Search for: All records

Electric fields withE< 1.2 V μm⁻¹amplitude andf< 100 Hz reduce entropy to induce isotropic–ferroelectric nematic (I–N_F) phase transition corresponding to an electrocaloric effect (ECE) with an EC responsivity of ∼ 1.7 × 10⁻⁶km V⁻¹. 

Most of the current highly polar rod-shaped molecules that form ferroelectric nematic (NF) phase do so only at elevated temperatures and multicomponent mixtures are generally needed to obtain a broad and room temperature range NF phase. In this work, we describe the synthesis, phase characterization and measurement of various physical properties of a new ferroelectric nematic compound 4-[(4-nitrophenoxy)carbonyl]phenyl 2-isopropoxy-4-methoxybenzoate (RT11165). The molecular structure of RT11165 with a 2-isopropoxy group differs only by a substitution of the 2-methoxy group found in the prototype ferroelectric nematic material 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). This small structure change produces a rather dramatic change in phase behavior leading to an NF phase from 63 °C down to room temperature. Below about 45°C the rotational viscosity of RT11165 increases critically and the temperature dependence indicates a glass transition at ~19°C. The transparent and polar glassy state of RT11165, which should be also piezoelectric, is a good candidate for energy storage, piezoecatalysis, data storage and other applications. 

Recently, a large family of at least 14 discotic liquid crystals was discovered that are exceptions to the conventional paradigm that discotic mesogens tend to feature long, flexible tails on their periphery. To understand why these materials are liquid crystals, as well as the structural determinants of discotic phase behavior, we studied a group of closely related small tail-free disk-like molecules, including both mesogenic and non-mesogenic compounds differing only in the position of a single fluorine substituent. The rigidity and structural simplicity of these molecules make them well suited to for study by large, fully all-atom simulations. Using a combination of static and dynamic metrics, we were able to identify several key features of the columnar mesophase and, thereby, conclusively identify a columnar liquid crystalline mesophase present in a subset of our systems. Our simulations feature molecules hopping between columns in the columnar mesophase and distinctive molecular rotations in 60° steps about the columnar axis. The ability to create and characterize columnar mesophases in silico provides a potent tool for untangling the structural determinants of liquid crystalline behavior in these and other tail-free discotic liquid crystals.