Abstract

Donald W. Brenner
Department of Materials Science and Engineering
North Carolina State University

 

April 16 , 2007
3:30- 4:30pm
MEC Rm. 341

"Multiscale Modeling of Fluid Flow and Liquid Lubrication: From Smart Nanofluidics and MEMS to Industrial Machines"

We have been using combinations of atomic simulation, analytic theory and numerical analysis to characterize fluid flow from the nano- to the macroscopic scale. This talk will emphasize three technological applications of our modeling. The first are simulations of fluid flow through nanopores containing grafted polyglutamic acid, where we use a combination of molecular modeling, analytic polymer scaling theory and continuum flow analysis. Swelling and collapse of the grafted polyglutamic acid is used to control water flow in response to changes in pH. We show that our modeling is able to reproduce experimental flow rates as a function of pH without the need for any experimental input. The second example is simulations of the diffusion of tricresylphosphate molecules on an octadecyltrichlorosilane self-assembled monolayer. This system is being explored as a "bound+mobile" lubricant to increase lifetimes for MEMS devices. Our simulations indicate that the molecules are mobile on the surface of the SAM for close-packed structures, but readily adsorb into defects with an anisotropic diffusion barrier. In the third example we have used self-consistent numerical solutions to a continuum surface diffusion equation to characterize flow under an oscillating AFM tip. These calculations have lead to a new analytic scaling relation that unifies requirements of liquid lubricants across scales from nanometers/nanoseconds to meters/seconds. The relation will be used to analyze and compare lubrication requirements for industrial machines to those for MEMS and magnetic hard disk drives.