Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes.
The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition. Unexpectedly, the starch volume fraction (as probed through thermal gravimetry) decreases with T at a higher rate than the free volume fraction (as probed through PALS).
Sharma
Sandeep Kumar
SK
Chimie Nucléaire, Institut Pluridisciplinaire Hubert Curien, UDS/IN2P3/CNRS, 23 rue du Loess, B.P. 28 670737 Strasbourg cedex 2, France.
Roudaut
Gaëlle
G
Fabing
Isabelle
I
Duplâtre
Gilles
G
D004583:Electrons; D005898:Glass / Q000737:chemistry*; D044367:Phase Transition; D013057:Spectrum Analysis; D013213:Starch / Q000737:chemistry*; D013395:Sucrose / Q000737:chemistry*; D013818:Thermogravimetry; D013997:Time Factors; D044366:Transition Temperature
D013395:Sucrose; D013213:Starch