Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

Sulfur adsorption on Fe(1 1 0): a DFT study

The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers.     

Quantitative measurement of tip-sample forces by dynamic force spectroscopy in ambient conditions

We introduce a dynamic force spectroscopy technique enabling the quantitative measurement of conservative and dissipative tip-sample forces in ambient conditions. In difference to the commonly detected force-vs-distance curves dynamic force microscopy allows to measure the full range of tip-sample forces without hysteresis effects caused by a jump-to-contact. The approach is based on the specific behavior of a self-driven cantilever (frequency-modulation technique). Experimental applications on different samples (Fischer-sample, silicon wafer) are presented.     

The role of surface science in bioengineered materials

Materials employed in biomedical technology are increasingly being designed to have specific, desirable biological interactions with their surroundings, rather than the older common practice of trying to adapt traditional materials to biomedical applications. Moreover, materials scientists are also increasingly deriving new lessons from naturally occurring materials (from mollusk shells to soft animal tissue) about useful composition–structure property relationships that might be mimicked with synthetic materials. Together, these two areas of effort constitute what we may call bioengineered materials. It is possible to set down a reasonably thorough set of characteristics that bioengineered materials have in common. Among these characteristics we discuss the following: self-assembly, bioengineered materials often rely on information content built into structural molecules to determine the order and organization of the material; hierarchical structure, in most bioengineered materials several different length scales of structure are essential and are formed spontaneously and simultaneously via self-assembly; precision synthesis, fundamental to biological material structures is the idea of macromolecules constructed in a precise manner; templating, ordered structures in bioengineered materials are often propagated from one element or set of instructions, to another; specific and non-specific interactions, the forces involved in holding biomaterials structures together. In the future, a carefully selected combination of this set of characteristics will enable us to bioengineer surfaces that are capable to direct and control a desired biological response. Eventually, such bioengineered surfaces will become important tools to comprehend and analyze how materials interact in nature.     

Relationship between paddy soil adhesion to steel and to rubber

Forty-three pairs of samples concerning adhesion of paddy soil to steel and to rubber are used to identify the relationship between these two groups of variables. Results show that there is no significant difference between them, implying that they are roughly equal to each other in engineering practice.     

Adhesion and fingering in the lifting Hele-Shaw cell: Role of the substrate

The lifting Hele-Shaw cell (LHSC) is used to study adhesion as well as viscous fingering. In the present paper we report a series of observations of development of the interface for different viscous fluids, both Newtonian and non-Newtonian, in a LHSC operated at a constant lifting force. Glass and perspex are used as the plates in two different sets of experiments. The objectives are 1) to measure the time required to separate the plates as a function of the lifting force and 2) to note the force above which viscous fingering appears. We find that for the Newtonian fluids, the plate separation time follows a universal power law with the lifting force, irrespective of fluid and substrate. The non-Newtonian fluids too, with proper scaling obey the same power law. The appearance of fingering, however, depends on the properties of the fluid as well as the substrate. We suggest a modified form of the capillary number which controls the onset of fingering; this new quantity, termed the “fingering parameter” involves the dielectric constants of the substrate and fluid in addition to the viscosity and surface tension.     

Electrostatic forces in micromanipulation: Experimental characterization and simulation including roughness

Manipulation by contact of objects between 1 m and 1 mm are often disturbed by adhesion between the manipulated object and the gripper. Electrostatic forces are among the phenomena responsible for this adhesive effect. Analytical models have been developed in the literature to predict electrostatic forces. Most models have been developed within the framework of scanning probe microscopy, i.e. for a contact between a conducting tip and a metallic surface. In our study, we developed a simulation tool based on finite elements modeling. The strength of this model lies in the fact that it integrates roughness parameters. Measurements of electrostatic forces in function of roughness were conducted by atomic force microscopy. The experimental results were compared with the simulation results showing very good correlation. This demonstrates the influence of surface topography on electrostatic forces, especially for very small separation distances and proves the utility of the simulation tool in designing surfaces with controlled adhesion. Some application fields to which these results can be applied are drug delivery devices and micromanipulation tools.     

A nanoscale understanding of the adhesion of polybutylene terephthalate on aluminum

The adhesion strength of polybutylene terephthalate (PBT) on aluminum was investigated using density functional theory-based total energy calculations. Aluminum atom was connected to a PBT monomer at different orientations and total energies were calculated in order to determine the most stable orientation. The energy differences showed that the Al oriented at 180° with the ester group of the monomer bonded strongly. Using this orientation, the PBT monomer-adhesion on aluminum surface and the aluminum atom adhesion on PBT bulk were also investigated.     

The influence of preparative parameters on the adhesion of alumina washcoats deposited on metallic supports

Well-adhered alumina washcoats on FeCrAl metallic supports were prepared using boehmite sols and alumina slurries. The microstructure and the surface performance of the washcoat/support were investigated by SEM, XRD, and ultrasonic vibration. The effects of the main preparative parameters on the coating adherence were studied. The optimal coating conditions are presented as follows: pre-oxidation of the metallic supports was performed at 900 °C for 10 h, the sol layer loadings were 2.0-6.6 wt.%, and the slurry layer loadings were less than 25.3 wt.%. The sol layer drying was performed at 30 °C for 1 h and that for the slurry layer the drying was performed at 120 °C for 2 h, and the coating calcining was performed at 900 °C for 2 h. The SEM photographs of coated samples show that alumina washcoats were well deposited on the metallic supports.     

Molecular dynamics simulation of peeling a DNA molecule on substrate

Molecular dynamics (MD) simulations are performed to study adhesion and peeling of a short fragment of single strand DNA (ssDNA) molecule from a graphite surface. The critical peel-off force is found to depend on both the peeling angle and the elasticity of ssDNA. For the short ssDNA strand under investigation, we show that the simulation results can be explained by a continuum model of an adhesive elastic band on substrate. The analysis suggests that it is often the peak value, rather than the mean value, of adhesion energy which determines the peeling of a nanoscale material.The project supported by the Distinguished Young Scholar Fund of NSFC (10225209) and key project from the Chinese Academy of Sciences (KJCX2-SW-L2)