Volume 29, Issue 4

We show that the method of non-equilibrium thermodynamics can be applied to describe the behaviour of systems defined at the meso-scale whose dynamics is mediated by the presence of fluctuations. The mesoscopic non-equilibrium thermodynamics approach we propose yields the kinetic equations for the evolution of the probability density governing the dynamics. We present applications to different mesoscopic systems undergoing linear and nonlinear transport and activated processes.

This article reviews our recent efforts to provide a rigorous description of the kinetics of nucleation processes from a mesoscopic and nonequilibrium perspective. Its usefulness to analyze different important aspects of the process, such as the validity of the Nucleation Theorem, the proper incorporation of translational and rotational degrees of freedom, and the influence of inhomogeneities and gradients in the process, is discussed. The theory sketched here provides a unified framework in which nucleation can be realistically described.

This paper provides a concise overview of three current and very active frontiers of the second law of thermodynamics; namely, non-equilibrium macroscopic systems, mesoscopic systems, and systems with quantum correlations. Rather than providing an extensive review of this very wide topic, we sketch some views on the basic ideas of several current explorations of the limits of the second law. Furthermore, we emphasise the relevance of a suitable definition of temperature in non-equilibrium situations to avoid some apparent paradoxes arising in Carnot cycles with driven heat reservoirs with quantum correlations.

The Soret coefficient of a binary mixture can be measured indirectly by considering its effect on the hydrodynamics induced by free convection. In this paper, we have analyzed the stability of two configurations commonly used for such measurements, the thermogravitational column and the Bénard cell. We have numerically integrated the three-dimensional partial differential equations that describe these systems in order to provide accurate data of stability boundaries suitable for comparison with experimental measurements.

The stability of a liquid layer with an undeformable interface open to the atmosphere, subjected to a horizontal temperature gradient, is theoretically analysed. Buoyancy and surface tension forces give rise to a basic flow for any temperature difference applied on the system. Depending on the liquid depth, this basic flow is destabilised either by an oscillatory instability, giving rise to the so-called hydrothermal waves , or by a stationary instability leading to corotating rolls. Oscillatory perturbations are driven by the basic flow and therefore one must distinguish between convective and absolute thresholds. The instability mechanisms as well as the different regimes observed in experiments are discussed. The calculations are performed for a fluid used in recent experiments, namely silicone oil of 0.65 cSt ( Pr = 10). In particular, it is shown that two branches of absolute instability exist, which may be related to the two types of hydrothermal waves observed experimentally.

The phase separation mechanism of a binary liquid mixture off-critically quenched in its miscibility gap is nucleation and growth, its homogeneous phase reaching a metastable equilibrium state. The successive stages of growth of the nucleated droplets are a diffusion-driven free growth, an intermediate regime and a coarsening by reduction of interface (Ostwald ripening or Brownian collisions induced coalescence). We have made light attenuation experiments to investigate the sedimentation in such systems. These results have given us access experimentally to two values predicted theoretically: the growth exponent of the intermediate regime and the crossover time between this regime and interface-reduction coarsening. These data, added to the literature results, have permitted to get a quite complete view of the growth scenario in very off-critical phase-separating liquids.

The adsorption of non-spherical nanoparticles at liquid/liquid interfaces is considered in the framework of the classical theory of capillarity. Spheroidal nanoparticles with aspect ratio α larger than a critical value α c cannot be adsorbed at a liquid/liquid interface. The critical shape α c (depending on the liquid-liquid surface tension and liquid-particle-liquid line tension) is computed explicitly using a simple expression for the Free Energy. The results show that particles can be surface active, that is, can be adsorbed at the interface according to its shape. In addition, the dependence of the line tension with the size of the liquid-particle-liquid contact line is also discussed.

Extended irreversible thermodynamics and the general equation for the non-equilibrium reversible–irreversible coupling are two thermodynamic theories that have recently received much attention, not only from the fundamental but also from the practical point of view. The objective of the present work is to compare the respective merits of these two approaches by emphasising their similarities and differences. To avoid formal and tedious developments, we have applied both formalisms to a concrete problem, namely thermo-diffusion in a binary fluid mixture of non-viscous fluids.