In our work we studied surface dynamics of the glass-forming liquid near the glass-transition region by Grazing Incidence X-ray Correlation Spectroscopy (GIXPCS). The sample used was polypropylene glycol with a molecular weight of 4000 (Tg ~ 205o K). We found that the dispersion relation of the surface oscillations deviates from the known model of over-damped capillary waves. The results are reviewed within the framework of linear viscoelasticity. We speculate that the observed effect is due to the low-frequency elasticity which points toward a solid-like low frequency response of the supercooled liquid. It is predicted that the elasticity will influence the static structure factor and surface roughness.
