Giant rodlike reversed micelles formed by sodium bis(2-ethylhexyl) phosphate in n-heptane
- Auburn Univ., AL (United States)
The solution behaviors of sodium bis(2-ethylhexyl) phosphate (NaDEHP) in n-heptane were investigated by light-scattering and viscosity measurements. NaDEHP forms giant rodlike reversed micelles, with a radius of gyration as large as 53 nm, which violently contrasts with the literature view that the average micellar aggregation numbers in nonaqueous or apolar media are much smaller (seldom exceeding 20) than those in aqueous media. Significantly, a small amount of water plays the role of an antimicellar growth agent; i.e., the reversed micellar size decreases remarkably when [open quotes]dry[close quotes] solutions are exposed to humid air from which water vapor is absorbed or when bulk water is directly added - a behavior which is distinctly opposite to that for sodium bis(2-ethylhexyl) sulfosuccinate/apolar medium systems. Thus, the literature views that large micelles can only be found in aqueous media and that the surfactant headgroups in reversed micelles are linked together by hydrogen bonds are misleading. It is suggested that the primary contribution to the driving force for the growth of rodlike NaDEHP reversed micelles is long-range electrostatic interactions among the headgroups of the surfactant molecules and their counterions, and a possible mechanism for the effect of water is also discussed. 27 refs., 7 figs., 1 tab.
- DOE Contract Number:
- FG05-85ER13357
- OSTI ID:
- 6970591
- Journal Information:
- Langmuir; (United States), Vol. 10:8; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
MICELLAR SYSTEMS
LIGHT SCATTERING
VISCOSITY
HEPTANE
LASERS
MATHEMATICAL MODELS
PHOSPHATES
RODS
SODIUM COMPOUNDS
SURFACTANTS
WATER
ALKALI METAL COMPOUNDS
ALKANES
HYDROCARBONS
HYDROGEN COMPOUNDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
SCATTERING
400201* - Chemical & Physicochemical Properties
990200 - Mathematics & Computers