Thermal noise in confined fluids

2017

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We propose an isothermal, one-dimensional, electroosmotic flow model for slit-shaped nanochannels. Nanoscale confinement effects are embedded into the transport model by incorporating the spatially varying solvent and ion concentration profiles that correspond to the electrochemical potential of mean force. The local viscosity is dependent on the solvent local density and is modeled using the local average density method. Excess contributions to the local viscosity are included using the Onsager-Fuoss expression that is dependent on the local ionic strength. A Dirichlet-type boundary condition is provided in the form of the slip velocity that is dependent on the macroscopic interfacial friction. This solvent-surface specific interfacial friction is estimated using a dynamical generalized Langevin equation based framework. The electroosmotic flow of Na + and Cl as single counterions and NaCl salt solvated in Extended Simple Point Charge (SPC/E) water confined between graphene and silicon slit-shaped nanochannels are considered as examples. The proposed model yields a good quantitative agreement with the solvent velocity profiles obtained from the non-equilibrium molecular dynamics simulations. Published by AIP Publishing. [http://dx.

Section: Simulation Detailsmentioning

confidence: 99%

Multiscale modeling of electroosmotic flow: Effects of discrete ion, enhanced viscosity, and surface friction

2017

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“…A standard choice for R(t) is to assume that it is Gaussian distributed. There are some studies [35][36][37] where MD simulation is used to study the statistical properties of the projected force in fluidic systems. All the studies report that for both bulk and confined fluids, the distribution of the projected force is not strictly Gaussian.…”

Section: Gle Simulationmentioning

confidence: 99%

“…However, using a Gaussian model for the projected force in the GLE simulations is found to reproduce several important single-particle properties of both bulk and confined fluids in good agreement with MD simulation results. 37,38 So, we assume a zero mean correlated Gaussian model for the projected force, with correlation defined through the FD relation (Eq. (3)).…”

Section: Gle Simulationmentioning

confidence: 99%

Memory effects in nanoparticle dynamics and transport

Sanghi

2016

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In this work, we use the generalized Langevin equation (GLE) to characterize and understand memory effects in nanoparticle dynamics and transport. Using the GLE formulation, we compute the memory function and investigate its scaling with the mass, shape, and size of the nanoparticle. It is observed that changing the mass of the nanoparticle leads to a rescaling of the memory function with the reduced mass of the system. Further, we show that for different mass nanoparticles it is the initial value of the memory function and not its relaxation time that determines the "memory" or "memoryless" dynamics. The size and the shape of the nanoparticle are found to influence both the functional-form and the initial value of the memory function. For a fixed mass nanoparticle, increasing its size enhances the memory effects. Using GLE simulations we also investigate and highlight the role of memory in nanoparticle dynamics and transport.

“…To calculate the species specific memory function in the mixture, we use the corresponding memory function equation (MFE) 53 that can be written as…”

Section: B Surface Friction: Boundary Conditionsmentioning

confidence: 99%

“…The numerical method for time integration of the GLE is discussed in Ref. 53. First 100 ps of the simulation trajectory was discarded to allow the equilibration of the species GLE particle.…”

Section: Simulation Detailsmentioning

confidence: 99%

A multiscale transport model for Lennard-Jones binary mixtures based on interfacial friction

2016

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We propose a one-dimensional isothermal hydrodynamic transport model for non-reacting binary mixtures in slit shaped nanochannels. The coupled species momentum equations contain viscous dissipation and interspecies friction term of Maxwell-Stefan form. Species partial viscosity variations in the confinement are modeled using the van der Waals one fluid approximation and the local average density method. Species specific macroscopic friction coefficient based Robin boundary conditions are provided to capture the species wall slip effects. The value of this friction coefficient is computed using a species specific generalized Langevin formulation. Gravity driven flow of methane-hydrogen and methane-argon mixtures confined between graphene slit shaped nanochannels are considered as examples. The proposed model yields good quantitative agreement with the velocity profiles obtained from the non-equilibrium molecular dynamics simulations. The mixtures considered are observed to behave as single species pseudo fluid, with the interfacial friction displaying linear dependence on molar composition of the mixture. The results also indicate that the different species have different slip lengths, which remain unchanged with the channel width.