Experimental evidence of a crossover in critical behaviour of water-in-oil microemulsions

Abstract

An extensive static and dynamic light-scattering experiment on a water-in-oil microemulsion system (water/n-decane/AOT) showed that the critical dynamics of this three-component microemulsion is completely governed by a Debye cut-off wavenumber qD, which is equal to the inverse diameter of the microemulsion droplet. Furthermore, the authors found occurrence of a crossover phenomenon for the statics and dynamics, at a correlation length xi c such that qD xi c=1, the crossover temperature being at about 10 degrees C below the critical temperature.

An introduction to critical points for biophysicists; observations of compositional heterogeneity in lipid membranes

“…At temperatures far from the critical point, structure factors derived from dynamic light scattering fit a form for individual droplets (45). Near the critical point, structure factors fit predictions relevant to critical fluctuations (45). …”

A Simple Analysis for Magnetic Behaviors of Exchange-Coupled Granular/Continuous Perpendicular Magnetic Recording Media

“…We have been able to fit our data, and also those of [21], from the critical and on offcritical constant volume fraction lines [9], by using a more complete mode-coupling theory including background effects on the transport coefficients [ 191 in conjunction with a linear model equation of state for the calculation of the correlation length for the off-critical lines [22]. In this model the transport coefficients, like the shear viscosity and the relaxation rate, can be written as a sum of a background and a critical part As we showed in [8] and [9], these quantities are given by rB(q, T ) = R(k,Tq3/6ny) 0.675(q/q,)'-'(l (2) and (4) can be compared with the experimental results provided that the Debye cut-off wavenumber 41, is known.…”

“…In this model the transport coefficients, like the shear viscosity and the relaxation rate, can be written as a sum of a background and a critical part As we showed in [8] and [9], these quantities are given by rB(q, T ) = R(k,Tq3/6ny) 0.675(q/q,)'-'(l (2) and (4) can be compared with the experimental results provided that the Debye cut-off wavenumber 41, is known. This can be obtained using the argument [lo] that the size of the microemulsion droplet sets the microscopic length scale and determines the reciprocal of the wavenumber cut-off entering in the mode-coupling theory.…”

“…The full set of data will be reported in a forthcoming paper [9], but we shall here focus on the most important new results obtainedfor the sample with the criticalvolume fraction. We have found an experimental $ Permanent address: Dipartimento di Fisica, Universiti degli Studi di Roma La Sapienza, P le A Moro 2, 1-00185 Roma, Italy.…”

“…In an analogous way, xT diverges like x1 = xo~-'*, where y* = y/(la) = 1.40, also from renormalisation group calculation [9]. In fitting the intensity data, we first subtract from the measured intensity a constant background which amounts to 4% of the total scattering.…”