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Dynamics of aqueous droplets at the interface of co-flowing immiscible oils in a microchannel K S Jayaprakash, Utsab Banerjee, and Ashis K. Sen Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b04116 • Publication Date (Web): 26 Jan 2016 Downloaded from http://pubs.acs.org on January 30, 2016

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Dynamics of aqueous droplets at the interface of co-flowing immiscible oils in a microchannel K. S. Jayaprakash, U. Banerjee and A. K. Sen* Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai-600036, India * Author to whom correspondence should be addressed. Email: [email protected] Abstract We report the dynamics of aqueous droplets of different size and viscosity at the interface of co-flowing stream of immiscible oils (i.e. primary and secondary continuous phases) in a microchannel, at low Re. The lateral migration of droplets introduced into the primary continuous phase towards the interface and subsequent selective migration of droplets across the interface into the secondary continuous phase is investigated. The interplay between the competing non-inertial lift and interfacial tension forces, which govern the migration of the droplets, is presented and discussed. The velocity and strain rate profiles, and interface location, which are critical for calculating the lift force and migration behaviour of droplets are presented. The trajectories of droplets of different size and viscosity in the primary continuous phase are obtained for different interface locations. During interfacial migration, the deformation behaviour of droplets of different viscosity is studied. Finally, sorting of droplets based on size contrast is demonstrated and sorting efficiency is found. A new paradigm of migration and sorting of droplets is reported, which could find importance in chemical and biological applications. 1. Introduction Dynamics of droplets in the presence of fluid-fluid interface has acquired immense attention due to its various applications in chemistry, materials and biological assays1,2. Motion of bubbles, droplets and rigid spheres in a low Reynolds number flow (Rekcr (i.e. a critical force ratio), the droplets completely migrate across the interface whereas for k kcr. The proposed technique can be further used for size based sorting of droplets and droplet encapsulated cells at fluid-fluid interface. Supporting Information Simple analytical model for high aspect ratio devices to predict velocity profile, strain rate profile and interface location. Comparison of flow profiles of the systems with and without droplet - 3D numerical simulation. Comparison of interface location - analytical model, 3D numerical simulation and experiment. This information is available free of charge via the Internet at http://pubs.acs.org. Author information Corresponding Author *E-mail: [email protected] Acknowledgements The authors would like to thank the Department of Science & Technology (DST) and Department of Biotechnology (DBT), India for providing the financial support for the project. We also acknowledge CNNP, IIT Madras for supporting the photolithography work. The authors thank NCCRD, IIT Madras, for extending support for chemical property measurements.

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