Sum frequency generation (SFG) vibrational spectroscopy has been used to characterize the effect that toluene solvent vapor has on the surface structure of polystyrene films. SFG spectra show that low surface tension toluene molecules preferentially coat the surfaces of polystyrene films that are exposed to a saturated toluene vapor environment. The SFG spectra indicate that phenyl side branches are well-ordered at the air/polystyrene interface prior to toluene exposure and that the phenyl branches become solvated and disordered when the polystyrene is exposed to toluene vapor. After exposure, as the toluene evaporates from the film, the partially solvated polystyrene surface rapidly reorders the phenyl side groups away from the surface.