Excessive water formation inside the polymer electrolyte membrane (PEM) fuel cell’s structures leads to the flooding of the cathode gas diffusion layer (GDL) and cathode gas flow channels. This results in a negative impact on water management and the overall cell performance. Liquid water generated in the cathode catalyst layer and the water moved from anode to cathode side due to electro-osmotic drag transport through the GDL to reach the gas flow field channels, where it is removed by air cathode gas stream. Due to high and uniform capillary force distribution effect of the pores through the GDL plane and surface tension between the water droplets and gas flow field channels surfaces, liquid water tends to block/fill the pores of the GDL and stick to the surface of the GDL and gas flow channels. Therefore, it is difficult to remove the trapped water in GDL structure which can lead to flood of the PEM fuel cell. The GDL surfaces are commonly treated uniformly with a hydrophobic material in order to overcome the flooding phenomena inside PEM fuel cell. Despite the importance impact of the surface wettability of both channel and GDL surface characteristics especially for the cathode side on the water management, few experimental studies have been conducted to investigate the effect of the two-phase flow in cathode gas flow channel and their crucial role. The work presented in this thesis covers contributions that provide insight, not only into the investigation of the effects of hydrophobic cathode GDL and cathode gas flow channels, on water removal, two phase flow inside the channel, and on PEM fuel cell performance, but also the superhydrophobic and superhydrophilic GDLs and gas flow channels effects. Further, the effects of a novel GDL designs with sandwich and gradient wettability with driving capillary force through GDL plane have been investigated. Two-phase flow especially in the cathode gas flow field channels of PEM fuel cell has a crucial role on water removal. Hence, in this research, ex-situ investigations of the effects of channels with different surface wettability; superhydrophobic, hydrophobic, slightly hydrophobic, and superhydrophilic on the two-phase flow characteristics have been tested and visualized at room temperature. Pressure drop measurements and two-phase flow visualization have been carried out using high speed camera. The effect of the various coating materials on graphite and GDL surface morphology, roughness, static contact angle (θ), and sliding contact angle (α) have been investigated using scanning electron microscopy (SEM), Profilometry, and sessile drop technique, respectively. It has been observed that the two-phase flow resistance is considerably affected by surface wettability of the channels. Further, the overall cell performance can be improved by superhydrophobic gas flow channels mainly at high current density over slightly hydrophobic and superhydrophilic cases tested. In addition, sandwich wettability GDL has been coated with a silica particle/ Polydimethylsiloxane (PDMS) composite. The porometric characteristics have been studied using, method of standard porosimetry (MSP). It has been found that sandwich wettability GDL has superhydrophobic surfaces with (θ = 162±2°), (α = 5±1°), and the internal pores are hydrophilic, while the mean pore radius is 7.1μm. This shows a low resistance to gas transport. On the other hand, performance testing indicates that (PEM) fuel cell equipped with sandwich wettability GDL results in the best performance compared to those with raw (non-coated) (slightly hydrophobic), PTFE coated (commercial with micro-porous layer (MPL)) (superhydrophobic), and silica coated (superhydrophilic) GDL. The wettability gradient has been introduced through plane of the one side hydrophobic GDL by coating one side of non-coated GDL with 15 wt. % of PTFE solution; however, the other side remains uncoated. The effects of wettability gradient on the water removal rate, droplet dynamics, and PEM fuel cell performance have been covered in this thesis. Water removal rate is determined using a 20 ml syringe barrel, wherein a 13 mm diameter GDL token is fixed on the barrel opening. The droplets penetrating through the GDL are visualized via a high speed camera to study the droplets’ dynamic characteristics. The GDL wettability gradient has a significant impact on water removal rate, droplets’ dynamic characteristics, and consequently enhances the overall PEM fuel cell performance.

