No description available.

No description available.

The adhesion of poly(dimethyl siloxane) (PDMS) to silica substrates was measured by 90 degree peel testing of PDMS strips cast on silica substrates. The objective of this work was to investigate the effects of silica surface chemistry on the adhesion between PDMS and silica substrate. Silica substrates with different surface chemistry were prepared by both chemical modification and physical adsorption. Silane coupling agents were used to provide octyl chains and primary amino groups on the silica surfaces. Also silica surfaces were coated with cetyltrimethylammonium bromide (CTAB), polyvinylamine (PVAm) or poly(N-isopropylacrylamide) (PNIPAM) by physical adsorption. The adhesion samples were prepared by casting Sylgard® 184 silicone elastomers on silica surfaces followed by thermal curing. Water contact angle measurements, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared microscopy (FTIR) were performed to measure the surface properties of the peel test samples. It is believed that hydrogen bonding between siloxane bonds in PDMS and silanol groups on silica substrate contributes to the strong adhesion of PDMS and silica surface. The adhesion forces significantly reduced by the adsorption of PVAm and PNIPAM onto silica surfaces. In addition, the introduction of primary amino groups on silica surface would poison the catalyst during the curing of PDMS, which causes the formation of low crosslinking PDMS in the outer surface and is expected to decline the adhesion force. Lastly, the slightly reduce of adsorbed PVAm (340 kDa) on the silica substrate after peel test is considered to be useful for long-term lubrication. / Thesis / Master of Applied Science (MASc)

No abstract provided / Thesis / Master of Science (MSc)

<p> The high-throughput micro-adhesion tester (HMAT) was constructed to test the adhesive strength of polymers. The design criteria included the ability to rapidly test many different samples in a serial format, and a probe design that would compliment this objective by being easy to place and pull from the samples and easy to mass produce. The HMAT was able to perform 48 adhesion tests at about 30s per test for a total of 24 min. The final probes were made from a capillary tube with a small metal cap on the top for ease of lifting. They are easy to make and easy to place and pull from the custom probe box. The probe box was designed to hold the probes upright while the polymer is drying and during the test while not interfering with the test itself. Tests on PDMS show reasonable repeatability with the standard deviation being about 20% of the mean value. Since the HMAT is meant to be used for primary screening, the accuracy of the measurements is not as critical as it would be for later tests. </p> / Thesis / Master of Applied Science (MASc)

No description available.

A wood surface, which is exposed to a high temperature condition, can experience inactivation. Surface inactivation results in reduced ability of an adhesive to properly wet, flow, penetrate, and cure. Thus, an inactivated wood surface does not bond well with adhesives. The changes in surface chemistry, wettability, and adhesion of inactivated wood surfaces, including heartwood of yellow-poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), were studied. Wood samples were dried from the green moisture content condition in a convection oven at five different temperature levels ranging from 50 to 200 °C. The comparative characterization of the surface was done by X-ray photoelectron spectroscopy (XPS), sessile drop wettability, and fracture testing of adhesive bonds. The oxygen to carbon ratio (O/C) decreased and the C1/C2 ratio increased with drying temperature. The C1 component is related to carbon-carbon or carbon-hydrogen bonds, and the C2 component represents single carbon-oxygen bond. A low O/C ratio and a high C1/C2 ratio reflected a high concentration of non-polar wood components (extractives/VOCs) on the wood surface, which modified the wood surface from hydrophilic to more hydrophobic. Wettability was directly related to the O/C ratio and inversely related to the C1/C2 ratio. Contact angle decreased with time and increased with the temperature of exposure. Southern pine had a lower wettability than yellow-poplar, which was due to a greater concentration of non-polar hydrocarbon-type extractives and heat-generated volatiles on the surface. Solvent extraction prior to drying did not improved wettability, whereas, extraction after drying improved wettability. A contribution of extractives migration and VOCs generation played a significant role in the heat-induced inactivation process of southern pine. The maximum strain energy release rate (Gmax) showed that surface inactivation was insignificant for yellow-poplar when exposed to drying temperatures < 187°C. The southern pine was most susceptible to inactivation at drying temperatures > 156°C, particularly when bonded with phenol-formaldehyde (PF) adhesive. Chemical treatments improved the wettability of inactivated wood surfaces, but an improvement in adhesion was not evident for specimens bonded with polyvinyl-acetate (PVA) adhesive. NaOH surface treatment was most effective for improving adhesion of the PF adhesive bond. / Ph. D.

