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Wheel-rail contact is an important aspect of railway, the forces transferred between the wheel and rail are the one that guide, brake, or accelerate the train, and that is why the understanding of the contact between wheel and rail is an interesting research topic. In this master thesis wheel-rail contact model named ANALYN is used to see the effect of the different geometrical input, like undeformed distance, relative longitudinal curvature, and relative lateral curvature calculation affect the contact patch estimation formed at the wheel-rail contact.  In the process, a geometrical contact search code is made to find the contact point between wheel and rail for certain lateral displacement, yaw angle, and roll angle of the wheelset. The codes used to calculate the three geometrical inputs are also prepared, with two methods are prepared for each input. The results that generated from combination of the geometrical contact search and geometrical input preparation are used as the input to ANALYN. The results showed that different geometrical input calculations do affect the shape of the contact patch, with the calculation of lateral curvature being the most important since it affects the shape of the contact patch greater than other geometrical inputs. It is also shown that taking yaw angle into account in the contact search will affect the shape of the contact patch.

Interfaces of water with water-repellent, or hydrophobic, materials are relevant in numerous natural and applied contexts. Examples include lotus leaves, membranes-assisted separation processes, and oil–water emulsions. Typically, water repellence is realized with the help of hydrocarbons and perfluorocarbons. Although these materials present low adhesion to water, their interfaces with water are known to be electrically charged. Origins of the electrification of water–hydrophobe interfaces is a century-old mystery that has been intensely debated on. A number of competing hypotheses have been proposed: specific interfacial adsorption of hydroxide ions, water dipole moment, partial interfacial charge transfer, specific interfacial adsorption of protons, cryptoelectrons, bicarbonate ions, and surfactant contamination. Given the significance of these interfaces, we investigated the origin of water–hydrophobe electrification. To disentangle the role of the various factors, we studied water’s interfaces with: solid hydrophobes, e.g., polypropylene; liquid hexadecane; and gas (air). Electrical charges incurred by water droplets formed using pipettes/tubes of hydrophobic (and hydrophilic) chemical make-up were quantified via electrometers and uniform electric fields. Specifically, we interrogated the contributions of water–hydrophobe surface area, surface chemistry, and water’s ionic strength, pH and dissolved CO2 content. We deduced that common solid hydrophobes have negatively charged surfaces even in air: when a hydrophobic pipette/tube is used to draw an aliquot of water from the bulk, hydrated cations form an electrical double layer at the liquid–solid interface. For the water–hexadecane interface, we tracked interfacial tensions over time. Our investigation revealed that trace amounts of impurities are present in the oil, despite purification, which interfere with purely interfacial effects. Lastly, we applied these fundamental insights to investigate slippery liquid-impregnated surfaces (SLIPS) realized using microtextured SiO2/Si wafers and sand dollar (Dendraster excentricus) templated PDMS surfaces. Recognizing the significant activity in triboelectric nanogenerators (TENGs), we conducted a parametric study of the device output and water–hydrophobe interfacial properties; and tested whether SLIPS could be incorporated in next-generation TENGs. The findings reported in this thesis address some long-standing questions on the spontaneous electrification of water–hydrophobe interfaces, and they should aid the rational development of practical applications such as SLIPS, TENGs, and beyond.

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The cornea is an avascular transparent tissue exposed to the environment and therefore highly susceptible to damage. With an increase in corneal refractive surgeries, corneal transplants, and corneal injuries, understanding and improving corneal healing mechanisms are extremely important. Impaired healing of corneal wounds can lead to decreased visual acuity and extreme pain. Serum eye drops, amniotic membranes, pharmaceutical agents, biopolymers, and cell transplants are just a few approaches that have been employed to improve wound healing. Bandage contact lenses (BCLs) have been proposed as a simple method to facilitate wound healing while reducing pain. The synthesis of a silicone hydrogel contact lens capable of surface binding hyaluronic acid (HA) for corneal wound healing was explored in the current work. HA was used as both a wetting agent and a therapeutic. The work presented describes the synthesis, characterization, and cell testing of the HA binding model silicone hydrogels, composed of the hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA) and a hydrophobic silicone monomer, methacryloxypropyltris (trimethylsiloxy) silane (TRIS). Three different methods were evaluated for increasing HA binding and improving surface wettability. “Caged lenses” utilized the same base polymer with the incorporation of methacrylated N-Hydroxysuccinimide (NHS). Hydrophilic polyethylene glycol (PEG) chains were then tethered from the NHS, forming a “cage” with the potential to physically entrap HA. Although surface wettability was improved, less HA was entrapped in the caged lenses compared to model silicone hydrogels, presumably due to the increased hinderance resulting from the PEG chains. “Tethered HA” lenses utilized PEG as a spacer to conjugate HA to the lens surface in order to improve surface hydrophilicity. Methacrylated HA conjugation resulted in a significant decrease in contact angle (p <0.01) compared to model pHEMA-co-TRIS whereas tethered thiolated HA did not lead to a significant decrease (p >0.05) in contact angle. It was clear that neither of these methods would lead to sufficient HA binding. Ionic interaction lenses utilize monomers and small molecules that contain a positive charge to bind to the negatively charged HA under physiological conditions. The monomer diethylaminoethyl methacrylate (DEAEM) was polymerized directly into the polymer backbone, but resulted in no significant decrease (p >0.05) in contact angle. In comparison, surface functionalization using thiolene “click” chemistry allowed conjugation of the small molecule, dimethylamino ethanethiol (DMAET) and diethylamino ethanethiol (DEAET). DMAET and DEAET modified lenses showed significantly higher (p <0.001) HA binding compared to model pHEMA-co-TRIS controls at all time points. The modified lenses improved release kinetics preventing an initial burst release and showed consistent release when unloaded and reloaded with HA. The contact angle was significantly decreased (p <0.05) for the modified lenses with HA without affecting the equilibrium water content. Optical transparency was reduced following lens modifications although the thickness of the disks prepared was higher than a typical contact lens. Finally, the modified lenses did not exhibit any cytotoxicity in vitro with human corneal epithelial cells (HCECs). The synthesis of silicone hydrogels capable of surface binding HA have potential to be used as a bandage contact lens while improving surface wettability and enhancing comfort. / Thesis / Master of Applied Science (MASc)

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