Effect of additives on the cloud point of polyethylene glycols

Abstract

Polyethylene glycol 20, 000 and 6, 000 were found to have an upper consolute temperature, called “cloud point”, and the effects of various additives on the polyethylene glycols were investigated in this study. Electrolytes lowered the cloud point in proportion to their concentrations through dehydration and electrostriction. It was found that anions played a more important role than cations and the effects of both the cations and the anions clearly followed the classical Hofmeister series. However, the Schultze-Hardy rule holds for the effect of anions, and fails for the effect of cations. Salts of large polarizable anions such as iodide and thiocynate rather raised the cloud point, and their effects were ascribed to the fact that they break the water structure and weaken hydrophobic bonding of the polyoxyethylene moiety. Nitrates of polyvalent cations also raised the cloud point. This was ascribed to the complex formation between the polyvalent cations and ether oxygens of the polyoxyethylenes. This explained the failure ‘of the Schultze-Hardy rule for cations. Uncharged aromatic compounds drastically lowered the cloud point, while aliphatic alcohols slightly lowered the cloud point, This result suggests that there might be some interaction between ether oxygens and aromatic nucleus.