BEHAVIOUR OF IMOGOLITE GELS UNDER SHEAR

概要

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Curves of shear stress against shear rate for aqueous imogolite suspensions have been determined using a rotary viscometer. At concentrations of 0.1 % (w/v) and above, these suspensions have a pronounced gel character and the curves obtained during acceleration and deceleration of the rotor do not coincide but form a (hysteresis) loop. With successive cycles of shearing, the area enclosed by such loops is progressively decreased, indicating that imogolite gels behave like a pseudoplastic material in that strong shearing action produces an irreversible breakdown of the gel structure. This is confirmed by scanning electron microscopy (SEM) of the quick-frozen gels, showing that shearing has distorted and ruptured the fibre bundles of imogolite. Raising the suspension pH from 7 to 9 gives rise to a phase consisting of a condensed, semi-rigid gel in which the fibre bundles have partially aggregated to form a sheet-like structure. Air-drying the suspension, followed by prolonged mechanical stirring in water, produce a system with no gel character. SEM shows that the air-dried material has a sheet structure from which fibre bundles are totally absent.
日本粘土学会の論文