Capillary Rise of Common Liquids and Nanofluids: Experiments and Modeling

Capillary dynamics of common liquids and nanofluids is a ubiquitous everyday phenomenon. It has practical applications in diverse fields, including ink-jet printing, lab-on-a-chip, biotechnology, and coating. Important as it is, this phenomenon has not been fully understood and requires tremendous effort in theoretical analysis and experimental investigations to gain further knowledge and guide the design of practical precesses whenever capillarity is essential.The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. This thesis presents an experimental study on the rise of the main meniscus in rectangular borosilicate glass and plastic (polystyrene) capillaries using three different liquids (water, ethanol, and hexadecane). A universal model (an extended two-wall model) based on the Laplace equation was developed to predict the equilibrium height of the main meniscus in rectangular capillaries. In capillary dynamics, it is crucial to understand the interaction between fluid molecules and a solid substrate (the wall) in molecular scale. Recent studies reveal that a layered molecularly thin wetting film (LMTWF) will develop ahead of the apparent three-phase contact line for the spreading of a wetting liquid on solid surfaces. Based on this fact, a novel molecular self-layering model is proposed to explain the dynamic wetting considering the role of the molecular shape on self-layering and its effect on the molecularly thin film viscosity in regards to the advancing (dynamic) contact angle. The proposed molecular self-layering model is then incorporated into the Lucas-Washburn-Rideal (LWR) equation to explain the capillary rise dynamics of fluids of spherical, cylindrical, and disk shape molecules in borosilicate glass capillaries. The abilities of the other popular dynamic contact angle models to correct the dynamic contact angle effect in the capillary rise process were also investigated. The LWR equation modified by molecular self-layering model predicts well the capillary rise of carbon tetrachloride, octamethylcyclotetrasiloxane and n-alkanes with the molecular diameter or measured solvation force data. The molecular self-layering model modified LWR equation also has good predictions on the capillary rise of silicone oils covering a wide range of bulk viscosities with the same key parameter W(0), which results from the molecular self-layering. Besides the open capillaries, the proposed molecular self-layering model is applied to explain the spontaneous rise of Newtonian liquids in closed-end capillaries. Contribution of the compressed air inside the closed capillaries is also modeled and experimentally verified. Finally, the research is extended to a liquid phase displacing another immiscible liquid in capillaries with the focus on surfactant solutions containing polymeric nanoparticles (nanofluids), which have been shown to have an improved wetting and spreading on solid surfaces. The polymeric nanoparticles can reduce the frictional coefficient by as much as four times by forming structured layers in the confined wedge film. The role of the interfacial tension on the frictional coefficient is also demonstrated.In summary, this thesis presents the physics of liquid rise in rectangular capillaries, effect of molecular self-layering in capillary dynamics in open and closed-end capillaries, and the contribution of nanofluids in the two-phase displacement dynamics