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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 34: Wetting, Droplets and Microfluidics I (joint session DY/CPP)

CPP 34.5: Vortrag

Mittwoch, 29. März 2023, 11:00–11:15, ZEU 148

Instability of Active Fluid Interfaces in Microfluidics — •Kuntal Patel and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Berlin, Germany

In recent years, microfluidic lab-on-a-chip devices have emerged as efficient miniaturized flow control platforms. Specifically, the advent of nonlinear microfluidics has opened a new avenue for chemical and biomedical applications such as droplet formation and cell sorting. In this work, we integrate ideas from active matter into a microfluidic setting and try to understand the mechanism and practical relevance of resulting microfluidic flows.

The present setup consists of two vertically stacked fluid layers with identical densities but different viscosities, sandwiched between the walls of a microfluidic channel. The interface separating both fluids is initialized with uniformly distributed active particles, which induce force dipoles that generate flows in the adjacent fluids.

Our hybrid lattice-Boltzmann finite-difference simulations reveal that when we perturb the fluid interface covered with extensile force dipoles ↑/↓, it eventually returns to its flat state irrespective of the strength of interfacial tension. In contrast, contractile force dipoles ↓/↑ lead to activity-driven interfacial instability. However, such instability emerges only above a critical value of the activity, which is proportional to the interfacial tension. We further examine the mechanism of instability and quantify the effect of viscosity contrast and perturbation wavelength. Lastly, we demonstrate the systematic formation of droplets using the present interfacial instability.