The focus of this research is to study the interaction between copper and the diffusion barrier/adhesion promoter. The behavior of copper sputter-deposited onto sputter-cleaned tantalum nitride is investigated. The data show that copper growth on tantalum nitride proceeds with the formation of 3-D islands, indicating poor adhesion characteristics between copper and Ta0.4N. Post-annealing experiments indicate that copper will diffuse into Ta0.4N at 800 K. Although the data suggests that Ta0.4N is effective in preventing copper diffusion, copper's inability to wet Ta0.4N will render this barrier ineffective. The interaction of copper with oxidized tantalum silicon nitride (O/TaSiN) is characterized. The data indicate that initial copper depositions result in the formation a conformal ionic layer followed by Cu(0) formation in subsequent depositions. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 800 K, copper "de-wetting" occurs for temperatures above 500 K. These results indicate that in conditions where the substrate has been oxidized facile de-wetting of copper may occur. The behavior of a sputter-deposited Cu0.6Al0.4 film with SiO2 (Cu0.6Al0.4/SiO2) is investigated. The data indicate that aluminum segregates to the SiO2 interface and becomes oxidized. For copper coverages less than ~ 0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. These data are in contrast with the observed behavior of copper metal deposited onto SiO2 (Cu/SiO2). The data for Cu/SiO2 show that copper does not wet SiO2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu0.6Al0.4/SiO2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K, while Cu diffusion into SiO2 occurs ~ 600 K. These data indicate that aluminum alloyed with copper at the SiO2 interface serves as an effective adhesion promoter and thermal diffusion barrier.

Studying the interactions between bacteria and soil colloidal particles in the environment is important for bioaugmentation purposes. Different factors affect the transport of the bacteria in porous media. For example, the soil type, the ionic strength of the substrate, and biological properties, such as the bacterial cell motility. Since organic materials are present in almost all subsurface media, the presence of natural organic matter (NOM) is considered an important factor influencing bacterial transport in porous media. In this work, a model system was developed to examine the interactions between natural colloidal particles and environmental bacteria using Atomic Force Microscopy (AFM). The natural colloids in the environment were modeled by a surface film of adsorbed NOM onto spherical SiO2 particles. Poly(methacrylic acid) (PMA), a simple linear polyelectrolyte, was used to mimic NOM since both are dominated by carboxylic acid functional groups. Soil Humic Acid (SHA) and Suwannee River Humic Acid (SRHA), two acidic polyelectrolytes, were used in further experiments to represent more complicated NOM. A smooth strain of Pseudomonas aeruginosa (PAO1) that coexpresses A-band and B-band polysaccharides, and its rough mutant (AK1401) that only expresses the A-band polysaccharides, were chosen to represent environmental bacteria. The model system was characterized through analysis of the measured forces between the chemically-modified colloidal probes and the bacterial cells. Interestingly, we found that PMA was not a good model for the more complex NOM substances. Differences were also observed in how each bacterium interacted with the three forms of NOM. For example, P. aeruginosa PAO1 had the highest adhesion with both complex forms of NOM, while P. aeruginosa AK1401 had the lowest adhesion with the complex forms of NOM. Since the lipopolysaccharide (LPS) structure is the only difference between the two strains, we attribute the different interactions to differences in LPS structure. The polymer density on the bacterial surface was found to be the most important factor in controlling the nature of the interaction forces.

"Bacteria during the course of their life undergo a lot of developments on their surface. The changes that occur inside a cell result in the production of a variety of biopolymers on the cell surface. These polysaccharides have been found to play a major role in deciding the adhesive or repulsive nature of a bacterial cell. Based on the application the adhesive nature of a cell sometimes needs to be manipulated such that bacteria are required to have higher adhesions for bioremediation applications and in the case of bioreactors bacteria must not stick to walls to avoid fouling. In order to control adhesions of a cell to a variety of substrates, knowledge of the polysaccharides present on its surface is needed. Therefore the goal of the present study is to detect the sugars present on the surface of Pseudomonas putida KT2442 using Atomic force microscopy and to relate properties of the polysaccharides to bacterial adhesion. Previous experiments suggested that cellulose and other sugars were produced by Pseudomonas putida KT2442. Thus the cells were grown to late exponential phase and treated with cellulase to degrade any cellulose, if present, on the surface of the cells. Control experiments were done on untreated cells and cells that were not treated with cellulase but were centrifuged, since centrifugation is a part of the cellulase treatment and may also affect the bacterial surface. An appropriate (Steric) fitting model for the atomic force microscope (AFM) approach curves was applied to calculate the height and density of the polymer brush layer present on the cell surface. There was a decrease in the density of the polymer brush and increase in the height of the brush upon treatment with cellulase. Centrifugation alone did not affect the approach curves. From looking at the retraction curves it verified the results got from the approach curves and indicated stretching out of the polymer brush to greater distances after the treatment with cellulase. Another batch of cells was treated with dextranase to check for the presence of dextran on the cell surface. Dextranase treated cells behaved identical to the control cells, suggesting that dextran is not one of the polysaccharides present on the bacterial surface. No change was observed in retraction curves data for dextranase treated and untreated cells."

