Synthesis of Monodisperse Microparticles from Non-Newtonian Polymer Solutions

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Original entry by Hyerim Hwang, AP 225, Fall 2011.

Reference

Adam R. Abate, Mikhail Kutsovsky, Sebastian Seiffert, Maike Windbergs, Luis F. V. Pinto, Assaf Rotem, Andrew S. Utada, and David Weitz, "Synthesis of Monodisperse Microparticles from Non-Newtonian Polymer Solutions with Microfluidic Devices", Adv. Mater. 2011 23, 1757-1760

Keywords

Multiple emulsions, Microchannels, Poly(dimethysiloxane)

Introduction

Figure 1. Schematic of a double emulsion drop maker consisting of two cross-channel junctions in series.
Figure 2. Emulsification of a viscoelastic polymer solution failing (left), using direct single emulsification, and succeeding (right), using one-step double emulsification.

This study presents a technique to create monodisperse particles from polymer solutions which are incompatible with synthesis in microfluidic chips. They demonstrates the use of the microfluidic technique to form particles from fluids that have been incompatible with microfluidic synthesis. This can be achieved using one-step emulsification to form emulsion droplets with narrow distribution from several classes of difficult-to-emulsify fluids, then the droplets are polymerized and finally formed particles of the desired materials.

Figure 3. Demonstration of failing and succeeding emulsification using single and one-step double emulsification. (A) Emulsification of a viscoelastic semidilute polymer solution and resultant particles below. (B) Emulsification of a viscous and viscoelastic polymer solution and the resultant particles below. (C) Emulsification of a low interfacial tension and viscous lipid melt and the resultant particles below.

Results

As shown in Figure 1, the microfluidic devices composed of two cross-channel junctions were used to form double emulsions and synthesize particles. The devices were fabricated using multilayer photolithography to create multiheight channels. The polymer fluid is injected into the central inlet of the first junction and surrounded by a chaperoning fluid injected into the two side inlets. A stable jet of the polymer fluid within the chaperone fluid is generated and these fluids then enter the second junction. In this experiment, they used non-Newtonian fluids of which conditions are difficult to achieve monodisperse dripping. As shown in left part of images of Figure 2, the extensional viscosity of the fluids resists the pinching needed to from drops, leading to the formation of long jets that break into drops of uncontrolled due to the instability. To overcome the limitation on control emulsifying,they used a second, coaxial Newtonian fluid.

Discussion

One-step double emulsification had several advantages when making particles. Yield of the particle formation is equal to the drop production rate of which maximum rate is limited by the dripping-to-jetting transition. The transition value depends on the fluid properties, mass, viscosity, and interfacial tension. Plus, One-step double emulsification enables formation of monodisperse particles from fluids that cannot be used in droplet-based microfluidics, including viscous or viscoelastic polymer solutions or low interfacial tension polymer melts. This research suggests that synthesis method for making new kinds of particles which are made from waxy lipids and semidilute entangled polymer solutions.