Christopher Devik Fjeldstad

arXiv2026

Kinetic Theory for the Shear Viscosity of Dense Binary Dipolar Fluid Mixtures

We construct a kinetic theory for the shear viscosity of dense binary fluid mixtures of strongly-interacting dipolar hard spheres. We derive an expression for the pairwise correlations in the binary mixtures that is accurate up to packing fractions around 0.35. The approach is based on Enskog-Thorne theory, and inspired by the theory for dense pure fluids developed by Pousaneh and de Wijn. It relies on effective coupling parameters obtained from the pure fluids combined with mixing rules and a heuristic expression for the collision integral. We compare our results to viscosities obtained numerically from molecular-dynamics simulations of dipolar hard-sphere fluids. Our expression for the shear viscosity of the binary mixtures captures the density and composition dependent behavior of the binary dipolar fluids up to packing fraction of $ξ\lesssim 0.3$ without any mixture-derived fit parameters.

cond-mat.soft↗

arXiv2026

Thermodynamic Approach to Momentum Transport in Dense Fluids

We present a new framework for extending Chapman-Enskog theory beyond the hard-sphere fluid model. Rather than relying on effective hard sphere diameters, the approach makes use of on an exchange function which can be related to the thermodynamic properties of the system. We show that two existing extensions, including modified Enskog theory (MET), fit into this new framework. Based on our approach, we propose an alternative to MET that takes into account the potential interaction energy associated with the inter-particle interactions in the fluid. The proposed expression is applied to predicting the shear viscosity of several different simulated fluid models across a wide set of densities $0.05 \leq ρ^* \leq 0.8$ and temperatures $1.5 \leq T^* \leq 4.0$ in Lennard-Jones units. The fluid models considered include both the Weeks-Chandler-Anderson (WCA) fluid and the Lennard-Jones (LJ) fluid. At low and intermediate density, here taken to be $ρ^* \leq 0.3$, we report mean relative prediction errors between $2\%$ and $4\%$ for both these. Across all densities considered, the largest mean relative errors reported are $4.4\%$ and $8.1\%$ for the WCA fluid and LJ fluid respectively. We also investigate other interaction models, including a diatomic molecular model, in order to better understand the limitations of our approach.

cond-mat.stat-mech↗