Using atomic force microscopy to probe the adsorption kinetics of poly(ethylene oxide) on glass surfaces from aqueous solutions

This paper presents force-distance measurements using the AFM in order to study the adsorption kinetics of high molecular weight polyethylene oxide (4million Da) with a broad molecular weight distribution onto glass surfaces. The measurements were conducted at different incubation times in the polymer solution. In 0.01M NaCl the PEO was found to take a relatively long time (>2 days) to attain full surface coverage, during the period from the first contact of the polymer solution with the surface to full surface coverage, the range of the interaction between the two surfaces increases from around 20nm to 130nm, indicating slow adsorption kinetics, which can be attributed to the exchange between the adsorbed layer with the polymer molecules in solution as well as a change that might occur in the conformation of the adsorbed chains. During this period, the adhesion observed on separation of the surfaces was found to be dependant with incubation time in the PEO solution reaching its maximum value in the time frame of 29-47h of incubation. These results seem to be different from earlier data obtained from adsorption of the PEO on the glass surface from the KNO₃ solutions on lower molecular weight polymers. Therefore experiments were also conducted in the presence of KNO₃ where it was found that the adsorption was faster and resulted in thicker layers compared to the adsorption from the NaCl solution. This is attributed mainly to the high concentration of K⁺ ions, which are effective binders of the lone pair electrons of the ether groups (-O-) of the PEO and the negatively charged silica on the glass surface.