A descriptive force‐balance model for droplet formation at microfluidic Y‐junctions

Abstract

In a previous article, we studied the basics of emulsification in microfluidic Y-junctions, however, without considering the effect of viscosity of the disperse phase. As it is known from investigations on many different microstructures that viscosity and viscosity ratio are governing parameters for droplet size, we here investigate whether this is also the case for microfluidic Y-junctions and do so for a wide range of process conditions. The investigated Y-junctions have a width of 19.9 or 12.8 lm and a depth of 5.0 lm, and the formed monodisperse droplets (CV \ 1%) are between 3 and 20 lm. We varied the disperse-phase viscosity using different oils (1-105 mPa s), and continuous-phase viscosity using glycerol-water and ethanol-water mixtures (1.0-6.2 mPa s), which corresponds to disperse-to-continuous-phase viscosity ratios from 0.4 to 105.0. Through the variation of the liquids, also a range in interfacial tensions (12-55 mN m À1) is assessed. The disperse-phase flow rate is varied from 0.039 to 18.0 lL h À1 , the continuous-phase flow rate from 1.39 lL h À1 to 0.41 mL h À1, and this corresponds to flow rate ratios from 1.1 Â 10 À3 to 0.14, which is once again based on wide range of conditions. For all these conditions, in which droplets are formed in the dripping and jetting regime, the droplet size could be described with a model based on the existing force-balance model, but now extended to incorporate the cross-sectional area of the droplet and the resistance with the wall. Surprisingly enough, it was found that the droplet size is not influenced by the disperse-phase viscosity, or the viscosity ratio, but it is dominated by the resistance with the wall and the continuous-phase properties. Because of this, emulsification with Y-junctions is intrinsically simpler than any other shear-based method as droplet size is only determined by the continuous phase.

Chiral Photonic Crystalline Microcapsules with Strict Monodispersity, Ultrahigh Thermal Stability, and Reversible Response

“…It is worth noting that C V s of PWPCMs in this work are all below 1% (see Figure S3). The reason for this sufficiently small size variation of PWPCMs can be ascribed to the simplified microfluidic setup only with single emulsification 31 and the distinctive immiscibility between the dispersed phase (organic CNLCs) and the continuous phase (5 wt % SDS aqueous solution).…”

The Importance of Interfacial Tension in Emulsification: Connecting Scaling Relations Used in Large Scale Preparation with Microfluidic Measurement Methods

“…Droplet growth consists of two stages: first the droplet liquid is pushed into the main channel, and second the neck starts forming and the droplet grows while feeding from the neck. The second stage has less effect on the total droplet volume than reported for T-junctions [56,72]. This makes the Y-junction a more valid option for dynamic interfacial tension measurements.…”

Solvodynamic Printing As A High Resolution Printing Method

“…The flow focusing effect is easily controlled by the relative pump rates of the two fluids 24 . By increasing the carrier solvent pump rate ( q c ) relative to the ink pump rate ( q i ), the shear force exerted by the carrier solvent stream on the ink stream increases and deforms it to flow within a narrower region.…”