Drop formation in microfluidic cross-junction: jetting to dripping to jetting transition

Nina M Kovalchuk,Daniele Vigolo,Masanobu Sagisaka,Kasparas Steponavicius,Mark J H Simmons

doi:10.1007/s10404-019-2269-z

Nina M Kovalchuk, Daniele Vigolo + Show 3 more

Open Access

https://doi.org/10.1007/s10404-019-2269-z

Copy DOI

Abstract

The regimes of drop generation were studied in a Dolomite microfluidic device which combined both hydrodynamic and geometrical flow focusing over a broad range of flow rates. A series of aqueous dispersed phases were used with a viscosity ratio between continuous and dispersed phases of close to unity. Surfactants were added to alter the interfacial tension. It was shown that the transition from dripping to jetting is well described by the capillary numbers of both the dispersed and continuous phases. Only the jetting regime was observed if the capillary number of the dispersed phase was above a critical value, whereas at smaller values of this parameter a jetting → dripping → jetting transition was observed by increasing the capillary number of the continuous phase. The analysis performed has shown that the conditions for a dripping to jetting transition at moderate and large values of the capillary number of the continuous phase can be predicted theoretically by comparison of the characteristic time scales for drop pinch-off and jet growth, whereas the transition at small values cannot. It is suggested that this transition is geometry mediated and is a result of the interplay of jet confinement in the focusing part and a decrease of confinement following entry into the main channel. The flow fields inside the jet of the dispersed phase were qualitatively different for small and large values of the capillary number of the continuous phase revealing the relative contribution of the dispersed phase flow in jet formation. The volume of the drops formed in the jetting regime increased as a power law function of the flow rate ratio of the dispersed to continuous phase, independent of the interfacial tension.

Highlights

Drop microfluidics is a rapidly developing area enabling considerable scale reduction for synthetic and analytical processes by manipulation of drops with volumes in the nanoand picolitre range (DeMello 2006; Whitesides 2006; Marre and Jensen 2010; Rakszewska et al 2014; Holtze et al 2017; Vladisavljević et al 2017)
Flow focusing has become the most popular method of drop production in flow microfluidics because it allows the formation of highly monodisperse drops over a wide size range using devices which are designed by soft lithography
There is a certain shift of the transition lines to larger Cac and smaller Cad with a decrease of the interfacial tension, Fig. 2a shows that the transition from dripping to jetting can be described reasonably well using the capillary numbers of the dispersed and continuous phases as parameters

Summary

Introduction

Drop microfluidics is a rapidly developing area enabling considerable scale reduction for synthetic and analytical processes by manipulation of drops with volumes in the nanoand picolitre range (DeMello 2006; Whitesides 2006; Marre and Jensen 2010; Rakszewska et al 2014; Holtze et al 2017; Vladisavljević et al 2017). Flow focusing has become the most popular method of drop production in flow microfluidics because it allows the formation of highly monodisperse drops over a wide size range using devices which are designed by soft lithography. Flow focusing can be achieved in various ways: by interaction of the flows of dispersed and continuous phases in a cross-junction (hydrodynamic focusing) (Cubaud and Mason 2008; Carrier et al 2015; Chen et al 2015), by passing coflowing dispersed and continuous phases through an orifice (geometrical focusing) (Anna et al 2003; Garstecki et al 2005; Lee et al 2009), by combination of hydrodynamic and geometrical focusing Flow focusing can be achieved in various ways: by interaction of the flows of dispersed and continuous phases in a cross-junction (hydrodynamic focusing) (Cubaud and Mason 2008; Carrier et al 2015; Chen et al 2015), by passing coflowing dispersed and continuous phases through an orifice (geometrical focusing) (Anna et al 2003; Garstecki et al 2005; Lee et al 2009), by combination of hydrodynamic and geometrical focusing (Ward et al 2010; Kovalchuk et al. Vol.:(0123456789)

Methods

Results

Conclusion