Phase equilibrium, dynamic behavior and detergency in surfactant systems

[摘要] Various model systems containing pure compounds of oil, water, and surfactant were studied to understand equilibrium phase behavior and nonequilibrium phenomena, especially their relationship to solubilization-emulsification mechanisms of detergency. Videomicroscopy was used to observe nonequilibrium phenomena such as intermediate phase formation, interfacial instabilities, and spontaneous emulsification. Of particular interest was observation of time-dependent behavior using a newly developed dynamic contacting technique where a small drop of oily soil was injected into an aqueous surfactant solution.It is important to know whether formation of an intermediate phase occurs since it brings about a substantial improvement in detergency, provided that it is capable of solubilizing significant quantities of oil. Diffusion path theory was used to predict conditions for intermediate phase formation. Results of contacting experiments for anionic and nonionic surfactants with pure polar oils were in good agreement with theoretical predictions based on this theory.Systems containing the pure triglyceride triolein and nonionic surfactants were studied. For the C$sb{12}$E$sb5$ system, soil removal was higher than with C$sb{12}$E$sb5$ and C$sb{12}$E$sb4$ due to formation of an intermediate microemulsion (D) phase capable of solubilizing triolein. For mixtures of triolein and n-hexadecane the D phase was found at low triolein contents and the D$spprime$(L$sb3$) phase having low solubilization of both oils at high triolein contents.Phase and dynamic behavior of a system containing mixtures of a pure nonionic surfactant and an anionic surfactant of the alkyl ethoxy sulfate type were studied. Rapid solubilization of oil was observed with videomicroscopy near the Phase Inversion Temperature (PIT) due to the formation of an intermediate middle-phase microemulsion. Soil removal was greatest near the PIT.Finally, oil drop contacting experiments were performed for mixed hydrocarbon-long-chain alcohol soils with different pure nonionic surfactants. Delayed formation of an intermediate liquid crystalline phase was observed for conditions above the PIT where excellent soil removal was also found. A quasi-steady state analysis requiring relatively little information on phase behavior was able to explain observed effects of drop size and surfactant concentration on the time when liquid crystal formation began.

[发布机构] Rice University

[效力级别] engineering