Ionic Liquid Crystals Confined in Nanoporous Solids: Self-Assembly, Molecular Mobility and Electro-Optical Functionalities

• Applicants: Professor Dr. Patrick Huber; Professorin Dr. Sabine Laschat; Professor Dr. Andreas Schönhals
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430146019

Ionic liquid crystals (ILC) bridge the gap between conventional liquid crystalline and ionic matter. Discotic columnar phases along with very high 1-D ion mobility in columnar phases have been found and studied with regard to potential functionalities. These functionalities depend strongly on the type of orientation and translation order. In principle, these orders can be optimized by embedding ILCs in nanostructured solid templates. However, very sparse knowledge is available about the effect of nanoconfinement on ILCs, even though it provides entirely novel self-assembly paths and thus electro-optical functionalities. Here we propose the exploration of the phase behavior of ionic liquid crystals in nanoporous solids and to relate it to the corresponding bulk phenomenology. It shall be scrutinized how the behavior changes as a function of pore-size and pore-surface chemistry, in particular with regard to hydrophilic and hydrophobic pore walls. To this end synchrotron-based X-ray diffraction, dielectric spectroscopy, calorimetry on ILCs confined in monolithic nanoporous silica, silicon and alumina membranes shall be performed. This will allow detailed insights in the structure and dynamics of the confined mesogens. The project particularly profits from the complementary expertise of the research groups involved, i.e. microscopic translational and orientational order (Huber), thermodynamics and molecular dynamics (Schoenhals) and tailored synthesis of ILCs (Laschat). Moreover, the functionalities with regard to optical anisotropy, optical activity, dielectric properties and electrical conductivity will be systematically explored and the mesogen interactions tailored with respect to mesophase formation and mesogen-pore wall interaction in order to optimize these functionalities. Specifically, we intend to explore ILCs forming discotic hexagonal phases with high charge carrier mobilities along the columnar axis. In addition, interactions of chiral ILCs with the pores will be studied regarding confinement-induced formation of chiral mesophases, absent in the bulk state. It is expected that by proper pore surface-grafting and pore-size selection optical and electrical functionalities can be tuned. The study is aimed at a fundamental understanding of the physical chemistry of confined ILCs, but also at the functionalities of the resulting hybrid materials, consisting of soft functional ILC fillings in monolithic solids providing mechanical stability.The successful realization of the project requires an intense cooperation between the three research groups because the chemical molecular structure (synthesis) determines the supermolecular structures and the molecular dynamics as well as the interaction with the confining walls in nanoporous solids. Besides the expected synergistic benefit on the scientific results the PhD students will significantly profit in their scientific education and from the cooperative spirit of this research project.

• DFG Programme: Research Grants