Interlamellar Liquid Sorption on Hydrophobic Silicates

Abstract

A particular advantage of adsorption measurements on layer silicates is that the adsorption between the silicate layers can be followed by X‐ray measurements. — When the external and internal surface of the silicate montmorillonite is modified by increasing amounts of hexadecylpyridinium cations, the surface character changes from hydrophilicity to hydrophobicity. The changes are evaluated from the excess adsorption isotherms for methanol‐benzene mixtures. The volume Vs of the adsorption phase derived from the isotherms is compared with the free interlayer volume Vf from X‐ray measurements. — On sodium montmorillonite methanol is preferentially adsorbed and the volume increase observed by X‐ray measurements coincides with Vs. If the sodium cations are progressively displaced by hexadecylpyridinium ions the azeotropic point of the type IV isotherms is shifted to lower mole fractions of methanol. The methanol molecules are increasingly displaced from the adsorption phase by benzene molecules. Vf becomes strikingly larger than Vs. — It is concluded that the adsorption layer is not homogeneous in the interlayer space: the methanol molecules are adsorbed on the silicate layers and the benzene molecules are in the vicinity of the hexadecylpyridinium ions. In addition to this adsorption layer the remaining volume is filled with methanol‐benzene mixtures having a composition different from the adsorbed phase and more similar to the bulk phase.

Time-dependent changes of adsorption and wetting properties of pillared montmorillonites

“…The surface excess isotherms for ethanol/cyclohexane are type-II isotherms (Schay-Nagy classification, Kipling, 1965). In contrast to similar isotherms observed for the Na form of montmorillonite (Dékány et al, 1985;Berger et al, 1997) the linear section of the composite isotherms did not extent to x 1 = 1; the deviation was more pronounced at higher Al contents.…”

“…Introducing poly(hydroxoaluminium) pillars into Namontmorillonite changed the hydrophilic/hydrophobic character of the internal and external surfaces. The degree of hydrophilicity was deduced from adsorption experiments using binary liquid mixtures (Dékány et al, 1985(Dékány et al, , 1986aDékány, 1992). When a mixture of two liquids with different polarity, e.g.…”

“…The total amount adsorbed is n s = n s 1 + n s 2 . The excess isotherms, n s(n) i = f(x i ), i = 1, 2, were analysed using the method of Schay and Nagy (Dékány et al, 1985(Dékány et al, , 1986aLagaly et al, 1997, chapter 14). One obtains the adsorbed amounts n s 1 and n s 2 at equilibrium concentrations corresponding to the linear section of the composite isotherm.…”

Expansion characteristics of organo montmorillonites during the intercalation, aging, drying and rehydration processes: Effect of surfactant/CEC ratio

“…Although sydration behavior of original montmorillonite has been extensively studied in past two decades [25][26][27][28][29], less attention has been paid to the structural characteristics of wet OMt [30][31][32]. Several previous reports indicated that X-ray diffraction (XRD) is still the most widely used method for characterizing the structure of OMt in water, and the results showed that water molecules can always cause evident swelling of OMt [33][34][35][36].…”

Microcalorimetric Control of Liquid Sorption on Hydrophilic/Hydrophobic Surfaces in Nonaqueous Dispersions

“…When the originally hydrophilic surface is modified by long alkyl chains [80][81][82][83][84][85][86][87][88][89][90][91][92], heats of immersion display significantly greater differences. This is well demonstrated by adsorption and X-ray diffraction measurements in toluene (Table 5).…”