ABSTRACT
This chapter presents theoretical considerations most closely relevant to conducting near-surface particle-tracking velocimetry (PTV). Particle-based velocimetry has long been used in flow visualization and measurement. The Brownian motion of small particles due to molecular fluctuations is generally well understood and can be significant in magnitude for nanoparticles commonly used for near-surface PTV. Particle rotation can also induce a lift force, which tends to make the particles migrate away from the wall. Electrostatic forces arise from the Coulombic interactions between charged bodies such as polystyrene tracer particles and glass immersed in water. A straightforward two-dimensional Gaussian fit used in nanoparticle identification has been demonstrated to be very accurate and is currently the gold standard in near-surface PTV. Near-surface particle tracking has made tremendous progress over the past several years due in large part to increased interest in nanofluidics and a demand for higher resolution diagnostic techniques.
