Experimental observation of structural crossover in binary mixtures of colloidal hard spheres

Using confocal-microscopy we investigate the structure of binary mixtures of colloidal hard spheres with size ratio q=0.61. As a function of the packing fraction of the two particle species, we observe a marked change of the dominant wavelength in the pair correlation function. This behavior is in excellent agreement with a recently predicted structural crossover in such mixtures. In addition, the repercussions of structural crossover on the real-space structure of a binary fluid are analyzed. We suggest a relation between crossover and the lateral extension of networks containing only equally sized particles that are connected by nearest neighbor bonds. This is supported by Monte-Carlo simulations which are performed at different packing fractions and size ratios.