Microfluidic Generation of High-Viscosity Droplets by Surface-Controlled Breakup of Segment Flow

Abstract

Fluids containing high concentration polymers, sols, nanoparticles, etc., usually have high viscosities, and high-viscosity fluids are difficult to be encapsulated into uniform droplets. Here we report a surface-controlled breakup method to generate droplets directly from various aqueous and nonaqueous fluids with viscosities of 1.0 to 11.9 Pa s and a dispersed-to-continuous viscosity ratio up to 1000, whereas the volume fraction of droplets up to 50% can be achieved. It provides a straightforward method to encapsulate high viscosity fluids, in a well-controlled manner in the rapid developing droplet-based applications, including materials synthesis, drug delivery, cell assay, bioengineering, etc.

Fabricating High-viscosity Droplets using Microfluidic Capillary Device with Phase-inversion Co-flow Structure

“…Therefore, the treatment of surface wettability of the exit of the middle tube is a critical step for the phase-inversion method, where the exit of the middle tube must be treated to be wetted by the low-viscosity phase to induce the phase inversion. In addition, there is a critical flow rate above which the elongated oil droplets will not breakup and the phase inversion will subsequently not occur 24 . When the oil droplets cannot breakup at the hydrophobic exit, lower the flow rates of both fluids with a fixed flow rate ratio, until the elongated oil droplets break and induce phase inversion.…”

“…To generate monodisperse droplets directly from a high-viscosity fluid with η > 1 Pa•s, surface-controlled phase-inversion methods have been investigated 24 . As the generation of low-viscosity droplets is much easier than that of high-viscosity droplets 12 , elongated low-viscosity droplets in a high-viscosity continuous phase are first generated using a typical co-flow structure, and then are broken up due to the change of surface wettability downstream of the co-flow structure.…”

“…The released low-viscosity fluid inversely encapsulates the downstream high-viscosity fluid into droplets so that phase inversion is completed. According to the phase inversion mechanism, monodisperse high-viscosity droplets can be generated based on a typical co-flow device, while the exit of the co-flow device is treated to be wetted by the low-viscosity fluid, and then connected to a wider tube 24,25 .…”

“…As the error bars of the standard deviation are smaller than the symbol used in the plot, they are not shown here. Reprinted with permission from[24]. Copyright 2017 American Chemical Society.…”

Size‐Dependent Phase Separation in Emulsion Droplets

“…[1,2] Hydrogels with complex structures such as core-shell, hollow,J anus, and multilayered structuresh ave many applications in cosmetics, [3,4] drug delivery, [5,6] oil recovery, [7][8][9] and cell encapsulation. [1,10] Compared with previous microfluidics methods for creatingd ouble or higher order emulsions, whichr elied on complicated microfluidic devices with accurate surface wettability that is tedious and difficult to construct, [11][12][13][14] the phase separationt echnique promises to be af acile and reliable way to produce monodisperse, high-order emulsions with complex structures on the order of one to hundreds of micrometers. [15][16][17][18] Phase separation can also be regarded as a" smart" process, because of it happens spontaneously if the original conditions, such as concentration and temperature,a re met.…”