Effect of a controlled air flow on a viscoelastic filament

Recent health crises have highlighted the need to better assess and prevent the risks associated with the release of potentially infectious particles into the air during human expiratory events, such as breathing, talking, sneezing, and coughing. Some of these particles originate from the stretching in the mouth of a volume of saliva, which leads to the formation of a beads-on-a-string (BOAS) structure. This structure is characteristic of the behavior of viscoelastic fluids when subjected to an elongational flow.

To simulate and analyze the effect of an expiratory event on a viscoelastic filament, an experimental bench was set up to stretch a sample of polymer solution and destabilize the BOAS structure formed, by a controlled air flow. The setup is fully automated, allowing statistical measurements on a large number of samples. The dynamics of the filament as well as the released drops are observed by multi-exposure and dual-wavelength inline digital holography. This method allows us to measure the size, position and velocity of the particles in a 3D volume.

The experiment presented here serves as a simple model for the atomization induced on a viscoelastic filament during a human expiratory event.