Phase separation and orientational ordering of synthetic Na-fluorohectorite clay particles in saline aqueous suspensions

Abstract

The main goal of the present thesis is to determine and better understand the phase diagram for the nano-layered synthetic clay sodium fluorohectorite dispersed in saline aqueous solutions. This system displays up to four distinct gravity-driven phases coexisting in different strata in a single sample tub

Visual observations were carried out at NTNU, including observations of birefringent textures when samples are placed between crossedpolarizers, and Small-Angle X-ray Scattering experiments were performed mainly at ESRF in Grenoble, France.

The visual observations confirmed the existence of a birefringent phase and more recently the study of this phase through polarized light microscopy showed textures in the samples arising from defects in the nematic phase. These observations allowinsight into the organization of the particles in the birefringent nematic phase.

The Small-Angle X-ray Scattering experiment examined tubes at different saline concentrations after settling under gravity. The results display SAXS patterns both with and without anisotropy. A method was developed to treat the data and analyze it in terms of eccentricity of the patterns that, together with the orientation of the anisotropies and the transmission data, permits the creation of the phase diagram for the system as function of electrolyte concentration and clay volume fraction.

Beyond the scope of the presentwork, there are still several open questions connected to these systems, to be addressed in the future.