Small-angle light scattering studies of dense AOT-water-decane microemulsions |
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Authors: | N Micali S Trusso F Mallamace S H Chen |
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Institution: | (1) Istituto di Tecniche Spettroscopiche del CNR, C.da Papardo, Salita Sperone 31, I-98166 Messina, Italy;(2) Dipartimento di Fisica, Università di Messina, Villaggio S. Agata C.P. 55, I-98166 Messina, Italy;(3) Department of Nuclear Engineering, 24-209, Massachusetts Institute of Technology, 02139-4307 Cambridge, MA, USA |
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Abstract: | Summary We have performed extensive studies of a three-component microemulsion system composed of AOT-water-decane (AOT=sodium-bis-ethylhexyl-sulfosuccinate
is an ionic surfactant) using small-angle light scattering (SALS). The small-angle scattering intensities are measured in
the angular interval 0.001–0.1 radians, corresponding to a Bragg wave number range of 0.14 μm−1<Q<<1.4 μm−1. The measurements were made by changing temperature and volume fraction ϕ of the dispersed phase (water + AOT) in the range
0.05<ϕ<0.75. All samples have a fixed water-to-AOT molar ratio,w=water]/AOT]=40.8, in order to keep the same average droplet size in the stable one-phase region. With the SALS technique,
we have been able to observe all the phase boundaries of a very complex phase diagram with a percolation line and many structural
organizations within it. We observe at the percolation transition threshold, a scaling behavior of the intensity data. This
behavior is a consequence of a clustering among microemulsion droplets near the percolation threshold. In addition, we describe
in detail a structural transition from a droplet microemulsion to a bicontinuous one as suggested by a recent small-angle
neutron scattering experiment. The loci of this transition are located several degrees above the percolation temperatures
and are coincident with the maxima previously observed in shear viscosity. From the data analysis, we show that both the percolation
phenomenon and this novel structural transition are derived from a large-scale aggregation between microemulsion droplets. |
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Keywords: | Brillouin and Rayleigh scattering other light scattering |
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