Optical Measurement of Mesoscale Dynamic Wetting of Nanofluid Droplets

Abstract

This paper reviews the authors’ studies on the optical measurement of mesoscale wetting dynamics using phase-shifting ellipsometry, highlighting its capability to capture nanometer-thick liquid film behavior near the contact line. The method enables precise analysis of film thickness profiles, dynamic contact angles, and precursor film lengths, providing valuable insights into the fundamental mechanisms of wetting. The authors’ work also investigates superspreading wetting, where certain nanofluid droplets exhibit larger spreading. While this phenomenon has primarily been associated with aqueous surfactant solutions in previous studies, the authors analyzed it using the phase-shifting ellipsometer and identified it as a phenomenon that cannot be explained by the previously proposed mechanisms. These experimental data and findings offer a novel perspective on droplet behavior on solid substrates.