Local composition fluctuations in strongly nonideal binary mixtures

Abstract

We study the static and dynamical aspects of small length scale composition fluctuations in strongly nonideal binary mixtures of two different type by isothermal-isobaric (NPT) ensemble molecular dynamics simulations. Both the two models studied consider strong attractive interaction between dissimilar species which discourage the phase seperation in the binary mixtures. We find that the joint probability distribution of the composition fluctuations within molecular sized volumes is nearly Gaussian. However, the distributions are rather broad in both the binary mixtures. This is to be contrasted with the density fluctuation which is nearly negligible. Spontaneous fluctuation in one component is found to be anticorrelated with the fluctuations in it's counterpart. The investigation of the dynamical correlation functions of the fluctuations reveal nonexponential relaxation with a slow long time tail. The cross-correlation function relaxes at a slower rate than the two pure correlations.