Adsorption of PEO from Toluene onto Mica: Does PEO Form Aggregates or Is It Truly Dispersed?

Abstract

The adsorption of PEO on mica surfaces has recently been the topic of controversy. Marra and Hair suggested that the adsorption of PEO on mica proceeds through aggregates that are excluded from the region between the surfaces upon their compression. Such behavior explains the presence of long-range hysteretic forces. On the other hand, Luckham and Klein reported that PEO was truly dispersed in toluene and that the forces experienced by the surfaces were in agreement with adsorbed polymer layers in a good solvent. The latter authors attributed these discrepancies to impurities ("dust") in nonfiltered solutions. In order to clarify the filtration issue (are aggregates, if any, removed by filtration or does the filtration process make any difference?), we discuss new experimental results obtained from surface force experiments on PEO adsorbed onto mica from toluene. The results obtained showed that the filtration process can effectively remove the aggregates initially but that they reform again on standing. Experiments using a PEO (Mw = 90,000) dissolved in toluene at 55-60°C for 5-7 days showed that "true" dissolution of PEO in toluene could be obtained. The forces experienced at room temperature by surfaces bearing layers of PEO adsorbed from such solutions are representative of adsorbed layers of polymer in a good solvent medium.