81 research outputs found
Photocatalytic Nanolithography of Self-Assembled Monolayers and Proteins
Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a helium–cadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni2+, enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope
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Effect of crosslinking on the microtribological behavior of model polymer brushes
Polymer brushes in good solvents are known to exhibit excellent tribological properties. We have modeled polymer brushes and their gels using a multibead-spring model and studied their tribological behavior via nonequilibrium molecular-dynamics (MD) simulations. Simulations of brush- against-wall systems were performed using an implicit solvent-based approach. Polymer chains were modeled as linear chains, randomly grafted on a planar surface. Quantities extracted from the simulations are the normal stress, shear stress and concentration profiles. We find that while an increase in the degree of crosslinking leads to an increase in the coefficient of friction, an increase of the length of crosslinker chains does the opposite. Effect of crosslinking can be understood in two ways: (i) there are fewer polymer chains in the outer layer as the degree of crosslinking increases to take part in brush-assisted lubrication, and (ii) crosslinked polymer chains are more resistant to shear than non-crosslinked ones
Surface-Initiated Polymer Brushes in the Biomedical Field: Applications in Membrane Science, Biosensing, Cell Culture, Regenerative Medicine and Antibacterial Coatings
Detailed studies of the density of states of amorphous NBSI obtained by synchrotron radiation photoemission
Partial densities of states in amorphous-Alloys from resonant photoemission and cooper minima
Partial densities of states in amorphous-Alloys from resonant photoemission - CUTI, CUZR, CUHF
Large-eddy simulation of kerosene spray combustion in a model scramjet chamber
Large-eddy simulation (LES) of kerosene spray combustion in a model supersonic combustor with cavity flame holder is carried out. Kerosene is injected through the ceiling of the cavity. The subgrid-scale (SGS) turbulence stress ensor is closed via the Smagorinsky’s eddyviscosity model, chemical source terms are modelled by a finite rate chemistry (FRC) model, and a four-step reduced kerosene combustion kinetic mechanism is adopted. The chamber wallpressure predicted from the LES is validated by experimental data reported in literature. The test case has a cavity length of 77mm and a depth of 8mm. After liquid kerosene is injected through the orifice, most of the droplets are loaded with recirculation fluid momentum inside the cavity. Due to lower velocity of the carrier fluid inside the cavity, sufficient atomization and evaporation take place during the process of droplet transportation, resulting in a rich fuel mixture of kerosene vapour accumulating inside the cavity. These rich fuel mixtures are mixed with fresh air by the approachmixing layer at the front of the cavity and are thus involved in burning accompanied with the approach boundary layer separation extending towards upstream. The combustion flame in the downstream impinges onto the rear wall of the cavity and is then reflected back to the front of the cavity. During the recirculation of hot flow, heat is compensated for evaporation of droplets. The circulation processes mentioned above provide an efficient flame-holdingmechanism to stabilize the flame.Comparisons with results froma shorter length of cavity (cavity length of 45mm) show that, due to insufficient atomization and evaporation of the droplets in the short distance inside the cavity, parts of the droplets are carried out of the cavity through theboundary layer fluctuation and evaporated in the hot flame layer, thus resulting in incomplete air fuel mixing and worse combustion performance. The flow structures inside the cavity play an important role in the spray istribution, thus determining the combustion performance
Systematic study of molecular beam epitaxy growth and magnetic properties of Fe on Au(111)
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