PHYSICAL MATHEMATICS SEMINAR


TOPIC:	DIMPLING AND BUCKLING OF VISCOELASTIC 
                  FREE SURFACES


SPEAKER:    ANDREW BELMONTE
	    W.G. Pritchard Laboratories
	    Department of Mathematics
	    Penn State University


ABSTRACT:

Among the instabilities which distinguish viscoelastic fluids from Newtonian 
(Navier-Stokes) fluids, those involving free surfaces are often the most striking. 
For instance, an air bubble rising in a viscoelastic fluid can have a steady 
cusp-like tail. I will describe two experiments initially inspired by such cusped 
bubbles. The first concerns the steady state shape of a polymer fluid drop falling 
through a viscous medium. At large volumes we observe a dimpled shape, which 
becomes unstable to an internal tip-streaming; at even larger volumes the drop 
has a stable, toroidal shape. The second experiment focuses on the stretched 
funnel-shaped surface formed by the dynamic wetting of a solid sphere sinking 
slowly into a viscoelastic fluid. As the sphere sinks, we observe a buckling 
instability which leads to long-lived surface folds. Mathematical 
models for these observations will also be presented.	

DATE:         Tuesday, March 30, 2004

TIME:                  2:30 PM

LOCATION:       Building 2, Room 338


Refreshments at 3:30 PM in Building 2, Room 349.


Massachusetts Institute of Technology Department of Mathematics
Cambridge,MA 02139