Levich Institute Seminar Announcement, 11/08/2011
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Ms. Elizabeth Knapp
Mr. Nima Sharifi Mood
City College of CUNY
Chemical Engineering Department
(Ph.D. Candidates with Charles Maldarelli)
"On the Diffusiophoretic Autonomous Motion of Micron to Submicron Motor"
Phoretic transport is the process by which colloidal particles migrate due to a gradient of a thermodynamic variable such as electric potential, temperature or concentration which is applied across the particle. Schemes which utilize phoretic transport to allow particles to propel themselves without externally applying a gradient are of great interest as motors to direct particles to a targeted location. One method for particle self propulsion is to utilize a surface chemical reaction on one part of the particle surface to create concentration gradients of solutes across the particle. These gradients drive a diffusiophoretic motion due to unbalanced (van der Waals) attractions between the particle and the solutes and solvent within an intermolecular length scale (L, 10-100 nm) of the particle surface. In the experimental section of this study, measurements are made of the velocity of diffusiophoretically self-propelled particles driven by the irreversible binding of solute to sites on the particle by video tracking beads which are half surface coated with gold. On the other hand, a theory based on continuum approach for obtaining a clearer insight into diffusiophoretic motion was developed. Prior continuum studies assume the interaction creates a local slip velocity at the particle surface, and the terminal velocity U of spherical particles to be independent of the radius a. We provide numerical solutions for U which account directly for the solute transport and ow within L, and matched asymptotic solutions as L=a tends to zero. The leading order expression for U is independent of a, but U decreases with the particle radius for L/a greater than .01. Molecular dynamics simulation is also undertaken using Lennard-Jones potentials to provide a more complete picture of nanoscale propulsion.