posted on 2024-01-10, 22:09authored byPolina
O. Sorina, Alexey I. Victorov
In this work, we develop a theory for predicting details
of the
local structure in nonuniform multicomponent fluids that may contain
chainlike and associating components. This theory is an extensionto
the fluid interfaces and mesoscopic structures of different geometryof
the multilayer quasichemical model originally proposed by Smirnova
to describe liquid solution in the vicinity of a planar solid wall.
The basis of the theory is the “cut-and-bond” approach,
much in spirit of SAFT, where an infinite attraction between the separated
monomeric units of a chainlike molecule mimics the chemical bonds
of the chain. We describe the equilibrium structure of the mixture,
including the spatial distribution of the monomeric units and the
local orientation of the chemical bonds in chainlike molecules, and
discuss the contribution of chemical bonds to the local chemical potential
in a nonuniform fluid. To test the new theory, we apply it to mixtures
containing combinations of model components: a strongly associating
solvent, an inert substance of varying chain length, and a chainlike
amphiphile. To compare predictions from the multilayer model with
the results of continuous description of nonuniform fluids, we also
address the square-gradient theory and derive an analytical expression
for the influence parameter that takes into account pair correlations
in the quasichemical approximation. The multilayer quasichemical model
developed in this work predicts formation of aggregates in liquid
solution and describes the local structure of the interfaces between
the coexisting liquid phases in the mixture. Our theoretical predictions
agree on a qualitative level with the accumulated knowledge about
the structure of different types of systems studied in this work.