Ref HAL: hal-01932950_v1
Exporter : BibTex | endNote
Résumé:

Dynamics in stretched nanocomposites

Ref HAL: hal-01922247_v1
Exporter : BibTex | endNote
Résumé:

ATRC is a new ligth scattering technique that measures by holography the field amplitude scattered by a sample, and analyze its spatial correlations. ATRC outperforms other light scattering techniques like DLS, DWS and TRC. Dynamic light scattering (DLS) [1], diffusing wave spectroscopy (DWS) [2] and time resolved correlation (TRC) [3] are well-established techniques for investigating the dynamics of a wide variety of systems in physics, chemistry, biology , and medicine. DLS and DWS consider the intensity time fluctuations of the scattered light, and study samples, whose dynamics are homogeneous in time. TRC considers the spatial fluctuations, and is able to study slow or temporally heterogeneous dynamics. We propose, in this work, to replace the TRC multi pixel detector by an holographic one, and to consider the spatial fluctuations of the field complex amplitude E as a new quantity of interest. We introduce thus a new tool called ATRC for Amplitude Time Resolved Correlation, which outperforms TRC and open new perspectives. Fig. 1. (a) TRCA typical setup. (b) Reconstructed image of a nanocomposite sample. Fig.1 (a) shows a simplified diagram of the TRCA setup. The sample S is illuminated by the laser beam L1. The light scattered by the sample is split by the beam splitter BS into two imaging paths, corresponding to cameras C1 and C2. Lens L made the image of the sample S on C1, which records the light intensity image I of S. On the other hand, the camera C2 records the interference pattern (i.e. the hologram) of the scattered light with the reference laser light L2, and the complex amplitude image E of S is calculated by holographic reconstruction. The optimize the detection sensitivity [4], holography is heterodyne [5] and off-axis. Fig.1 (b) shows the intensity reconstructed image (I = |E| 2) of a 30 × 10 mm 2 Styrene-Butadiene/Silica nanocom-posite sample, which is observed in reflection. Because 2 phase detection is used, both the +1 and-1 image of the sample are seen (right and left hand side images of Fig.1 (b)). To analyze the dynamic of the sample, TRC considers

Ref HAL: hal-01924508_v1
Ref Arxiv: 1805.06017
DOI: 10.1063/1.5040975
WoS: 000448216600025
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
11 Citations
Résumé:

We propose a computational method to measure the configurational entropy in generic polydisperse glass-formers. In particular, our method resolves issues related to the diverging mixing entropy term due to a continuous polydispersity. The configurational entropy is measured as the difference between the well-defined fluid entropy and a more problematic glass entropy. We show that the glass entropy can be computed by a simple generalisation of the Frenkel-Ladd thermodynamic integration method, which includes permutations of the particle diameters. This approach automatically provides a physically meaningful mixing entropy, and includes contributions that are not purely vibrational. The proposed configurational entropy is thus devoid of conceptual and technical difficulties due to continuous polydispersity, while being conceptually closer and technically simpler than alternative free energy approaches.

Commentaires: 11 pages, 4 figures. Réf Journal: J. Chem. Phys. 149, 154501 (2018)

Ref HAL: hal-01904079_v1
Ref Arxiv: 1804.01810
DOI: 10.1073/pnas.1717403115
WoS: 000429012500051
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
19 Citations
Résumé:

Material failure is ubiquitous, with implications from geology to everyday life and material science. It often involves sudden, unpredictable events, with little or no macroscopically detectable precursors. A deeper understanding of the microscopic mechanisms eventually leading to failure is clearly required, but experiments remain scarce. Here, we show that the microscopic dynamics of a colloidal gel, a model network-forming system, exhibit dramatic changes that precede its macroscopic failure by thousands of seconds. Using an original setup coupling light scattering and rheology, we simultaneously measure the macroscopic deformation and the microscopic dynamics of the gel, while applying a constant shear stress. We show that the network failure is preceded by qualitative and quantitative changes of the dynamics, from reversible particle displacements to a burst of irreversible plastic rearrangements.

Commentaires: . Réf Journal: PNAS 115, 3587 (2018)

Ref HAL: hal-01896690_v1
DOI: 10.1039/c8sm00911b
WoS: WOS:000442269000021
Exporter : BibTex | endNote
1 Citation
Résumé:

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.