Cluster Formation in Aqueous Electrolyte Solutions Observed by Dynamic Light Scattering

Using dynamic light scattering we show that aqueous super- to undersaturated solutions of NaCl, (NH4)2SO4, and Na-citrate contain submicrometer size clusters at room temperature. The particle size distributions deduced by Laplace inversion of the spectra contain two predominant components. The smaller components with radii below 1 nm are attributed to mixtures of solvated ions and the larger with radii between 50−500 nm to ion clusters. Knowledge of the mesoscale structure of concentrated electrolyte solutions may be necessary to describe effective protein−protein interactions which are of importance in biochemical applications such as protein crystallization.