Molecular dynamics simulation of the motion of colloidal nanoparticles in a solute concentration gradient and a comparison to the continuum limit.
Chemical-mechanical transduction mechanisms which can actuate the movement of colloids through liquids are highly sought after as engines to propel miniaturized micro- and nanobots. One mechanism involves harnessing the long-range van der Waals attractive forces between the colloid and solute molecules dissolved in the liquid around the particle. If a concentration gradient of this solute is applied across the particle, then the imbalance in the van der Waals attraction drives the particle towards the higher concentration of solute. We present a molecular dynamics simulation using Lennard-Jones interactions between molecules of the solvent, solute, and colloid cluster which include short-range repulsive and long-range attractive potentials. The simulations demonstrate that a solute gradient can propel nanosized colloids, and that the velocity decreases with the colloid size. The solute-colloid short-range repulsive interactions are observed to be restricted to a region of specifically adsorbed solutes on the particle surface which are symmetrically adsorbed and do not contribute to the motion. The size of this region provides a cutoff for a continuum level description of the motion, and with this cutoff, continuum calculations are in excellent agreement with the molecular dynamics simulation results, completing a description of the propulsion from the nano- to the microscale.
Benjamin Levich Institute and Department of Chemical Engineering, City College of the City University of New York, New York, New York 10031, USA.
Nima
N
Sharifi-Mood
Joel
J
Koplik
Charles
C
Maldarelli
D003102:Colloids / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry
D003102:Colloids; D012996:Solutions