Studying polymer diffusiophoresis with non-equilibrium molecular dynamics

Abstract

We report a numerical study of the diffusiophoresis of short polymers using non-equilibrium molecular dynamics simulations. More precisely, we consider polymer chains in a fluid containing a solute that has a concentration gradient and examine the variation of the induced diffusiophoretic velocity of the polymer chains as the interaction between the monomer and the solute is varied. We find that there is a non-monotonic relation between the diffusiophoretic mobility and the strength of the monomer–solute interaction. In addition, we find a weak dependence of the mobility on the length of the polymer chain, which shows clear difference from the diffusiophoresis of a solid particle. Interestingly, the hydrodynamic flow through the polymer is much less screened than for pressure driven flows.

Challenges in modelling diffusiophoretic transport

“…However, for large ε cs , the closest solutes to the colloid are tightly bound and lose their mobility. Hence, they stop contributing to the flow around the colloid (see a discussion in [36]).…”

“…We attempted to swap 10 4 particle identities every 10 steps for the first 10 5 steps, thereby generating an equilibrium distribution of solutes around the colloid, and an equimolar solution in the bulk. The equilibration step is crucial as our aim to carry out simulations under conditions where the composition of the bulk fluid is kept fixed, even as we varied the colloidsolute interaction ε cs [36].…”

“…More recent simulations have used both equilibrium and non-equilibrium MD techniques to study diffusio-osmosis [27,28,31,46]. In addition, there have been several reports on MD sim-ulations of diffusiophoresis of colloids [38,44] and short polymers [36].…”

Electroosmosis in nanopores: Computational methods and technological applications

“…Finally, in some cases, the kinetic energy associated with the streaming velocity is a very small fraction of the total kinetic energy [116,118]. For example, in situations where R λ D the net force on the system in small as the net force vanishes outside the Debye layer [162,165]. Hence, the application of a standard thermostat that acts on all the three translational degrees of freedom is expected to be satisfactory to infer transport coefficients.…”

Challenges in modelling diffusiophoretic transport

“…More recent simulations have used both equilibrium and non-equilibrium MD techniques to study diffusio-osmosis [46,27,28,31]. In addition, there have been several reports on MD simulations of diffusiophoresis of colloids [38,44] and short polymers [36].…”