Dynamic and free volume aspects of spin probe TEMPO in organic glass formers: Polymer cis-1,4-poly(isoprene)

Abstract

In this paper, we relate the spin probe reorientation dynamics of 2,2,6,6-tetramethyl-piperidinyl-1-oxyl (TEMPO) to the free volume in polymeric cis-1,4-poly(isoprene) (cis-1,4-PIP 10k) as obtained using electron spin resonance (ESR) or positron annihilation lifetime spectroscopy (PALS), respectively. The correlation time, τc, of the cis-1,4-PIP 10k / TEMPO system over a wide temperature range from 100 K up to 350 K exhibits five regions of different behaviour, i.e., two region within slow regime at TX1slow, TX2slow = TX,inifast followed by the slow to fast motion regime transition region at Tc and finally, two fast regimes at TX2fast. These findings are in good coincidence with the changes in ortho-positronium (o-Ps) lifetime with temperature at the characteristic PALS temperatures TgPALS, Tb1L and Tb2L suggesting the common origin of the underlying physical processes.