ABSTRACT
Gelation is a common effect in aqueous suspensions of charged colloidal clay platelets at concentrations as low as 1 wt%. However, in systems of charged gibbsite [Al(OH)3] platelets, gelation can be delayed to concentrations as high as 50 wt% depending on the ionic strength. We investigated the phase behaviour of this system approaching the state of gelation in the delicate region between attractive and repulsive states that originate from competition between Coulomb repulsion and van der Waals attraction. As a function of the ionic strength, isotropic-nematic, nematic-columnar and isotropic-columnar phase separations were observed. Moreover, compression by gravitational forces allowed us to observe phase separation that is arrested by gelation in the homogeneous suspensions.
ABSTRACT
The behavior of mixtures of silica spheres and smaller silica-coated gibbsite plates is studied by means of confocal microscopy. Addition of plates slows down the crystallization of the settling spheres. Liquidlike microphases of the plates are found in the sediments of the spheres. It is argued that this is due to simultaneous sedimentation of the plates and spheres as well as depletion interaction between both species. Typical length scales in the sediments, derived from Fourier transforms of the confocal images, suggest there are still specific interactions present.
