  The screened Coulomb interaction between uniformly charged flat plates is
considered at very small plate separations for which the Debye layers are
strongly overlapped, in the limit of small electrical potentials. If the plates
are of infinite length, the disjoining pressure between the plates decays as an
inverse power of the plate separation. If the plates are of finite length, we
show that screening Debye layer charges close to the edge of the plates are no
longer constrained to stay between the plates, but instead spill out into the
surrounding electrolyte. The resulting reduction in the disjoining pressure is
calculated analytically. A similar reduction of disjoining pressure due to loss
of lateral confinement of the Debye layer charges should occur whenever the
sizes of the interacting charged objects become small enough to approach the
Debye scale. We investigate the effect here in the context of a two dimensional
model problem that is sufficiently simple to yield analytical results.
