Swelling and dispersion of smectite clay colloids: determination of structure by neutron diffraction and small-angle neutron scattering

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Abstract
The structural changes which occur during the swelling and dispersion in water (D2O) of montmorillonite and Laponite RD (a model synthetic hectorite-type clay) have been investigated by neutron diffraction and small-angle neutron scattering (SANS). By using samples where the clay platelets are initially aligned in the dry state, it has been possible to follow the progressive development of orientational disorder and eventually a randomly oriented isotropic structure, over a wide range of concentration (water/clay, w/w = 0.2–31). Such changes have been determined from measurements of the anisotropic SANS on a two-dimensional detector with the samples in a defined alignment to the incident beam. Interpretation of these results has been derived from model calculations based on the theory of scattering for platelet-shaped particles with a dimension similar to that of the hectorite clay, which has relatively uniform and well defined properties. Results are consistent with a predominantly one-dimensional swelling mechanism out to interlayer spacings of ca. 300 Å for hectorite, although significantly less for montmorillonite. At the lowest concentrations (ca. 3 × 10–2 g cm–3) the dispersions have a randomly oriented structure, although here there is still evidence of interparticle correlation, due to long-range double-layer interaction. The significance of this structural feature to the thixotropic properties of smectite clays is discussed.

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