Abstract
The dielectric permittivity and loss of LiClO4 solutions in poly(propylene glycol (PPG)), molecular weight 2000, have been measured over a concentration range up to a ratio of Li+ to oxygen atoms in PPG of 33.3:100, between 77 and 350 K. The data have been analyzed in both the permittivity and electrical modulus formalisms. Addition of LiClO4 to poly(propylene glycol) first increases the height of the β-relaxation peak, and ultimately a second sub-Tg relaxation peak at a higher temperature emerges. This is in addition to the β-relaxation peak due to the reorientation of PPG dipoles, whose strength decreases from that in pure PPG-2000. For a fixed temperature, the dc conductivity initially decreases with increasing Li+ concentration up to 20 Li+ per 100 O atoms and thereafter increases. This concentration corresponds to that at which the Tg of the solution reaches its limiting value of ca. 310 K. It is concluded that the formation of ion pairs causes a second and slower sub-Tg relaxation process and that the increase in the efficiency of chain packing reduces the strength of the β-relaxation of the polymer.