The adhesion of bacteria to uroepithelial cells or urinary catheters is the first step in the development of biofilm formation and urinary tract infections (UTIs). Previous research has suggested that consumption of cranberry juice can prevent the recurrence of UTIs by decreasing bacterial adhesion since isolated compounds in cranberries, known as A-type proanthocyanidins (PACs), change the conformation of proteinaceous fimbriae that help attach bacteria to epithelial cell receptors. Most clinical and laboratory studies have shown the effects of cranberry juice cocktail (CJC) on large communities of bacteria; however, very few studies have evaluated how cranberry affects the adhesion forces of a single bacterium as well as effects on cellular composition and biofilm formation. We used atomic force microscopy (AFM) to investigate the effects of CJC and PACs on the adhesion forces between E. coli and a silicon nitride tip. Bacterial cultures were grown in tryptic soy broth (TSB), supplemented with 0 and 10 wt.% light cranberry juice cocktail (L-CJC) or 128 µg/mL PACs. E. coli bacteria were continuously cultured in the presence of cranberry products up to twelve times. Experiments were conducted at different scales to test bacterial attachment and adhesion forces. At the macroscale, bacteria were incubated with uroepithelial cells and the number of bacteria attached per uroepithelial cell was determined. In nanoscale experiments, the forces of adhesion between E. coli and a silicon nitride AFM tip were probed for bacteria grown in L-CJC or PACs for different numbers of culture times. Successive replacement of media and continued culture in L-CJC and PACs resulted in a significant decrease in adhesion forces for E. coli strains. Finally, during the continuous exposure of L-CJC to bacteria we examined the growth, morphology, and ability to form biofilms of E. coli. We found a decrease in growth rates related to changes in Gram staining with increasing number of cultures in L-CJC. Growth of bacteria in L-CJC or PACs inhibited the development of biofilms on polyvinyl-chloride, which can model biofilm formation on urinary catheters. We also determined that growth of E. coli in L-CJC results in prevention of the expression of indole which can be linked to the inhibition of biofilm formation. Our results help support the molecular mechanisms for the role of cranberry in preventing the adhesion of E. coli to biotic and abiotic surfaces, thus helping to scientifically validate the use of cranberry juice as a prophylactic treatment for the prevention of UTIs.

This doctoral research was realized within the frame of the SMARTNET Project which aimed at developing coatings to improve the cleanability of stainless steel, targeting open surface applications. Throughout this thesis, the radial-flow cell was selected to study the removal of different soils due to its ability to generate well-controlled wall shear stress distributions on the investigated surfaces. Model surfaces were selected for their different physico-chemical and mechanical properties to study the interactions between the soils and the surfaces in detail. A thin layer chromatography sprayer giving a narrower and more reproducible droplet sizes distribution was preferred to mimic splashing and produce controlled spatters. The first experimental campaign involving oil droplets showed that the analytical models available to relate the detachment radius with the critical wall shear stress (minimal wall shear stress required for soil detachment) and the soil adhesion strength in the radial flow cell could only be applied for weakly adherent soils for which removal occurs below 3 Pa, due to the complex hydrodynamics near the inlet. Consequently, the flow inside the radial-flow cell has been characterized using computational fluid dynamics over the whole inlet laminar regime and validated experimentally. Studying the adherence of starch granule aggregates in the radial-flow cell revealed that the conversion of critical radius into critical wall shear stress may be biased when the adhering aggregate height is not negligible with respect to the channel height and when the adherence is such that flow rates above creeping flow conditions are required for soil detachment. The influence of several environmental factors and substrate properties was then examined to improve the understanding of the mechanisms affecting soiling and cleanability. By influencing droplet spreading and competition between capillary forces at the granule-substrate and granule-granule interfaces, substrate wettability affects the shape and compactness of the adhering aggregates, the efficiency of shear forces upon cleaning, and finally the adherence of soiling particles. Macromolecules originating from the starch granules suspension are adsorbed on the substrate from the liquid phase or carried by the retracting film and accumulated at the granule-substrate interface. They influence granule adherence by acting as an adhesive joint, the properties of which seem to be influenced by the detailed history of drying and exposure to humidity. On compliant substrates, the aggregate-substrate interactions induce stresses at the granule-substrate interface which may lead to substrate deformation and promote a more intimate contact between the granules and their substrate, thereby appreciably increasing adherence.

