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Effect of water on glass transition in starch/sucrose matrices investigated through positron annihilation lifetime spectroscopy: a new approach

Abstract : Glass transition is studied through positron annihilation lifetime spectroscopy (PALS) in maize starch matrices containing 10 (batch STS10) and 20 (STS20) w/w% sucrose, as a function of temperature (T) and water content (cw). To circumvent important losses of water upon heating while recording the PALS spectra, a new method is developed: instead of a series of measurements of τ3, the triplet positronium lifetime, at different T, the latter is kept constant and the series relates to cw, which is left to decrease at a constant rate. Similarly to the changes in τ3 with T, the τ3vs. cw plots obtained show a smooth linear increase until a break, denoting the occurrence of glass transition, followed by a sharper increase. The gradients appear to be independent of T. The variation of the glass transition temperature, Tg, with cw shows a broad sigmoid with a large linear central part; as expected from the plasticising effect of sucrose, the plot for STS20 lies some 10 K below that for STS10. Results from differential scanning calorimetry for STS20 yield Tg values some 15 K higher than from PALS. On the basis of the general shape of the τ3vs. T variations, a general equation is set for τ3(T, cw), leading one to expect a similar shape for τ3vs. cw, as experimentally observed.
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Submitted on : Monday, November 25, 2019 - 11:15:09 AM
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Sandeep Kumar Sharma, Abdelhadi Zaydouri, Gaëlle Roudaut, Gilles Duplâtre. Effect of water on glass transition in starch/sucrose matrices investigated through positron annihilation lifetime spectroscopy: a new approach. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2011, 13 (43), pp.19338. ⟨10.1039/c1cp21243e⟩. ⟨hal-02378455⟩

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