In the present studies we investigated the effects of mechanical rubbing on the surface characteristics of polymer liquid crystal alignment layers. Contact angles of water droplets in contacted with the rubbed polyimide were measured using a surface tension meter, and the surface free energy of the polymer thin films were evaluated. We found that the contact angle of water and surface free energy on rubbed polyimide is anisotropic, and rubbing caused decrease in surface free energy and wettability of the polyimide surface. It was also seen that the contact angle hysteresis and the surface free energy measured in the direction parallel to the rubbing direction is smaller than that in the direction anti-parallel to the rubbing direction. We found that when the pile impression of the velvet fibers is 0.3 mm and the cumulative number of rub is 3 times, the contact angle hysteresis in direction parallel or anti-parallel to the rubbing direction will to be close. Be suitable choosing rubbing conditions, the SSFLCs without zigzag defects was produced. The pretilt angle and the response time of liquid crystal increased with the cumulative number.

Excessive water formation inside the polymer electrolyte membrane (PEM) fuel cell’s structures leads to the flooding of the cathode gas diffusion layer (GDL) and cathode gas flow channels. This results in a negative impact on water management and the overall cell performance. Liquid water generated in the cathode catalyst layer and the water moved from anode to cathode side due to electro-osmotic drag transport through the GDL to reach the gas flow field channels, where it is removed by air cathode gas stream. Due to high and uniform capillary force distribution effect of the pores through the GDL plane and surface tension between the water droplets and gas flow field channels surfaces, liquid water tends to block/fill the pores of the GDL and stick to the surface of the GDL and gas flow channels. Therefore, it is difficult to remove the trapped water in GDL structure which can lead to flood of the PEM fuel cell. The GDL surfaces are commonly treated uniformly with a hydrophobic material in order to overcome the flooding phenomena inside PEM fuel cell. Despite the importance impact of the surface wettability of both channel and GDL surface characteristics especially for the cathode side on the water management, few experimental studies have been conducted to investigate the effect of the two-phase flow in cathode gas flow channel and their crucial role. The work presented in this thesis covers contributions that provide insight, not only into the investigation of the effects of hydrophobic cathode GDL and cathode gas flow channels, on water removal, two phase flow inside the channel, and on PEM fuel cell performance, but also the superhydrophobic and superhydrophilic GDLs and gas flow channels effects. Further, the effects of a novel GDL designs with sandwich and gradient wettability with driving capillary force through GDL plane have been investigated. Two-phase flow especially in the cathode gas flow field channels of PEM fuel cell has a crucial role on water removal. Hence, in this research, ex-situ investigations of the effects of channels with different surface wettability; superhydrophobic, hydrophobic, slightly hydrophobic, and superhydrophilic on the two-phase flow characteristics have been tested and visualized at room temperature. Pressure drop measurements and two-phase flow visualization have been carried out using high speed camera. The effect of the various coating materials on graphite and GDL surface morphology, roughness, static contact angle (θ), and sliding contact angle (α) have been investigated using scanning electron microscopy (SEM), Profilometry, and sessile drop technique, respectively. It has been observed that the two-phase flow resistance is considerably affected by surface wettability of the channels. Further, the overall cell performance can be improved by superhydrophobic gas flow channels mainly at high current density over slightly hydrophobic and superhydrophilic cases tested. In addition, sandwich wettability GDL has been coated with a silica particle/ Polydimethylsiloxane (PDMS) composite. The porometric characteristics have been studied using, method of standard porosimetry (MSP). It has been found that sandwich wettability GDL has superhydrophobic surfaces with (θ = 162±2°), (α = 5±1°), and the internal pores are hydrophilic, while the mean pore radius is 7.1μm. This shows a low resistance to gas transport. On the other hand, performance testing indicates that (PEM) fuel cell equipped with sandwich wettability GDL results in the best performance compared to those with raw (non-coated) (slightly hydrophobic), PTFE coated (commercial with micro-porous layer (MPL)) (superhydrophobic), and silica coated (superhydrophilic) GDL. The wettability gradient has been introduced through plane of the one side hydrophobic GDL by coating one side of non-coated GDL with 15 wt. % of PTFE solution; however, the other side remains uncoated. The effects of wettability gradient on the water removal rate, droplet dynamics, and PEM fuel cell performance have been covered in this thesis. Water removal rate is determined using a 20 ml syringe barrel, wherein a 13 mm diameter GDL token is fixed on the barrel opening. The droplets penetrating through the GDL are visualized via a high speed camera to study the droplets’ dynamic characteristics. The GDL wettability gradient has a significant impact on water removal rate, droplets’ dynamic characteristics, and consequently enhances the overall PEM fuel cell performance.