The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.

No description available.

Cell adhesion to extracellular matrix proteins is critical to physiological and pathological processes as well as biomedical and biotechnological applications. Cell adhesion is a highly regulated process involving initial receptor-ligand binding, and subsequent clustering of these receptors and rapid association with the actin cytoskeleton as focal adhesions are assembled. Focal adhesions enhance adhesion, functioning as structural links between the cytoskeleton and the extracellular matrix and triggering signaling pathways that direct cell function. The objective of this thesis research is to develop a mechanical and biochemical analysis of the adhesion strengthening response. Our central hypothesis was that focal adhesion size and position regulate cell adhesion strength by controlling the distribution of mechanical loading. We engineered micropatterned surfaces to control the size and position of focal adhesions in order to analyze the contributions of these specialized adhesive structures to adhesion strengthening. By applying surface micropatterning techniques, we showed robust control over cell-substrate contact area and focal adhesion assembly. Using a hydrodynamic shear assay to quantify adhesion strength to micropatterned substrates, we observed significant adhesive area- and time-dependent increases in adhesion strength. Complimentary biochemical assays allowed us to probe the role of structural proteins recruited to focal adhesions and examine the structure-function relationships between these adhesive structures and adhesion strength. These findings provide insights into the role of focal adhesions in adhesion strengthening, and may contribute to tissue engineering and biomaterials applications.

Atomic force microscopy (AFM) is adapted to the measurement of adhesion forces between indoor-air-pollutant bioparticulates and synthetic carpet fiber materials. This novel technology is used to characterize the adhesion and release of a model bioparticulate, the bacterium E. coli on Nylon. This knowledge will lead to expanded studies of a wider range of biocontaminants, and ultimately to the ability to design carpet and rugs upholstery that reduce the spread of indoor air pollutants. Such an advance would improve life significantly for the 20+ million Americans who suffer from asthma, and countless others who are afflicted with allergies and illness spread via bioparticulates.

During hemostatic and inflammatory responses, cell adhesion molecules play a major role in regulating the leukocytes and platelets adhesion to vascular surfaces under the hydrodynamic environment of the circulation. Selectin-ligand interactions (bonds) mediate leukocyte rolling on vascular surfaces. The molecular basis for differential ligand recognition by selectins is poorly understood. Using atomic force microscopy (AFM), the kinetics of three mutants L-selectin interacting with surrogates of PSGL-1 and PNAd, is compared with those of wild-type L-selectin. The interaction between glycoprotein Ib (GPIb) and von Willebrand Factor (VWF) mediates platelet translocation at the vascular vessel damage sites, which plays a critical role in initiating the platelets adhesion and thrombus formation. Translocation of platelets on VWF requires a shear threshold, suggesting a possible catch bond at work there. We characterized the kinetics of GPIbα interacting with VWF A1 domain, confirming the catch bond existed. Two type 2B VWD A1 mutants eliminated the catch bond and gave longer low force lifetimes. The prolonged lifetimes at low force resulted in more agglutination of platelets with A1 coated microspheres in flow. During the process of hemostasis, the size of prothrombotic ULVWF affects the affinity of VWF to platelets bearing GPIbα on the membrane. ADAMTS13 has been identified and characterized as a multi-domain metalloprotease that regulate the size of ULVWF. We studied how force regulated the binding and cleavage of ADAMTS13 on VWF. We found the cleavage effects could only be observed after the catastrophic structural change of A1A2A3. The unfolding exposed the ADAMTS13 cleavage site and favored the cleavage. Two protocols using different stretching molecules (GPIbα and CR1) and A1A2A3 immobilization methods revealed the cleavage effects diminished with increasing stretching force. This study elucidated mechanisms of the binding kinetics of L-selectin with different structure components from PSGL-1 and PNAd by structural variants. It also provided new insights into our current knowledge of the dynamic adhesion and regulation of GPIbα-VWF interaction in vivo. Using single molecule method, the chemical catalytic reaction between enzyme and substrate has been targeted. These results help us understand this important enzyme-substrate interaction involved in the hemostasis.