arXiv subjects

Éric Freyssingeas

Publications and source records attributed to Éric Freyssingeas.

5 recordsLinked to original sources

arXiv2026

Inverse Laplace Transform for Dynamic Light Scattering: Impact of Regularization

Dynamic Light Scattering (DLS) analyzes particle dynamics from the autocorrelation functions of scattered light intensity, yet extracting accurate relaxation time distributions from noisy data is challenging. We develop an inverse problem approach to recover this distribution by inverting the Laplace transform with physics-based regularization, called the CONTIN method. We improve it to use it on noisy data, across a wide range of time scales, with a selection of the regularization strength through a data-driven L-curve criterion. Our approach enhances robustness under high noise and reveals multi-scale dynamics in complex systems. Validation is performed on simulated data, compared to the Cramér-Rao bound and to parametric methods, and on experimental data from Carbopol microgels. It demonstrates superior accuracy over parametric methods, especially for broad time distributions. The algorithm's logarithmic discretization and variance-reduced correlation estimation enhance performance, offering a powerful tool for non-parametric DLS analysis and deeper insights into soft matter dynamics.

cond-mat.soft↗

arXiv2015

Structural Transition in the Isotropic Phase of the C$_{12}$EO$_6$/H$_2$O Lyotropic Mixture: A Rheological Investigation

We study the structural changes occurring in the isotropic phase of the C$_{12}$=EO$_6$/H$_2$O lyotropic mixture (up to 35% surfactant weight concentration) upon increasing the concentration and temperature, from small individual micelles to an entangled network which subsequently becomes connected. High-frequency (up to $ω= 6 \times 10^4$ rad/s) rheological measurements give us access to the viscoelastic relaxation spectrum, which can be well described by the sum of two Maxwell models with very different temperature behaviors: the slower one ($τ_1 \simeq 10^{-4}$ s) is probably due to reptation, and its associated viscosity first increases with temperature (micellar growth) and then decreases after reaching a maximum (appearance of connections). The fast mechanism ($τ_2 \simeq 10^{-6}$ s) remains practically unchanged in temperature and can be related to the relaxation of local micellar order, as observed at higher concentration in a previous investigation. This interpretation is confirmed by additional measurements in aqueous mixtures of the related surfactant C$_{12}$EO$_8$ (which forms smaller micelles), where only the fast mechanism -related to local order- is detected.

cond-mat.soft↗

arXiv2015

High-frequency rheological behaviour of a multiconnected lyotropic phase

High-frequency (up to $ω = 6 \, 10^4$ rad/s) rheological measurements combined with light-scattering investigations show that an isotropic and multiconnected phase of surfactant micelles exhibits a terminal relaxation time of a few μs, much smaller than in solutions of entangled wormlike micelles. This result is explained in terms of the local hexagonal order of the microscopic structure and we discuss its relevance for the understanding of dynamic behaviour in related systems, such as wormlike micelles and sponge phases.

cond-mat.soft↗

arXiv2015

Short-range dynamics of a nematic liquid-crystalline phase

Using x-ray photon correlation spectroscopy, we studied the dynamics in the nematic phase of a nanorodsuspension. The collective diffusion coefficient in the plane perpendicular to the director varies sharply with the wave vector. Combining the structure factor and the diffusion coefficient, we find that the hydrodynamic function of the phase decreases by more than a factor of 10 when going from length scales comparable to the interparticle distance toward larger values. Thus, the collective dynamics of the nematic phase experiences strong and scale-dependent slowing down, in contrast with isotropic suspensions of slender rods or of spherical particles.

cond-mat.soft↗

arXiv2015

Slow dynamics of a colloidal lamellar phase

We used x-ray photon correlation spectroscopy to study the dynamics in the lamellar phase of a platelet suspension as a function of the particle concentration. We measured the collective diffusion coefficient along the director of the phase, over length scales down to the interparticle distance, and quantified the hydrodynamic interaction between the particles. This interaction sets in with increasing concentration and can be described qualitatively by a simplified model. No change in the microscopic structure or dynamics is observed at the transition between the fluid and the gel-like lamellar phases.

cond-mat.soft↗