Two phase microfluidics with inviscid drops: Effects of total flow rate and delayed surfactant addition
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Two phase microuidics with inviscid drops: Effects of total ow rate and delayed surfactant addition Fabian Friess, Andreas Lendlein and Christian Wischke MRS Advances / FirstView Article / July 2016, pp 1 - 6 DOI: 10.1557/adv.2016.493, Published online: 04 July 2016
Link to this article: http://journals.cambridge.org/abstract_S205985211600493X How to cite this article: Fabian Friess, Andreas Lendlein and Christian Wischke Two phase microuidics with inviscid drops: Effects of total ow rate and delayed surfactant addition. MRS Advances, Available on CJO 2016 doi:10.1557/adv.2016.493 Request Permissions : Click here
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MRS Advances © 2016 Materials Research Society DOI: 10.1557/adv.2016.493
Two phase microfluidics with inviscid drops: Effects of total flow rate and delayed surfactant addition Fabian Friess1,3, Andreas Lendlein1,2,3, Christian Wischke1,2 1 Institute of Biomaterial Science and Berlin-Brandenburg Center for Regenerative Therapies, Kantstr. 55, 14513 Teltow, Germany 2 Helmholtz Virtual Institute , Multifunctional Biomaterials for Medicine, Kantstr. 55, 14513 Teltow, Germany 3 Institute of Chemistry, University of Potsdam, 14469 Potsdam, Germany ABSTRACT The microfluidic production of droplets is a well controllable process, which allows templating small spherical containers that can subsequently be transferred into uniformly sized polymer microgel particles by a crosslinking reaction. Recently, the per-channel production rate of N-isopropylacrylamide (NIPAAm) droplets (w-phase) dispersed in a low-viscosity fluorocarbon oil (o-phase) could be increased by a delayed surfactant addition, while maintaining the advantageous dripping regime. Here it should be evaluated, if delayed surfactant addition can be applied to enhance droplet production also for high viscosity continuous phases, which is associated with a change to an inviscid drop scenario compared to the previously used setting of viscous drops. It could be illustrated that the concept of delayed surfactant addition holds true also for viscous continuous phases and allows ~8 fold increased flow rates in the dripping regime. Surprisingly, the droplet size increased at higher total flow rate with constant flow rate ratios of w- and o-phases, which is discussed in the light of viscous dissipation, microchannel bulging and viscosity of the continuous phase. More rigid microchannels such as from glass may allow further exploring this phenomenon in the future. INTRODUCTION Microfluidic preparation allows obtaining uniformly sized droplets in a process driven by interfacial instabilities in a flow field rather than by external actuation. Using a flow focusing geometry, a stream of the inner phase 1 is contacted and squeezed by the continuous phase 2, resulting in thinning and eventually break-up of the thread of phase 1 [1]. This process is
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