Abstract
Dynamical properties of the three polymorphic phases α, β′ and β of tristearin [C 3H 5(OCOC 17H 35) 3] have been studied by incoherent quasi-elastic neutron scattering and X-ray diffraction. At 293 K the difference in the lateral packing density of hydrocarbon chains significantly affected the mean square displacement 〈 U 2 〉 . As compared with β, an increase by 4% in the cross-sectional area for β′ resulted in a twofold increase in 〈 U 2 〉 . In case of α, an increase by 7% led to a threefold increase in 〈 U 2 〉 . The molecular motion in the α phase was analyzed using the model of the uniaxial rotational diffusion in a onefold cosine potential. It has been clarified that the rotational fluctuation about the chain axis in the α phase is rather restricted compared with that in the rotator phase of n-alkanes. The 〈 U 2 〉 in the α phase decreased significantly with the temperature, and reached the level of the 〈 U 2 〉 in the β phase at 193 K.
Published Version
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