Surfactants in droplet-based microfluidics

Abstract

Surfactants are an essential part of the droplet-based microfluidic technology. They are involved in the stabilization of droplet interfaces, in the biocompatibility of the system and in the process of molecular exchange between droplets. The recent progress in the applications of droplet-based microfluidics has been made possible by the development of new molecules and their characterizations. In this review, the role of the surfactant in droplet-based microfluidics is discussed with an emphasis on the new molecules developed specifically to overcome the limitations of 'standard' surfactants. Emulsion properties and interfacial rheology of surfactant-laden layers strongly determine the overall capabilities of the technology. Dynamic properties of droplets, interfaces and emulsions are therefore very important to be characterized, understood and controlled. In this respect, microfluidic systems themselves appear to be very powerful tools for the study of surfactant dynamics at the time- and length-scale relevant to the corresponding microfluidic applications. More generally, microfluidic systems are becoming a new type of experimental platform for the study of the dynamics of interfaces in complex systems.

Droplet formation in microfluidic T-junction generators operating in the transitional regime. III. Dynamic surfactant effects

“…These gradients may be formed by concentration gradients within the solution or if the dilation rate is not uniform across the interface [3]. Under certain conditions the stresses may cause the interface to act like a solid rather than a liquid (no-slip condition) [1]. If this is the case, then Eq.…”

“…Surfactants are often added to reduce the interfacial tension and prevent unwanted coalescence of droplets [1][2][3]. However, their presence adds additional complexity to the emulsification process as there exists intensive coupling between the mass transport of surfactant and the droplet formation process through the interfacial tension.…”

High-throughput screening for industrial enzyme production hosts by droplet microfluidics

“…[16][17][18][19] Picoliter sized monodisperse aqueous droplets are generated in a continuous fluorinated oil phase and stabilized using surfactants to prevent coalescence. 20 These droplets can be manipulated at rates of thousands per second, using microfluidic devices manufactured by soft lithography. 21 Single cells can be encapsulated in such droplets, each droplet constituting the equivalent of a miniature test tube where each specific cell can be assayed.…”

Droplet microfluidics: A tool for biology, chemistry and nanotechnology

“…Too little surfactant may lead to crosstalk between droplets, droplet merging and leakage of materials from droplets [22], while too much surfactant might cause droplet splitting due to low surface tension, or lead to micelle formation and loss of droplet content [23,24]. Furthermore, one should note that surface functionalization of channels, and surfactant concentration, are related: surfactants can get adsorbed to the channel surface and functional layers desorbed from the surface.…”