Droplet microfluidics for studying surfactant-rich interfaces
found in aerosols, emulsions and foams
Cari Dutcher,
University
of Minnesota, Minneapolis, USA
Abstract
The presence of
droplets suspended in a liquid or gas is known to play an essential role in
fields ranging from materials to atmospheric science. Often, the dispersed phase is stabilized by
surface active compounds and surfactants, resulting in complex chemical composition
and material properties at the fluid-fluid interface. In this talk, recent advancements in use of
microscale flow fields will be highlighted for measuring properties of aqueous
multiphase, interface-rich systems. Systems studied will include atmospheric
aerosol droplets and liquid-liquid emulsions. Microfluidic contractions, traps,
and wells are used to measure surface-bulk partitioning and
temperature-dependent liquid-liquid phase separation of aqueous droplets,
towards better understanding of suspensions of aerosol droplets in our atmosphere.
Advanced measurements of droplet shape deformations and coalescence will also
be presented for both water-in-fuel and oil-in-water emulsions, for improved
treatment and separation of emulsions. Dynamic interfacial tensions
measurements were performed using a microfluidic tensiometer, demonstrating a
dependence on if the surfactant approaches the interface from inside
(dispersed) versus outside (continuous), implying phase dependent surfactant
transport to curved interfaces at the microscale. Droplet coalescence and film
drainage experiments are also performed in a microfluidic Stokes trap across a
range of viscosity ratios and surfactant concentrations. Results are used to
explore the influence of interfacial mobility and Marangoni stresses on film
stability with soluble surfactants.
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