Title: Concave bending of contact line due to polarization and surface trapping

Biography:

Dr. Jiangtao Cheng received his Ph.D. degree in Physics from Purdue University in 2002. He also has a M.S. degree in Computer Science from Purdue University and a B.S. degree in Applied Physics from Peking University at Beijing. Prior to joining the Department of Mechanical Engineering at Virginia Tech in 2015 as Associate Professor, Dr. Cheng was a research associate at the Pennsylvania State University and a research scientist at Teledyne Scientific Company (formerly Rockwell Science Center). He has served as the principal investigators of several research projects funded by DOE, NASA, DARPA and NSF respectively. He has authored/co‐authored more than 50 papers in journals and conferences. Dr. Cheng has won numerous awards in his career including four times of Best Paper Awards in international conferences and 2013 Outstanding Overseas Young Scholar Award from China NSF. In 2010, Dr. Cheng’s project “Optofluidic Solar Concentrators” was announced by the U.S. Department of Energy as one of the “six transformational energy research and development projects that could revolutionize how the country uses, stores, and produces energy”. Dr. Cheng has extensive experience in thermal-fluid sciences, renewable energy, micro/nano-fluidics, optofluidics, multiphase fluid flow, nano-fabrications and CFD numerical simulation."

Abstract

The formation and configuration of three phase (solid/liquid/vapor) contact line is of central importance in understanding wetting dynamics and electrowetting. The contact zone can be divided into four regions: the macroscopic region, the mesoscopic region, the proximal region, and the molecular region. However, the contact angle and the contact line profile within the molecular region still remain obscure. In this study, we used molecular dynamics simulation to examine the contact line profile in the molecular region. It is found that the contact line experiences concave bending at the molecular region, which is induced by the polarization of water molecules therein and the friction among the layered structure of trapped water molecules. The polarization near the solid surface manifest in the form of orientation bias of water molecules. The surface trapping of water molecules in the proximity of solid surface occurs in the form of oscillating peak densities in the density profile. Both effects, which are restricted to approximately 1 nm away from the solid surface, contribute to additional energy dissipation in the process of contact line formation and work jointly as an extra term in the modified Young-Laplace equation.