Titanium has been used in bio-medical implants for decades due to its superior biocompatibility. To improve the osseointegration of dental and orthopaedic implants, various surface modification techniques have been used including laser surface texturing. In particular, short-pulsed lasers, such as femtosecond and picosecond lasers, are widely used for surface modification. In this thesis, commercially pure Ti surfaces are modified by a femtosecond laser to explore the relationship between surface topography, surface chemistry, surface wettability, and biocompatibility with the goal of improving the osseointegration of implants. The laser textured surfaces consist of 1μm wide grooves spaced 10 μm, 4.8 μm, 2.4 μm and 1.2 μm apart. Gradient configurations where the groove spacing varies are also investigated. Surface morphology was characterized using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). A custom-build contact angle measurement apparatus is used to investigate the wettability of the laser textured surfaces using the sessile drop method. Freshly laser-treated commercially pure Ti surfaces are found to be super-hydrophilic and become hydrophobic over time when exposed to air. The presence of grooves can accelerate the evolution of the contact angle over time, and introduces anisotropy in the wetting behavior (along vs. across the grooves). The hydrophilicity of laser treated surfaces can be retained by storing samples in ethanol. X-ray Photoelectron Spectroscopy (XPS) shows that the relative carbon content increases over time when Ti samples are exposed to air, which results in the subsequent evolution of the contact angle and cell response to laser textured Ti surfaces. Besides, laser treatment promotes the oxidation of pure Ti, and the product, TiO2, is responsible for the better biocompatibility. In vitro experiments using MG 63s osteoblast-like cells are implemented on laser-treated Ti surfaces and polished surfaces (control) with 1 day, 3 days and 7 days of cell culture. The best cell outcome was obtained by storing samples in air for 1 week, where storing for shorter or longer times resulted in the worst outcome, especially in the early stages of cell adhesion. There does not appear to be a direct link between wettability and the fate of cells on Ti surfaces. Indeed, while samples stored in air and ethanol have drastically different contact angle measurements (the former being hydrophobic and the latter hydrophilic), the cell behavior was unaffected. In addition, while wettability and laser treatment can affect the early stages of cell adhesion, they do not have a strong effect on the number of cells at longer incubation times (3 and 7 days). Laser machining does however affect the cell morphology and alignment, where cells preferentially align themselves parallel to the direction of the laser machined grooves with an elongated morphology.

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Surface science is a multidisciplinary subject which affects us on a daily basis. Surfaces are of particular interest because the chemical bonding and atomic structure is different at the surface compared to the bulk properties of a material. This interface is of great significance because it is where charge exchange, or new chemical bonds occur. One essential aspect of surface science is surface wettability, which can be harnessed to produce self-cleaning surfaces. This very lucrative notion, where surfaces with low adhesion to liquids, can result in quick and autonomous shedding, has inspired a multitude of device fabrication and implementation. Over the past decade, several self-cleaning surfaces have been fabricated from superhydrophobic surfaces, which depends on a stable interface between solid, liquid and gas. These surfaces, however, are restricted in their applications and fail to operate upon mechanical damage or nonhomogeneous fabrication processes. Recent advances in wettability science have produced omniphobic lubricant-infused surfaces (OLIS). These surfaces are created by tethering a liquid to a surface, providing a stable liquid interface, which results in excellent aqueous and organic liquid repellency, and high robustness toward physical damage. This thesis will encompass an overview of the classical models for surface wettability, new models for liquid mobility, the criteria required to obtain OLIS, as well as some of the biomedical engineering applications fabricated from this technology. Herein, a novel manufacturing process was developed to produce smooth channeled polymeric microfluidic devices from rough 3D printed molds. Additionally, we integrated OLIS technology with electroconductive sensors to create high surface area electroactive material with self-cleaning properties, ideal to combat non-specific adhesion of biomolecules. Furthermore, our fabrication methods are inexpensive and have the potential to be easily integrated into manufacturing processes to create highly functional microfluidic devices, optimal for lab-on-chip diagnostic platforms. / Thesis / Master of Applied Science (MASc) / Recent advances in wettability science have produced omniphobic lubricant-infused surfaces (OLIS) inspired by the Nepenthes pitcher plant. These surfaces are created by tethering a liquid to a surface, providing a stable liquid interface, which results in excellent aqueous and organic liquid repellency, as well high robustness toward physical damage and high pressure dispensing scenarios. The motivation for this thesis is to expand on the applications for OLIS devices. Herein, a novel manufacturing process was developed to produce smooth channeled polymeric microfluidic devices from rough 3D printed molds. Additionally, we integrated OLIS technology with electroconductive sensors to create high surface area electroactive material with self-cleaning properties, ideal to combat non-specific adhesion of biomolecules.

