Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field

Abstract

Using fundamental measure density functional theory we investigate paranematic-nematic and nematic-nematic phase coexistence in binary mixtures of circular platelets with vanishing thicknesses. An external magnetic field induces uniaxial alignment and acts on the platelets with a strength that is taken to scale with the platelet area. At particle diameter ratio λ = 1.5 the system displays paranematic-nematic coexistence. For λ = 2, demixing into two nematic states with different compositions also occurs, between an upper critical point and a paranematic-nematic-nematic triple point. Increasing the field strength leads to shrinking of the coexistence regions. At high enough field strength a closed loop of immiscibility is induced and phase coexistence vanishes at a double critical point above which the system is homogeneously nematic. For λ = 2.5, besides paranematic-nematic coexistence, there is nematic-nematic coexistence which persists and hence does not end in a critical point. The partial orientational order parameters along the binodals vary strongly with composition and connect smoothly for each species when closed loops of immiscibility are present in the corresponding phase diagram.

Phase Behavior of Lyotropic Liquid-Crystalline Polymers under Varying Solvent Conditions: Effect of External Fields on the Phase Diagram

“…Third, the critical and triple lines could potentially intersect in the three-dimensional (temperature−pressure-field strength) phase diagram, resulting in the appearance of tricritical, "double-critical", and "criticaltriple" points. 20,47,69,70 We note that all these rich and varied phase diagram morphologies have been already observed in extensive theoretical studies of simple "spin fluids" in external fields. 71−75 The important difference of semiflexible polymers from these well-studied systems is the presence of an additional control parameter, i.e.…”

“…It will be shown that the phase diagram morphology is governed by a delicate interplay between the chain stiffness κ and the field strength ϕ, which will result in various nontrivial effects, such as the appearance of "double critical" and "critical triple" points. 20,47,69,70 Before addressing this complicated scenario, we begin by studying the good solvent case in Section 3.1, where there are only two relevant intensive variables pressure and field strength parameter.…”

“…First, given that the external field strength serves as an additional intensive variable, the aforementioned critical and triple points observed in zero-field case 68 will become critical and triple lines, respectively. 47,69,70 Second, the I−N phase coexistence will turn into P−N phase coexistence, resulting in the appearance of P−N critical line (as opposed to P−N critical point observed for hard-core systems, 24 where temperature does not have an effect). Third, the critical and triple lines could potentially intersect in the three-dimensional (temperature−pressure-field strength) phase diagram, resulting in the appearance of tricritical, "double-critical", and "criticaltriple" points.…”

Guided Electro-Optical Switching of Small Graphene Oxide Particles by Larger Ones in Aqueous Dispersion

“…Polydispersity reportedly expands the biphasic region in the phase diagram as a function of concentration. , However, the effect of the polydispersity of GO particles on electro-optical switching has not been explored. The application of electric fields to an isotropic GO colloid induces antinematic ordering of GO particles, and the field-induced ordering behavior of the antinematic binary mixture can produce quite new phenomena. , …”

“…The application of electric fields to an isotropic GO colloid induces antinematic ordering of GO particles, 28 and the field-induced ordering behavior of the antinematic binary mixture can produce quite new phenomena. 29,30 In this study, we investigate electro-optical switching of binary mixtures of two GO colloids with small and larger GO particles, where the GO concentration is adjusted to be constant. Interestingly, the addition of a small amount of large GO particles into a colloid containing small GO particles dramatically enhances the electro-optical birefringence.…”