Nontranslational Diffusive Motion on Two Different Time Scales in Alkane Nanoparticles

High-energy-resolution quasielastic neutron scattering on three complementary spectrometers has been used to investigate molecular diffusive motion in solid nanoparticles of the alkane n-C32H66. Nontranslational molecular diffusive motion in the plastic phase occurs on two different timescales: a "fast" motion corresponding to uniaxial rotation about the long molecular axis; and a "slow" motion attributed to conformational changes of the molecule. Contrary to the conventional interpretation in bulk alkanes, the fast uniaxial rotation begins in the low-temperature crystalline phase.