Volume 34, Issue 1

The application of concepts, principles, and methods of thermodynamics of equilibria and processes to bioengineering systems has led to a new and growing field: engineering biothermodynamics. This article is the second in a series devoted to presenting to the biophysical chemist and the biochemical engineer the fundamentals and also the possibilities of this field, the latter aspect being demonstrated by examples. Here we will elaborate on the thermodynamics of adsorption phenomena of proteins on solid surfaces. Equilibria and processes of single- and multi-component protein solutions including an inert sorbent surface to adsorb proteins will be considered. Also, phenomena such as multi-contact adsorption of a (big) protein on a surface and the (often irreversible) denaturation process of a protein after adsorption will be discussed in brief.

Gravimetric equilibrium isotherms, thermodynamic parameters, and diffusion of p -xylene in silicalite-1 were investigated at several temperatures using an intelligent gravimetric analyzer (IGA). Both plateau and hysteresis loops appeared in the isotherms obtained at 323 and 343 K, respectively. Heat of sorption ( Q st ), free energy change (Δ G ), entropy change (Δ S ), and entropy ( S a ) of the adsorbed phase at various sorption coverages were determined from the adsorption isotherms. The diffusion coefficients at different loadings were also calculated using Fick's equation. The calculated thermodynamic and kinetic parameters satisfactorily explain the adsorption process and isotherm features.

A description of mixtures, including matter diffusion and suspensions, is analyzed from a thermodynamic viewpoint with internal variables. In order to consider dissipative effects due to thermo-diffusion we introduce a set of N independent scalar internal variables, which we denote by γ A . The behavior of the mixture is therefore described by a state space W including the classical variables mass density, mass concentration, temperature, and internal variables together with their first and second gradients satisfying evolution equations. General thermodynamic restrictions and residual dissipation inequalities are obtained by the Clausius–Duhem inequality.

Using a non-equilibrium molecular dynamics (NEMD) simulation, we have investigated the dependence of the thermal diffusion factor and thermal conductivity of binary diatomic mixtures on molecular parameters such as molecular mass, bond length, potential well depth, and molecular size. On the basis of the results obtained for the energy fluxes in the mixtures, a phenomenological description of these transport properties is explained. The results show that the thermal diffusion factor increases with increasing bond length as well as potential well depth ratio and it decreases with increasing molecular size ratio. Calculations of the energy flux indicate that the kinetic energy of a mobile particle and the intermolecular energy transfer due to the motion of a particle in the field of the other particles have a significant effect in determining the ability of the migration of two components in the mixtures. Moreover, the calculations indicate that in contrast to the thermal diffusion factor the thermal conductivity is not sensitive to the intermolecular potential parameters.

If a discrete non-equilibrium system is in contact with an equilibrium reservoir exchanging heat, power, and material with each other, a non-equilibrium non-additive entropy rate of the system can be defined by use of non-equilibrium contact quantities: contact temperature and dynamic chemical potentials. The integrability of the entropy rate and the corresponding Maxwell relations are investigated. The dissipation inequality is exploited for a simple material whose state space includes the time rate of the contact temperature. A non-equilibrium efficiency is introduced.