Abstract--Samples of Na-saturated, Upton montmorillonite were prepared with different contents of water (H20 or D20) by: (1) adsorption of water from the vapor phase at a specific value of p/p*, the relative humidity, (2) adsorption of water from the vapor phase at p/p* = 1.0 followed by desorption of the water into the vapor phase at a specific p/p* < 1.0, and (3) adsorption of water from the liquid phase followed by desorption of the water into the vapor phase at a specific p/p* < 1.0. Water adsorbed initially from the vapor phase was called V-adsorbed water, and water adsorbed initially from the liquid phase was called L-adsorbed water. The water contents of these samples were determined by gravimetric analysis, the c-axis spacings by X-ray powder diffraction, the O-D stretching frequencies by IR spectroscopy, and the heats of immersion by differential microcalorimetry. No difference was found between V-adsorbed and L-adsorbed water; however, if the final water content was established by adsorption, the system was in a different state than if the final water content was established by desorption. In particular, hysteresis was observed in the following properties: the relative humidity of the adsorbed water, the O-D stretching frequency in this water, and the degree of order in the stacking of the clay layers. The only property that did not exhibit hysteresis was the heat of immersion. Apparently, hysteresis occurred because the orderliness of the system was not reversible, and, thus, any property that depended on orderliness was hysteretic.
The frequencies of Si-O stretching, νSi-O, in layers of montmorillonite and of H-O-H bending, ν2, in the interlayer water were investigated by infrared spectroscopy. Oriented gels of Li-and Na-montmorillonite equilibrated at different water contents, mw/mc, were obtained by using a miniature pressure membrane apparatus. One part of each gel was used for the gravimetric determination of mw/mc. 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-O and ν2 on mw/mc was determined in the same samples. The absorption bands for Si-O stretching were resolved by using a curve-fitting technique to determine the frequency, area, and height of the component peaks. Two prominent peaks, labeled peak III and peak IV, were selected for analysis. It was found that ν Si-O for each peak and the ratio of the areas (or heights) of the two peaks were all exponential functions of mc/mw. Moreover, a linear relation was found between ln(νSi-O) and ln(ν2). These results were interpreted to mean that the Si-O stretching vibrations in the montmorillonite layers and the H-O-H bending vibrations in the interlayer water are coupled and that both change as the layers come closer together.
Experimental data were presented to show that the value of fa, the electric potential at the outer Helmholtz plane, is -60 mV for Na-smectites. This value of fa was used with electric double-layer theory to predict the relation that would exist between II, the swelling pressure, and X, the distance between adjacent smectite layers, if swelling were due to excess osmotic pressure in the interlayer solution. Data showing the observed relation between II and X were also presented. These data were derived from a study in which X was determined by X-ray diffraction at successively higher values of II. Comparison of the predicted relation with the observed relation demonstrated that the former was relatively insignificant. Hence, it was concluded that the osmotic contribution to II is negligible. This conclusion was discussed with reference to the work of other investigators. The results of previous studies were used to establish the fact that both (II + 1) and J\/Ji, the ratio of the value of any property, i, of the water in the smectite-water system to that of pure water, are exponential functions of 1/t, the reciprocal of the average thickness of the water films on the surfaces of the smectite layers. Elimination of 1/t between the two functions yielded an equation relating (II + 1) to JJJ\. This equation indicated that the development of II and the deviation of j from J/ were caused by the same factor, i.e., the structural perturbation of the water under the influence of the layer surfaces. Hence, it was concluded that the structural component of the swelling pressure is primarily responsible for the swelling of smectites.
Data are presented on several properties of water in montmorillonite‐water systems. The data indicate that these properties differ from the same properties of bulk water because of differences in intermolecular bonding. Also, it is found that the value, J, of each property is described by the general equation J = J° exp β/(mw/mm) in which J° is the value of the given property in pure bulk water, mw/mm is the mass ratio of water to montmorillonite and β is a constant. The proposal is made that, since all of the water properties obey a common equation, their deviation from the corresponding properties of bulk water must be caused by a common factor. By making appropriate substitutions for mw/mm and analyzing the resulting equations, the common factor is shown to be interaction of the water with the surfaces of the montmorillonite layers. The nature of this interaction, and ways in which it might affect intermolecular bonding, are discussed.
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