Using molecular dynamics simulations, we identified in previous work a new adsorption phenomenon in which, for poorly wetting fluids, a suspended particle, initially moving along the center of the nanochannel, is adsorbed onto the tube wall while displacing all the fluid molecules from the particle-wall gap and then exhibits stick-slip motion following adsorption on the tube wall. However, direct molecular simulations are typically limited to time-scales less than microseconds. We present here a simple, hierarchical approach that bridges the molecular domain to the Brownian time scales and allows us to simulate the particle behavior at several orders of magnitude larger time scales. First, we measure the thermodynamic free-energy of the system and show the molecular basis for the adsorption/no-adsorption transition. We then demonstrate that a Langevin-type description that accounts for the mean-force potential captures the dynamics of the particles and fluid molecules at the Brownian level. We also investigate the hysteresis in the variation of the number of fluid molecules in the narrow gap between the particle and the wall, as the particle is pushed into contact with the wall and then pulled back. Finally, we discuss the non-equilibrium effects as the particles displaying stick-slip behavior also exhibit spontaneous desorption.
Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2005 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: May 8, 2005
Pages: 587 - 588
Industry sector: Sensors, MEMS, Electronics
Topic: Micro & Bio Fluidics, Lab-on-Chip