Sessile droplet freezing and ice adhesion on aluminum with different surface wettability and surface temperature

This paper focused on the sessile droplet freezing and ice adhesion on aluminum with different wettability(hydrophilic, common hydrophobic, and superhydrophobic surfaces, coded as HIS, CHS, SHS, respectively) over a surface temperature range of ?9°C to ?19°C. It was found that SHS could retard the sessile droplet freezing and lower the ice adhesion probably due to the interfacial air pockets(IAPs) on water/SHS interface. However, as surface temperature decreasing, some IAPs were squeezed out and such freezing retarding and adhesion lowering effect for SHS was reduced greatly. For a surface temperature of ?19°C, ice adhesion on SHS was even greater than that on CHS. To discover the reason for the squeezing out of IAPs, forces applied to the suspended water on IAPs were analyzed and it was found that the stability of IAPs was associated with surface micro-structures and surface temperature. These findings might be helpful to designing of SHS with good anti-icing properties.     

Capillary Adhesion of Microbeams： Finite Deformation Analysis

Capillary force may cause adhesion of devices at micro- and nano-scales. Considering the fact that large deformation is often involved in adhesion of microbeams, we analysed the capillary adhesion of two beams using finite deformation elasticity theory. The critical adhesion condition can be obtained from the present method as a function of the bending stiffness, Young＇s contact angle, the spacing of the two beams as well as the surface tensions of the solid and liquid phases. The solution for the capillary adhesion of a beam with a rigid substrate is also given. The results from the finite deformation analysis are compared with that of infinitesimal deformation method in order to show the necessity of accounting for the nonlinear effect associated with large deflection. The method adopted in this study can also be used to solve other adhesion problems associated with van der Waals force or electrostatic force.     

Measurement of interaction force between RGD-peptide and Hela cell surface by optical tweezers

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) are found to promote cell adhesion, they are modified at numerous materials surface for medical applications such as drug delivery and regenerative medicine. Peptide-cell surface interactions play a key role in the above applications. In this letter, we study the adhesion force between the RGD-coated bead and Hela cell surface by optical tweezes. The adhesion is dominated by the binding of α5β1 and RGD-peptide with higher adhesion probability and stronger adhesion strength compared with the adhesion of bare bead and cell surface. The binding force for a single α5β1 -GRGDSP pair is determined to be 16.8 pN at a loading rate of 1.5 nN/s. The unstressed off-rate is 1.65 × 10-2s-1 and the distance of transition state for the rigid binding model is 3.0 nm.     

A polynomial hybrid reflection model and measurement of its parameters based on images of sample

Reflectance model is a basic concept in computer vision.Some existing models combining the classical diffuse reflectance model and those for surfaces containing specular components can approximately describe real reflectance.But the ratio of diffuse and specular reflection decided manually has no clear meaning. We propose a new polynomial hybrid reflectance model.The reflectance map equation with a known shape (for example cylinder)as a sample is used to estimate parameters of the proposed reflectance model by least square regression algorithm.Then the reflectance parameters for surfaces of the same class of materials can be determined.Experiments are performed for a metal surface.The synthesis images produced by the proposed method and existing ones are compared with the real acquired image,and the results show that the proposed reflectance model is suitable for describing real reflectance.     

Ab initio study of oxygen-vacancy LaAlO3（001） surface

Density functional theory is used to investigate the surface structures and the energies of two possible terminated LaAlO3 （001） surfaces with oxygen vacancies, i.e. LaO- and AlO2-terminated surfaces. The large displacements of ions, deviated from their crystalline sites, can lead to the formation of the surface rumpling. From thermodynamics analysis, the AlO2-terminated surface with oxygen-vacancies is less stable than the LaO-terminated one. Some states in the gap lie under the Fermi level by about -1eV in the LaO-terminated surface with oxygen vacancies. For the AlO2- terminated oxygen-vacancy surface, some O 2p states move into the mid-gap region and become partially unoccupied. The two types of termination surfaces exhibit conduction related to oxygen vacancies. Our results can contribute to the application of LAO films to high dielectric constant materials.     

The autocorrelation of speckles in deep Fresnel diffraction region and characterizations of random self-affine fractal surfaces

This paper studies the correlation properties of the speckles in the deep Fresnel diffraction region produced by the scattering of rough self-affine fractal surfaces. The autocorrelation function of the speckle intensities is formulated by the combination of the light scattering theory of Kirchhoff approximation and the principles of speckle statistics. We propose a method for extracting the three surface parameters, i.e. the roughness w, the lateral correlation length ξ and the roughness exponent α, from the autocorrelation functions of speckles. This method is verified by simulating the speckle intensities and calculating the speckle autocorrelation function. We also find the phenomenon that for rough surfaces with α= 1, the structure of the speckles resembles that of the surface heights, which results from the effect of the peak and the valley parts of the surface, acting as micro-lenses converging and diverging the light waves.     

