Changes of relaxation dynamics of a hydrogen-bonded glass former after removal of the hydrogen bonds.

Dielectric relaxation spectra of two closely related glass formers, dipropylene glycol [H–(C₃H₆O)₂–OH] and dipropylene glycol dimethyl ether [CH₃–O–(C₃H₆O)₂–CH₃], were measured at ambient and elevated pressures in the supercooled and the glassy states are presented. Hydrogen bonds formed in dipropylene glycol are removed when its ends are replaced by two methyl groups to become dipropylene glycol dimethyl ether. In the process, the primary relaxation, the excess wing, and the resolved secondary relaxation of dipropylene glycol are all modified when the structure is transformed to become dipropylene glycol dimethyl ether. The modifications include the pressure and temperature dependences of these relaxation processes and their interrelations. Thus, by comparing the dielectric spectra of these two closely related glass formers at ambient and elevated pressures, the differences in the relaxation dynamics and properties in the presence and absence of hydrogen bonding are identified. [ABSTRACT FROM AUTHOR]