Capillary wetting and interfacial phenomena in microstructures

• Main Author: Radiom, Milad
• Other Authors: Chan Weng Kong
• Format: Theses and Dissertations
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: https://hdl.handle.net/10356/40630
• Institution: Nanyang Technological University

Fluid penetration into capillary tubes resulting from the interplay between solid-liquid adhesive interactions and liquid-liquid cohesive interactions is a ubiquitous phenomenon. In nature, the rise of underground water in the soil is due to capillary pressure. Moreover, a wide variety of technological applications, e.g. oil extraction through porous rocks, washing process with detergents, surface coating etc, are based fundamentally on capillarity effects. As a result, studies with respect to the physics of capillary flows, both from the engineering and applied sciences and from a theoretical point of view, have been constantly renewed for almost a century. In addition, carrier liquids containing nano-sized particles are termed as nanofluids that can result in novel thermophysical properties and thus are of practical importance. Many practical applications like underfill flow process in flip chip technology and spin coating involve flow of nanofluids driven by wetting forces. In addition, with the trend towards device miniaturization, cooling of microelectronics with the aid of surface tension driven nanofluid flow has become a potential application. Thus, characterization of the capillarity of nanofluids is essential for flow control purposes in those applications. In order to better understand the physics involved in the motion of three-phase contact line over a solid surface, this thesis research primarily presents investigations on the capillarity of simple liquids in two novel configurations. Firstly, the capillary filling with the effect of pneumatic pressure of trapped air is studied. The novelty of this work is on the effect of air backpressure on the capillary flow; such a pressure is built up as a result of the air confined within the closed end of the capillary. Both the filling experiment and the theoretical prediction have been done and compared. Secondly, experiment and theoretical study on the capillary flow from a pendant droplet are performed. The effects of finite sized reservoir on the dynamics of flow are examined. The novelty of this work is on the effect of changes in pendant droplet surface area on the capillary flow, resulting in much faster displacement of the meniscus. Both systems studied herein are of practical importance in techniques employed in the field of microfluidics. In continuance, surface tension and contact angle, spreading and capillarity of nanofluids are studied. For many years, the physics involved in the shape and contact angle of a droplet on a solid surface has received considerable attention and the physiochemical and physical-statistical parameters controlling surface wettability have been clarified for a long time. For nanofluids, however, there is a lack of systematic studies on the effect of nanoparticles concentration on surface tension, contact angle and wetting behavior. Presence of nano-sized particles within a very thin nanofluid film over the solid surface results in complex flow patterns and new phenomena. The results from the first-part of this thesis research can help to enhance our understanding of the physics involved in the capillarity of nanofluids. Both experiments and theoretical predictions have been conducted and compared.