PROBE TRANSLATIONAL AND ROTATIONAL DIFFUSION IN POLYMERS NEAR T-G - ROLES OF PROBE SIZE, SHAPE, AND SECONDARY BONDING IN DEVIATIONS FROM DEBYE-STOKES-EINSTEIN SCALING

Rotational and translational dynamics of a variety of probes are compa red in several polymers near the glass transition temperature, T-g. Se cond harmonic generation was used to measure the rotational relaxation distribution and average rotational relaxation time, [tau], and fluor escence nonradiative energy transfer was used to measure D-trans, the translational diffusion coefficient. D-trans is affected greatly by pr obe size and shape, typically with a temperature dependence in the rub bery state near T-g which violates Debye-Stokes-Einstein (DSE) scaling and an apparent enhancement in translational diffusion; in contrast, [tau] is largely unaffected by probe size and shape (for the ranges st udied), as long as the probe is sufficiently bulky to have its dynamic s coupled to the polymer alpha-relaxation, and follows DSE scaling. Th ese effects are associated with the short-time side of the distributio n of reorientation relaxation times being sensitive to probe size and aspect ratio and the fact that D-trans is dominated by short-time rela xations while [tau] is dominated by long-time relaxations. With hydrog en bonding between probe and polymer, both D-trans and [tau] may be af fected. (C) 1998 Elsevier Science B.V. All rights reserved.