On the thermodynamic theory of colloidal suspensions

Colloidal suspensions can be considered as continuous media, like molecular solutions, in the main area of theoretical research. However, they have a number of features that distinguish them from true solutions and coarse suspensions. The paper considers the thermodynamic theory of weak solutions as applied to colloidal suspensions that are in a gravity field. This problem is not clear because the colloidal suspensions are multi component systems, and, strictly, the mutual influence of the suspended particles and the liquid carrier molecules should be taken into account in thermodynamic models. It is shown that the distribution of nanoparticles by height is determined by the density of the mixture as a whole, and not by the density of the dispersion medium. Equations describing the equilibrium distribution of nanoparticles in a colloidal solution have been obtained. Investigation of the dependence of the density on the impurity concentration in a weak solution has shown that if the additivity properties of the component volumes are preserved, then the quadratic coefficient in the Gibbs energy expansion does not depend on pressure. It is shown that the theory of a weak solution gives an equation for the equilibrium distribution of the dispersed phase, which has almost identical solutions for a large range of parameters of a problem with a well-known in the literature equation obtained in the framework of the hard sphere gas model. However, the individual contributions to the thermodynamic potential of the solution (specialized by the field of gravity and interparticle interaction) in the models under consideration are different. These differences can occur in non-equilibrium processes or in the presence of additional flows of a substance (magnetophoresis, thermal diffusion, etc.).