Microfluidic generation of uniform water droplets using gas as the continuous phase

Kunqiang Jiang; Annie Xi Lu; Panagiotis Dimitrakopoulos; Don L DeVoe; Srinivasa R Raghavan

doi:10.1016/j.jcis.2015.02.023

Microfluidic generation of uniform water droplets using gas as the continuous phase

J Colloid Interface Sci. 2015 Jun 15:448:275-9. doi: 10.1016/j.jcis.2015.02.023. Epub 2015 Feb 13.

Authors

Kunqiang Jiang¹, Annie Xi Lu², Panagiotis Dimitrakopoulos², Don L DeVoe³, Srinivasa R Raghavan⁴

Affiliations

¹ Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, United States.
² Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742, United States.
³ Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, United States. Electronic address: ddev@umd.edu.
⁴ Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, United States; Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742, United States. Electronic address: sraghava@umd.edu.

PMID: 25744861
DOI: 10.1016/j.jcis.2015.02.023

Abstract

Microfluidic schemes for forming uniform aqueous microdroplets usually rely on contacting the aqueous liquid (dispersed phase) with an immiscible oil (continuous phase). Here, we demonstrate that the oil can be substituted with gas (nitrogen or air) while still retaining the ability to generate discrete and uniform aqueous droplets. Our device is a capillary co-flow system, with the inner flow of water getting periodically dispersed into droplets by the external flow of gas. The droplet size and different formation modes can be tuned by varying the liquid and gas flow rates. Importantly, we identify the range of conditions that correspond to the "dripping mode", i.e., where discrete droplets are consistently generated with no satellites. We believe this is a significant development that will be beneficial for chemical and biological applications requiring clean and contaminant-free droplets, including DNA amplification, drug encapsulation, and microfluidic cell culture.

Keywords: Dripping mode; Droplets; Microfluidics.