Interfacial flow tracing for gas-liquid mass transfer processes

Objetivo

Seeing is believing - but until now, flow at gas-liquid interfaces has remained invisible. While Particle Image Velocimetry (PIV) has revolutionized the study of bulk flow, no equivalent technique exists for interfaces. Conventional tracer particles accumulate at the interface and disturb the flow, leaving hydrodynamics and mass transfer poorly understood. This is a critical gap, as the behaviour at interfaces heavily impacts mass transfer in chemical, bioprocess, and environmental systems. Surface-active molecules, i.e. surfactants, strongly change interfacial flow and hence mass transfer by factors of two to five.

This project will develop two complementary strategies enabling interfacial flow tracing.

For measurements in the field or in-line, particles are needed that are easy to detect. For that, I will design self-functionalizing Janus macrotracers: floating hollow glass spheres of sub-mm size that autonomously form hydrophobic caps during vapor-phase polymerization, precisely defining their interfacial anchoring. Their performance will be tested under alternating gravity in parabolic flights to identify buoyancy-neutral, minimally invasive designs. These tracers will then reveal whether interface-driven convection contributes to the extraordinary gas-exchange efficiency of the invasive aquatic plant Salvinia molesta, both in controlled experiments and in natural ponds.

For high-resolution studies, I will optimize fluorescent microtracers, stabilized by electrostatic repulsion to prevent agglomeration. They will allow to quantify interfacial flow and gas transfer at rising bubbles under controlled surfactant conditions, disentangling the coupled effects of Marangoni stresses and interfacial resistance. The resulting knowledge will not only close a long-standing gap in interfacial hydrodynamics and mass transfer. It also can be directly used to restrict the growth of Salvinia by biocompatible surfactants which most effectively reduce gas exchange.