Exchangeable Cation and Solvent Effects Upon the Interlamellar Environment of Smectites: Esr Spin Probe Studies

Abstract

Abstract--The ESR spin probe, TEMPAMINE +, was used to study the interlamellar behavior of adsorbed organic cations on hectorites solvated with water, ethanol, and water-ethanol mixtures, and saturated with several monovalent and divalent metallic cations. The mobility and orientation of the probe was affected greatly by the solvent, and to a lesser extent by the predominant exchangeable cation on the silicate surface. Most of the effects could be interpreted in terms of the basal spacings of the hectorite. In all instances, the adsorbed probe was much less mobile than in solution despite the different interlamellar volumes available for molecular motion.

Cationic Spin Probes on Hectorite Surfaces: Demixing and Mobility as a Function of Adsorption Level

“…Previous studies of TEMPAMINE + adsorbed on smectites solvated in ethanol and methanol have shown spectra attributable to highly oriented as well as nearly randomly tumbling species (McBride, 1976(McBride, , 1977a(McBride, , 1977b. The present study reveals that the former species predominates at very low adsorption levels, while the latter solutionlike species becomes more prevalent at higher levels ( Figure 6).…”

“…The nature of the spectrum of the adsorbed probe has been discussed previously (McBride, 1976(McBride, , 1977a(McBride, , 1977b) and will not be described in detail here. However, an additional broad resonance centered on the Mt = 0 (middle) resonance of the TEMPAMINE + spectrum is evident at the 10% loading level, increasing in relative intensity to the 40% level, and finally decreasing again at the 100% level.…”

“…The K § ion was chosen as the complementary cation in order to permit free swelling of clay platelets at low probe-adsorption levels, thereby maximizing the possibility of homogeneous clay-waterprobe system. Previous work has shown that the type of exchange cation has relatively little influence on the surface mobility of the probe (McBride, 1977b).…”

“…Infrared and X-ray techniques have generally required that the clays have high organic cation contents and could not be used to study clay-water systems at equilibrium. However, recent investigations have shown that electron spin resonance (ESR) spectroscopy of clays containing small quantities of adsorbed organic radical cations provides insight into clay--organic interactions in water and various other solvents (McBride, 1976(McBride, , 1977a(McBride, , 1977b. The advantages of this approach are (1) a very small fraction of the total exchange sites can be occupied by the organic cation, resulting in little effect of the adsorption upon the hydration and expanding properties of the clay, (2) adsorption can be studied over a wide range of organic cation concentrations because of the sensitivity of the ESR technique, and (3) studies can be made of aqueous suspensions as well as dry powders and films.…”

“…The present investigation is designed to observe the effect of molecular cation concentration on the clay surface upon mobility and orientation, since previous results (McBride, 1977b) have shown that the ESR spectrum of the adsorbed cation is dependent upon the Agronomy Paper No. 1261.…”