Fabrication of Nanoparticle Pattern Through Atomic Force Microscopy Tip—Induced Deposition on Modified Silicon Surfaces

With an atomic force microscopy (AFM)tip used as a “nib” and gold colloidal particles as “ink”,patterns of gold colloidal particles have been deposited successfully from the AFM tip onto specific regions of silicon surfaces modified by bifunctional mercaptosilane,i.e.(3-mercaptopropyl)-triethoxysilane.This was used as an adhesion agent and can immobilize nanoparticles delivered from the AFM tip onto the substrate surface.     

200 nm-1000 nm spectra of light emitted in the impact of ~(40)Ar~(10+) upon Al and Si solid surfaces

This paper reports the measured results of the 200 nm-1000 nm characteristic spectral lines of Al, Si and Ar atoms when highly charged ions 40Ar10+ are incident upon Al and P-type Si surfaces. The ion 40Ar10+ is provided by the ECR ion source of the National Laboratory of the Heavy Ion Accelerator in Lanzhou. The results show that when the low-speed ions in the highly charged state interact with the solid surfaces, the characteristic spectral lines of the target atoms and ions spurted from the surfaces can be effectively excited. Moreover, because of the competition of the non-radiation de-excitation of the hollow atom by emitting secondary electrons with the de-excitation process by radiating photons, the spectral intensity of the characteristic spectral lines of Ar atoms on the P-type Si surface is, as a whole, greater than that of Ar atoms on the Al surface.     

First-principles study of the （001） surface of cubic PbHfO3 and BaHfO3

Using first-principles techniques,we investigate the(001) surfaces of cubic PbHfO3(PHO) and BaHfO3(BHO) terminated with both AO(A=Pb and Ba) and HfO2.Surface structure,partial density of states,band structure,and surface energy are obtained.The BaO surface is found to be similar to its counterpart in BHO.For the HfO2-terminated surface of cubic PHO,the largest relaxation appears on the second-layer atoms but not on the first-layer ones.The analysis of the structure relaxation parameters reveals that the rumpling of the(001) surface for PHO is stronger than that for BHO.The surface thermodynamic stability is explored,and it is found that both the PbO-and the BaO-terminated surfaces are more stable than the HfO2-terminated surfaces for PHO and BHO,respectively.The surface energy calculations show that the(001) surface of PHO is more easily constructed than that of BHO.     

Mechanism of SO2 Promotion for NO Reduction With NH3 over Activaed Carbon—Supported Vanadium Oxide Catalyst

SO2 shows a significant promoting effect on the activity of V2O5/AC catlayst for No reduction with ammonia at low temperatrures (180-250℃）.In the present study,the mechanism of the SO2 promotion was studied.It was found that the promoting effect of SO2 on the catalytic activity is due to the formation of a sulfate species on the catalyst surace.The sulfate species is linked to carbon surfaces other the vanadium or mineral surfaces.There is a synergetic role between carbon and V2O5 for the formation of surface sulfate species.A possilbe mechanism is proposed.SO2 is adsorbed and oxidized by oxygen to SO3 on the vanadium surface, and the formed SO3 shifts to the carbon surface and converts into sulfate species.The formed sulfate species acts as a new acid site,improves significantly the NH3 adsorption,and hence promotes the activity of the catalyst.During the reaction in the presence of SO2 at low temperatures,the sulfate species stays on the catalyst surface,while the ammonium ions react with NO continuously to avoid the formation and deposition of excess ammonium sulfate salts on the catalyst surface.     

Fractal Analysis of Surface Roughness of Particles in Porous Media

A fractal dimension for roughness height （RH） is introduced to characterize the degree of roughness or disorder of particle surface characters which significantly influence physical-chimerical processes in porous media. An analytical expression for the fractal dimension of RH on statistically self-similar fractal surfaces is derived and is expressed as a function of roughness parameters. The specific surface area （SSA） of porous materials with spherical particles is also derived, and the proposed fractal model for the SSA of particles with rough surfaces is expressed as a function of fractal dimension for RH and fractal dimension for particle size distribution, relative roughness of particle surface, and ratio of the minimum to the maximum particle diameters of spherical particles.     

Water droplet impact on superhydrophobic surfaces with microstructures and hierarchical roughness

Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied.Experimental data shows that the critical impact velocity induced wetting transition of droplet on the superhydrophobic surfaces is strongly determined by the perimeter of single micropillar,the space between the repeat pillars and the advancing contact angle of the sidewall of the micropillars.The proposed model agrees well with the experimental results,and clarifies that the underlying mechanism which is responsible for the superhydrophobic surface with hierarchical roughness could sustain a higher liquid pressure than the surfaces with microstructures.     

Symmetrical adhesion of two cylindrical colloids to a tubular membrane

With the full treatment of the Helfrich model we theoretically study the symmetrical adhesion of two cylindrical colloids to a tubular membrane. The adhesion of the rigid cylinders with different radius from the membrane tube surface can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. These significant structural behaviors can be obtained by analyzing the system energy. A second order adhesion transition from the desorbed to weakly adhered states is found, and a first order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered states can be obtained as well.     

