An analysis of the Morphological behavior of substrate-supported diblock copolymer [polystyrene-block-poly(tert-butyl acrylate) (PS-b-PtBA)] films was carried out with the help of selective hydrolysis. The hydrolysis was a pseudo-first-order rate reaction as proven by infrared (IR) spectra. With the hydrolysis, the water-swelled poly(acrylic acid) (PAA) phase was obtained on the PtBA phase, and the surface morphology transformation was investigated by tapping mode atomic force microscopy (TMAFM). Together with the equilibrium swelling experiments, the morphology changes with hydrolysis were recorded in situ and time-dependent variation of the phase separation was successfully detected. The study made it possible to detect in situ the reorientation of functional groups in phase-separated films, which may find broad applications in the field of nanosensing.