The Isotropic−Nematic Interface in Suspensions of Na−Fluorohectorite Synthetic Clay

Abstract

Colloidal suspensions of Na-fluorohectorite synthetic clay platelets in saline water exhibit coexisting isotropic and nematic phases, due to gravitational separation of the polydisperse particles. We study the ordering of the platelets at the interfaces between various coexisting phases. Four different experimental techniques are employed: visual observation of birefringence, synchrotron wide angle and small-angle X-ray scattering, and magnetic resonance imaging. We find that at the narrow isotropic sol-nematic sol interface the platelets are lying horizontally, i.e. with their mean platelet normal along the vertical direction. The experiments indicate that the platelets align homeotropically both at the isotropic sol-nematic sol interface and at the nematic sol-wall interface. We further investigate the complex alignment effect of a horizontally applied magnetic field in the nematic sol, and we compare it with the adjacent nematic gel.

Phase behavior of hard colloidal platelets using free energy calculations

“…11,12,[39][40][41] Surprisingly, the IN coexistence for platelets is only weakly dependent on size polydispersity. 37 For these reasons, a relatively large amount of effort has been devoted to locating the isotropic-nematic coexistence for OHSC in the present paper by employing three different methods: (i) event-driven MD simulations, (ii) histogram method to determine the probability distribution of the nematic order parameter S 2 , and (iii) direct NPT MC simulations.…”

Barrier Properties of Synthetic Clay with a Kilo‐Aspect Ratio

“…Free rotation of clay platelets is hampered owing to large hydrodynamic radii and excluded volumes are generated between the platelets [ 33 ] resulting in liquid-crystalline ordering and birefringence. [ 34 ] In the same line, continuously increasing concentrations of suspensions by evaporation forces alignment of platelets. As might be anticipated, the degree of alignment is, however, strongly ( Figure 2D ).…”

Gelation via Ion Exchange in Discotic Suspensions

“…However, research in the past decade has revealed the existence of nematic phases for selected natural and synthetic clays [8][9][10], whose I-N transition occurred at concentration lower than the sol-gel transition point that is strongly dependent on the ionic strength of the solvent. To date, there seems to be little work showing the ionic strength controlled phase diagrams of charged, discotic suspensions that display both gel phase and stable liquid crystal phases.…”