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

Abstract

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, β-process related to intramolecular movement in liquid and glassy state and emerging during cold crystallization α′-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.