arXiv subjects

M. Medina-Noyola

Publications and source records attributed to M. Medina-Noyola.

10 recordsLinked to original sources

arXiv2024

Aging of the Linear Viscoelasticity of Glass- and Gel-forming Liquids

We report a novel approach based on the non-equilibrium self-consistent generalized Langevin equation (NESCGLE) theory that allows for the first principles prediction of the zero-shear viscosity in glass- and- gel-forming materials. This new modulus of the NESCGLE theory facilitates the theoretical description and interpretation of experimental data concerning out-of-equilibrium rheological properties of viscous liquids during their amorphous solidification. The predictive capability of our approach is illustrated here by means of a quantitative comparison between theoretical and experimental results for the zero shear viscosity in suspensions of oligomer-tethered nanoparticles in a polymeric host, finding an almost perfect correspondence between experiments and theory. This comparison also highlights the crucial relevance of including a kinetic perspective, such as that provided by the NESCGLE theory, in the description of dynamic and viscoelastic properties of amorphous states of matter.

cond-mat.soft↗

arXiv2024

Non-equilibrium theory of the linear viscoelasticity of glass and gel forming liquids

We propose a first-principles theoretical approach for the description of the aging of the linear viscoelastic properties of a colloidal liquid after a sudden quench into a dynamically arrested (glass or gel) state. Specifically, we couple a general expression for the time-evolving shear-stress relaxation function $η(τ;t)$ (whose $τ$-integral is the instantaneous viscosity $η(t)$), written in terms of the non-equilibrium structure factor $S(k;t)$ and intermediate scattering function $F(k,τ;t)$, with the equations that determine $S(k;t)$ and $F(k,τ;t)$, provided by the non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. In this manner, we obtain a closed theoretical scheme that directly connects inter-particle forces with experimentally accessible rheological properties of non-equilibrium amorphous states of matter. The predictive capability of the resulting theoretical formalism is illustrated here with its concrete application to the Weeks-Chandler-Andersen (WCA) model of a soft-sphere fluid.

cond-mat.soft↗

arXiv2024

From equilibrium to non-equilibrium statistical mechanics of liquids

Relevant and fundamental concepts of the statistical mechanical theory of classical liquids are ordinarily introduced in the context of the description of thermodynamic equilibrium states. This makes explicit reference to probability distribution functions of \emph{equilibrium} statistical ensembles (canonical, microcanonical, ...) in the derivation of general and fundamental relations between inter-particle interactions and measurable macroscopic properties of a given system. This includes, for instance, expressing the internal energy and the pressure as functionals of the radial distribution function, or writing transport coefficients (diffusion constant, linear viscosity, ...) in terms of integral relations involving both, static and dynamic auto-correlation functions (density-density, stress-stress, ...). Most commonly, however, matter is not in thermodynamic equilibrium, and this calls for the extension of these relations to out-of-equilibrium conditions with the aim of understanding, for example, the time-dependent transient states during the process of equilibration, or the aging of glass- and gel-forming liquids during the formation of non-equilibrium amorphous solid states. In this work we address this issue from both, a general perspective and an illustrative concrete application focused on the first principles description of rheological and viscoelastic properties of glass- and gel-forming liquids.

cond-mat.stat-mech↗

arXiv2022

Structural relaxation, dynamical arrest and aging in soft-sphere liquids

We investigate the structural relaxation of a soft-sphere liquid quenched isochorically ($ϕ=0.7$) and instantaneously to different temperatures $T_f$ above and below the glass transition. For this, we combine extensive Brownian dynamics simulations and theoretical calculations based on the non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. The response of the liquid to a quench generally consists of a sub-linear increase of the $α$-relaxation time with system's age. Approaching the ideal glass-transition temperature from above ($T_f>T^a$) sub-aging appears as a transient process describing a broad equilibration crossover for quenches to nearly arrested states. This allows us to empirically determine an equilibration timescale $t^{eq}(T_f)$ that becomes increasingly longer as $T_f$ approaches $T^a$. For quenches inside the glass ($T_f\leq T^a$) the growth rate of the structural relaxation time becomes progressively larger as $T_f$ decreases and, unlike the equilibration scenario, $τ_α$ remains evolving within the whole observation time-window.These features are consistently found in theory and simulations with remarkable semi-quantitative agreement, and coincide with those revealed in the similar and complementary exercise [Phys. Rev. {\bf 96}, 022608 (2017)] that considered a sequence of quenches with fixed final temperature $T_f=0$ but increasing $ϕ$ towards the hard-sphere dynamical arrest volume fraction $ϕ^a_{HS}=0.582$. The NE-SCGLE analysis, however, unveils various fundamental aspects of the glass transition, involving the abrupt passage from the ordinary equilibration scenario to the persistent aging effects that are characteristic of glass-forming liquids. The theory also explains that, within the time window of any experimental observation, this can only be observed as a continuous crossover.

cond-mat.soft↗

arXiv2017

Crossover from Equilibration to Aging: (Non-equilibrium) Theory vs. Simulations

Understanding glasses and the glass transition requires comprehending the nature of the crossover from the ergodic (or equilibrium) regime, in which the stationary properties of the system have no history dependence, to the mysterious glass transition region, where the measured properties are non-stationary and depend on the protocol of preparation. In this work we use non-equilibrium molecular dynamics simulations to test the main features of the crossover predicted by the \emph{molecular} version of the recently-developed multicomponent non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. According to this theory, the glass transition involves the abrupt passage from the ordinary pattern of full equilibration to the aging scenario characteristic of glass-forming liquids. The same theory explains that this abrupt transition will always be observed as a blurred crossover by the unavoidable finiteness of the time window of any experimental observation. We find that within their finite waiting-time window, the simulations confirm the general trends predicted by the theory.

