Molecular reorientational freedom in urea inclusion compounds at low temperatures

ISSN： 1362-3028

Source： Molecular Physics, Vol.21, Iss.2, 1971-01, pp. : 225-240

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Abstract

The molecular reorientational freedom in urea inclusion compounds has been studied for the following long chain molecules: 16-hentriacontanone, 12-bromotricosane, 3-hexadecanone, 1-bromohexadecane. In addition to the classical impedance bridge technique, the depolarization thermocurrent method was used. This technique is characterized by its great sensitivity and allows measurements at low temperatures. Its interest lies in the possibility of separating experimentally the different relaxation processes. The whole body of experimental results cannot be explained by Lauritzen's model. The calculation of the potential energy of interaction between the guest molecules and the host lattice is re-examined here with particular attention directed to the coefficients of the 6–12 Lennard-Jones interaction. As a result of the present work, it appears that the polarization observed by Meakins at high frequency is only partial, whereas the carbon atoms of the urea lattice—whose contribution was neglected by Lauritzen—play a predominant part. Taking into account the modified potential energy of interaction and allowing for a contraction of the lattice, it is possible to propose a reasonable interpretation of relaxation times as slow as those observed (as a general rule five domains are observed).