ABSTRACT
The characteristic angle measured through the droplet phase between the solid-liquid interface interfacial control of multiphase fluids in miniaturized devices and the plane of the liquid-vapor interface at the contact line is referred to as the contact angle and is the most common measure of wettability. This chapter focuses on the interplay of geometry and chemistry in determining wetting behavior and the implications for passive control of fluids in microfluidic systems where immiscible fluids meet. The chapter reviews the fundamentals of surface wettability with respect to ideal and nonideal surfaces, metastable wetting behavior, and wetting dynamics. It describes several approaches to modifying microchannel wettability and discusses several key applications of wetting in microfluidic devices and structures. These include wetting-controlled spontaneous filling, valving, flow stability, phase separation, and the role of wettability in droplet (or bubble)-based microfluidics.
