Clustering of water molecules in aqueous solutions: Effect of water–solute interaction

Clustering of water molecules in partially miscible aqueous solutions (with immiscibility gap) was studied by Monte Carlo (MC) simulations. Liquid–liquid coexistence curves were determined by MC simulations in the Gibbs ensemble. Water cluster size distributions were studied in the organic-rich one-phase region. At the coexistence curve we observe the broadest distribution of cluster sizes in agreement with the Fisher droplet model. There are no percolating water clusters in aqueous mixtures of solutions of hydrophobic particles in the studied concentration range. In contrast, in an aqueous solution of hydrophilic solutes crossing the coexistence curve approximately coincides with the 3D percolation threshold of water. An infinite water cluster (percolating cluster or droplet of the second phase) appears in an aqueous solution, when the average number of water–water H-bonds per molecule exceeds ca. 1.6.