Scales of Roughness

2) This is caused by the fact that water has hydrogen bonds and their number decrease with increasing temperature. 

L Daikhin in Piezoelectric Sensors , Series Ed. O. S.Wolfbeis, Vol. 5, Eds C. Steinem and A Janshoff. Springer Series on Chemical Sensors and Biosensors, p. 121, (2006). 

The characteristic length relevant to the vibration of the EQCM is related to the depth in solution where the liquid still oscillates as a result of the oscillation of the surface of the crystal. This is given by 

For a dilute aqueous solution at room temperature this yields a value of 0.23 pm, placing it between the atomic scale and the scale relevant to mass-transport-con-trolled processes. 

SO it can be said that within a distance of about 1 pm these vibrations essentially die out. 

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Several surface roughness measurement techniques are in common usage. The optimum method will depend upon the type and scale of roughness to be measured for a particular application. 

As the scale of roughness becomes finer, the effective increase in A can become enormous. Consequently Fg may be raised to very high value. Indeed, as many engineering surfaces are fractal in nature [36], we can only retain the concept of area at all, if we accept that it can be considered as indefinitely large. The practical adhesion does not become infinite, because the joint with a strong interfacial region will fail (cohesively) in some other region where Fg is smaller [89],... 

This dependence on the degree and scale of roughness is illustrated in Fig. 5,... 

Fig. 5. Wedge test results for Ti adherends with several different surface treatments having differing degrees and. scales of roughness. Specimens were exposed to 100% relative humidity at 60 C. Data from Ref. 132. ...

Wall friction depends on the roug ess of the die wall and its lubrication. For walls with a scale of roughness larger than the diameter of the powder, the wall friction is essentially the same as the internal friction of the powder. This is because the rough wall traps small amounts of the powder in its reguosity and the sliding of the powder mass against this trapped powder produces the effective wall friction. If the wall has a scale of rou mess smaller than the diameter of the powder, the wall friction is controlled particle—wall friction. In both... 

In most chronoamperometry, with measurement times of 1 ms to 10 s, the diffusion layer is several micrometers to even hundreds of micrometers thick. These distances are much larger than the scale of roughness on a reasonably polished electrode, which will have features no larger than a small fraction of a micrometer. Therefore, on the scale of the diffusion layer, the electrode appears flat the surfaces connecting equal concentrations in the diffusion layer are planes parallel to the electrode surface and the area of the diffusion field is the geometric area of the electrode. When these conditions apply, as in Figure 5.23a, the geometric area should be used in the Cottrell equation. 

Surfaces of certain plants — such as the leaf of the Lotus plant — have a surface topography with two scales of roughness in the form of a base profile with peak-to-peak distances of the order of several micrometers and a superposed fine structure with peak-to-peak distances significantly below one micrometer [7-11]. Given this, the Lotus leaf follows the Cassie-Baxter state as sketched in Fig. Ic. Surfaces with... 

More recently with metal (strictly metal oxide) surfaces, evidence indicates that a very much smaller scale of roughness or porosity is important. Provided that the surface itself is strong and coherent, then a roughness with fibres or pores of micron diameter will increase strength in an adhesive bond. 

The hierarchy may have to do also with the simple fact that the surface must be able to repel both macroscopic and microscopic drops. Experiments with artificial fog (microdrops) and artificial rain (large drops) show that surfaces with only one scale of roughness repel rain drops well. However, they cannot repel small fog drops which are trapped in the valleys between the bumps. ... 

This quantifies the phenomenon illustrated in Fig. 16 as the pressure gradient increases, the scale of roughness decreases parabolically (VP 1/w ). An important consequence of this relation is that the drying front roughens as it advances into the body, because the pressure gradient in the drained region decreases. 

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