Structural and dynamical transformations between neighboring dense microemulsion phases
- Department of Physics, Rochester Institute of Technology, Rochester, New York 14623 (United States)
- Texaco Research Center, P.O. Box 509, Beacon, New York 12508 (United States)
- Department of Biology, Brookhaven National Laboratory, Upton, New York 11973 (United States)
A small-angle x-ray scattering (SAXS) study of dense AOT-water-decane microemulsions (AOT denotes sodium bis(2-ethylhexyl) sulfosuccinate) was undertaken in order to delineate clearly the phase behavior and corresponding structural transitions for AOT-plus-water volume fractions ranging from {phi}=0.60 to 0.95. Spectra were collected for temperatures between {ital T}=3 and 65 {degree}C. The resulting {ital T}-vs-{phi} phase diagram indicates three distinct structural domains when the water-to-AOT molar ratio is fixed at {ital W}=40.8, namely, the previously investigated {ital L}{sub 2} droplet phase, a high-temperature {ital L}{sub {alpha}} lamellar phase, and a low-temperature {ital L}{sub 3} phase consisting of randomly connected lamellar sheets. A significantly wide coexistence region accompanies the droplet-to-lamellar phase transition, which is demonstrated to be first order. For {ital W} between 15 and 40, an analysis of the lamellar structure using a one-dimensional paracrystal model produces a Hosemann {ital g} factor indicative of an approximately constant variation in the lamellar spacing of about 8%. The SAXS study was supplemented by dielectric-relaxation, shear-viscosity, and quasielastic light-scattering measurements in order to substantiate the observed phase transitions and further our understanding of the structural and dynamical properties of the {ital L}{sub 3} phase. It was found that the {ital L}{sub 3} phase exhibits Newtonian behavior up to a shear rate of 790 s{sup {minus}1}, in contradiction to previous theoretical considerations. The phase exhibits two distinct relaxation modes. A relaxation time of {similar to}1 ms characterizes the Brownian motion of a single lamellar sheet, while the motion of the entire interconnected sheet assembly has a relaxation time on the order of 1 s.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7039487
- Journal Information:
- Physical Review A. General Physics; (United States), Vol. 46:2; ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MICROEMULSIONS
PHASE TRANSFORMATIONS
CORRELATIONS
QUANTITY RATIO
SHEAR PROPERTIES
SMALL ANGLE SCATTERING
STRUCTURE FACTORS
VISCOSITY
WATER
X-RAY DIFFRACTION
COHERENT SCATTERING
COLLOIDS
DIFFRACTION
DISPERSIONS
EMULSIONS
HYDROGEN COMPOUNDS
MECHANICAL PROPERTIES
OXYGEN COMPOUNDS
SCATTERING
360602* - Other Materials- Structure & Phase Studies