Shape-dynamic growth, structure, and elasticity of homogeneously oriented spherulites in an isotropic/smectic-A mesophase transition

Abstract

A Landau-de Gennes model that integrates the nematic quadrupolar tensor order parameter and complex smectic-A order parameters is used to simulate the two-dimensional growth of an initially homogeneous smectic-A spherulite in an isotropic matrix. These simulations are performed in the shape-dynamic (nano-scale) regime of growth under two material conditions: isotropic nematic elasticity and equal splay-bend nematic elasticity. A comparison of the growth kinetics, spherulite morphology, interfacial/bulk energy landscapes between both cases is made showing that equal nematic splay-bend elasticity is required to reproduce past experimental and theoretical observations. Additionally, a previously unknown undulation instability during spherulite growth is found which, in conjunction with preferred planar anchoring and defect shedding mechanisms at micron length scales, could explain the formation mechanism of focal conic curvature defects and ultimately smectic-A "batonnet" structures observed experimentally. of this mesophase via modelling and simulation. The key role that this mesophase plays in biological systems alone shows the importance of this single contribution of de Gennes. In his Nobel lecture in 1991, he states that "smectics bring me naturally to another important feature of complex fluids -namely that, in our days, it is sometimes possible to create new forms of matter" which alludes to the types of applications of smectics that could be developed in the future and to their roles in biological systems.The most simple of the smectics is the smectic-A mesophase, which displays lamellar translational ordering, in addition to the orientational ordering of nematics. Recently an increasing amount of interest in this mesophase, in particular of materials exhibiting a direct isotropic/smectic-A (disordered/ordered) transition, has resulted in many experimental and theoretical results. Nonetheless, the understanding of this mesophase is in a nascent stage. Much of this is due to the time and length scales at which the structures and dynamics occur being on the nanoscale. These properties provide a obvious application of theoretical study through modelling and simulation in order to both enhance experimental research and make predictions independently.A fascinating range of liquid crystal growth morphologies have been the focus on much study (6). The smectic-A mesophase, with its lamellar ordering on the molecular scale, exhibits growth, defect, and texture phenomena not seen in the nematic phases, including the lamellar-like cholesteric mesophase. Focusing on the growth phenomena solely, on transition from the isotropic/disordered phase, a variety of self-assembled smectic-A structures have been observed to form. These unique morphologies can be attributed to complex dynamics involving interfacial tension anisotropy, which results in preferred anchoring, and bulk texturing.The current study is a part of an overall effort to understand kinetics, dynamics, and morphology of the direct isotropic/smectic-A liquid cry...

Field-driven dynamics of nematic microcapillaries

“…Lattice-based simulations [5][6][7][8] are able resolve sub-micron domains and have mainly been applied to study the effects of sub-micron cylindrical confinement where geometry and anchoring affects the stability of the nematic phase. However, continuum simulations [12][13][14][15][16][17][18][19][20][21][22][23][24] have been able to overcome the length and timescales required to simultaneously capture defect dynamics (nanoscale) and domain shape (≥ µm).…”

“…Continuum simulations of confined LC domains [12][13][14][15][16][17][18][19][20][21][22][23][24] have been conducted using either Frank-Oseen vector theory [25] or Landau-de Gennes tensor theory [9][10][11]. While many of these past studies have focused on circular/spheroidal [12][13][14] and elliptic/ellipsoidal [15][16][17][18][19][20] confined LC domains, they have relied on Frank-Oseen theory which cannot capture orientational defects and phase transition.…”

Modeling smectic layers in confined geometries: Order parameter and defects

“…It further led to prediction of twist-grain-boundary phases, liquidcrystal analogues of the Abrikosov flux lattice in type-II superconductors [9]. Most recently, it has led to calculations for smectic layer configurations in confined geometries [10][11][12][13][14][15][16], which may be useful for design of smectic devices [17].…”

Nonisothermal Model for the Direct Isotropic/Smectic-A Liquid-Crystalline Transition

“…The general phenomena of meta-stable states in phase transitions involving dual non-conserved order was theoretically shown over a decade ago [39], but this generalized approach is not suitable for liquid crystal phase transitions (1). A first-approximation of the experimental system [37], taking into account shape kinetics/growth kinetics/texturing (see 1), has been modeled [40] shedding light on some of the nano-scale phenomena resulting in these experimental observations.…”