Anisotropic Wetting Property of Superhydrophobic Surfaces and Electrokinetic Flow on Liquid-Filled Surfaces

Understanding the wetting property of rough surface is critical in guiding droplets and novel superhydrophobic surface design. The Cassie-Baxter model and Wenzel model are always used to describe the totally non-wetting and completely wetting states, however, there were few discussions about the intermediate state. Through measuring the contact angles of groove patterned surfaces in different groove orientations, the anisotropic wetting properties of groove patterned superhydrophobic surface were investigated. The degree of water penetration into the grooves was experimentally observed and it was found that the degree of water penetration was different with groove orientations, which would affect the corresponding contact angle. Besides guiding droplets, superhydrophobic surfaces are also very important in microfluidic due to their ability to generate fluid slip and flow enhancement. After a deeper understanding of the wetting property of groove patterned superhydrophobic surface, I further investigated its important role in microfluidics. In this dissertation, I mainly focus on electrokinetics on groove patterned surface and liquid-filled slippery surfaces, a new kind of surface by filling low surface tension oil into the interstices of groove patterned surfaces. I experimentally measured the streaming potential on flat parylene surface, air-filled groove patterned surface and liquid-filled surfaces and compared their effects in streaming potential enhancement. The liquid-filled surfaces were shown to be able to enhance the generated streaming potential due to its slippery property and liquid-oil interface charges. As the electrokinetic on liquid-filled surfaces is a new phenomenon, the underlying physics is still not clear. I further investigated the influences of filled oil properties and groove orientation on streaming potentials and fluid slip. Oils with different densities, viscosities, dielectric constant, conductivities and surface tensions were filled into the interstices of groove patterned surfaces to make different types of liquid-filled surfaces. The streaming potentials on liquid-filled surfaces with different oils were experimentally measured. An empirical relationship between streaming potential and oil properties was found and the effects of electrical properties, such as interface charge density and dielectric constant of filled oil, on fluid slip were also studied. Finally, the groove orientation was varied to study the tensorial effects on streaming potential. Through both streaming potential measurement and theoretical analysis, it was found that the streaming potential at 45° was always smaller than the arithmetic mean of those at 0° and 90°, and the pressure gradient in the transvers direction generated by tensorial effects was important in the streaming potential modification. My work will be important in guiding droplets, flow patterning, lab-on-chip devices and the development of electrokientic based power sources

Summary of NASA landing-gear research

Research relative to tire tread, powered-wheel taxiing, air cushion landing systems, and crosswind landing gear is discussed

Scaling Laws for Spreading of a Liquid Under Pressure

We study squeeze flow of two different fluids (castor oil and ethylene glycol) between a pair of glass plates and a pair of perspex plates, under an applied load. The film thickness is found to vary with time as a power-law, where the exponent increases with load. After a certain time interval the area of fluid-solid contact saturates to a constant value. This saturation area, increases with load at different rates for different fluid-solid combinations.Comment: 10 pages, 5 figure

Radiation-Hydrodynamics of Hot Jupiter Atmospheres

Radiative transfer in planetary atmospheres is usually treated in the static limit, i.e., neglecting atmospheric motions. We argue that hot Jupiter atmospheres, with possibly fast (sonic) wind speeds, may require a more strongly coupled treatment, formally in the regime of radiation-hydrodynamics. To lowest order in v/c, relativistic Doppler shifts distort line profiles along optical paths with finite wind velocity gradients. This leads to flow-dependent deviations in the effective emission and absorption properties of the atmospheric medium. Evaluating the overall impact of these distortions on the radiative structure of a dynamic atmosphere is non-trivial. We present transmissivity and systematic equivalent width excess calculations which suggest possibly important consequences for radiation transport in hot Jupiter atmospheres. If winds are fast and bulk Doppler shifts are indeed important for the global radiative balance, accurate modeling and reliable data interpretation for hot Jupiter atmospheres may prove challenging: it would involve anisotropic and dynamic radiative transfer in a coupled radiation-hydrodynamical flow. On the bright side, it would also imply that the emergent properties of hot Jupiter atmospheres are more direct tracers of their atmospheric flows than is the case for Solar System planets. Radiation-hydrodynamics may also influence radiative transfer in other classes of hot exoplanetary atmospheres with fast winds.Comment: 25 pages, 4 figures, accepted for publication in ApJ (minor revisions

