Viscous fluids, molecular dynamics

The transport of a sub-critical Lennard-Jones fluid in a cylindrical mesopore is investigated here, using a combination of equilibrium and non-equilibrium as well as dual control volume grand canonical molecular dynamics methods. It is shown that all three techniques yield the same value of the transport coefficient for diffusely reflecting pore walls, even in the presence of viscous transport. It is also demonstrated that the classical Knudsen mechanism is not manifested, and that a combination of viscous flow and momentum exchange at the pore wall governs the transport over a wide range of densities. 

The static and dynamic properties of DNA have been studied by the temperature-dependent Stokes shift of the intercalated dye acridine orange [192] and by molecular dynamic simulation [193]. A large part of the Stokes shift of the intercalated dye in DNA is found to be frozen out at low temperature, as in the solution. Thus, the interior of DNA is found to have the diffusive and viscous dynamic characteristics of a fluid rather than the purely vibrational characteristics of a crystal. The results suggest that the probe dye molecule senses the movement of DNA and at high viscosity the rate of DNA motion is limited by the rate of solvent motion. 

Ladd AJC (1984) Equations of motion for non-equilibrium molecular dynamics simulations of viscous flow in molecular fluids. Mol Phys 53 459 63... 

The theoretical framework in which it is possible to provide high quality studies of the microscopic structure of the ionic liquid is mainly represented by classical molecular mechanics and, only very recently, by ab-initio molecular dynamics. While the employed theoretical techniques are not very different from those used for conventional fluids, many difficulties arise because of the microscopic nature of ionic liquids. In particular these substances are extremely viscous and simulation times become quickly prohibitive if one wants to describe dynamical properties, even as simple as diffusion coefficients. Recent technological advances such as the introduction of GPU clusters might allow unprecedented possibilities in the simulation of these material opening the route to the simulation of rare events and long time scale phenomena. 

Continuum theory has also been applied to analyse tire dynamics of flow of nematics [77, 80, 81 and 82]. The equations provide tire time-dependent velocity, director and pressure fields. These can be detennined from equations for tire fluid acceleration (in tenns of tire total stress tensor split into reversible and viscous parts), tire rate of change of director in tenns of tire velocity gradients and tire molecular field and tire incompressibility condition [20]. 

Liquid crystals (LCs) are molecules that have the ability to self-assemble into organized mesophases with properties intermediate between those of crystalline solids and isotropic liquids [1,2]. In LC phases, the molecules are dynamic and collectively behave as a viscous liquid but retain on average a degree of organization reminiscent of an ordered, crystalline solid. Consequently, they can be considered ordered fluids, as a more accurate definition. LCs can be subdivided into two general classes—thermotropic LCs and lyotropic LCs—depending on the environmental and molecular factors that govern how they form ordered fluid phases. 

Fluid permeation. Fluid permeation can be investigated by a classical stationary or a dynamic technique. It provides an effective pore diameter that is the result of the size distribution and the connectivity of the pores the latter can be expressed in term of the tortuosity t which is the ratio of the path that the fluid actually takes and the width over which the pressure gradient is applied (usually the sample thickness). If viscous flow rather than molecular diffusion is the dominant mechanism the weight of the pore size distribution with respect to its impact on the fluid permeation transport is shifted to the large pores. 

An understanding of multiphase microflows is critical for the development and application of microstructured chemical systems in the chemical industry. As one of the most important meso-scientific issues, interfacial science could be a bridge connecting microscopic molecular components and macroscopic fluid behaviors in these systems. Working together with viscous and inertial forces, the interfacial force also dominates complicated multiphase flow patterns and well-controlled droplets and bubbles. In this review, the generation mechanisms of different flow patterns and the break-up rules for droplets and bubbles in microchannels are introduced first. The effects of the adjustable fluid/solid interfaces, or so-called wetting properties, of microchannels on multiphase flow patterns, as well as microchannel surface modification methods, are then discussed. The dynamic fluid/fluid interfaces in multiphase microflows with variable... 

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