Absolute molecular structure of the polystyrene at the buried polystyrene/silica interface and its relationship to dewetting during annealing

•The specific surface-and phase-sensitive SFG spectroscopy revealed the absolute PS structure at the buried PS/silica interface.•The PS nanolayer near the substrate gradually formed during annealing.•The dewetting occurred at the non-adsorbed PS/the flattened PS nanolayer interface due to the autophobic effect.•As the solvent quality reduced, the dewetting rate of the PS film became slower.•This study provides a molecular-level understanding of the dewetting property of the polymer thin film.