ABSTRACT
Fig. 14 The shear modulus ~G~ and the dilational modulus ~E~ as a
function of the adsorbed amount. Both curves are the combined result of various BSA concentrations at increasing surface age. BSA concentrations:
0.001 g/l, Ƒ 0.005 g/l, Ÿ 0.03 g/l, Ŷ 0.1 g/l; Z= 0.42 s-1
In Fig. 14 ~G~ is plotted as a function of the surface concentration for different BSA concentrations. For the sake of comparison the dilational modulus vs. surface concentration curve (~E~(ī)) is given as well. The adsorption data were obtained by ellipsometry, not at the same surfaces, but under identical experimental conditions. The adsorption time was used to link adsorbed amount to the shear modulus. The data in this plot were obtained by measuring the shear modulus in the course of the adsorption process, consequently at increasing surface ages. So equality of adsorptions for different concentrations means higher surface ages for the lower concentration. If the formation of intermolecular bonds is slow compared to the rate of adsorption, moduli determined at equal adsorptions, but at different protein concentrations, would be higher for the lower concentration. However, the results with the
0 0.5 1 1.5 2
different concentrations seem to merge into one master curve of ~G~(ī). Consequently we can conclude that, (i) not the intermolecular bond formation step, but the adsorption rate controls the increase of the shear modulus with time and (ii) the adsorbed amount dominates the value of the shear modulus.
