Molecular bridging between water-dispersed particles and gelatin-coated surfaces

An atomic force microscope (AFM) was used to measure the distance dependenc e of the forces between microscopic-size glass spheres coated with gelatin and a solid surface in the presence of aqueous solution. It was observed th at the adhesion and binding of microscopic objects on gelatin-coated surfac es is a result of competition between (i) screened electrostatic forces due to charged surfaces, (ii) repulsive entropic forces due to compression of surface-adsorbed gelatin, and (iii) binding and detachment of polymer chain s from an adsorbing surface. Whereas the electrostatic and entropic forces have a typical decay length of several tens of nanometers, it was found tha t the binding and detachment of gelatin molecules from adsorbing surfaces p roceeds over extraordinary large surface-to-surface distances of several hu ndreds of nanometers. As a result, the surface-binding energy of a micromet er-size particle on a gelatin-coated surface is of the order of 10(3) to 10 (4) k(B)T.