%0 Journal Article %T Phase transitions in polymorphic materials probed using space-resolved diffusing wave spectroscopy %+ Laboratoire Charles Coulomb (L2C) %+ Formulaction, Toulouse, France %A Nagazi, Med Yassine %A Dieudonne-George, Philippe %A Brambilla, Giovanni %A Meunier, Gerard %A Cipelletti, Luca %< avec comité de lecture %Z L2C:18-152 %@ 1744-683X %J Soft Matter %I Royal Society of Chemistry %V 14 %N 31 %P 6439-6448 %8 2018-08-21 %D 2018 %R 10.1039/c8sm00911b %Z Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft]Journal articles %X We use space-resolved dynamic light scattering in the highly 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 microscopic dynamics measured using PCI-DWS show remarkable, non-monotonic behavior upon heating: they transiently accelerate when crossing 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 in density at 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. %G English %L hal-01896690 %U https://hal.science/hal-01896690 %~ CNRS %~ L2C %~ MIPS %~ UNIV-MONTPELLIER %~ UM-2015-2021