Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cyrus K. Aidun; Committee Member: Marc K. Smith; Committee Member: S. Mostafa Ghiaasiaan. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 129-147).

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Thesis--Liège. / Summaries in Dutch, English, German, and Italian. Includes bibliographical references (p. [127]-130).

We report on the surface properties of a photoresponsive surfactant that incorporates the light-sensitive azobenzene group into its tail. Cis-trans photo-isomerization of this group alters the ability of the surfactant to pack into adsorbed monolayers at an air-water interface or into aggregates in solution, causing a significant variation in bulk and surface properties upon changes in the illumination conditions. NMR studies indicate that a solution left in the dark for an extended period of time contains trans isomer almost exclusively, while samples exposed to light of fixed wavelength eventually reach a photostationary equilibrium with significant amounts of both isomers present. Dynamic surface tension studies performed on this system under different illumination conditions (dark, UV light, visible light) show profoundly different approaches to equilibrium. At concentrations well above the CMC, the same equilibrium tension is reached in all three cases, presumably corresponding to a surface saturated with the trans (more surface active) isomer. The dark sample shows a simple, single-step relaxation in surface tension after creation of a fresh interface, while the UV and visible samples exhibit a more rapid initial decrease in tension, followed by a plateau of nearly constant tension, and end with a final relaxation to equilibrium. It is hypothesized that this behavior of the UV and visible samples is caused by competitive adsorption between the cis and trans isomers present in these mixtures. Presumably the cis surfactant reaches the interface more quickly, leading to a cis-dominated interface having a tension value corresponding to the intermediate plateau, but is ultimately displaced by the trans isomer. Diffusional time scale arguments which consider the extremes of possible micellar dissolution rates are used to analyze the relaxation data of the dark sample, and the results indicate that micellar dissolution in these samples is slow. / Singapore-MIT Alliance (SMA)

Master of Science / Department of Mechanical and Nuclear Engineering / Bruce R. Babin / A Surface Tension Element (STE), device was successfully constructed and tested as the primary moisture removal device in a condensing dryer. The STE was tested via the SAE ARP901 bubble-point test method and resulted in an average micron rating of 46.8 microns. The operation of the STE was compared to that of the typical air-to-air heat exchanger/condenser used in condensing dryers. The total power consumption and IEC efficiency of each case were averaged and compared. The results indicated that the STE used an average of 0.616 kilowatt-hours per kilogram dry laundry while the air-to-air heat exchanger/condenser used an average of 0.643 kWh/kg. This resulted in an improvement of the European efficiency label from class C to Class B. An analytical model was also constructed that well predicted the operation of the STE under steady state conditions.

This thesis is concerned with the deformation and adhesion of thin elastic sheets that come into contact with an underlying substrate. The focus of this work is on the interplay between material and geometric properties of a system and how this interplay determines the equilibrium states of sheet and substrate, particularly in the regime of geometrically nonlinear deformations. We first consider the form of an elastic sheet that is partially adhered to a rigid substrate, accounting for deflections with large slope: the Sticky Elastica. Starting from the classical Euler Elastica we provide numerical results for the profiles of such blisters and present asymptotic expressions that go beyond the previously known, linear, approximations. Our theoretical predictions are confirmed by desktop experiments and suggest a new method for the measurement of material properties for systems undergoing large deformations. With the aim to gain better understanding of the initial appearance of blisters we next investigate the deformation of a thin elastic sheet floating on a liquid surface. We show that, after the appearance of initial wrinkles, the sheet delaminates from the liquid over a finite region at a critical compression, forming a delamination blister. We determine the initial blister size and the evolution of blister size with continuing compression before verifying our theoretical results with experiments at a macroscopic scale. We next study theoretically the deposition of thin sheets onto a grooved substrate, in the context of graphene adhesion. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives phys- ical insight into recent observations of ‘snap-through’ from flat to conforming states and emphasises the crucial role of substrate shape in determining the nature of this transition. We finally present a theoretical investigation of stiction in nanoscale electromechanical contact switches. Our model captures the elastic bending of the switch in response to both electrostatic and van der Waals forces and accounts for geometrically nonlinear deflections. We solve the resulting equations numerically to study how a cantilever beam adheres to a fixed bottom electrode: transitions between free, pinned and clamped states are shown to be discontinuous and to exhibit significant hysteresis. The implications for nanoscale switch design are discussed.

Measurement of surface tension of solids usually requires manual processing of photographs of droplets of liquids with known properties on the measured material's surface, during which the contact angle is manually determined. The objective of this work is to implement an algorithm that can determine these contact angles from photographs and does not require the photographs to be made under specific light conditions. The implementation cannot depend on paid libraries and must be simple to incorporate into existing software.

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