Surfactants in droplet-based microfluidics

TLDR

Surfactants are essential for droplet‑based microfluidics, stabilizing droplet interfaces, ensuring biocompatibility, enabling molecular exchange, and their emulsion properties and interfacial rheology critically determine the technology’s performance, prompting development of new molecules and use of microfluidic systems as platforms to study surfactant dynamics. This review examines surfactants in droplet‑based microfluidics, focusing on newly developed molecules designed to overcome the limitations of standard surfactants. The authors analyze surfactant behavior using microfluidic systems that allow precise study of surfactant dynamics at the time‑ and length‑scales relevant to droplet‑based applications.

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.