Vibrationally resonant sum-frequency generation (VR-SFG) has been used to characterize the molecular orientation of the phenyl groups at the interface between polystyrene (PS) films and surface-modified glass substrates. Both the interface structure and the film adhesion are found to vary as the substrate surface is changed from hydrophobic to hydrophilic. The improved adhesion on the hydrophilic substrate is attributed to the development of attractive hydrogen bonds between surface hydroxyl (OH) groups and the pi electron cloud of the phenyl ring. This interaction is manifest by changes in the orientation distribution of the phenyl rings at the interface. Published by Elsevier Science B.V.