On the interpretation of scattering peaks from bicontinuous microemulsions

Abstract

In several recent small angle neutron scattering (SANS) experiments made with three-component microemulsions in the one-phase region having oilwater contrast, one often finds in the SANS intensity distribution function a single prominent peak occuring at some finite Bragg wave number Q _m . This peak can be due either to spatial correlations between closely spaced microemulsion droplets when the droplet picture is valid, or to the length scale ξ which is kown to exist in bicontinuous microemulsions, when this type of description is appropriate. In this paper we examine a series of scattering patterns taken in the one-phase channel of AOT/water (0.6% NaCl)/decane ionic microemulsions. We propose a criterion for distinguishing between the bicontinuous and the droplet type microemulsions, based on analyses of the peak position and the peak height. We conclude that a bicontinuous structure can best be described as having a mean characteristic length d with a certain amount of dispersion around it.