Dynamics of the Crystal to Plastic Crystal Transition in the Hydrogen Bonded N-Isopropylpropionamide

Abstract

N-Isopropylpropionamide (NiPPA), which can self-associate via hydrogen bonds, was found to undergo a solid-solid transition as identified by DSC and X-ray diffraction. Below the melting temperature of 51 °C NIPPA adopts a plastic crystalline state with a tetragonal unit cell until it transforms into an ordered crystal with a monoclinic structure at temperatures e10 °C. Dielectric spectroscopy was used to characterize the dynamics of the system, determining the activation parameters for the plastic to crystalline phase transition. The activation enthalpy is relatively high, as expected for a system that involves hydrogen bonds. However, most of the activation energy as the plastic phase assumes a more crystalline state is due to the activation entropy, suggesting that the increased cooperativity observed in the relaxation processes is due to a steric locking of the molecules.

On relaxation and vibrational dynamics in the thermodynamic states of a chiral smectogenic glass-former

“…The splitting into two processes may suggest the increase of the degree of anisotropy of molecular motions. 47 The activation energy of the Cr (1b) process is the same as that obtained for the (2) mode in the Cr2 phase. We suppose that relaxation processes in crystal phases originate from intramolecular stochastic movements.…”

Relaxation dynamics and crystallization study of glass-forming chiral-nematic liquid crystal S,S-2,7-bis(4-pentylphenyl)-9,9-dimethylbutyl 9H-fluorene (5P-Am*FLAm*-P5)

“…7(a)). To extract the relaxation rate for his process, the data were analysed according to an approach proposed by Wübbenhorst and Turnhout [38,39]. This method is based on the assumption Frequency-dependent dielectric loss of 5P-Am * FLAm * -P5 for selected temperatures obtained upon heating after fast cooling (15 K/min).…”

“…The secondary β and γ relaxations are Arrhenius-like, as are the processes in the crystalline phases. In the Cr2 phase, the low-temperature process (II) observed in the Cr1 crystal splits into two processes, which suggests that the degree of anisotropy of molecular motions increases [39]. Due to The fit of derivative loss spectra ε der (f ).…”

Structure of 1,6-anhydro-β-D-glucopyranose in plastic crystal, orientational glass, liquid and ordinary glass forms: molecular modeling and X-ray diffraction studies

“…Moreover, it is worth stressing that not many compounds exhibiting hydrogen bonds are known to form plastic crystals. Presumably, this is due to the fact that the hydrogen-bond network may hinder the molecular rotation (Meersman et al, 2010).…”