Relaxation of the Adsorbed Molecule

Spreading leads to a larger nnmber of polymer-surface contacts and, consequently, it becomes more difficult for the whole polymer molecule to detach. Spreading may 

FIGURE 15.9 Relative rate of adsorption of a lipase on a surface as a function of the preadsorbed amount of polyethylene oxide, PEO. (Adapted from Schroen, C.G.P.H. et al., Langmuir, 11, 3068,1995.) 

FIGURE 15.10 Effect of polymer concentration on the kinetics of adsorption onto a silica surface for (a) polystyrene from decalin and (b) subtilisin from water. The polymer fluxes Jf toward the surface are indicated in the figures. (Adapted from Norde, W. and Giacomelli, C.E., Macromol. Symp., 145, 125, 1999.) 

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One can also analyze the rotational relaxation of the adsorbed molecules.140 Figure 27a shows a time sequence of a single molecule with an overlay of the unit vector u(t) defined as the direction of the longer principal axis of the gyration tensor. An instantaneous polymer configuration may be described by an ellipse, and therefore, the simplest conformational change is the rotational motion of an ellipse. The time correlation function of u(t) decays exponentially where zr denotes the rotational relaxation time, °c exp(-f/rr). 

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