Effect of molecular weight on the interactions between poly(ethylene oxide) layers adsorbed to glass surfaces

Abstract

We have investigated the adsorption of poly(ethylene oxide) (PEO) of molecular weights 56000, 205000, 685000 onto glass surfaces using a development of the atomic force microscope technique. In this method a glass particle is glued to a silicon cantilever to give a particle probe surface forces apparatus. Data are presented for the polymers adsorbed onto one and two surfaces at low and high coverage of adsorbed polymer. In the case of polymers adsorbed onto one surface a strong adhesion is noted on separation of the surfaces. This is due to PEO being pulled off the glass surface on separation. Similar effects are also observed when the polymer is adsorbed onto both surfaces at low surface coverage of polymer. However, rarely is any attraction noted as the surfaces are brought together. This is a consequence of the rapid rate of approach in this method not allowing sufficient time for polymer rearrangement and adsorption to occur. At high coverage of polymer on both surfaces repulsive steric interactions were observed. The range of these interactions increased with the molecular weight of the adsorbed polymer, such that the adsorbed layer thickness δ scales roughly with the molecular weight M through a power law with exponent 0.4.