Slow Molecular Mobility in the Amorphous Solid State of Fructose: Fragility and Aging
Article first published online: 21 OCT 2009
© 2009 Institute of Food Technologists®
Journal of Food Science
Volume 74, Issue 9, pages E526–E533, November/December 2009
How to Cite
Correia, . N. T., Diogo, . H. P. and Moura Ramos, . J. J. (2009), Slow Molecular Mobility in the Amorphous Solid State of Fructose: Fragility and Aging. Journal of Food Science, 74: E526–E533. doi: 10.1111/j.1750-3841.2009.01363.x
- Issue published online: 9 NOV 2009
- Article first published online: 21 OCT 2009
- MS 20090290 Submitted 4/2/2009, Accepted 7/31/2009.
- amorphous state;
- glass transition;
- glassy state;
- secondary relaxations
ABSTRACT: 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 Tg = 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.