Interaction with the Interface Attachment and Detachment

FIGURE 14.2 Molecule interacting with an interface through adsorption and desorption. 

The forward flux responds to c. and the fraction of unoccupied sorbent surface area 

9 = Tniax being the adsorbed amount when the sorbent surface is saturated with adsorbate 

dr/dtl+ varies linearly with d9/dll+. This definition of 0 holds for molecules that do not change their conformation when they adsorb. This is the case for small, rigid molecules. Polymers, including proteins, may show adsorption-induced conformational changes. The relation between T and 0 then usually is more intricate this is discussed in Section 15.1. 

The value of is lowered by any repulsive barrier to attachment. The origin of such a barrier might be electrostatic repulsion, solvation effects, or it could be that the residence time at the sorbent surface for a fraction of the molecules is too short for attachment. Because the repulsive barrier may be affected by the degree of coverage of the surface by the adsorbate, k may vary with 9 and, hence, with time. 

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