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Slow Molecular Mobility in the Amorphous Solid State of Fructose: Fragility and Aging
Author(s) -
Correia Natália T.,
Diogo Hermínio P.,
Moura Ramos Joaquim J.
Publication year - 2009
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1750-3841.2009.01363.x
Subject(s) - fragility , amorphous solid , relaxation (psychology) , glass transition , dielectric , chemistry , molecular solid , intramolecular force , materials science , analytical chemistry (journal) , nuclear magnetic resonance , crystallography , polymer , molecule , stereochemistry , organic chemistry , physics , psychology , social psychology , optoelectronics
The molecular mobility of β‐D‐fructose was studied by thermally stimulated depolarization currents (TSDC) in the amorphous solid state. The amorphous solid samples were prepared in such a way that the tautomeric mixture was near the equilibrium composition. A broad secondary relaxation was observed, that merges, at high temperatures, with the alpha relaxation. The alpha relaxation temperature provided by the TSDC technique is T g = 13 °C (at 4 K min −1 ). The fragility index calculated from TSDC data is m = 34, significantly lower when compared with the values reported in the literature obtained from Dielectric Relaxation Spectroscopy (DRS). The physical significance of the fragility obtained by the 2 dielectric techniques is discussed. The influence of physical aging on the secondary relaxation in amorphous fructose was analyzed as the glass structurally relaxes. A complex behavior was observed such that the faster components (lower temperature) of the secondary relaxation are negligibly dependent on aging and may be ascribed to intramolecular modes of motion, while the slower motional modes (higher temperature) show a significant dependence on aging and correspond to the genuine Johari–Goldstein β‐relaxation.