The article published by Nathanaël Guigo and Nicolas Sbirrazzuoli from LPMC, in collaboration with Sergey Vyazovkin (Department of Chemistry, University of Alabama, USA) is honored in the last Soft Matter issue by illustrating the cover !
This paper describes the first application of ultrafast scanning calorimetry to the process of gelation in concentrated (40 wt%) aqueous gelatin solutions. It demonstrates that the regular gelation that occurs on cooling can be outrun at sufficiently fast cooling rates (≥ 500 K.s—1) so that the solution reaches a metastable supercooled liquid state. Successive heating of the supercooled solution reveals an atypical process of gelation that takes place while continuously raising the temperature. Isoconversional kinetic analysis is applied to treat the atypical gelation process and to compare it with regular gelation on cooling. Although atypical and regular gelation occur on significantly different time scales they appear to have common dynamics.
This picture represents a new chip calorimeter, the instrument recently developed by Mettler Toledo (Flash DSC 1) which uses MEMS (Micro-Electro-Mechanical-Systems) sensors. A gel sample of few nanograms was directly put onto the chip sensor which allows for accurate heat flow measurements at the cooling rates from 0.1 to 5000K.s-1 and heating rates from 0.1 to 40 000 K.s-1. A combination of the small thermal resistance of the chip and a minuscule amount of a sample allows to obtain such ultra-fast heating/cooling rates. This opens new perspectives to the comprehension of chemical reactions, physical transitions in the field of macromolecules, gels, polymers, composites, organic glasses and metals. The new analytical method of kinetic data which has been developed for several years in collaboration with the University of Alabama gives new insight to better understand the atypical and classical gelation dynamic.
Link to the Soft Matter issue.
Fluides & Matériaux Complexes, Matériaux Éco-compatibles
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