Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 123-125). Also available on the World Wide Web.

The contact angle defined by Young's equation depends on the ratio between solid and liquid surface energies. Young's contact angle is constant for a given system, and cannot explain the stability of fluid droplets in capillary tubes. Within this framework, large variations in contact angle and explained aassuming surface roughness, heterogeneity or contamination. This research explores the static and dynamic behavior of fluid droplets within capillary tubes and the variations in contact angle among interacting menisci. Various cases are considered including wetting and non-wetting gluids, droplets in inclined capillary tubes or subjected to a pressure difference, within one-dimensional and three-dimensional capillary systems, and under static or dynamic conditions (either harmonic fluid pressure or tube oscillation). The research approach is based on complementary analytical modeling (total energy formulation) and experimental techniques (microscopic observations). The evolution of meniscus curvatures and droplet displacements are studied in all cases. Analytical and experimental results show that droplets can be stable within capillary tubes even under the influence of an external force, the resulting contact angles are not constant, and bariations from Young's contact angle aare extensively justified as menisci interaction. Menisci introduce stiffness, therefore two immiscible Newtonian fluids behave as a Maxwellian fluid, and droplets can exhibit resonance or relaxation spectral features.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 189-198).

As drop-on-demand (DOD) applications continue to gain ground in desktop inkjet-printing, 3D printing, fluid mixing, and other areas the demand for higher frequency operations are beginning to push against the current physical boundaries in DOD technology. The current research is exploring the possibility of controlling drop volume and velocity at high frequency ranges where meniscus vibrations can occur between drop formations and affect drop formation characteristics. A periodic voltage is applied to a piezoelectric disk in order to generate pressure fluctuations in a single nozzle droplet generator, causing the fluid meniscus at the nozzle to vibrate. A single stronger pulse is then superimposed over the periodic waveform at different phases in order to drive drop ejection. The characteristics of the resulting drop, specifically the volume and velocity, are experimentally measured using a high speed camera with precise timing control. The results of these experiments are then compared to a lumped element model (LEM) developed for the droplet generator geometry used. Within the LEM model framework, special attention was given to the definition of a novel method by which one can measure drop volume within an electroacoustic circuit and also allow meniscus dynamics to affect present and future drop formations. Experimental results indicate a strong dependence of both drop volume and drop velocity on the phase of the vibrating meniscus at the start of drop formation. Positive meniscus displacements and momentums resulted in large drop volumes and velocities while negative displacements could reduce drop volume or altogether eliminate drop formation. Specifically, positive displacements and momentum of a vibrating meniscus could lead to drop volumes approximately 50% larger than the original drop volume without a vibrating meniscus. Meanwhile, negative meniscus displacements and momentums were shown to have the ability to completely prevent drop formation. Additional potential for drop characteristic control with a vibrating meniscus is discussed alongside observations on the stabilizing affect the vibrating meniscus appears to have on drop velocity as a function of time. Also, flow visualization of the drop formation is provided to demonstrate the added affect the meniscus vibrations have on the drop shapes and break-off profiles. The LEM model presented demonstrates qualitative agreement with the experimental model, but fails to quantitatively predict drop volumes. Sources of error for the LEM model and potential improvements are discussed. / Graduation date: 2012