This thesis is concerned with the study of morphology and properties of sub-micron thin Nafion® films. The motivation of the work arises from the need to characterize the 4 -10 nm thin ionomer films in the catalyst layer of polymer electrolyte fuel cell (PEFC). A protocol for the fabrication of self-assembled ultra-thin Nafion® films on planar substrates was successfully developed. Films of thickness ranging 4 nm-300 nm, determined by three different techniques - variable angle spectroscopy ellipsometry (VASE), atomic force microscope (AFM) and x-ray photo-electron spectroscopy (XPS), could be reproducibly generated on SiO2/Si wafer. The 4 nm thin film is one of the thinnest, continuous film of Nafion® ever reported. This is the first time that the structure/properties of such thin Nafion® film have been investigated. An interesting finding is the thickness-dependent structure and property of these films. Films with thickness <55 nm exhibited hydrophilic-free surface but thicker films (>55 nm) had hydrophobic surface. Similarly, sub-55 nm films had a lower and thickness-independent protonic conductivity compared to thicker films that exhibited thickness-dependent conductivity. Anomalously high water uptake (by quartz crystal microbalance) and swelling (by ellipsometry) of sub-55nm films indicate that low conductivity is not due to low water content However, differences in surface morphology were observed by the AFM phase contrast analysis. The lack of ionic domain was also observed in the thinner films (4-30 nm) from the grazing incidence small x-ray scattering (GISAXS) experiments. Thermal annealing over a range of temperature (110-160 oC) revealed a dramatic switching of the film surface from hydrophilic to hydrophobic was observed for sub-55 nm films with lower thickness film requiring higher annealing temperature. Bulk proton conductivity was significantly reduced after annealing for all films. An interesting finding was the regeneration of conductivity after to prolonged liquid water exposure and a corresponding switching back of the surface to hydrophilic. The thickness-dependent structure/property of ultra-thin Nafion® films is attributed to substrate induced confinement effect. Self-assembly of Nafion® on various substrates (SiO2, carbon, Pt and Au) was studied. The ionomer/substrate interaction and resulting film morphology followed a trend with respect to substrate surface energies and Nafion® dispersion compositions. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-09-29 12:36:19.05

Magnesium and its alloys have been considered for load-bearing implant materials due to their similar mechanical properties to the natural bone, excellent biocompatibility, good bioactivity, and biodegradation. Nevertheless, the uncontrollable corrosion rate in biological environment restrains their application. Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is a widely used bio-ceramic which has bone-like mineral structure for bone fixation. Poor fracture toughness of HA makes it not suitable for load-bearing application as a bulk. Thus, HA is introduced into metallic surface in various forms for improving biocompatibility. Recently friction stir processing (FSP) has emerged as a surface modification tool for surface/substrate grain refinement and homogenization of microstructure in biomaterial. In the pressent efforts, Mg-nHA composite surface on with 5-20 wt% HA on Mg substrate were fabricated by FSP for biodegradation and bioactivity study. The results of electrochemical measurement indicated that lower amount (~5% wt%) of Ca in Mg matrix can enhance surface localized corrosion resistance. The effects of microstructure,the presence of HA particle and Mg-Ca intermetallic phase precipitates on in vitro behavior of Mg alloy were investigated by TEM, SEM, EDX,XRD ,and XPS. The detailed observations will be discussed during presentation.