Phonon thermophoresis of crystalline nanoparticles in liquids.

Our nonequilibrium thermodynamic model of thermodiffusion in molecular liquid systems is used to examine the role of thermal phonons in the thermophoresis of liquid suspensions of crystalline nanoparticles, which tend to have high thermal conductivity. The Soret coefficient used to characterize stationary thermodiffusion is related to differences in entropy between a particle and the body of liquid that it displaces. Calculated phonon Soret coefficients for graphite and diamond nanoparticles in three polar solvents are used to establish parameters where the phonon mechanism is expected to dominate particle thermophoresis compared to slip-flow caused by forces induced in the surface layer by the temperature gradient.

Nonequilibrium thermodynamic model of thermoelectricity and thermodiffusion in semiconductors.

We present a self-consistent model rooted in nonequilibrium thermodynamics for defining concentration gradients in the electron/hole pairs and electric-field gradients in an intrinsic semiconductor created upon exposure to a temperature gradient. The model relies on the equation for entropy production expressed through phenomenological equations for the electron/hole flux, with the imposed condition that the resulting concentration profiles of the electrons and holes are identical. The chemical potentials of electrons, holes, and parent atoms of the lattice, which are contained in the flux equations, are calculated on the basis of the temperature-dependent equilibrium dissociation reaction: lattice atom ↔ electron + hole.

Nonequilibrium thermodynamic material transport equations for thermodiffusion of isotopes and isomers in multicomponent systems.

We extend our nonequilibrium thermodynamic model of thermodiffusion in binary systems to multi-component mixtures. The fundamental parameter is the difference in molecular entropy of the components, which can be obtained in one of three ways; (i) derived as temperature derivatives of the respective equilibrium chemical potentials at constant pressure using equilibrium statistical mechanics; (ii) obtained in the literature from computer simulations; or (iii) obtained as empirical values in the literature. The model is used to relate thermodiffusion in multicomponent mixtures of related isomers or isotopes to isomer/isotope effects in binary mixtures that are commonly enumerated in one of two ways: (i) as a difference in the Soret coefficients measured on two binary mixtures, each containing one of two related isomers/isotope in a common solvent; or (ii) as this difference from two binary mixtures, each consisting of a common solute dissolved in one of the two related isomers/isotopes as the solvent.

Statistical Mechanic and Phenomenological Approaches to Isomeric Effects in Thermodiffusion.

We present a model that explains variance in the thermodiffusion of hydrocarbon isomers in binary liquid mixtures. The model relies on material transport equations for binary nonisothermal liquid systems that were derived through a nonequilibrium thermodynamic approach in a previous work, coupled with one of two methods: (i) use of equilibrium chemical potentials for each component under conditions of constant pressure, derived using statistical mechanics or (ii) use of the temperature derivative of chemical potential expressed phenomenologically as molecular entropy. The model is evaluated using Soret coefficients () measured in binary solutions of heptane isomers in benzene.

Internal Degrees of Freedom as a Basis for Isotopic Effects in Thermodiffusion.

We present a model that relates isotope effects in thermodiffusion to changes in internal degrees of freedom associated with rotational and vibrational motion. The model uses general material transport equations for binary non-isothermal liquid systems, derived using non-equilibrium thermodynamics in our previous work. The equilibrium chemical potentials of the components at constant pressure are derived using statistical mechanics.

Thermophoretic Random Walks and Enhancement of Diffusion.

The contribution of the stochastic thermodiffusion to the diffusion enhancement is studied. The thermodiffusion of particles suspended in a liquid may hold place when the spontaneous endo- or exothermal nanoscale events similar to elementary acts of enzymatic reactions occur as the random series in the space and time. In these events, the energy can be emitted or absorbed at nanoscale during few to hundreds of picoseconds.

Coupled Heat and Mass Transport in Liquid Films that Contain Thermophoretically Active Particles.

We consider the spontaneous redistribution of thermophoretically active particles suspended in a thin film of liquid, made to absorb energy and transmit it in the form of heat to the surrounding medium. When the opposing boundaries to the thin dimension are maintained at a constant temperature, a nonuniform temperature profile is formed across the film because of differential heat dissipation, which is maximized at the boundaries. Thermophobic particles move and concentrate at the opposing (cooler) boundaries, whereas thermophilic particles concentrate within a layer midway between the boundaries.

Thermoosomosis in microfluidic devices containing a temperature gradient normal to the channel walls.

We analyze a microfluidic pump from the literature that utilizes a flat channel with boundary walls at different temperatures and tilted elongated pillars within in order to construct an adequate theory for designing devices in which the temperature gradient between channel walls is transformed into a longitudinal temperature gradient along the channel length. The action of the device is based on thermoosmosis in the secondary longitudinal temperature gradient associated with the specific geometry of the device, which can be described using physicochemical hydrodynamics without invoking the concept of thermophoretic force. We also describe a rotating drive device based on the same principle and design.

Comment on "Soret motion in non-ionic binary molecular mixtures" [J. Chem. Phys. 135, 054102 (2011)].

The material transport equations derived in the article by Leroyer and Würger [J. Chem. Phys.

Molecular thermodiffusion (thermophoresis) in liquid mixtures.

Thermodiffusion (thermophoresis) in liquid mixtures is theoretically examined using a hydrodynamic approach. Thermodiffusion is related to the local temperature-induced pressure gradient in the liquid layer surrounding the selected molecule and to the secondary macroscopic pressure gradient established in the system. The local pressure gradient is produced by excess pressure due to the asymmetry of interactions with surrounding molecules in a nonuniform temperature field.

Symmetric diffusion equations, barodiffusion, and cross-diffusion in concentrated liquid mixtures.

In models of diffusion in multicomponent mixtures, the current practice is to derive equations for an isobaric system. The equations are nonsymmetric in relation to the components of the mixture, and the concentration of solvent is assumed to be governed by the conservation of mass instead of its own corresponding diffusion equation. For concentrated mixtures, the solvent component is selected arbitrarily, which makes interpretation of the experimental data dependent on the choice of the interpreter.