Electrohydrodynamic deformation and rotation of a particle-coated drop

A dielectric drop suspended in conducting liquid and subjected to an uniform electric field deforms into an ellipsoid whose major axis is either perpendicular or tilted (due to Quincke rotation effect) relative to the applied field. We experimentally study the effect of surface-adsorbed colloidal particles on these classic electrohydrodynamic phenomena. We observe that at high surface coverage (>90%), the electrohydrodynamic flow is suppressed, oblate drop deformation is enhanced, and the threshold for tilt is decreased compared to the particle-free drop. The deformation data are well explained by a capsule model, which assumes that the particle monolayer acts as an elastic interface. The reduction of the threshold field for rotation is likely related to drop asphericity

Hydraulic bearing puller

A bearing puller tool is an essential repair aid when working on an engine or machine that has pressure-set bearings in its mechanisms. Without the tool, repair of bad bearings would be difficult and prone to a high risk of damage to the shaft or casing block of gearbox and engine. It is designed as a tool to make the removal and installation of bearings simple and efficient, bearing pullers often resemble a pair of scissors. In some cases, the configuration of the puller will allow the extraction of both gears and bearings, including those that are connected with a series of shafts within the mechanism. Different sizes of bearing pullers make it possible to use the device on everything from a pair of skates to complicated industrial machinery. ‘Hydraulic Bearing Puller' is one of the products that have been modified from the original product in the market. Extensive studies have been conducted on service centers to implement this product. Most workers remove the bearing from the shaft (shaft) a way tap so that it can be removed. Apart from that they also use the 'bearing puller' common but with high cost. From the original product, we have made modifications to equipment for easy used by employees

A novel technique of contrast-enhanced optical coherence tomography imaging in evaluation of clearance of lipids in human tears

Purpose: The aim of this work was to gather preliminary data in different conditions of healthy eyes, aqueous tear deficient dry eyes, obstructive meibomian gland disease (MGD) and non-obvious obstructive MGD (NOMGD) individuals, using a new, contrast-enhanced optical coherence tomography (OCT) imaging method to evaluate the clearance of lipids in human tears. Methods: Eighty-two adult patients presenting with complaints of ocular irritation were studied for abnormalities of the ocular surface and classified as healthy (n = 21), aqueous tear deficient dry eyes (n = 20), obstructive MGD (n = 15) and NOMGD (n = 26) individuals. A lipid-based tracer, containing an oil-in-water emulsion, was used to obtain an enhanced OCT imaging of the lower tear meniscus. After instillation, a dramatic initial increase of reflectivity of the lower tear meniscus was detected by OCT, followed by a decay back to baseline values over time. Based on this finding, the clearance of lipids was measured in real-time by Fourier-domain anterior segment OCT. Results: The differences in the clearance of lipids among the four groups as well as the correlations between symptom questionnaire score, standardized visual scale test, fluorescein break-up time, ocular surface fluorescein staining score, Schirmer I test scores were found to be statistically significant. The individual areas under the curve of the clearance of lipids calculated by the receiver operating characteristic curve technique ranged from 0.66 to 0.98, suggesting reliable sensitivity and specificity of lipid-enhanced OCT imaging. Conclusions: This new technique of contrast-enhanced OCT imaging of the tear film following lipid-based tracer instillation provides a measure of the clearance of lipids. The quantitative values found are in agreement with other methods of evaluation of the lacrimal system. An improvement of the clinician's ability in the diagnosis and understanding of abnormalities of the ocular surface may be achieved by this simple approach

Spreading of Fluids on Solids Under Pressure: Effect of Slip

Spreading of different types of fluid on substrates under an impressed force is an interesting problem. Here we study spreading of four fluids, having different hydrophilicity and viscosity on two substrates - glass and perspex, under an external force. The area of contact of fluid and solid is video-photographed and its increase with time is measured. The results for different external forces can be scaled onto a common curve. We try to explain the nature of this curve on the basis of existing theoretical treatment where either the no-slip condition is used or slip between fluid and substrate is introduced. We find that of the eight cases under study, in five cases quantitative agreement is obtained using a slip coefficient.Comment: 6 figure