Surface Roughness and Activity on Atomic Length Scales

Surface Roughness and Activity on Atomic Length Scales 

For the characterization of surface roughness of carbon blacks, different experimental techniques have been applied in the past. Beside microscopic investigations, e.g., AFM that give an impressive but more qualitative picture [90-92], scattering techniques such as SANS [93] and SAXS [94-96] as well as gas adsorption techniques [79-84, 97-99] have been used for a fractal analysis of surface roughness. The results discussed in the literature appear somewhat controversy, since almost flat surfaces with ds 2 [98, 99] and also rough surfaces with 2.2 ds 2.6 [79-84, 93-96] are found. 

Waals- and surface tension interaction, respectively. Dependent on the dominance of one of the two potentials, remarkably different estimates of surface roughness are obtained. For that reason a proper analysis of these factors is necessary for getting reliable results. 

In the present chapter we will summarize results of two different evaluation procedures for the surface roughness of carbon blacks. In the mono-layer regime we refer to the scaling behavior of the estimated BET-surface area with the size of adsorbed probe molecules (yardstick method). On smooth flat surfaces the BET-area is independent of the adsorbed probe or applied yardstick, while on rough surfaces it decreases with increasing probe (yardstick) size due to the inability of the large molecules to explore smaller cavities. This is shown schematically in Fig. 5. 

An important point in the above evaluation of carbon black surface morphology is the correct estimation of the cross-section a of the applied probe molecules. This is done by referring to the mass density p of the probe molecules in the bulk liquid state that are considered as spheres in a hexagonal close packing  

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