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Simulation of bicontinuous microemulsions: comparison of simulated real‐space microstructures with scattering experiments
Author(s) -
Chen S.H.,
Chang S.L.,
Strey R.
Publication year - 1991
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889891001462
Subject(s) - microemulsion , spinodal decomposition , scattering , length scale , correlation function (quantum field theory) , condensed matter physics , debye , bar (unit) , function (biology) , dispersion (optics) , physics , thermodynamics , materials science , phase (matter) , quantum mechanics , pulmonary surfactant , evolutionary biology , biology , meteorology , dielectric
The ubiquitous scattering peak found in all disordered bicontinuous microemulsions, when scattering measurements are made with an oil‐water contrast, is attributed to the existence of two length scales in the system. The two lengths, d and ξ , appear explicitly in the Debye correlation function for the microemulsion in a phenomenological model proposed by Teubner & Strey [ J. Chem. Phys. (1987), 87 , 3195–3200] (T–S model). The precise physical meaning of these two lengths, however, was not clear in the original paper. Cahn's scheme for simulating the morphology of the late‐stage spinodal decomposition of a phase‐separating two‐component alloy is extended to the case of bicontinuous microemulsions with an equal volume fraction of oil and water. In the simulation, a length scale =2 π /, representing the average interdomain distance (proportional to the average domain size), and another parameter z , relating to the dispersion of the domain size by Δk / = ( z + 1) −1/2 , are imposed. It is shown that the ratio ξ / d in the T–S model is a unique function of the parameter 1/ z . The extended Cahn model gives both the real‐space structure of a disordered bicontinuous microemulsion and the exact Debye correlation function for the calculation of the corresponding scattering intensity. A criterion is given for the realisation of the disordered bicontinuous structure in terms of a universal range for the dispersion ( i.e. ξ / d ). The existence of the two lengths, having a universal ratio, also implies that the scattering function I ( Q ) satisfies a certain scaling relation. Our SANS data are used to support the validity of such a scaling relation.