la5b01138_si_001.pdf (5.57 MB)
Decoupling of Mass Transport Mechanisms in the Stagewise Swelling of Multiple Emulsions
journal contribution
posted on 2015-05-19, 00:00 authored by Jana Bahtz, Deniz Z. Gunes, Eric Hughes, Lea Pokorny, Francesca Riesch, Axel Syrbe, Peter Fischer, Erich J. WindhabThis contribution reports on the
mass transport kinetics of osmotically
imbalanced water-in-oil-in-water (W1/O/W2) emulsions. Although frequently
studied, the control of mass transport in W1/O/W2 emulsions is still
challenging. We describe a microfluidics-based method to systematically
investigate the impact of various parameters, such as osmotic pressure
gradient, oil phase viscosity, and temperature, on the mass transport.
Combined with optical microscopy analyses, we are able to identify
and decouple the various mechanisms, which control the dynamic droplet
size of osmotically imbalanced W1/O/W2 emulsions. So, swelling kinetics
curves with a very high accuracy are generated, giving a basis for
quantifying the kinetic aspects of transport. Two sequential swelling
stages, i.e., a lag stage and an osmotically dominated stage, with
different mass transport mechanisms are identified. The determination
and interpretation of the different stages are the prerequisite to
control and trigger the swelling process. We show evidence that both
mass transport mechanisms can be decoupled from each other. Rapid
osmotically driven mass transport only takes place in a second stage
induced by structural changes of the oil phase in a lag stage, which
allow an osmotic exchange between both water phases. Such structural
changes are strongly facilitated by spontaneous water-in-oil emulsification.
The duration of the lag stage is pressure-independent but significantly
influenced by the oil phase viscosity and temperature.