Smooth versus Rough Surfaces

One other item should be discussed before we begin, and that is the question of smooth versus rough surfaces. In meteorological applications, the surface features leading to roughness are usually so closely distributed (e.g., grass, crops, bushes) that only the height... 

There are two predictive relationships based on wind speed. Liss and Merlivat (1986) used a physical rationale to explain the increase in the Kl versus wind speed slope at higher wind velocities in wind-wave tunnel and lake measurements, resulting in a piecewise linear relationship with two breaks in slope. These breaks are presumed to occur at the transition between a smooth surface and a rough surface and between a rough surface and breaking waves. In dimensionless form, this relationship is given as... 

At present, many authors I20-I26 follow another concept From the plot of pj p [M /t) versus the surface tension of the liquids, the geometric factor K is calculated for those liquids that should wet the solid completely. By inserting this K value and [t]/p- ] M2/t for these liquids into Eq. (13). their contact angles 0 are calculated and used for the interpretation of the solid-vapor surface tension of the porous material. This procedure is dubious, because it can be expected that the contact angles, calculated from the Washburn equation, are affected by roughness and porosity. If we apply this procedure to the PTFE powder for hexadecane, a contact tingle 0 = 88 would be obtained. However, it is well known that the contact angle of hexadecane on a flat and smooth... 

Figure 4.17 Shift and change of the resonance frequency of a quartz crystal microbalance, real part of the admittance versus frequency, /q, Wq, resonance frequency and full width at half maximum (FWHM) of the initial gold electrode,/j, w, resonance frequency and FWHM of a gold electrode after formation of a rigid and smooth surface film (no damping), resonance frequency and FWHM of a gold electrode after formation of a viscoelestic and/or rough surface film (strong damping).

Figure 7,34. Illustration of the effect that surface roughness has on the wetting of a solid by a liquid drop. The plot shows schematically the evolution of the cosine of the contact angle on a rough surface (%) versus the same quantity on a smooth surface with the same surface composition (0c). The theoretical line refers to equation (7.27)...

Although interfaces usually constitute a small fraction of the total volume of a composite, the effects of their properties on the bulk properties are large because of the large surface area of the interfaces. The properties of the interface depend on whether or not there has been a reaction at the interface, the type of bonding at the interface, and on the nature (crystalline or amorphous) and morphology of the interface material. The consequences of having a smooth versus a rough interface are far more important in structural applications where one phase, such as a fiber, must be able to slide out of the matrix to some extent, in order to achieve optimum mechanical behavior. 

Incorporation of nanosized SiC particles in the EL NiP matrix increased the hardness from 627 43 to 704 60HVqqj. However, incorporation of micronsized SiC particles increased the hardness to 1669HVqqj. The cumulative mass loss versus time (see Fig. 8.26) due to cavitation erosion corrosion in 3.5% NaCl is found to be very low for EL Ni-P-nano SiC composite coating compared with its coimterpart incorporating micron-sized SiC particles. The EL Ni-P-nano SiC coated specimen exhibits a smooth and uniform surface after the cavitation erosion corrosion test with no visible pits (see Fig. 8.27). The uniform distribution of the nanosized SiC particles in the EL NiP matrix (R 0.95 0.060 pm) inhibits the formation of pits. However, the higher surface roughness (R 1.72 0.051 pm) promotes bubble formation and causes detachment of the SiC particles, which results in the formation of small cavities on the surface of EL Ni-P-micro SiC coated steel (see Fig. 8.27). Hence, it is evident that incorporation of nanosized particles in EL NiP matrix could provide a better cavitation erosion corrosion resistance and inhibit the onset of erosion damage near surface defects. 

In considering how SERS intensities can be affected by electrode potential in the absence of a redox process, it is to be expected that for many molecules the surface concentration, F, can change with potential, i.e., F = F(V). It should be mentioned that SERS-active surfaces stabilize adsorption so F(V) may be less affected by potential on a rough surface than on a smooth surface. Figure 25 shows that the position of the I versus V profile depends on the vibrational mode. Obviously, if different bands show very different / versus V curves, there are other factors in addition to the surface concentration which depend on potential and which affect intensities. Changes in orientation of surface molecules as a function of electrode potential have been considered... 

The species on the smooth twigs of Fraxinus excelsior comprise a community quite different from that on rougher, older twigs from the same tree (Degelius, 1964). On rough and fissured bark, some lichens can be seen to colonize the crevices and some the plates (Brodo, 1968 Yarranton, 1967) although it is not clear whether in this case it is a matter of colonization ability on rough versus smooth surfaces, or survival in moist (crevice) versus dry (plate surface) microhabitats. 

---