Lattice Boltzmann simulation of liquid–vapor system by incorporating a surface tension term

In this study,we investigate the pseudopotential multiphase model of lattice Boltzmann method(LBM)and incorporate a surface tension term to implement the particle interaction force.By using the Carnahan–Starling(CS)equation of state(EOS)with a proper critical pressure–density ratio,a density ratio over 160000 is obtained with satisfactory numerical stability.The added surface tension term offers a flexible choice to adjust the surface tension strength.Numerical tests of the Laplace rule are conducted,proving that smaller spurious velocity and better numerical stability can be acquired as the surface tension becomes stronger.Moreover,by wall adhesion and heterogeneous cavitation tests,the surface tension term shows its practical application in dealing with problems in which the surface tension plays an important role.     

Measurement of large aspheric surfaces by annular subaperture stitching interferometry

A new method for testing aspheric surfaces by annular subaperture stitching interferometry is introduced. It can test large-aperture and large-relative-aperture aspheric surfaces at high resolution,low cost,and high efficiency without auxiliary null optics.The basic principle of the method is described,the synthetical optimization stitching model and effective algorithm are established based on simultaneous least-square fitting.A hyperboloid with an aperture of 350 mm is tested by this method.The obtained peak-to-valley (PV) and root-mean-square (RMS) values of the surface error after stitching are 0.433λand 0.052λ(λis 632.8 nm),respectively.The reconstructed surface map is coincide with the entire surface map from null test,and the difference of PV and RMS errors between them are 0.031λand 0.005λ,respectively. This stitching model provides another quantitive method for testing large aspheric surfaces besides null compensation.     

Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

A microtribometer is used to measure and compare pull-off forces and friction forces exerted on (a) micro-dimpled silicon surfaces, (b) bare silicon surfaces, and (c) octadecyltrichlorosilane (OTS) treated silicon surfaces at different relative humidity (RH) levels separately. It is found that above a critical RH level, the capillary pull-off force increases abruptly and that the micro-dimple textured surface has a lower critical RH value as well as a higher pull-off force value than the other two surfaces. A micro topography parameter, namely sidewall area ratio, is found to play a major role in controlling the capillary pull-off force. Furthermore, micro-dimpled silicon surface is also proved to be not sensitive to variation in RH level, and can realize a stable and decreased friction coefficient compared with un-textured silicon surfaces. The reservoir-like function of micro dimples is considered to weaken or avoid the breakage effect of liquid bridges at different RH levels, thereby maintaining a stable frictional behaviour.     

Experimental investigation of enhancing the subsurface damage threshold of Nd-doped phosphate glass

Experimental investigation was performed with a 1064-nm,10-ns Nd:YAG laser to determine the effects of the surface hydrogen acid etching on laser damage,compared with damage of conventionally polished surface.The investigation was helpful for us to understand the negative effects of Nd-doped phosphate glass surface and subsurface damage(SSD)on laser induced damage threshold(LIDT).A set of samples was polished,and then chemically etched in a cool buffered 10%HF 20%H_2SO_4 solution at different times.Another set of samples was ground and etched in the hot-buffered solution,and then polished.All the samples were irradiated with Nd:YAG laser and characterized by optical microscopy.Results of LIDT were obtained according to International standard ISO/DIS 11254-1.2.Chemical treatment can remove the contaminants in the polished re-deposition layer and the SSD for improving the laser damage resistance of Nd-doped phosphate glass surfaces.The method of using hot solution was more effective than that of using cool solution.     

Laser—Surface Interaction of Compound Semiconductors—Desorption Induced by Electronic Excitation of Surface States

In this talk a review is given of currently carricd out studies on laser-induced desorption from surfaces of compound semiconductors.The reviewincludes only the non-thermal processes.which can be detected by eitherirradiation with laser of subgap photon energies or with extremely low-intensity pulsed lasers.It is emphasized also that laser induced non-thermaldesorption is a powerful technique for surface characterization and surfacecleaning.     

Aggregation Behaviors of Cr Atoms Sputtering Deposited on Flat and Curved Liquid Surfaces

We report on the aggregation behaviors of Cr atoms deposited on flat and curved silicone oil substrates by the sputtering technique. It is found that the Cr atoms are prone to form quasi-circular clusters first and then these clusters connect with each other to form ramified or network-shaped aggregates. In the case of a fiat liquid surface, large quasi-circular clusters are frequently observed and their sizes increase with the deposition time. In the case of a curved surface with a larger curvature, the Cr atoms and dusters tend to move toward to the oil drop edge, and ramified aggregates with small widths are shaped. In the case of a curved surface with smaller curvature, large quasi-circular clusters and ramified aggregations can coexist. Based on the motion features of the Cr atoms and clusters on different liquid surfaces, various distinct film morphologies are discussed in detail.     

Heat Transfer from a dc Laminar Plasma—Jet Flow to Different Solid Surfaces

The beat flux distributions were measured by using transient method for an argon dc laminar plasma-jet flow impinging normally on a plate surface embedded with copper probes.Different powders were coated on the probe surfaces and the effect of powder coating on the heat transfer from jet flow to the probe surface was examined Experimental results show that the maximum values of the heat flux to the probe increase with the coating of fine metal powders,while for the surfaces coated with fine ceramic powders,the maximum values of heat flux decrease,compared with that to the bare copper probe surface.