Colloquium: Dr. Alexander Wagner

Department of Physics

North Dakota State University

Fargo, ND

Evaporation of Colloidal Suspensions

When a drop of colloidal suspension evaporates we usually find that a large portion of the colloids is deposited at the edges of the drop, which we are all familiar with because this is also known as the coffee ring effect. The underlying reason for this deposition is that the edges of the drop is pinned and this causes a hydrodynamic flow of material towards the edges which drags the small particles towards the edge of the drop.

A separate phenomenon is that suspended particles typically like to aggregate at an interface. The timescale for this is related to the time it takes a particle undergoing Brownian motion to reach the interface. Once the interface is coated with particles, this will reduce the evaporation from the covered surface. This raises the possibility that a particle suspension where a noticeable fraction of the surface is covered with particles near the edges will show a much reduced hydrodynamic flow and thereby a reduction of deposition of particles at the rim of the drop.

In this talk we will analyze the effects of evaporation and present our analytical predictions of the difference in evaporation rates as a function of the covering of the surface with particles and validate our analytical predictions with numerical simulations and speculate on the feasibility of utilizing this mechanism to generate (more) uniform particle distributions as a result of the evaporation process.