Adsorption Phenomena in the Transport of a Colloidal Particle through a Nanochannel Containing a Partially Wetting Fluid

German Drazer, Joel Koplik, Andreas Acrivos, and Boris Khusid

Phys. Rev. Lett. 89, 244501 – Published 25 November 2002

Abstract

Using molecular dynamics simulations, we study the motion of a closely fitting nanometer-size solid sphere in a fluid-filled cylindrical nanochannel at low Reynolds numbers. At early times, when the particle is close to the middle of the tube, its velocity is in agreement with continuum calculations, despite large thermal fluctuations. At later times, partially wetting fluids exhibit novel adsorption phenomena: the sphere meanders away from the center of the tube and adsorbs onto the wall, and subsequently either sticks to the wall and remains motionless on average, or separates slightly from the tube wall and then either slips parallel to the mean flow or executes an intermittent stick-slip motion.

Received 7 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.244501

Authors & Affiliations

German Drazer^*, Joel Koplik^†, and Andreas Acrivos^‡

Benjamin Levich Institute and Department of Physics, City College of the City University of New York, New York, New York 10031

Boris Khusid^§

Department of Mechanical Engineering, New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102

^*Electronic address: drazer@mailaps.org
^†Electronic address: koplik@sci.ccny.cuny.edu
^‡Electronic address: acrivos@sci.ccny.cuny.edu
^§Electronic address: boris.khusid@njit.edu

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Vol. 89, Iss. 24 — 9 December 2002

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Images

Figure 1
The radial position of the solid particle as a function of time for six independent MD simulations with $A = 0.1$ , $0.4$ , and $0.7$ . The left graph corresponds to cases in which the particle remains motionless on average (“stick”), while on the right graph at the same values of $A$ we show cases in which the particle is adsorbed but moves along the tube axis (“slip”). The difference in the radial position after adsorption between $A = 0.7$ and the other cases can be attributed to the discrete nature of the tube, which results in an anisotropy between diagonals and sides of the tube (see Fig. 5). This discrete nature of the tube along with the softness of the Lennard-Jones interaction is likewise the origin of radial positions greater than $R - a$ , observed in the other cases.Reuse & Permissions
Figure 2
(a) The particle position along the tube as a function of time, for $A = 0.1$ and $R = 2 a$ . After the particle has been adsorbed ( $t \sim 400$ ), alternative stick and slip situations can be observed. (b) Time evolution of the radial position for the same realization shown in (a).Reuse & Permissions
Figure 3
Mean particle velocity along a tube for long simulation runs, $O (10^{4} τ_{0})$ (the mean velocity of eventually adsorbed particles is computed after adsorption has occurred). For values of $A ≲ 0.7$ all particles get eventually adsorbed, whereas for $A ≳ 0.8$ no adsorbed particles are observed. The observed fluctuations in the average velocities for $A ≲ 0.7$ are a consequence of the described “stick-slip” phenomenon.Reuse & Permissions
Figure 4
The solid symbols correspond to the probability density function (PDF) for the radial position of the solid particle averaged over six different realizations for $A = 0.1$ . Two peaks, corresponding to stick and slip, can be observed. The dashed lines refer to the PDF’s of the two realizations shown in Fig. 1 for $A = 0.1$ , where the particle is either motionless or translating along the tube wall.Reuse & Permissions
Figure 5
Snapshots of the solid particle adsorbed to the wall for the case $A = 0.7$ shown in Fig. 1. On the left-side snapshot the sphere is motionless whereas on the right side the particle is translating along the tube. In both cases, however, the gap between the sphere and the wall is smaller than the size of a single fluid atom.Reuse & Permissions
Figure 6
Mean particle velocity along a tube at short times, when a constant force is acting on the sphere and for $A = 1$ . Points correspond to MD simulations and the solid line corresponds to the continuum results of Bungay and Brenner [15]. The error bars correspond to temporal fluctuations in the instantaneous velocity of the solid particle.Reuse & Permissions

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