Dodecyldiammonium vermiculite

The structure and the sorption properties of partially hydrophobized silicates (do-decylammonium and dodecyldiammonium vermiculites) were investigated in aqueous solutions of n-butanol. The alcohol is preferentially adsorbed on the surface. The interlayer composition is calculated from adsorption and X-ray diffraction data. In the air-dried state the organic cations lie flat on the interlamellar surface. In aqueous n-butanol solutions, the basal spacing of dodecylammonium vermiculite gradually increases with the extent of n-butanol adsorption because the chains increasingly point away from the surface. The basal spacing of dodecyldiammonium vermicuiite is virtually independent of the interlayer composition, because the expansion of the interlayer space is sterically restricted and a... 

FIG. 29 Free enthalpy of adsorption in n-butanol-water solutions on ( ) dodecylam-monium vermiculite and on ( ) dodecyldiammonium vermiculite. 

FIG. 31 Thermodynamic potential functions of the adsorption layer on dodecyldiammonium vermiculite in n-butanol-water solutions. 

The swelling of the dodecyldiammonium vermiculite is restricted by the bridging alkyl chains (Fig. 28b). The constancy of the basal spacing indicates that the chain orientation (at an angle of 56° to the silicate layer) is independent on the composition of the hquid mixture. The free enthalpy of displacement of water by butanol, A21G, tras calculated from the surface excess isotherms [Eq. (23)]. It decreases with increasing X and reaches smaller values for the aUcylammonium vermiculites (—10 and —8.4 J/g) than for the dodecyldiammonium derivative (-4 J/g) (Fig. 29). 

FIG. 27 Basal spacings of ( ) dodecylammonimn veimiculite and ( ) dodecyldiammonium vermiculite in n-butano 1-water solutions. 

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