Adsorption and interaction of a graft copolymer of poly(ethylene imine) and poly(ethylene oxide)

The adsorption of proteins and particles onto surfaces carrying firmly adsorbed or covalently bound chains of poly(ethylene oxide) (PEG) is generally very low. This makes it of fundamental and practical interest to learn about the structure of PEO coatings and how PEG-coated surfaces interact with each other and, for example proteins. A prerequisite for such studies is, of course, that stable PEG-coated surfaces can be obtained. For this purpose we employed a two-step method to coat negatively charged surfaces, such as mica or silica, with PEG. In the first reaction step, cationic poly(ethylene imine) is adsorbed onto the negatively charged surface. In the next step, the adsorbed polyelectrolyte is reacted with a functionalized PEO chain. Both reaction steps were followed both by ellipsometry and by direct measurement of surface forces. From these measurements we obtained information concerning the adsorbed amount and the layer thickness, as well as the dependence on range and distance of the interaction between two PEG-coated surfaces.