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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Wetting, Superamphiophobicity, Micro- and Nanofluidics I

CPP 18.12: Vortrag

Dienstag, 1. April 2014, 12:30–12:45, ZEU 222

Adsorption kinetics of surfactants in droplet-based microfluidics using pH measurements at the micron scale — •Birte Riechers, Quentin Brosseau, Florine Maes, and Jean-Christophe Baret — Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany

Interfaces are omnipresent in biological and man-made systems like emulsions and foams. In biology, interfaces are particularly important for encapsulation and compartmentalization [Theberge et al. Angewandte 2010]. They can be stabilized using surfactants which, upon adsorption, influence properties of the interface (e.g. surface tension and interfacial rheology) and of the bulk phases (e.g. pH) [Baret LabChip 2012]. The determination of interfacial properties (equilibrium, adsorption kinetics to the interface) at the scale of the emulsion droplets is crucial for their use in biotechnological applications and solves a fundamental problem.

We present a new method for the determination of the dynamics of surfactant adsorption and surfactant coverage at the interface using droplet-based microfluidics. Water-in-oil emulsions are studied using a fluorescence setup. In combination with a pH sensitive dye inside the droplets, adsorption kinetics of an acidic surfactant are monitored. As the surfactant adsorbs to the interface and deprotonates, it changes the pH inside the dispersed phase giving rise to adsorption and equilibration properties. We show the effectiveness of surfactant adsorption in droplet-based microfluidics and unravel the kinetics of adsorption at the micron scale with a millisecond time-resolution.