cond-mat.soft↗

arXiv2016

Equilibration and aging of liquids of non-spherically interacting particles

The non-equilibrium self-consistent generalized Langevin equation theory of irreversible processes in liquids is extended to describe the positional and orientational thermal fluctuations of the instantaneous local concentration profile $n(\mathbf{r},Ω,t)$ of a suddenly-quenched colloidal liquid of particles interacting through non spherically-symmetric pairwise interactions, whose mean value $\overline{n}(\mathbf{r},Ω,t)$ is constrained to remain uniform and isotropic, $\overline{n}(\mathbf{r},Ω,t)=\overline{n}(t)$. Such self-consistent theory is cast in terms of the time-evolution equation of the covariance $σ(t)=\overline{δn_{lm}(\mathbf{k};t) δn^{\dagger}_{lm}(\mathbf{k};t)}$ of the fluctuations $δn_{lm}(\mathbf{k};t)=n_{lm}(\mathbf{k};t) -\overline{n_{lm}}(\mathbf{k};t)$ of the spherical harmonics projections $n_{lm}(\mathbf{k};t)$ of the Fourier transform of $n(\mathbf{r},Ω,t)$. The resulting theory describes the non-equilibrium evolution after a sudden temperature quench of both, the static structure factor projections $S_{lm}(k,t)$ and the two-time correlation function $F_{lm}(k,τ;t)\equiv\overline{δn_{lm}(\mathbf{k},t)δn_{lm}(\mathbf{k},t+τ)}$, where $τ$ is the correlation \emph{delay} time and $t$ is the \emph{evolution} or \emph{waiting} time after the quench. As a concrete and illustrative application we use the resulting self-consistent equations to describe the irreversible processes of equilibration or aging of the orientational degrees of freedom of a system of strongly interacting classical dipoles with quenched positional disorder.

cond-mat.soft↗

arXiv2014

Colloidal liquids of yolk-shell particles

In this paper we develop statistical mechanical tools to describe the intermediate- and long-time collective- and self-diffusion properties of a liquid of strongly-interacting hollow spherical particles (shells), each bearing a smaller solid sphere (yolk) in its interior. To decouple two complex effects we assume that the hydrodynamic interactions can be accounted for through the effective short-time self-diffusion coefficients $D^0_s$ and $D^0_y$ that describe the short-time Brownian motion of the yolk and the shell particles, and develop a self-consistent generalized Langevin equation theory to describe the intermediate- and long-time effects of the direct shell-shell, yolk-shell and yolk-yolk interactions. In a concrete application, we consider the simplest yolk-shell model system involving purely repulsive hard-body interactions between all (shell and yolk) particles. Using a softened version of these interparticle potentials we perform Brownian dynamics simulations to determine the mean squared displacement of both types of particles, as well as the intermediate scattering function of the yolk-shell complex. We compare the theoretical and simulation results between them, and with the results for the same system in the absence of yolks. We find that the yolks, which have no effect on the shell-shell static structure, influences the dynamic properties in a predictable manner, fully captured by the theory.

cond-mat.soft↗

arXiv2014

Dynamics of a suspension of interacting yolk-shell particles

In this work we study the self-diffusion properties of a liquid of hollow spherical particles (shells)bearing a smaller solid sphere in their interior (yolks). We model this system using purely repulsive hard-body interactions between all (shell and yolk) particles, but assume the presence of a background ideal solvent such that all the particles execute free Brownian motion between collisions,characterized by short-time self-diffusion coefficients D0s for the shells and D0y for the yolks. Using a softened version of these interparticle potentials we perform Brownian dynamics simulations to determine the mean squared displacement and intermediate scattering function of the yolk-shell complex. These results can be understood in terms of a set of effective Langevin equations for the N interacting shell particles, pre-averaged over the yolks' degrees of freedom, from which an approximate self-consistent description of the simulated self-diffusion properties can be derived. Here we compare the theoretical and simulated results between them, and with the results for the same system in the absence of yolks. We find that the yolks, which have no effect on the shell-shell static structure, influence the dynamic properties in a predictable manner, fully captured by the theory.

cond-mat.soft↗

arXiv2009

Generalized Onsager-Machlup's theory of thermal fluctuations for non-equilibrium systems

In this work a generalization of Onsager-Machlup's theory of time-dependent thermal fluctuations of equilibrium systems is proposed, to the case in which the system relaxes irreversibly along a non-equilibrium trajectory that can be approximated as a sequence of stationary states. This generalization is summarized by a canonical description of the dependence of the two-time correlation function C(t+τ,t), and of the equal-time correlation function σ(t)= C(t,t) (the covariance of the fluctuations), on the non-equilibrium relaxation time t.

cond-mat.stat-mech↗

arXiv2007

Simplified Self-Consistent Theory of Colloid Dynamics

One of the main elements of the self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics [Phys. Rev. E {\bf 62}, 3382 (2000); ibid {\bf 72}, 031107 (2005)] is the introduction of exact short-time moment conditions in its formulation. The need to previously calculate these exact short-time properties constitutes a practical barrier for its application. In this note we report that a simplified version of this theory, in which this short-time information is eliminated, leads to the same results in the intermediate and long-time regimes. Deviations are only observed at short times, and are not qualitatively or quantitatively important. This is illustrated by comparing the two versions of the theory for representative model systems.

cond-mat.mtrl-sci↗