Evanescent Wave Based Flow Diagnostics

Abstract

Miniaturized flow systems have been developed for various applications, including integrated chemical analyses and thermal management of microelectronics. Understanding interfacial transport is important in designing and optimizing such flow systems, since surface effects become significant due to the large surface areas and small volumes at these length scales. Recently, various nearwall flow diagnostic techniques have been developed based on evanescentwave illumination. Since evanescent waves only illuminate the fluid in the region over the first few hundred nanometers next to the wall, these techniques have much better spatial resolution than conventional methods based on epifluorescence microscopy. This paper presents recent advances in evanescent wavebased flow diagnostics using fluorescent tracers, including evanescentwave particle velocimetry applied to flows driven by both pressure and voltage gradients and evanescentwave fluorescence, which has been used to measure nearwall liquid temperature and pH fields, as well as the surface charge, or wall خ¶potential, distributions.