Microscopic roughness

Although the rate of dissolving measurements do thus give a quantity identified as the total surface area, this area must include that of a film whose thickness is on the order of a few micrometers but basically is rather indeterminate. Areas determined by this procedure thus will not include microscopic roughness (or fractal nature). 

He concluded that for aluminium and titanium certain etching or anodization pretreatment processes produce oxide films on the metal surfaces, which because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth . 

Surface Morphology. The initial Integrity of an adhesively bonded system depends on the surface oxide porosity and microscopic roughness features resulting from etching or anodization pretreatments. (17) The SAA surface characterized in this study consists of a thick (9 ym), porous columnar layer which provides excellent corrosion resistance in both humid and aggressive (i.e., Cl ) media. I The thinner FPL oxide provides a suitable substrate surface for evaluating the candidate inhibitors. 

Fig. 13.8. Atomic metallic ion emission and nanotip formation, (a) At high temperature, the atoms on a W tip becomes mobile. The tip surface is macroscopically flat but microscopically rough, (b) By applying a high field (1.2-1.8 V/A,), the W atoms move to the protrusions, (c) The apex atom has the highest probability to be ionized and leave the tip. The W ions form an image of the tip on the fluorescence screen, (d) A well-defined pyramidal protrusion, often ended with a single atom, is formed. By cooling down the tip and reversing the bias, a field-emission image is observed on the fluorescence screen. The patterns are almost identical. (Reproduced from Binh and Garcia, 1992, with permission.)...

The invention of the electron microscope in the 1930s by Knoll and Ruska cleared the way for scientists to take an even closer look at vesicles and other colloidal structures [5]. Improving the resolution of the optical microscope roughly by the factor that the optical microscope improved that of the unaided eye, the finer structures of colloidal systems became visible. With the electron microscope, single bilayers can be made visible and the distance between lamellae can be determined. Thus, the structure of a given system can be determined to up to 1/10000000 of a millimeter, which is about the distance of six atoms in a molecule. The most impressive results are obtained with the freeze fracture and cryo-TEM methods [6]. 

Another consideration is the quality of the tools purchased from different manufacturers, where differences in the finish on the punch face may occur. Substantially different surfaces can be obtained from tools supplied by different vendors. Although this may not be noticeable to the naked eye, and the tools may meet specifications, a microscopic rough finish could lead to picking and/or sticking on the punch surface. 

Recently, many research efforts have been directed at developing pretreatments for metal surfaces which produce oxide layers with pores, fibrous projections, or microscopic roughness which can enhance metal/polymer adhesion by mechanical means. In order for the pretreatments to lead to an increase in durability, the oxide layers formed must be stable under environmental conditions. The bulk 3l-33 S2-128> of the research in this area has been completed in an attempt to increase the durability of... 

Mechanical Interlocking Theory. A practical adhesion can be enhanced if the adhesive is applied to a surface which is microscopically rough. 

The stability of heparin-amine complexes depends to a large extent on the structure of the constituent amine. The best results were obtained for dimethylaniline and pyridine (Table 6) 65). The amount of bound heparin is, as is seen, proportional to the amount of immobilized amine, while the molar ratio amine/heparin is predetermined by the structure of the surface. Microscopically rough surfaces were shown to prevent association between heparin and amine as the portion of the amine is sterically inaccessible for the macromolecules of heparin. 

With the preparation on the microscope roughly in focus adjust the substage condenser to focus the iris diaphragm (partially closed), if necessary centering this to the field. 

Fig. 2.1 Fracture surface of an alumina/20 vol.% SiC whisker composite showing microscopically rough surface. Presence of whiskers readily evident due to debonding along the matrix-whisker interface.

For this mechanism to operate, debonding along the crack-whisker interface (often associated with crack deflection) must occur during crack propagation and allow the whiskers to bridge the crack in its wake. Examination of the fracture surfaces of whisker-reinforced composites reveals that they are microscopically rough with whiskers readily evident (Fig. 2.1). 

In addition to water rinse, certain other procedures also produce flatter surfaces. It has been reported that a BHF-treated surface is flatter than one treated with HE. A photocurrent-assisted etching followed by a dark current transient has been found to reduce microscopic roughness. A multistep process, involving formation of an anodic oxide, dissolution in 0.2 M NH4F at pH 4 and then at pH 4.9, produced a completely monohydride-terminated (111) surface. ... 

Continuous films deposited on microscopically rough surfaces (generally at room temperature). 

Low viscosity permits penetration of the microscopic rough areas of the substrate and aids adhesion. 

It has been discussed (Section 5.1.1) that most of the attraction forces have only a short range their magnitude and strength decreases quickly with increasing distance. Therefore, because the surfaces of all particulate matter are, at least microscopically, rough (see Section 5.1.1, Fig. 5.11), and the mass of the particles decreases with the third power of the particle size, the adhesion tendency increases with decreasing particle dimensions. 

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