arXiv subjects

Marceau Hénot

Publications and source records attributed to Marceau Hénot.

11 recordsLinked to original sources

arXiv2026

Fast temperature up steps as a test of the Tool-Narayanaswamy formalism

We investigated the aging dynamics of a glass-forming liquid triethyl-2-acetylcitrate (TEAC), following fast temperature up steps with amplitudes ranging from 0.3 to 13.6 K. The initial states were either at equilibrium or prepared at increasing levels of out-of-equilibrium through a prior down step experiment. Our goal was to test the predictive power of the Tool-Narayanaswamy (TN) formalism which assumes that the non-linear re-equilibration of a liquid can be linked to its linear response to a small perturbation. We determined the TN parameters for steps with small to moderate amplitude ($\leq$ 3.3 K) and crucially took advantage of down step aging experiments below the glass transition temperature to constrain the determination of the equilibrium relaxation time. We tested the TN predictions and found very good agreement for differences in fictive temperature characterizing the distance from equilibrium as high as 10 K. For larger steps, however, the prediction progressively fails to capture the aging dynamics. This likely indicates that the re-equilibration mechanism is no longer related to the equilibrium dynamics. Finally, we discuss the possibility of obtaining a general criterion for the limit of validity of the TN formalism, which we compare to other systems from the literature.

cond-mat.soft↗

arXiv2026

Molecular dynamics insights into the Debye process of 1-propanol

We reproduce the Debye process in the dielectric response of liquid 1-propanol by all-atom molecular dynamics simulations between 340 K and 200 K. The analysis of dipolar correlations reveals that the $α$ relaxation originates from hydrogen-bond (HB) breaking, while the dominant Debye process results from long-ranged cross-correlations extending over several molecular diameters. By separating intra- and extra-cluster contributions, we demonstrate that HB supramolecular clusters account for the main part of the static dielectric response, with extra-cluster molecules playing only a minor role at low temperatures. Besides, clusters do not preserve connectivity on timescales exceeding the $α$ relaxation time. This indicates that clusters stabilize orientational correlations beyond individual molecular relaxation times by transmitting alignment to newly incorporated molecules. These findings provide microscopic evidence that the Debye relaxation in mono-alcohols arises from the collective dynamics of HB clusters and offer a framework to study dielectric spectra in other hydrogen-bonded liquids.

cond-mat.soft↗

arXiv2025

Computing dielectric spectra in molecular dynamics simulations: using a cavity to disentangle self and cross correlations

Dielectric spectra are typically obtained in molecular dynamics (MD) simulations by analyzing the fluctuations, in the absence of an applied electric field, of the total dipole moment of the simulation box. We compare this standard method with a protocol that focuses on a virtual cavity whose size is chosen to include short-range dipolar cross-correlations, while excluding long-range correlations that are affected by the choice of electrostatic boundary conditions. We tested this protocol on three non-polarizable systems with different dielectric permittivities. We showed that it produces the same dielectric spectra as the standard method while being less sensitive to noise. The question of the decomposition of a dielectric spectrum into self and cross contributions is discussed in the context of both methods. We propose that, for a liquid with a sufficiently high dielectric permittivity, the cavity protocol yields a self-spectrum consistent with the electrostatic boundary conditions applicable to the experimental situation.

cond-mat.soft↗

arXiv2025

Emergence of a Hump in the Cubic Dielectric Response of Glycerol

We report a direct determination of the cubic dielectric spectra of a realistic polar molecule, glycerol, from molecular dynamic (MD) simulations. From the liquid state to the mildly supercooled regime, we observed the emergence and growth of a hump in the cubic modulus, traditionally associated with collective effects in the dynamics. Its evolution follows that of dynamical correlations probed by the four-point susceptibility and that of the activation energy of the relaxation time. In particular, its appearance at high temperature coincides with the onset of super-activation. We show that, for this system, the shape of cubic spectra is only weakly affected by dipolar cross-correlations. The good agreement with experimental observations, despite the difference in temperature range, demonstrates the relevance of this approach to help get an insight into the intricate effects probed by non-linear dielectric spectroscopy.

cond-mat.soft↗

arXiv2023

Orientational dynamics in supercooled glycerol computed from MD simulations: self and cross contributions

The orientational dynamics of supercooled glycerol using molecular dynamics simulations for temperatures ranging from 323 K to 253 K, is probed through correlation functions of first and second ranks of Legendre polynomials, pertaining respectively to dielectric spectroscopy (DS) and depolarized dynamic light scattering (DDLS). The self, cross, and total correlation functions are compared with relevant experimental data. The computations reveal the low sensitivity of DDLS to cross-correlations, in agreement with what is found in experimental work, and strengthen the idea of directly comparing DS and DDLS data to evaluate the effect of cross-correlations in polar liquids. The analysis of the net static cross-correlations and their spatial decomposition shows that, although cross-correlations extend over nanometric distances, their net magnitude originates, in the case of glycerol, from the first shell of neighbouring molecules. Accessing the angular dependence of the static correlation allows us to get a microscopic understanding of why the rank-1 correlation function is more sensitive to cross-correlation than its rank-2 counterpart.

cond-mat.soft↗

arXiv2023

Non-linear physical aging of supercooled glycerol induced by large upward ideal temperature steps monitored through cooling experiments

