The behavior of viscosity, $\eta$, as a function of concentration in dense fluids remains an unsolved problem, as is the case with other transport coefficients. Boltzmann's theory and the Chapman-Enskog method predict the value of the viscosity at low concentrations, ${\eta }_0$. Here, the hypothesis $\eta =\varphi {\eta }_0$ is proposed, where $\varphi$ is a function of the thermodynamic state that represents the effects of interactions as concentration increases. We consider that ${\eta }_0$ is the viscosity in an ideal hypothetical system, where the condition of small interactions applies for the whole density range ($\varphi \to 1$ for low concentration). The method proposed to verify this hypothesis involves coupling the system with a solvent represented by a Langevin thermostat, characterized by a damping time $t_d$. Molecular dynamics simulations show that different values of noise intensity modify $\eta$ and ${\eta }_0$, but do not affect $\varphi$. This result supports the assumption that $\varphi$ is a state function, since the thermodynamic state remains unaltered by the presence of damping and noise. Simulations were conducted for particles that interact via a pseudohard sphere or a Lennard-Jones potential.

Close

PrevNext

View figure in article

• Brownian motion
• Fluctuations & noise
• Stochastic processes
• Transport phenomena
• Classical fluids
• Viscosity
• Brownian dynamics
• Langevin equation
• Molecular dynamics