Translational and Rotational Diffusion of Spin Probes in Nylon Films

Abstract

ABSTRACT:The translational diffusion of nitroxide spin probes in nylon films was investigated by means of a sublimative desorption method, and compared with their rotational diffusion as determined by an electron spin resonance (ESR) technique in our previous papers. The translational diffusion coefficients D calculated using McBain's formula were dependent on the structures of the spin probes, and on the structures of the nylons. The Arrhenius plots of D defined one distinct crossover point for each probe in the temperature range examined, which was quite consistent with that found in the Arrhenius plots of the rotational diffusion coefficients R. This suggests that the motional change of the nylon chains affects not only the translational motions of the probes but also their rotation. However, the activation energies for translational and rotational diffusion were very different; the activation energies for translation were larger below the crossover point than above it, whereas those for rotation behaved in the opposite manner. This discrepancy can perhaps be explained by the differences between the time-scales of the motions detected in the translational and rotational measurements. The results obtained here are compared with those for polyethylene, natural rubber, and polyisobutylene reported elsewhere.KEY WORDS Spin Probe / Nitroxide / Diffusion / Nylon / Molecular Motion/ The relationship between translational and rotational diffusion is of interest in the fields of membrane science and dyeing chemistry. Knowledge of this relationship should provide useful information on the mechanism of transport.We have investigated the rotational mobilities of spin probes in nylon films by means of an electron spin resonance (ESR) technique.1-6 It was found that the rotational mobilities were strongly influenced not only by the structures of the spin probes and of the nylons, but also by the molecular interactions between the probe molecules and the polymer chains. In addition, the rotational motions of the probe molecules in the "high" temperature region were interpreted by taking into account their simultaneous translational diffusion. 3 From this point of view, it is worthwhile to examine the translational diffusion of the spin probes by an independent method, for comparison with their rotational diffusion.Some papers have reported on the relationships between translational and rotational diffusion of nitroxide spin probes in polymer matrices. 7 -11 Stryukov used a method of scan-1 Permanent address:

Mobility of Spin Probes in Micelles of Cationic Gemini Surfactants Having Dodecyl Groups.

“…E.R in the DC3-12 micelle was similar to those in the conventional surfactant micelles, whereas the higher activation energies were found in the DC6-12 micelles. As was pointed out in previous papers [28][29][30], the mode of rotation should be taken into consideration to interpret the activation energies. If the motion of the spin probes consists of rotation and translation, E.R includes a part of the activation energy for translation in addition to that for rotation [30].…”

“…As was pointed out in previous papers [28][29][30], the mode of rotation should be taken into consideration to interpret the activation energies. If the motion of the spin probes consists of rotation and translation, E.R includes a part of the activation energy for translation in addition to that for rotation [30]. This suggests that the rotational mode of the spin probes is probably different between DC3-12 and DC6-12 micelles.…”