Static structure and colloidal interactions in partially quenched quasibidimensional colloidal mixtures

Partially quenched quasibidimensional colloidal suspensions are obtained by confining a bidisperse aqueous suspension of polystyrene spheres between two glass plates. The larger particles are fixed between the plates, forming a disordered bidimensional matrix of obstacles, with respect to which the colloidal suspension of the smaller species of particles equilibrates. Digital video microscopy is used to measure the static structure of both the colloidal suspension and the matrix for various fixed particles concentrations. The effective pair potentials between the mobile particles u(11)(r) and between mobile and fixed particles u(12)(r) are obtained by deconvoluting the structural information of the system via the Ornstein-Zernike equation. The measured pair potential u(11)(r) exhibits two attractive components. One of them; at intermediate distances, is present at all fixed particle concentrations, while the second one, of longer range, develops as the number of obstacles increases. The pair potential u(12)(r) also has an attractive component at intermediate distances.