Effects of Monovalent, Exchangeable Cations and Electrolytes on the Infrared Vibrations of Smectite Layers and Interlayer Water

Infrared spectroscopy was used to investigate how νSi–O, the frequency of Si–O stretching, in layers of Li- and Na-montmorillonite and ν2, the frequency of H–O–H bending, in the interlayer water were affected by increasing the concentration,C, of LiCl and NaCl, respectively. Oriented gels of Li- and Na-montmorillonite equilibrated with solutions having various values ofCwere obtained by using a miniature pressure membrane apparatus. One part of each gel was used for the gravimetric determination ofmw/mc, the water content. The other part was transferred to an FTIR spectrometer where the spectrum of the gel was measured by attenuated total reflectance. Thus, the dependence of both νSi–Oand ν2onmw/mcwas determined in the same samples. The results showed that increasingChad little or no effect on the relation between νSi–Oandmw/mc, or on the relation between ν2andmw/mc. The vibrational coupling of Si–O stretching in the montmorillonite layers and H–O–H bending in the interlayer water was demonstrated. It was essentially independent of the species of exchangeable cation andC. Thus neither the species of exchangeable cation norChad any specific effect on the structure of the clay layers or the structure of the interlayer water.