Dynamics of polydisperse multiple emulsions in microfluidic channels

Abstract

Multiple emulsions are a class of soft fluid in which small drops are immersed within a larger one and stabilized over long periods of time by a surfactant. We recently showed that, if a monodisperse multiple emulsion is subject to a pressure-driven flow, a wide variety of non-equilibrium steady states emerges at late times, whose dynamics relies on a complex interplay between hydrodynamic interactions and multi-body collisions among internal drops. In this work we use lattice Boltzmann simulations to study the dynamics of polydisperse double emulsions driven by a Poiseuille flow within a microfluidic channel. Our results show that their behavior is critically affected by multiple factors, such as initial position, polydispersity index and area fraction occupied within the emulsion. While at low area fraction inner drops may exhibit either a periodic rotational motion (at low polydispersity) or arrange into non-motile configurations (at high polydispersity) located far from each other, at larger values of area fraction they remain in tight contact and move unidirectionally. This decisively conditions their close-range dynamics, quantitatively assessed through a time-efficiency-like factor. Simulations also unveil the key role played by the capsule, whose shape changes can favor the formation of a selected number of non-equilibrium states in which both motile and non-motile configurations are found.

Spontaneous motion of a passive fluid droplet in an active microchannel

“…Its physics is described using a combination of phase field modeling and active liquid crystal hydrodynamics, an approach already adopted in previous works. 32,[53][54][55][56] More specifically, we consider two scalar phase fields f i (r, t) (i = 1, 2) accounting for the density of the droplet and the layer, a polar field P(r, t) capturing the mesoscale orientation of the active material confined within the layer, the density r(r, t) of the fluid and its global velocity v(r, t). The presence of a further active component (such an extensile layer on the top wall) would require the inclusion of additional scalar and polar fields.…”