Among the above three types of surfactant, the alkylpoly(oxyethylene) sulfates are shown to be the best surfactant for their practical uses in hard water, since their sodium and calcium salts as well as their mixtures are readily soluble at room temperature.The Krafft point vs. composition curves observed in binary surfactant mixtures have been classified into two groups.In group I, there exists a minimum in the Krafft point at a certain composition, whereas the Krafft point varies monotonously with the composition change in group II.It is found from the composition analysis of the solid phase that both components are immiscible in group I but are completely miscible even in the solid phase in group II.The thermodynamic theory for freezing-point depression has been favorably applied to the Kraff point vs. composition curves in group I.Theoretical calculations for the Krafft point vs. composition curves (liquidus curve) and the corresponding solidus curves in group II have also been made, assuming the ideal solutions in both liquid (micellar) and solid phases.The calculated curves are in poor agreement with the observed ones probably because of the nonideality of the solution especially in the solid phase.
