Measurement and Characterization of Liquid Transfer between Two Solid Surfaces Open Access
- Other title
Contact Angle Hysteresis
- Type of item
- Degree grantor
University of Alberta
- Author or creator
- Supervisor and department
Amirfazli, Alidad (Mechanical Engineering)
Tang, Tian (Mechanical Engineering)
- Examining committee member and department
Tsai, Amy (Mechanical Engineering)
Flynn, Morris (Mechanical Engineering)
Chandra, Sanjeev (Department of Mechanical & Industrial Engineering, University of Toronto)
Department of Mechanical Engineering
- Date accepted
- Graduation date
Doctor of Philosophy
- Degree level
Drop transfer from one solid surface to another through stretching liquid bridges between them is important for many industrial applications. Due to the different dominate forces, three possible regimes exist: Quasi-static Regime, where the transfer process is only dominated by surface forces; Dynamic Regime, where inertia and viscous forces are the dominate forces; and Transition Regime, where all three types of forces are important. In this dissertation, the transfer processes in all of the three different regimes are studied.
For liquid transfer in Quasi-static Regime, the effects of contact angle hysteresis (CAH) are typically ignored in the literature. In this dissertation, with both the experimental measurements and simulation results from an analytical model, the importance of surface CAH in the transfer process is shown. Systematic studies on the role of advancing contact angle (θa), receding contact angle (θr) and CAH in determining the transfer ratio (α), maximum adhesion force (Fmax) and pull-off force (Fpf) are performed. The transfer ratio is found to be governed by contact line pinning at the end of the stretching stage caused by CAH, which is controlled by θr of the surfaces. An empirical equation which is able to predict the transfer ratio by only knowing θr of the two surfaces is provided.
The value of Fmax is found to be strongly influenced by the contact line pinning in early stretching stage. For symmetric liquid bridge between two identical surfaces, Fmax may be determined only by θa, only by θr, or by both θa and θr, depending on the magnitude of the contact angles. For asymmetric bridges, Fmax is found to be affected by the length of the contact line pinning period on the two surfaces. For Fpf, it is found that when one of the surfaces has a θr larger than 90o, Fpf decreases with the increase of θr on either surface. For the cases where θr of both surfaces are smaller than 90o, significantly smaller Fpf is seen when contact line pinning occurs on both surfaces, as compared to Fpf when contact line pinning occurs only on one of the surfaces.
For the liquid transfer in Transition and Dynamic Regimes, based on the value of Reynolds number (Re), the transfer process can have two different scenarios: one with negligible inertia effects (Re<<1) and the other with significant inertia effects (Re >1). For the liquid transfer with negligible inertia effects, the viscosity of the liquid is shown to act as a velocity shift such that, given the surface contact angle and the minimum separation between the two surfaces at which stretching begins, the transfer ratio is only a function of the Capillary number (Ca). Specifically, α converges from one plateau value to 0.5 with the increasing of Ca. The low-Ca plateau is the value in the Quasi-static Regime, whereas the high- Ca plateau of 0.5 is caused by the symmetric breakage shape of liquid bridge. Based on the observations, an empirical function α=F(Ca) was proposed and validated with experimental results. With this equation, by only knowing transfer ratio at two different stretching speeds in the Transition Regime, the transfer ratio under any value of stretching speed can be estimated. When the inertia effects become important (large Re), satellite drops appear when the liquid bridge breaks. Different from the transfer cases with negligible inertia effects, asymmetric shape of liquid bridge at the breakage is observed. Due to both the satellite drop and asymmetric breakage shape, α does not converge to 0.5 as it is observed in the system with negligible inertia effects.
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
- Citation for previous publication
H. Chen, T. Tang and A. Amirfazli, "Fabrication of Polymeric Surfaces with Similar Contact Angle but Dissimilar Contact Angle Hysteresis", Colloids and Surfaces A: Physicochemical and Engineering Aspects, 408, 17-21 (2012)H. Chen, A. Amirfazli and T. Tang, "Modeling Liquid Bridge between Surfaces with Contact Angle Hysteresis", Langmuir, 29, 3310-3319 (2013).H. Chen, T. Tang and A. Amirfazli, "Mechanism of Liquid Transfer between Two Surfaces and the Role of Contact Angles", Soft Matter, 10, 2503-2507 (2014).H. Chen, T. Tang and A. Amirfazli, "Effect of Contact Angle Hysteresis on Breakage of a Liquid Bridge", Eur. Phys. J. Special Topics, 224, 277–288, (2015).Submitted to Soft Matter as H. Chen, T. Tang, H. Zhao, K-Y Law, and A. Amirfazli “Transfer (it) by Pinning (it): How Contact Angle Hysteresis Governs Liquid Transfer”.Submitted to Physics of Fluids as H. Chen, T. Tang and A. Amirfazli, "Effects of Surface Contact Angle on Fast Liquid Transfer "Submitted to Langmuir as H. Chen, T. Tang and A. Amirfazli, " Fast Liquid Transfer between Surfaces: Breakup of Stretching Liquid Bridges".
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