Surface Tension‐Dominated Flows

In microfluidics, surface effects play a dominant role. Surface effects are also known as capillary effects. This chapter presents some of the flow physics related to surface tension-dominated flows and their application to microdevices. The effects of surface and interfacial tensions give rise to many phenomena in the liquid behavior. Gibbs free energy (G) is the measure of work produced from thermodynamic system at constant temperature and pressure. It helps in understanding the capillary effects. Surface tension depends on the two materials on each side of the surface, that is, solids, liquid, or gases. The Young-Laplace equation can also be obtained using Gibbs free energy concept. The chapter also discusses the behavior of liquid droplets on a surface, the influence of surface tension force on the movement of droplet over the hydrophilic-hydrophobic surface boundary and the theoretical background for the flows driven by surface tension gradient.