title: Spontaneous transfer of droplets across microfluidic laminar interfaces.
abstract: The precise manipulation of droplets in microfluidics has revolutionized a myriad of drop-based technologies, such as multiple emulsion preparation, drop fusion, drop fission, drop trapping and drop sorting, which offer promising new opportunities in chemical and biological fields. In this paper, we present an interfacial-tension-directed strategy for the migration of droplets across liquid-liquid laminar streams. By carefully controlling the interfacial energies, droplets of phase A are able to pass across the laminar interfaces of two immiscible fluids from phase B to phase C due to a positive spreading coefficient of phase C over phase B. To demonstrate this, we successfully perform the transfer of water droplets across an oil-oil laminar interface and the transfer of oil droplets across an oil-water laminar interface. The whole transfer process is spontaneous and only takes about 50 ms. We find that the fluid dynamics have an impact on the transfer processes. Only if the flowrate ratios are well matched will the droplets pass through the laminar interface successfully. This interfacial-tension-directed transfer of droplets provides a versatile procedure to make new structures and control microreactions as exemplified by the fabrication of giant unilamellar vesicles and cell-laden microgels.
authors.affiliation: School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China. chuly@scu.edu.cn.
authors.forename: Nan-Nan
authors.identifier: 0000-0001-7183-7973
authors.initials: NN
authors.lastname: Deng
authors.affiliation: School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China. chuly@scu.edu.cn and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China. chuly@scu.edu.cn and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
authors.forename: Xiao-Jie
authors.initials: XJ
authors.lastname: Ju
authors.affiliation: School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China. chuly@scu.edu.cn and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Xie
authors.affiliation: School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, China. chuly@scu.edu.cn and State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, China and Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing, Jiangsu 211816, China.
authors.forename: Liang-Yin
authors.initials: LY
authors.lastname: Chu