Paper Number
IR24
Session
Interfacial Rheology
Title
Interfacial compressional rheology of saliva droplets in the context of aerosol evaporation
Presentation Date and Time
October 11, 2022 (Tuesday) 1:30
Track / Room
Track 5 / Sheraton 2
Authors
- Rodriguez-Hakim, Mariana (ETH Zürich, Department of Materials)
- Novaes Silva, Maria C. (ETH Zürich, Department of Materials)
- Vermant, Jan (ETH Zürich, Materials)
Author and Affiliation Lines
Mariana Rodriguez-Hakim, Maria C. Novaes Silva and Jan Vermant
Department of Materials, ETH Zürich, Zürich, Switzerland
Speaker / Presenter
Rodriguez-Hakim, Mariana
Keywords
experimental methods; bio-fluids; interfacial rheology; polymer solutions; rheometry techniques
Text of Abstract
Some contagious diseases, such as COVID-19, spread primarily though the airborne transmission of aerosols and droplets [1]. The largest of these particles (i.e. droplets, >100um) settle rapidly towards the ground and subsequently deposit themselves on solid surfaces. The smallest particles (i.e. aerosols, <100um) remain suspended in the air, where they fully evaporate until a solid-like nucleus remains. Thus, understanding the factors that dictate the lifetime of salivary droplets and aerosols is necessary to inform effective strategies for the mitigation of respiratory contagious diseases. Less than 1% of the total salivary mass is composed of dissolved compounds such as salts, enzymes, proteins, and mucins. The presence of solutes can extend the lifetime of salivary droplets when compared to pure water droplets by reducing solvent diffusivity, inducing gelation, and lowering water’s chemical activity, all of which reduce the driving force for evaporation [2,3]. Aside from these bulk effects, the adsorption of surface-active compounds and the subsequent buildup of a rheologically-active interface can also inhibit droplet drying. We investigate the role of interfacial rheology on the evaporation dynamics of salivary droplets using a pendant drop / rising bubble setup coupled to a pressure transducer, which is necessary to determine the anisotropic stress distribution on viscoelastic interfaces. We perform two types of experiments: (1) step-strain compression experiments of an air bubble suspended inside a saliva solution, to investigate the influence of aging time, compression rate, and interface curvature on the mechanical properties of the interface and its resistance to compression, and (2) evaporation experiments on a saliva droplet suspended in air, to monitor the kinematics of evaporation and the evolution of the Laplace pressure in relation to pure water droplets. [1] Bourouiba, L., Annu. Rev. Biomed. Eng, 2016. [2] Salmon, J. B., et al., Phys. Rev. E, 2017. [3] Basu, S., et al., Phys. Fluids, 2020.