Molecular mobility and the glass transition in amorphous glucose, maltose, and maltotriose.
We have used measurements of the phosphorescence intensity decay of the triplet probe erythrosin B, dispersed in amorphous glucose, maltose, and maltotriose at probe:sugar mole ratios of approximately 1:10(4), to monitor the molecular mobility of the sugar matrix in the glass and melt around the glass-transition temperature (Tg). Intensity decays were well fit using a stretched-exponential decay model in which the Kohlrausch-Williams-Watts lifetime tau and the stretching exponent beta are the physically meaningful parameters. When normalized to the glass-transition temperature, the erythrosin lifetime decreased in the order glucose>maltose>maltotriose. Analysis of the lifetime provided an estimate of the collisional quenching constant for deexcitation of the triplet state (kTS0); kTS0 increased in the order glucose<maltose<maltotriose over the range of T-Tg from about -40 to 50 degrees C. Although approximately constant in the glass, the magnitude of beta decreased around Tg in the order glucose>maltose>maltotriose, indicating that the lifetime heterogeneity increased in the order glucose<maltose<maltotriose. These data demonstrate that both the average rate of matrix molecular mobility and the width of the distribution of matrix mobility rates around the glass transition increase with an increase in the molecular size of the sugar in this homologous series.
Shirke
Sonali
S
Department of Food Science, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ 08901-8520, USA.
Ludescher
Richard D
RD
D005898:Glass; D005947:Glucose / Q000737:chemistry*; D007700:Kinetics; D008163:Luminescent Measurements; D008320:Maltose / Q000737:chemistry*; D013816:Thermodynamics; D014312:Trisaccharides / Q000737:chemistry*
D014312:Trisaccharides; C008317:maltotriose; D008320:Maltose; D005947:Glucose