Abstract
In this work, the thermodynamic scaling framework has been used to emphasize the limitations of fully flexible coarse grained molecular models to yield shear viscosity of real liquids. In particular, extensive molecular dynamics simulations have confirmed that, while being reasonable to describe the viscosity of short normal alkanes, the fully flexible Lennard-Jones and Mie chains force fields are inadequate to capture the density dependence of shear viscosity of medium to long alkanes. In addition, it is shown that such a weakness in terms of coarse grained molecular models can be readily quantified by using the thermodynamic scaling framework. As a simple alternative to these force fields, it is demonstrated that the insertion of a variable intramolecular rigidity in the Lennard-Jones chains model exhibits promising results to model medium to long chain-like real fluids from both thermodynamic and viscosity points of view.
Highlights
The knowledge of thermophysical properties of fluids in both dilute and dense phase is essential to understand and predict their behavior in many natural and industrial systems
The shear viscosity was computed for various thermodynamic states and estimated by using the NEMD method of Müller-Plathe [36], which consists in performing a momentum exchange between molecules in the central and the edge parts of the simulations domain in order to be compatible with periodic boundary conditions
This subsection is devoted to the evaluation the ability of the fully flexible LJ chains model to describe the viscosity of normal alkanes within the Thermodynamic Scaling (TS) framework
Summary
The knowledge of thermophysical properties of fluids in both dilute and dense phase is essential to understand and predict their behavior in many natural and industrial systems. The shear viscosity of liquids is a key element in many industrial applications [1,2]. A lot of research teams are interested in developing a rigorous theory which could describe thermodynamic and transport properties accurately and simultaneously from microscopic information. As a matter of fact, current theories usually describe only one type of properties accurately and are often property dependent. Engineering tools allow for the prediction of well-known fluids in classical conditions satisfyingly, but they are often revealed to be inadapted when used to deal with “new” fluid types and/or complex thermodynamic conditions
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