Nanoconfinament effects over the structure and phase transitions in ionic liquid crystals

Abstract

Liquid crystals are a physical state of matter that exhibits intermediate properties between solids and liquids. They present an anisotropic character similar to that of crystalline solids due to the preferential orientation of the molecules or ions that constitute them. Still, they present fluidity characteristic of a liquid and lower long-range order than a solid. The orientation of the molecules and the structure of liquid crystals themselves can be manipulated by external factors such as temperature, electric field, and interaction with surfaces. These properties are exploited in a range of technological applications that go far beyond the well-known LCD (liquid crystal display) screens, including applications such as smart windows, capable of regulating the flow of heat and light, and biosensors. Most of these applications use liquid crystals based on neutral molecules confined in the form of thin films between flat surfaces. However, great interest has arisen in liquid crystals based on ionic compounds, in which the strong cation/anion correlations generate, in addition to the preferential orientation, structural patterns distinct from those observed in molecular liquid crystals. Furthermore, confinement in other geometries, especially in cylindrical pores, has aroused interest because it alters both the phase transition temperature to the isotropic phase and the optical properties of the material. In the present project, we will compare the effects of confinement in planar and cylindrical geometries for the ionic liquid crystal formed by 1-dodecyl-3-methylimidazolium tetrafluoroborate by means of classical molecular dynamics simulations using coarse-grained models, where groups of atoms are grouped in a few interaction sites, reducing the computational cost while maintaining an adequate description of the intermolecular interactions, allowing the study with larger model systems. By performing the simulations at different temperatures, we will determine, for each type of confinement, the transition temperature at which the anisotropic structure of the liquid crystal is broken, resulting in an isotropic liquid. In addition, structural and dynamic analyses will be performed in each simulation to understand how different confinements affect the molecular organization of the liquid crystals and their fluidity. Such a study could contribute to the development of new materials using liquid crystals with different confinements for technological applications.