We study suspensions of charged mesoscopic spheres (colloids) near typical
dielectric interfaces. Having a dielectric constant that is different from
that of the suspension, the interface gives rise to image-charge-induced fo
rces which compete with the usual double-layer forces acting between the co
lloids. Within the framework of Poisson-Boltzmann theory we calculate the t
otal force acting on an interfacial macrosphere for a broad range of possib
le system parameters. These are: the ratio of dielectric constants of the t
wo media, the charge and size of the macroion, its distance from the wall,
the temperature and volume fraction of the suspension. To reduce the number
of parameters, use is made of the scaling property of the Poisson-Boltzman
n equation in the salt-free approximation. We have furthermore performed Mo
nte Carlo simulations to investigate finite-size effects of the microions.
We discuss, quite generally, how both confinement effects and image charges
affect the structural properties of interfacial colloidal suspensions and
explain how our results can be used for estimating their effects in experim
ents.