Fluctuations and micro-heterogeneity in mixtures of complex liquids.

The role of concentration fluctuation and micro-heterogeneity in aqueous methanol mixtures are examined by two different methods: computer simulations of two systems with sizes of 2048 and 16 384 molecules, and site-site Ornstein-Zernike integral equation theory with two different closures. The focus is on the short and long range behaviour of the correlation functions, their running integrals and the structure factors. It is found that the micro-heterogeneous nature of these mixtures does not allow a proper stabilisation of the long range tail of the correlations as obtained through computer simulations, even over 6 ns runs. Similarly, approximate closures provide poor estimates of the concentration fluctuations and micro-structure of the mixtures. Interestingly, the analysis of the inadequacies of both these studies provide interesting insights about the nature and interplay of the concentration fluctuations and the micro-heterogeneity in these mixtures.