A new technique for determination of melting temperature of poly(ethylene glycol) by ultrasonic velocimetry

Ultrasonic velocity and density of poly(ethylene glycol) (PEG) (mol. wt. 2000 and 8000) solutions in water and benzene have been studied as a function of temperature from which respective isentropic compressibility has also been calculated. The velocity (as well as isentropic compressibility) undergoes a sudden change near melting temperature, T _m, of the solute polymer. Normally, we expect only one peak in viscoelastic properties at the T _m of PEG. However, we see two peaks (T _m1 and T _m2) in the case of the aqueous solution of PEG while there is only one peak for the case of benzene solution. This has been interpreted on the basis that one of the peaks (T _m1) is for unsolvated PEG and the other peak (T _m2) is that of PEG with water solvation shell. Such solvation shell is not formed with the aprotic solvent (benzene).