Molecular Dynamics and Kinetics of Isothermal Cold Crystallization with Tunable Dimensionality in a Molecular Glass Former, 5'-(2,3-Difluorophenyl)-2'-ethoxy-4-pentyloxy-2,3-difluorotolane

Tomasz ROZWADOWSKI, Hiroshi NODA, Lukaz KOLEK, Mizuki ITO, Hideki SAITOH, Yasuhisa YAMAMURA and Kazuya SAITO,

This paper characterizes the molecular mobility that triggers the cold crystallization abilities in 5'-(2,3-difluorophenyl)-2'-ethoxy-4-pentyloxy-2,3-difluorotolane (short name DFP25DFT) material by broadband dielectric spectroscopy (BDS). We analyze the properties of identified molecular motions by referring to the Vogel-Fulcher-Tammann (VFT) model for the structural α-process associated with molecular rotation in isotropic liquid and the Eyring and Starkweather approach for the thermally activated processes, beta-process related to intramolecular movement in liquid and glassy state and emerging during cold crystallization alpha'-process ascribed to confined movements of molecules located adjacent to crystalline surfaces. To characterize the material, we employ single-crystal X-ray diffraction, differential scanning calorimetry (DSC), adiabatic calorimetry, and polarizing optical microscopy (POM) while we utilize molecular mechanics simulations (MM2) to explore molecular flexibility. Our study focuses on inter- and intramolecular interactions that determine the cold-crystallization tendency. We demonstrate that the solidification path is controlled by the fragility of the system, the dipole-dipole attraction, and the intramolecular dynamics. The study of cold crystallization kinetics under isothermal conditions reveals the complexity of the process: the formation of two crystalline phases, Cr2 and Cr3, proceeding in different modes. This feature discloses the possibility of switching the crystal growth between three- and two-dimensional in the cold-crystallization process driven by different mechanisms.
(Phys. Chem. Chem. Phys., 25, 724-735 (2023))


Interplay between Melt and Cold Crystallization in a Smectic Liquid Crystal, 4-Pentylphenyl 4-(trans-4-Pentylcyclohexyl)benzoate

Tomasz ROZWADOWSKI, Yasuhisa YAMAMURA and Kazuya SAITO,

In this study, we apply differential scanning calorimetry (DSC) and polarizing microscopy (POM) to elucidate the interplay of crystallization mechanisms controlling the tendency to melt- and cold-crystallization from partially ordered smectic B phase in 4-pentylphenyl 4-(trans-4-pentylcyclohexyl)benzoate (5CPB5) mesogen. For this purpose, we pay attention to the kinetics of nonisothermal crystallization revealed by several complementary approaches, including Ozawa, Mo, and the isoconversional method. Additionally, we adopt the Hoffman-Lauritzen theory for analyzing the temperature dependence of crystallization activation energy, allowing us to describe the multistep crystallization of the smectic B mesophase. Our investigation shows the possibility to design the mechanism controlling different crystallization paths. Moreover, we demonstrate the ability to switch the dimensionality of crystal growth by modifying the dominance of molecular mobility through the experimental rate.
(Cryst. Growth Des., 21, 2777-2785 (2021))


Designing the Disorder: Kinetics of Nonisothermal Crystallization of Orientationally Disordered Crystalline Phase in a Nematic Mesogen

Tomasz ROZWADOWSKI, Malgorzata JASIURKOWSKA-DELAPORTE, Maria MASSALSKA-ARODZ, Yasuhisa YAMAMURA and Kazuya SAITO,

This article presents the molecular dynamics and solidification behavior of a 2,3-difluoro-4-propylphenyl 2,3-difluoro-4-(4-pentylcyclohexyl)benzoate nematic liquid crystal (5C4FPB3) observed by broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). Polarized optical microscopy (POM) is also performed to confirm the phase transition temperatures. Our investigation reveals rare crystallization of the orientationally disordered crystal (ODIC) phase from the nematic phase and a glass transition of the crystal at cooling rates higher than 1 K min-1. The deconvolution of the dielectric spectra with derivative techniques is necessary because of the complex molecular dynamics in the crystalline phase. The BDS method enables us to capture the relaxation processes reflecting pre-crystallization molecular movements. The kinetics of nonisothermal crystallization is studied using the Ozawa, Mo, and isoconversional methods. The present studies suggest that the dominant factor of the crystal growth mechanism depends on the cooling rate. Two types of crystallization mechanisms are identified at cooling rates lower and higher than 5 K min-1. We design a diagram with crystallization and glass transition borders against the cooling rates. Estimations show that crystallization of the present compound can be bypassed at cooling rates higher than 78 kK min-1, at which a glass transition of the nematic phase occurs. We show various scenarios of the molecular order and the crystallization mechanism designed based on the process rate.
(Phys. Chem. Chem. Phys., 22, 24236-24248 (2020))


Return to Kazuya's Home Page