Isotropic-to-Nematic Phase Transition in a Liquid-Crystal Droplet

Abstract

In this paper, we focus on the isotropic-to-nematic phase transition in a liquid-crystal droplet. We present the results of an experiment to measure the growth of the nematic phase within an isotropic phase liquid-crystal droplet. Experimentally, we observe two primary phase transition regimes. At short time scales, our experimental results (R(t) approximately t0.51) show good agreement with a Stefan-type model of the evolution of the nematic phase within the isotropic phase of a liquid crystal. As time progresses, the growth of the nematic phase is restricted by increased confinement of the droplet boundary. During this stage of growth, the nematic phase grows at a slower rate of R(t) approximately t0.31. The slower growth at later stages might be due to a variety of factors such as confinement-induced latent heat reduction; a change of defect strength during its evolution; or interactions between the defect and the interface between the liquid crystal and oil or between adjacent defects. The presence of two growth regimes is also consistent with the molecular simulations of Bradac et al. (Bradac, Z.; Kralj, S.; Zumer, S. Phys. Rev. E 2002, 65, 021705) who identify an early stage domain regime and a late stage confinement regime. For the domain and confinement regimes, Bradac et al. (Bradac, Z.; Kralj, S.; Zumer, S. Phys. Rev. E 2002, 65, 021705) obtained growth exponents of 0.49 +/- 0.05 and 0.25 +/- 0.05. These are remarkably close to the values 0.51 and 0.31 observed in our experiments.

Endotoxin-Induced Structural Transformations in Liquid Crystalline Droplets

“…The surface diffusion time for a droplet with a radius of 3 μm was calculated to be ~0.6 s; the experimentally measured characteristic time was ~1 s (Fig. 3C) (22, 23). This result suggests a physical process in which the dynamics of the ordering transition induced by endotoxin are governed by the lateral transport of endotoxin across the surface of the LC droplet, a process that would be necessary to localize endotoxin at surface defects (boojums) to initiate the ordering transition.…”

“…We measured the characteristic time interval between the formation of the nematic phase during cooling and the establishment of radial ordering (Fig. 3C) (22, 23). The time interval was found to scale with the square of the droplet radius, consistent with a physical process underlying the ordering transition that involved diffusion of the lipid.…”

Peculiarities of Defective Formations in Heterophase Regions of the Thermotropic Phase Transitions in Liquid Crystals

“…In the case of the droplets with the axial configuration, anchoring must be weak or here must be strong external influence (i.e., thermal regime) (Figure c). For this configuration, the splay ( K 11 ) and bend ( K 33 ) elastic deformations is important …”

Stability of a sharp uniaxial–isotropic phase interface

“…Also, such an understanding may shed light on the nature of the instabilities observed in the experiments of Chen et al [5].…”

“…Experiments on the isotropic-to-nematic phase transformation in a liquid crystal droplet surrounded by the silicone oil were performed by Chen et al [5]. These experiments reveal that the droplet exhibits different regimes of growth and that its interface can become unstable.…”