Patricia Goldstein

A new generalization of Enskog's equation for mixtures of dense gases

Enskogs kinetic equation for a dense gas of hard spheres has been generalized in this paper to a mixture of dense gases which is consistent with the requirements of irreversible thermodynamics. The pair-correlation functions which provide a correction for the collision frequency in Enskogs equation are not the correct functions in the case of the mixture. These functions are determined using the phenomenological restrictions imposed by irreversible thermodynamics and a heuristic criterium of minimal entropy production. Formal expressions for the most relevant physical quantities are also given.

A thermodynamic basis for transport phenomena in viscoelastic fluids

A calculation for the longitudinal stress modulus in a viscoelastic medium is obtained introducing the stress tensor, its trace and the heat flux as additional variables, without requiring the specific form of the dynamic structure factor of the system. By using extended irreversible thermodynamics, we derive the time evolution equations for the state variables. These equations are used to obtain general wave vector and frequency dependent expressions for measurable properties of the system. We recover for a particular case results that have been derived previously in the literature.

On the Stokes-Einstein relation in glass forming liquids

Nowadays, the experimental evidence of a crossover between two dynamical regimes for supercooled glass-forming liquids at a temperature Tc,Tc>Tg, where Tg is the glass transition temperature, has been widely reported in the literature. On one hand, it is a well-known fact that in the region Tg<T<Tc, fragile glass forming liquids do not follow the Vogel–Fulcher–Tammann law. On the other hand, in the same region the Stokes–Einstein relation between the viscosity and the translational diffusion coefficient breaks down. Using the temperature derivative analysis, we present, for three glass-forming liquids, an empirical law for log10f, where f is the frequency, and we exhibit the break down of the Stokes–Einstein relation.

Brownian dynamics simulations of confined tethered polymers in shear flow: the effect of attractive surfaces

Coarse grain Brownian dynamics simulations of the bead-spring model are used to investigate the effect of attractive surfaces on the stretching of confined tethered polymers under shear flow. The weak and strong adsorbed regimes have been addressed by means of a coarse grain van der Waals potential to simulate polymer substrate interactions. Different stationary cyclic dynamics are observed upon varying shear flow intensity and surface potential strength. Polymer stretching decreases as increasing the attractive potential strength, breaking down the scaling predictions for non-adsorbed polymers. We found that adsorption is enhanced by the shear flow strength in agreement to simulations of adsorbed non-tethered polymers.Graphical abstract

An H-theorem for the Enskog equation of a binary mixture of dissimilar hard spheres

Within the context of a standardlike Enskog theory, we prove the existence of both a global and a local H-theorem for a system consisting of a binary mixture of dissimilar hard spheres. The semipositive character of the entropy production, in addition to previous results on the proof of Onsager’s theorem, exhibits the complete compatibility of our theory with linear irreversible thermodynamics.

Irreversible thermodynamics of a binary mixture of dissimilar hard spheres

Within the framework of the Standard Enskog Theory, we prove the consistency of the kinetic theory of a binary mixture of dissimilar hard spheres with Linear Irreversible Thermodynamics. The thermodynamic fluxes and forces arise from the entropy production which may be derived from a proposed kinetic entropy function. A straightforward proof of Onsagers reciprocity theorem is presented.

Irreversible thermodynamics of a binary mixture of hard spheres: The Onsager relations

Using the kinetic description of a binary mixture of dissimilar hard spheres following a standard-like Enskog theory, we prove the reciprocity of the Onsager relations within the rigorous framework. This proof, added to previous results, places our description in complete agreement with linear irreversible thermodynamics. A discussion on the form of the derived entropy flux is also presented.

A thermodynamic basis for charged particles transport in viscoelastic fluids

A calculation for the generalized longitudinal stress modulus and electric conductivity in an ionic-viscoelastic medium is presented. The system is described within the framework of extended irreversible thermodynamics in terms of the regular conserved variables and of an additional set of independent variables consisting of the stress tensor, its trace, and the electric flux. Using the standard procedure, we derive the time evolution equations for the additional variables. These equations are used to obtain general wave vector and frequency dependent expressions for measurable properties of the system. We obtain for the linear case results that have not been derived previously in the literature.