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 t wo 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. Digi tal video microscopy is used to measure the static structure of both the co lloidal suspension and the matrix for various fixed particles concentration s. The effective pair potentials between the mobile particles u(11)(r) and between mobile and fixed particles u(12)(r) are obtained by deconvoluting t he structural information of the system via the Ornstein-Zernike equation. The measured pair potential u(11)(r) exhibits two attractive components. On e of them; at intermediate distances, is present at all fixed particle conc entrations, while the second one, of longer range, develops as the number o f obstacles increases. The pair potential u(12)(r) also has an attractive c omponent at intermediate distances.