For binary fluid mixtures of spherical particles in which the two species are sufficiently different in size, the dominant wavelength of oscillations of the pair correlation functions is predicted to change from roughly the diameter of the large species to that of the small species along a sharp crossover line in the phase diagram [C. Grodon et al., J. Chem. Phys. 121, 7869 (2004)]. Using particle-resolved colloid experiments in 3d we demonstrate that crossover exists and that its location in the phase diagram is in quantitative agreement with the results of both theory and our Monte-Carlo simulations. In contrast with previous work [J. Baumgartl et al., Phys. Rev. Lett. 98, 198303 (2007)], where a correspondence was drawn between crossover and percolation of both species, in our 3d study we find that structural crossover is unrelated to percolation.
REFERENCES
An equivalent procedure, fitting gij(r) to the results obtained by Fourier transforming the analytical PY formulae for the partial structure factors of an additive binary hard sphere mixture,37,38 was used to determine the packing fractions ηb and ηs for the binary colloidal mixtures.
We choose to divide the averaged radius of gyration by the box diagonal d. Although the simulation box is cubic, the experimentally measured sample volume is not. Each has a length of 512 pixels of size 178 nm (0.062 σb) in x- and y-direction, whereas the z-direction is smaller and varies. Typical image depths are 100–200 pixels of size 168 nm (0.058 σb).
