On the use of excess entropy scaling to describe the dynamic properties of molecular fluids
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Relationships between thermodynamic and kinetic properties of molecular fluids have a wide variety of applications. The development of these relationships provides a means to predict one property based upon knowledge of the other. In this dissertation, we explore the applicability of these relationships for a range of molecular fluids including confined molecular systems. In particular, we focus three different fluids, bulk, confined and complex fluids. We focus on identifying the most relevant scaling variable for molecular fluids. We show via simulations that the thermodynamic excess entropy generally serves as a suitable metric. Outside of the water's anomalous region, reduced transport property data collapse onto a common curve when expressed as a function of the thermodynamic excess entropy. Inside of the anomalous region, data fall onto isochore-specific curves. We next examine the connections between several dynamic properties and various measures of the excess entropy of two Lennard-Jones dumbbell models. Our results indicate the thermodynamic excess entropy provides the best metric for describing kinetic properties. We also find the total two-body term contributes significantly to the excess entropy, and therefore this quantity generally serves as a suitable scaling variable. With better understanding of the relevant scaling variable for bulk molecular fluids, we then examine the ability of excess entropy scaling relations to describe the kinetic properties of a confined molecular system. We carefully consider the choice for the reference state used to define the excess entropy of a confined fluid. Our finding show when the reference state includes information related to the one-body correlations in a confined fluid, to a very good approximation, bulk and confined data for a specified dynamic property at a given temperature collapse onto a common curve when plotted against the excess entropy. Finally, we examine the connections between dynamic properties and the excess entropy for isomers of complex fluids. We focus on a wide range of structural isomers of octane, ranging from a linear chain to a more spherical shaped molecule. We find the reduced transport property data collapse onto isomer-specific curves when expressed as a function of the excess entropy.
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