smectites increased during the initial stages of hydration. Infrared spectroscopy was used to investigate how n Si-O , the Later, Lerot and Low (4) found that the height of the infrared frequency of Si-O stretching, in layers of Li-and Na-montmorilabsorption peak for Si-O stretching in montmorillonite inlonite and n 2 , the frequency of H-O-H bending, in the interlayer creased as long as hydration progressed. Any change in the water were affected by increasing the concentration, C, of LiCl and height of this peak is indicative of changes in O-Si-O NaCl, respectively. Oriented gels of Li-and Na-montmorillonite angles and Si-O bond lengths and, hence, in the crystal equilibrated with solutions having various values of C were obstructure of the montmorillonite. tained by using a miniature pressure membrane apparatus. One In a recent paper, Yan et al. (5) observed that the frepart of each gel was used for the gravimetric determination of m w / quency of Si-O stretching in montmorillonite layers and m c , the water content. The other part was transferred to an FTIR spectrometer where the spectrum of the gel was measured by atten-the frequency of H-O-H bending in the interlayer water uated total reflectance. Thus, the dependence of both n Si-O and n 2 changed progressively until the thickness of the interlayer on m w /m c was determined in the same samples. The results showed water far exceeded that of the layers themselves. In addition, that increasing C had little or no effect on the relation between they observed that the Si-O stretching was coupled with the n Si-O and m w /m c , or on the relation between n 2 and m w /m c . The H-O-H bending. These observations suggest that energy vibrational coupling of Si-O stretching in the montmorillonite changes accompanying structural changes in the montmorillayers and H-O-H bending in the interlayer water was demonlonite layers and interlayer water might contribute to the strated. It was essentially independent of the species of exchangeswelling of the montmorillonite.
able cation and C. Thus neither the species of exchangeable cation It has been shown that electrolytes reduce the swelling of nor C had any specific effect on the structure of the clay layers montmorillonite (6-15). Since swelling is a very important or the structure of the interlayer water.