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C02 - Interface dynamics: Bridging stochastic and hydrodynamic descriptions

Head(s): Prof. Dr. Roland Netz (FU Berlin), Prof. Dr. Marita Thomas (FU Berlin)
former head(s): Dr. Robert Patterson (WIAS)
Project member(s): Sina Zendehroud, Julian Kern
Participating institution(s): FU Berlin, WIAS

Project Summary

In the preceding two funding periods (FPs), we gained considerable understanding of the hydrodynamics and thermodynamics of interfaces that are coupled to bulk phases and developed methods to bridge the short-time behavior (affected by microscopic interactions and properties) with the long-time behavior (affected by conservation laws). A typical example for this class of problems, which is very timely in light of the present Corona pandemic, is the airborne infection pathway, which involves the evaporation and sedimentation of solutecontaining aerosols and thereby is dominated by entangled bulk-interface multiscale dynamics. In the last FP, the coupled transport equations of water vapor and heat around an evaporating droplet were analytically solved and it was shown that evaporation significantly decreases the mass of sedimenting droplets and therefore increases their sedimentation time, which in turn increases the viral air load in case an infected person produces droplets by speaking, coughing or breathing. Solute concentration gradients inside the droplet, which can lead to crust formation at the droplet surface, were not considered. In the next FP, the coupled diffusion of solutes and water inside a droplet, the evaporation and condensation dynamics at the interface and the water vapor and heat diffusion outside the aerosol droplet shall be studied for a single and for multiple droplets. A suitably chosen free-energy functional will account for water vapor-liquid coexistence and possible solute-solution phase separation inside the droplet. The effects of flow advection on sedimentation and diffusion will be studied by scaling methods. The effects of aerosol coalescence and breakup on the aerosol size distribution will be studied by quasi-stationary distribution approaches. Viscoelastic and diffusional properties in the gel-like crust will be studied. The dependence of the diffusion constant of water and solutes on the water and solute concentration is crucial and will be determined using lattice models, from which also density-fluctuation effects on the diffusivity and the interfacial condensation and evaporation rate coefficients will be derived. Molecular-dynamics simulations of the water liquid-vapor interface will be used to determine water evaporation and condensation rates.

Publications C02