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Phase transitions in polymorphic materials probed by space-resolved diffusing wave spectroscopy


We use space-resolved dynamic light scattering in the higly multiple scattering regime (Photon Correlation Imaging Diffusing Wave Spectroscopy, PCI-DWS) to investigate temperature-induced phase transitions in polymorphic materials. We study paraffin wax as a simple model system and chocolate, a prototypical example of fat-based products exhibiting complex, history-dependent phase transitions. We find that the microscopic dynamics measured by PCI-DWS have a remarkable, non-monotonic behavior upon heating: they transiently accelerate when crossing a phase transition and slow down above the transition temperature. Sub-micron resolution measurements of the local drift of the sample surface reveal that the speed-up of the dynamics is due to the strain field induced by the change of density at the transition temperature. The transition temperatures obtained from PCI-DWS are found to be in excellent agreement with those inferred from complementary differential scanning calorimetry and X-ray scattering experiments, thereby validating PCI-DWS as a new, powerful tool for the characterization of phase transitions in complex soft matter. Finally, we demonstrate the unique possibilities afforded by space-resolved DWS by investigating the spatially heterogeneous response of poorly manufactured or composite chocolate samples.

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Publication details

The article was received on 03 May 2018, accepted on 03 Jul 2018 and first published on 04 Jul 2018

Article type: Paper
DOI: 10.1039/C8SM00911B
Citation: Soft Matter, 2018, Accepted Manuscript
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    Phase transitions in polymorphic materials probed by space-resolved diffusing wave spectroscopy

    M. Y. Nagazi, P. Dieudonné-George, G. Brambilla, G. Meunier and L. Cipelletti, Soft Matter, 2018, Accepted Manuscript , DOI: 10.1039/C8SM00911B

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