The interaction between Atomic Force Microscope (AFM) tips and glass substrates coated in polyelectrolyte multilayers (PEM) of polyacrylic acid and polydiallyldimethylammonium chloride has been investigated using an evanescent wave atomic force microscope (EW-AFM). The films were prepared in situ on glass substrates and silicon nitride AFM cantilevers using a base layer of polyethyleneimine. We find that when the films are first prepared in salt, the films do not swell when the salt concentration is increased. However, when the films are prepared in water, the films do swell with increasing salt concentration. Force versus separation curves show that the interactions are composed of long-range electrostatic and short-range steric forces, indicative of a charged film adsorbed to the interfaces. We show that the mechanical response of the PEM is similar to the AFM measurement time scale (1-60s). Therefore there are slow rearrangements of the polymer films on this timescale that should be considered during AFM measurements, and in the use of such polymer films.