Interaction and flocculation of spherical colloids wetted by a surface-induced corona of paranematic order

TL;DR

This paper investigates how particles in liquid crystals interact via surface-induced paranematic coronas, demonstrating that a Yukawa potential accurately describes these interactions and extends understanding of colloidal flocculation near phase transitions.

Contribution

It analytically and numerically characterizes particle interactions mediated by paranematic coronas and applies this to extend flocculation phase diagrams in colloidal dispersions.

Findings

Yukawa potential effectively describes particle interactions at large separations.

Extended flocculation diagrams to broader electrostatic parameter ranges.

Discovered kinetically stabilized dispersions near the nematic-isotropic transition.

Abstract

Particles dispersed in a liquid crystal above the nematic-isotropic phase transition are wetted by a surface-induced corona of paranematic order. Such coronas give rise to pronounced two-particle interactions. In this article, we report details on the analytical and numerical study of these interactions published recently [Phys. Rev. Lett. 86, 3915 (2001)]. We especially demonstrate how for large particle separations the asymptotic form of a Yukawa potential arises. We show that the Yukawa potential is a surprisingly good description for the two-particle interactions down to distances of the order of the nematic coherence length. Based on this fact, we extend earlier studies on a temperature induced flocculation transition in electrostatically stabilized colloidal dispersions [Phys. Rev. E 61, 2831 (2000)]. We employ the Yukawa potential to establish a flocculation diagram for a much larger range of the electrostatic parameters, namely the surface charge density and the Debye screening length. As a new feature, a kinetically stabilized dispersion close to the nematic-isotropic phase transition is found.