Adsorption of polystyrene onto noble metals from theta solvents

Abstract

The adsorption of polystyrene onto noble metals from 3.3% solutions in five different theta solvents was measured on six noble metals at temperatures a few degrees above the theta temperatures. The amounts adsorbed (in mg m −2) on any given metal were of the same order of magnitude from all five of the theta solvents, but decreased two or three orders of magnitudes with a change of noble metals, in the following order: gold⪢silver⪢palladium, silver-palladium ⪢platinum⪢iridium. The amounts adsorbed on gold from cyclohexane at 60°C decreased seven-fold with a forty-fold decrease of molecular weight, as predicted by Scheutjens and Fleer, but there was no molecular weight dependence to the weak adsorption observed on platinum and iridium. A direct method was used to determine the amount of polymer adsorbed on these metal powders. After the polymer solution and metal powder were equilibrated, the powder was washed free of excess polymer solution with fresh theta solvent and then the adsorbed polystyrene was removed from the metal by rinsing in chloroform, a very good solvent, in which the amount of polystyrene was determined by UV spectroscopy. With the high molecular weight polystyrene (1.8·10 6) the differences in duplicate samples were about 2%, but with the lower molecular weight polystyrene (5·10 4) they were about 25%. It is proposed that the high reproducibility of adsorption results observed with the high molecular weight polymer indicates negligible desorption during rinsing with the theta solvent, but that this rinsing step was less reproducible with the low molecular weight polymer.