  We explore theoretically the modifications to the interactions between
charged surfaces across an ionic solution caused by the presence of dielectric
polymers. Although the chains are neutral, the polymer physics and the
electrostatics are coupled; the intra-surface electric fields polarise any low
permittivity species (e.g., polymer) dissolved in a high permittivity solvent
(e.g., water). This coupling enhances the polymer depletion from the surfaces
and increases the screening of electrostatic interactions with respect to a
model which treats polymeric and electrostatic effects as independent. As a
result, the range of the ionic contribution to the osmotic interaction between
surfaces is decreased, while that of the polymeric contribution is increased.
These changes modify the total interaction in a nonadditive manner. Building on
the results for parallel surfaces, we investigate the effect of this coupling
on the phase behaviour of polymer-doped smectics.
