| Summary: | 碩士 === 臺灣大學 === 化學工程學研究所 === 98 === The wetting behavior of a droplet on a planar solid surface is well-known. Due to the geometrical constraint of the fiber, however, the equilibrium shapes of a droplet on fibers are more complicated and therefore are less studied. A combined numerical simulation and experimental investigation were employed to examine the conformations of a droplet on a fiber. The energy calculation results were accurately achieved by using a powerful modeling tool, the Surface Evolver, to present the fiber-droplet system in mathematical model taking surface tension, gravity energy, and other geometrical constraints into consideration. In the first part, we simulate our fiber-droplet system with no gravity and compare the results to Carroll’s and McHale’s work. Our results show that the existence of inflection point for barrel shape is a good criterion in determining if a barrel shape droplet could exist. We also find the coexistent region of two configurations. In the second part, we simulate our fiber-droplet system with gravity. Our results demonstrate that several regimes can be found. If the droplets volume is too small to cover the fiber in a barrel shape, the droplets can only exist in shapes of downward and upper clam-shell(Regime I). For droplets where the gravity effect is not too significant, shapes of upper clam-shell, barrel, and downward clam-shell can co-exist (Regime II). As volume increases, the upper clam-shell droplet becomes unstable (Regime III); if the volume grows larger further, the barrel also ceases to exist, leaving only the downward clam-shell one (Regime IV). Finally, gravity turns out to be the most important factor and the droplet can no longer be attached to the fiber (Regime V). Our results also indicate that the intrinsic surface property (e.g. the contact angle) of the fiber has significant effect on these regimes, number of the regimes changes as the contact angle varies. This work can be related to a number of industrial applications regarding fiber-based microfludics such as low-cost medical diagnostic and cell cultivation.
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