Nanoscale View of Alignment and Domain Growth in a Hexagonal Columnar Liquid Crystal.

Highly ordered liquid crystalline (LC) phases have important potential for organic electronics. We studied the molecular alignment and domain structure in a columnar LC thin film with nanometer resolution during in situ heating using four-dimensional scanning transmission electron microscopy (4D STEM). The initial disordered vapor-deposited LC glass thin film rapidly ordered at its glass transition temperature into a hexagonal columnar phase with small (<10 nm), well-aligned, planar domains (columns oriented parallel to the surface).

Erratum: Hydrogen Bonding Exchange and Supramolecular Dynamics of Monohydroxy Alcohols [Phys. Rev. Lett. 132, 058201 (2024)].

This corrects the article DOI: 10.1103/PhysRevLett.132.

High Density Two-Component Glasses of Organic Semiconductors Prepared by Physical Vapor Deposition.

Physical vapor deposition (PVD) is widely utilized for the production of organic semiconductor devices due to its ability to form thin layers with exceptional properties. Although the layers in the device usually consist of two or more components, there is limited understanding about the fundamental characteristics of such multicomponent vapor-deposited glasses. Here, spectroscopic ellipsometry was employed to characterize the densities, thermal stabilities, and optical properties of covapor deposited NPD and TPD glasses across the entire range of composition.

Hydrogen Bonding Exchange and Supramolecular Dynamics of Monohydroxy Alcohols.

We unravel hydrogen bonding dynamics and their relationship with supramolecular relaxations of monohydroxy alcohols (MAs) at intermediate times. The rheological modulus of MAs exhibits Rouse scaling relaxation of G(t)∼t^{-1/2} switching to G(t)∼t^{-1} at time τ_{m} before their terminal time. Meanwhile, dielectric spectroscopy reveals clear signatures of new supramolecular dynamics matching with τ_{m} from rheology.

Molecular Mechanism of the Debye Relaxation in Monohydroxy Alcohols Revealed from Rheo-Dielectric Spectroscopy.

Rheo-dielectric spectroscopy is employed to investigate the effect of external shear on Debye-like relaxation of a model monohydroxy alcohol, i.e., the 2-ethyl-1-hexanol (2E1H).

Ion dynamics in pendant and backbone polymerized ionic liquids: A view from high-pressure dielectric experiments and free-volume model.

Polymerized ionic liquids (PILs) are typically single-ion conductors, where one kind of ionic species is either placed as the pendant group to the chain (pendant PILs) or directly incorporated into the polymeric backbone (backbone PILs). This paper compares the thermodynamics, ionic dynamics, and mechanical properties of pendant and backbone PILs. The results indicate that near the glass transition, the energy barrier for ion hopping is much lower for pendant PIL while the backbone PIL shows a much stronger sensitivity to pressure.

Pressure-induced liquid-liquid transition in a family of ionic materials.

Liquid-liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena. Here, we report a first-order LLT in a series of ionic liquids containing trihexyl(tetradecyl)phosphonium cation [P] and anions of different sizes and shapes, providing an insight into the structure-property relationships governing LLT. In addition to calorimetric proof of LLT, we report that ion dynamics exhibit anomalous behavior during the LLT, i.

Complex Reorientation Dynamics of Sizable Glass-Formers with Polar Rotors Revealed by Dielectric Spectroscopy.

We present the results of dielectric measurements for three sizable glass-formers with identical nonpolar cores linked to various dipole-labeled rotors that shed new light on the picture of reorientation of anisotropic systems with significant moment of inertia revealed by broadband dielectric spectroscopy. The dynamics of sizable glass-formers formed by partially rigid molecular cores linked to small polar rotors in many respects differs from that of typical glass-formers. For instance, the extraordinarily large prefactors (τ > 10 s) in the Vogel-Fulcher-Tammann equation were found.

Magnitude of Dynamically Correlated Molecules as an Indicator for a Dynamical Crossover in Ionic Liquids.

In this work, we show how the structure and intermolecular interactions affect the dynamic heterogeneity of aprotic ionic liquids. Using calorimetric data for 30 ionic samples, we examine the influence of the strength of van der Waals and Coulombic interactions on dynamic heterogeneity. We show that the dynamic length scale of spatially heterogeneous dynamics decreases significantly with decreasing intermolecular distances.

Thorough studies of tricyanomethanide-based ionic liquids - the influence of alkyl chain length of the cation.

The glassy, supercooled, and normal liquid states of the 1-alkyl-3-methylimidazolium tricyanomethanide series [CnC1im][TCM] (n = 2, 4, 6, 8, and 16) were investigated by dielectric and mechanical (rheological) experiments supplemented by X-ray diffraction. The conductivity relaxation was found to be accompanied by a pronounced secondary relaxation. However, based on ambient and high-pressure results as well as the coupling model, we assumed that the latter one can not be classified as Johari-Goldstein relaxation.

The behavior of conductivity dynamic modulus and its connection to thermodynamic bulk modulus in ionic liquids.

In this paper, we investigate the interplay between the dynamics and thermodynamics of aprotic ionic liquids in the supercooled and normal liquid states. For this purpose, the conductivity dynamic modulus Mσp-T, being defined as the ratio of activation energy (Ep) and activation volume (VT), and its relation to bulk modulus BT under isobaric and isothermal conditions is examined. We found that both isobaric cooling and isothermal compression lead to an increase in Mσp-T.