Dynamics of the crystal to plastic crystal transition in the hydrogen bonded N-isopropylpropionamide.
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 ≤10 °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.
Meersman
Filip
F
Division of Molecular and Nanomaterials, Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
Geukens
Barbara
B
Wübbenhorst
Michael
M
Leys
Jan
J
Napolitano
Simone
S
Filinchuk
Yaroslav
Y
Van Assche
Guy
G
Van Mele
Bruno
B
Nies
Erik
E