Attractive potential between confined colloids at low ionic strength

Digital video microscopy is used to locate the positions of 1.27 \ensuremath{\mu}m diameter polystyrene spheres suspended in low ionic strength water and confined between two glass plates. A method is developed to obtain the pair potential of the colloidal particles from measurements of the pair-correlation function of both dilute and moderately concentrated dispersions. We find that the measured pair potential has an attractive component much greater than predicted by the Derjaguin-Landau-Verwey-Overbeek theory of nonconfined colloids and suggest that the confining plates are responsible for the observed deviations from theory.