NSF GOALI Project: Aerosol Droplets Migration in Fibrous Media

Determining the force required to detach a droplet from a fiber or from an assembly of fibers is of great importance to many applications. A novel technique is developed to measure this force experimentally by using ferrofluid droplets in a magnetic field. This method allows one to study the capillarity of the droplet–fiber system in an isolated environment.

Video 1: Magnetic Detachment of a Ferrofluid Droplet from a Fiber

Video 2: Magnetic Detachment of a Ferrofluid Droplet from Crossing Fibers

 

Combining the results of numerical simulation and ferrofluid experiments, we developed a universal equation that can be used for droplet detachment force prediction without the need for running an experiment or conducting a computer simulation. This equation is valid for any droplet–fiber combinations with a YLCA greater than about 20 degrees.

  

We also developed a method to use a magnetic force to measure the force of detachment for nonmagnetic droplets from a fiber for the first time. This is accomplished by adding a small amount of a ferrofluid to the original nonmagnetic droplet to create a compound droplet with the ferrofluid nesting inside or cloaking the nonmagnetic droplet. 

 

Video 3: Magnetic Detachment of a Non-Magnetic Oil Droplet from a Fiber

Video 4: Magnetic Detachment of a Non-Magnetic Water Droplet from a Fiber

 

Studying the mechanical forces acting on a liquid bridge between dissimilar fibers in parallel and orthogonal configurations, we formulated the contribution of the geometrical and wetting properties of the fibers competing for the droplet that results from the liquid bridge detachment. We also developed an easy-to-use mathematical expression to predict the fate of this droplet.

Video 5: Liquid Bridge - Parallel Fibers

Video 6: Liquid Bridge - Orthogonal Fibers