In this work, we have used the previously designed controlled uniaxial swelling (CUS) cell to obtain predetermined extents of swelling in montmorillonite. Using the CUS cell, a simultaneous measurement of swelling pressure is done with controlled swelling. Undisturbed clay samples at well-defined swelling (0%-75%) were removed from the CUS cell and analyzed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. In addition, orientation-dependent microattenuated total reflectance (micro-ATR) spectroscopic investigations are also conducted on the controlled swelled samples. Significant changes in the silicate (Si-O) stretching region (1150-950 cm(-1)) have been observed with changes in swelling and orientation. The band at 1005 cm(-1) (attributed in the literature to arising from Si-O vibrations when montmorillonite platelets are normal to incident radiation) is most pronounced for the 0%-swelled sample and diminishes with swelling. The band associated with perpendicular vibration (at 1078 cm(-1)) increases with swelling. Thus, the intensity of this band increases with misorientation of clay particles. Our results indicate that the reduced particle size, as ascertained from SEM cryoimaging, with increased swelling is related to increased misorientation of the clay platelets. At 0% swelling, the clay platelets are most oriented and have largest particle size. The rearrangement of clay platelets as seen in the orientation-dependent spectra is a direct result of the breakdown of the clay particles with increased hydration resulting from increased swelling.