Knowledge of the mechanical properties of clathrate hydrates is central for studying the mechanical properties of hydrate-bearing sediments, their associated applications in wellbore stability, exploitation in stratum deformation, geological disaster prevention, and risk assessment of CO₂ buried in oceans. However, because of the limited understanding of hydrate formation conditions and limited methods to investigate these, the understanding of the mechanical properties of hydrates is still poor and even controversial to some extent. This paper reviews current experimental and theoretical results on mechanical properties of hydrates, and discusses the typical difficulties faced in this area. On the experimental side, the most important problem is obtaining pure hydrate samples. Theoretically, the essential origin of the mechanical properties has not been explained in terms of molecular interactions. The hope is to resolve these issues by combining novel macroscopic experiments and microscopic methods. In order to avoid difficulties caused by impurities, it is proposed to use molecular dynamics simulations. This technique can be used to reveal the nature of the mechanical characteristics of hydrates at the molecular and nanometre scale. The goals of this paper are to establish a bridge between the micromechanical nature and the macromechanical properties of hydrates, and to lay a solid theoretical basis for the study of the mechanical properties of hydrate-bearing sediments. These goals are important for the future safe and efficient exploitation of natural hydrates, hydrate-induced seabed geological disaster prevention, the safety of CO₂ geological burial, and the deployment of a reliable long-term seabed-borehole coupled hydrate observation system in the integrated Ocean Drilling Program.

Understanding the thermal and mechanical properties of CH₄ and CO₂ hydrates is essential for the replacement of CH₄ with CO₂ in natural hydrate deposits as well as for CO₂ sequestration and storage.

In this paper we apply the general analysis described in our first paper to a binary mixture of cyclohexane and $n$-hexane. We use the square gradient model for the continuous description of a nonequilibrium surface and obtain numerical profiles of various thermodynamic quantities in various stationary state conditions. Details of the numerical procedure are given and discussed. In the second part of this paper we focus on the verification of local equilibrium of the surface as described with excess densities. We give a definition of the temperature and chemical potentials of the surface and verify that these quantities are independent of the choice of the dividing surface. We verify numerically that the surface in a stationary state of the mixture can be described in terms of Gibbs excess densities, which are found to be in good approximation equal to their equilibrium values at the stationary state temperature and chemical potentials of the surface.

In earlier work a systematic extension of the van der Waals square gradient model to nonequilibrium one-component systems was given. In this work the focus was on heat and mass transfer through the liquid-vapor interface as caused by a temperature difference or an over- or underpressure. We will give an extension of this approach to multicomponent nonequilibrium systems in the systematic context of nonequilibrium thermodynamics. An explicit expression for the pressure tensor is derived valid also for curved surfaces. It is shown how the Gibbs relation should be modified in the interfacial region, in both equilibrium and nonequilibrium. The two-dimensional isotropy of a curved interface is discussed. Furthermore, we give numerically obtained profiles of the concentration, the mole fraction, and the temperature, which illustrate the solution for some special cases.