Wednesday, March 20, 2013

Superomniphobicity or how nanopants are affecting the no slip condition 

When I was an undergraduate majoring in chemical engineering, my favorite class was fluid dynamics. It was so much more visual and relevant than thermodynamics or a lot of the mass balance-type problem sets that we spent so much time solving. When I thought of fluid dynamics, I thought about scuba diving or tubing down a river. It was easier to understand turbulent and laminar flow when you could close your eyes and think of a riverbed. However, I have just learned that one of the primary assumptions that I made in all those calculations in fluid dynamics – that is the no slip at the wall is, thanks to nanotechnology, being shown to be not so simple. According to Dr. Doug Natelson’s blog Nanoscale Views, developments in surface chemistry have made coatings that are so water repellent that no slip boundary condition a poor assumption in many cases. Back in in the No Slip days was assumed that at the fluid-surface the molecules stuck on the surface and didn’t move, then because of shear stresses and viscosity, a velocity profile would develop that in a cylindrical pipe, would have a maximum in the center of the pipe. Now, however, the latest in surface coatings are Superomniphobic. These coatings are more advanced than the coatings on khaki nanopants, which were designed to repel water and minimize staining. While eliminating the no slip boundary condition will challenge many student’s concepts and calculations in fluid dynamics, it does make for some cool videos (see For more information on Superomniphobicity please see Dr. Doug Natelson’s blog Nanoscale Views