The effect of normal load, contact velocity, and dwell time on the coefficient of adhesion at slip in braking was investigated. A test rig that simulated locomotive wheel/rail interactions was used for the experimentation. The results indicated a drop in the coefficient of adhesion with increasing speed. However, normal load, contact velocity, and dwell time, as operating variables, did not have any effect on the variation of the coefficient of adhesion. A description of the investigation and recommendations for further studies is included. / Master of Science

The diversity of adhesive/adherend pairs has created innumerable unique combinations of thermodynamic, kinetic, chemical, physical and rheological contributions with which to explain adhesion processes. So complex are the interrelationships of these contributions to the overall composite system that little information can be extracted about the role of the adhesive properties themselves. This study attempts to simplify the number of variables influencing the strength of adhesive joints by employing a series of styrene-isoprene-styrene linear triblock copolymers as model hot-melt adhesives for titanium 6-4 alloy substrates. The block copolymer samples have narrow molecular weight distributions and styrene contents ranging from 20 to 60% by weight. For these systems a finite number of "dominant" variables are defined including 1) adherend wettabf lity, 2) mechanical properties, 3) rheology, 4) adhesive and adherend contamination, and 5) temperature-pressure cycles for joint formation. Characterization of the block copolymer series in each of these areas is presented. Copolymer morphology emerges as an important variable affecting the material and adhesive properties of these systems. The adhesive joints prepared from these samples are simple lap shear specimens. Comparative joint strengths and joint fracture energies of the series of copolymer adhesives are rationalized in terms of styrene content, styrene domain connectivity and domain orientation. Scanning electron microscopy is employed to examine the surface characteristics of the fractured adhesives. Distinctive failure features are associated with the styrene content and dissipative capacities of the adhesives. / Master of Science

CD44 is a transmembrane glycoprotein found on a variety of cells including those of myeloid and lymphoid origin. CD44 is highly conserved among various species and is involved in the homing of lymphocytes and monocytes to lymph nodes, Peyer's patches, and sites of inflammation. In the present study, we demonstrate that monoclonal antibody (mAb) 9F3, directed against murine CD44 expressed on cytotoxic T lymphocytes (CTls), can trigger the lytic activity of CTls and redirect CTl-mediated lysis to antigen-negative Fc receptor-positive target cells. Similar redirected lysis was also inducible using mAb MEL - 14, directed against the lymphocyte homing receptor for endothelium (gp - 90MEL-14). The redirected lysis induced by mAbs 9F3 and MEl-14 in the CTL was similar to that induced by mAbs against the aβ T-cell receptor or CD3. In contrast, mAbs directed against CDS, CD45R, and CD11a (LFA-1, lymphocyte function-associated antigen 1) failed to evoke lytic activity. Furthermore, CD44 and MEl-14 mAbs were able to mediate NK cell lysis of the NK-resistant tumor PS15. The current study demonstrates that CD44 and gp_90MEL-14 molecules, in addition to participating in T-cell homing and adhesion, may play a major role in delivering the transmembrane signal to the CTl that triggers the lytic activity, even when the T cell receptor is not occupied. The alternate pathway of CTL activation characterized in this study may exhibit both beneficial and deleterious effects on the host. On one hand, this property may enable CTL to kill cancer cells or virally-infected cells which may fail to express major histocompatibility complex (MHC)-encoded antigens. On the other hand, this alternate pathway may contribute to nonspecific tissue damage seen at sites of inflammation. / Master of Science