The physical aging of supercooled glycerol induced by upward temperature steps of amplitude reaching 45 K was studied by a new method consisting in heating a micrometer-thick liquid film at a rate of up to 60 000 K/s, holding it at a constant high temperature for a controlled duration before letting it quickly cool down to the initial temperature. By monitoring the final slow relaxation of the dielectric loss, we were able to obtain quantitative information on the liquid response to the initial upward step. The so-called TNM (Tool-Narayanaswamy-Moynihan) formalism provided a good description of our observations despite the large distance from equilibrium, provided that different values of the nonlinearity parameter were used for the cooling phase and for the (much further from equilibrium) heating phase. In this form, it allowed to precisely quantify how to design an ideal temperature step, i.e., where no relaxation occurs during the heating phase. It helped bringing a clear physical understanding of how the (kilosecond long) final relaxation is related to the (millisecond long) liquid response to the upward step. Finally, it made possible the reconstruction of the fictive temperature evolution immediately following a step, evidencing the highly non-linear character of the liquid response to such large amplitude temperature steps. This work illustrates both the strengths and limitations of the TNM approach. This new experimental device offers a promising tool to study far-from-equilibrium supercooled liquids through their dielectric response.

cond-mat.soft↗

arXiv2023

How dirt cones form on glaciers: field observation, laboratory experiments and modeling

Dirt cones are meter-scale structures encountered at the surface of glaciers, which consist of ice cones covered by a thin layer of ashes, sand or gravel, and which form naturally from an initial patch of debris. In this article, we report field observations of cone formation in the French Alps, laboratory-scale experiments reproducing these structures in a controlled environment, and two-dimensional discrete-element-method-finite-element-method numerical simulations coupling the grains mechanics and thermal effects. We show that cone formation originates from the insulating properties of the granular layer, which reduces ice melting underneath as compared to bare ice melting. This differential ablation deforms the ice surface and induces a quasi static flow of grains that leads to a conic shape, as the thermal length become small compared to the structure size. The cone grows until it reaches a steady state in which the insulation provided by the dirt layer exactly compensates for the heat flux coming from the increased external surface of the structure. These results allowed us to identify the key physical mechanisms at play and to develop a model able to quantitatively reproduce the various field observations and experimental findings.

physics.flu-dyn↗

arXiv2021

Onset of glacier tables

A glacier table consists of a rock supported by a slender column of ice and form naturally on glaciers. We investigate the onset of their formation at a smaller scale in a controlled environment. Depending on the size and thermal conductivity of a cap, it can either form of a table standing on an ice foot, or sink into the ice block. A one-dimension conduction model shows that the differential ice melting is controlled by a competition between two effects: a geometrical amplification, and a heat flux reduction due to the higher temperature of the cap as compared to the ice. Our model captures the transition between the two regimes and identifies a dimensionless number which controls the onset of glacier tables formation.

physics.flu-dyn↗

arXiv2018

Temperature-Controlled Slip of Polymer Melts on Ideal Substrates

The temperature dependence of the hydrodynamic boundary condition between a PDMS melt and two different non-attractive surfaces made of either an OTS (octadecyltrichlorosilane) self-assembled monolayer (SAM) or a grafted layer of short PDMS chains has been characterized. A slip length proportional to the fluid viscosity is observed on both surfaces. The slip temperature dependence is deeply influenced by the surfaces. The viscous stress exerted by the polymer liquid on the surface is observed to follow exactly the same temperature dependences as the friction stress of a cross-linked elastomer sliding on the same surfaces. Far above the glass transition temperature, these observations are rationalized in the framework of a molecular model based on activation energies: increase or decrease of the slip length with increasing temperatures can be observed depending on how the activation energy of the bulk viscosity compares to that of the interfacial Navier's friction coefficient.

cond-mat.soft↗

arXiv2018

Sensing adsorption kinetics through slip velocity measurements of polymer melts

The evolution over time of the non-linear slip behavior of a polydimethylsiloxane (PDMS) polymer melt on a weakly adsorbing surface made of short non-entangled PDMS chains densely end-grafted to the surface of a fused silica prism has been measured. The critical shear rate at which the melt enters the nonlinear slip regime has been shown to increase with time. The adsorption kinetics of the melt on the same surface has been determined independently using ellipsometry. We show that the evolution of slip can be explained by the slow adsorption of melt chains using the Brochard-de Gennes's model.

physics.flu-dyn↗

arXiv2017

Friction of polymers: from PDMS melts to PDMS elastomers

The slip behavior of polydimethylsiloxane (PDMS) polymer melts flowing on non-adsorbing surfaces made of short non-entangled PDMS chains densely end-grafted to silica has been characterized. For high enough shear rates, constant slip lengths proportional to the bulk fluid viscosity have been observed, in agreement with Navier's interfacial equation, and demonstrating that the interfacial Navier's friction coefficient is a local quantity, independent of the polymer molecular weight. Comparing the interfacial shear stresses deduced from these measured slip lengths to available friction stress measured for crosslinked PDMS elastomers, we directly compared the interfacial melt or elastomer friction coefficient to the monomer-monomer friction.

cond-mat.soft↗