Accurately describing liquids and their mixtures beyond equilibrium remains a significant challenge in modern chemical physics and physical chemistry, especially regarding the calculation of transport properties in liquid-phase systems. This paper introduces a phenomenological nonequilibrium theory specifically designed for multicomponent liquid-phase solutions. Our field-theoretical framework, rooted in nonequilibrium statistical mechanics, incorporates quasi-stationary concentration fluctuations that align with equilibrium liquid theory as described by classical density functional theory. This method serves as a phenomenological extension of the established Dean–Kawasaki stochastic density functional theory, enabling the computation of shear viscosity. We apply our approach to derive a general formula for the shear viscosity in single-solute solutions. Our findings yield new results and successfully reproduce previously established results for such systems as solutions containing soft-core particles, hard spheres, one-component plasma, and near-critical solutions.
