Effects of droplet size and surfactants on anchoring in liquid crystal nanodroplets

Exploring the interplay of liquid crystal orientation and spherical elastic shell deformation in spatial confinement

The application of liquid crystal technology typically relies on the precise control of molecular orientation at a surface or interface. This control can be achieved through a combination of morphological and chemical methods. Consequently, variations in constrained boundary flexibility can result in a diverse range of phase behaviors. In this study, we delve into the self-assembly of liquid crystals within elastic spatial confinement by using the Gay-Berne model with the aid of molecular dynamics simulations. Our findings reveal that a spherical elastic shell promotes a more regular and orderly alignment of liquid crystals compared to a hard shell. Moreover, during the cooling process, the hard-shell confined system undergoes an isotropic-smectic phase transition. In contrast, the phase behavior within the spherical elastic shell closely mirrors the isotropic-nematic-smectic phase transition observed in bulk systems. This indicates that the orientational arrangement of liquid crystals and the deformations induced by a flexible interface engage in a competitive interplay during the self-assembly process. Importantly, we found that phase behavior could be manipulated by altering the flexibility of the confined boundaries. This insight offers a fresh perspective for the design of innovative materials, particularly in the realm of liquid crystal/polymer composites.

Elucidating Molecular-Scale Principles Governing the Anchoring of Liquid Crystal Mixtures on Solid Surfaces

Computational chemistry calculations are broadly useful for guiding the atom-scale design of hard-soft material interfaces including how molecular interactions of single-component liquid crystals (LCs) at inorganic surfaces lead to preferred orientations of the LC far from the surface. The majority of LCs, however, are not single-component phases but comprise of mixtures, such as a mixture of mesogens, added to provide additional functions such as responsiveness to the presence of targeted organic compounds (for chemical sensing). In such LC mixtures, little is understood about the near-surface composition and organization of molecules and how that organization propagates into the far-field LC orientation. Here, we address this broad question by using a multiscale computational approach that combines density functional theory (DFT)-based calculations and classical molecular dynamics (MD) simulations to predict the interfacial composition and organization of a binary LC mixture of 4'-cyano-4-biphenylcarbolxylic acid (CBCA) and 4'-n-pentyl-4-biphenylcarbonitrile (5CB) supported on anatase (101) titania surfaces. DFT calculations determine the surface composition and atomic-scale organization of CBCA and 5CB at the titania surface, and classical MD simulations build upon the DFT description to describe the evolution of the near-surface order into the bulk LC. A surprising finding is that the 5CB and CBCA molecules adopt orthogonal orientations at the anatase surface and that, above a threshold concentration of CBCA, this mixture of orientations evolves away from the surface to define a uniform far-field homeotropic orientation. These results demonstrate that molecular-level knowledge achieved through a combination of computational techniques permits the design and understanding of functional LC mixtures at interfaces.

Photonic features of blue phase liquid crystals under curved confinement

Blue phase (BP) liquid crystals represent a fascinating state of soft matter that showcases unique optical and electro-optical properties. Existing between chiral nematic and isotropic phases, BPs are characterized by a three-dimensional cubic lattice structure resulting in selective Bragg reflections of light and consequent vivid structural colors. However, the practical realization of these material systems is hampered by their narrow thermal stability and multi-domain crystalline nature. This feature article provides an overview of the efforts devoted to stabilizing these phases and creating monodomain structures. In particular, it delves into the complex relationship between geometrical confinement, induced curvature, and the structural stability and photonic features of BPs. Understanding the interaction of curved confinement and structural stability of BPs proves crucially important for the integration of these materials into flexible and miniaturized devices. By shedding light on these critical aspects, this feature review aims to highlight the significance of understanding the coupling effects of physical and mechanical forces on the structural stability of these systems, which can pave the way for the development of efficient and practical devices based on BP liquid crystals.

Long term phase separation dynamics in liquid crystal-enriched microdroplets obtained from binary fluid mixtures

The dynamics of long term phase separation in binary liquid mixtures remains a subject of fundamental interest. Here, we study a binary liquid mixture, where the minority phase is confined to a liquid crystal (LC)-rich droplet, by investigating the evolution of size, defect and mesogen alignment over time. We track the binary liquid mixture evolving towards equilibrium by visualising the configuration of the liquid crystal droplet through polarisation microscopy. We compare our experimental findings with computational simulations and elucidate differences between bulk phases and confined droplets based on the respective thermodynamics of phase separation. Our work provides insights on how phase transitions on the microscale can deviate from bulk phase diagrams with relevance to other material systems, such as the liquid-liquid phase separation of polymer and protein solutions.

Engineered liquid crystal nano droplets: insights from multi-scale simulations

Liquid crystal (LC) droplets have been investigated for a wide range of applications, from displays to sensors. Over the years, a need has arisen for complete understanding of the behaviour of LCs in droplets under different conditions for the development of advanced devices, for which accurate modelling is necessary. We show here, for the first time, both qualitative and quantitative agreement between coarse-grained molecular models and Q-tensor theory calculations for liquid crystal (LC) droplets. The approach is demonstrated for two types of droplet surfaces, which possess strong planar degenerate and strong homeotropic anchoring, respectively. Once its reliability has been proven, our approach was used to identify defects due to changes in anchoring in a small region on the LC droplet surface, which could be triggered, for example, by the adsorption of a nano-particle or a protein. Both coarse-grained simulations and Q-tensor analysis show the appearance of defects in well-determined locations within the LC droplet, albeit sometimes affected by degeneracy due to the symmetry of the systems being investigated. These results suggest the possibility of using LC droplets, in the future, as platforms for advanced sensing as well as for signal intensification.