Microcalorimetric studies of the complexation between poly(ethylene oxide) and alkaline salts in solution

Abstract

AbstractA series of microcalorimetric measurements have been done on complex formation between poly(ethylene oxide) (PEO) and some alkaline metal salts in solution at 25°C. Heat of complexation measurements as a function of PEO content were done with a Tian‐Calvet microcalorimeter and heat capacity measurements have been done with a Picker dynamic microcalorimeter. A very weak exothermic interaction between the species has been found for the PEO‐KSCN pair in water indicating that complexation is difficult to obtain due to the important hydration of both solutes. However, a comparatively large exothermic interaction has been observed for the same pair in anhydrous methanol. Exothermic interactions have also been found for PEO‐KI, ‐NaI and ‐LiI systems in methanol with decreasing absolute values for heats of complexation going from KI to LiI. In methanol, heats of complexation pass through a rather flat and broad maximum at PEO/salt molar ratios going from 1:1 to 4:1 for KSCN and KI. For NaI, the maximum appears for a molar ratio of 2:1 and for LiI, this ratio is 4:1. Heat capacity measurements do not indicate any specific feature for any of the systems except in the case of KSCN in methanol. Experimental results are discussed in terms of ion size and of ion solvation.