VIBRATIONAL PROBE STUDIES OF WATER INTERACTIONS WITH MONTMORILLONITE

Interaction of water with montmorillonite exchanged with Na+, K+, Co2, and Cu2+ cations as a function of water content was examined using a n FTIR/gravimetric cell designed to collect spectroscopic and sorption data simultaneously. Correlation of water desorption isotherms with i nfrared spectra of the clay-water complex showed that the position of the HOH bending band of water decreased as a function of water content . The largest decreases in frequency were observed for CU2+ and Co2+; smaller decreases were found for Na+ and K+. In addition. the molar ab sorptivity of sorbed water increased upon decreasing the water content . The decrease in frequency and the concomitant increase in molar abso rptivity were attributed to polarization effects on the sorbed water m olecules by exchangeable cations. The interference fringes of a self s upporting clay film permitted d-spacings to be determined optically an d, therefore. changes in frequency, molar absorptivity, and water sorp tion behavior to be related directly to changes in interlayer spacing. The d-spacings obtained from the interference fringes were consistent ly larger by approximately 0.5 angstrom than those determined using po wder XRD.