Surface coverage steric factors

The linear plot in Figure 7 of log( —j<—) (see Table 2, footnote g) and the Taft-Hammett (23) ap parameter for these complexes Ru(bpy)2(4 -X-stilb)2 + arises because the increasing ap parameter reflects the more anodic redox potential for the vinyl ligand, which results in a greater concentration of initiator, a more rapid polymerization reaction, and hence a greater amount of polymer deposition on the electrode surface. Such a correlation is indeed remarkable because it implies a greater surface coverage per unit time only if factors such as steric bulk, polymer conformation and rate of polymer precipitation remain relatively constant for the substituted trans-stilbazole series. 

The constant segment density model is, of course, only an approximation at best. It would be expected that in general the segment density would be a function of the distance from the surface of the particle. The precise form adopted by the segment density distribution function should depend upon the steric layer properties. These properties will be determined by such factors as the chemical nature of the surface and the polymer, the quality of the solvency of the dispersion medium, the surface coverage, and the mechanism of attachment of the polymer chains to the surface. Some of these expectations have been confirmed by the recent experimental determinations of the segment density distribution functions for several different systems. 

Besides the spatial control of surface modification (patterning), control over surface coverage (functional group densities) is a centrally important point. As in any organic chemical reaction, the functional groups involved, the medium and the reaction conditions (such as temperatme) influence the reactivity. However, for surface-based reactions, additional factors must be taken into accoimt [36,37]. These include, among others, steric and an-chimeric effects of the reactants, prevented or hindered access of the reactive species from the solution to the reaction centers, or interactions of neighbor-... 

It can be considered that two factors determine low friction, namely, better coverage and a strong interaction between the lubricant and the media surface. Better coverage is ascribed to the balance of the hydrophobic and hydrophilic properties of the lubricant. It is well-balanced when the hydrocarbon chain is introduced. The polar group of the ammonium salt without steric hindrance has strong interactions at the surface. 

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