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On the microscopic mechanism behind the purely orientational disorder–disorder transition in the plastic phase of 1-chloroadamantane

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Abstract

Globular molecules of 1-chloroadamantane form a plastic phase in which the molecules rotate in a restrained way, but with their centers of mass forming a crystalline ordered lattice. Plastic phases can be regarded as test cases for the study of disordered phases since, contrary to what happens in the liquid phase, there is a lack of stochastic translational degrees of freedom. When the temperature is increased, a hump in the specific heat curve is observed indicating a change in the energetic footprint of the dynamics of the molecules. This change takes place without a change in the symmetry of the crystalline lattice, i.e. no first-order transition is observed between temperatures below and above the calorimetric hump. This implies that subtle changes in the dynamics of the disordered plastic phase concerning purely orientational degrees of freedom should appear at the thermodynamic anomaly. Accordingly, we describe, for the first time, the microscopic mechanisms behind a disorder–disorder transition through the analysis of neutron diffraction and QENS experiments. The results evince a change in the molecular rotational dynamics accompanied by a continuous change in density.

Graphical abstract: On the microscopic mechanism behind the purely orientational disorder–disorder transition in the plastic phase of 1-chloroadamantane

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Publication details

The article was received on 30 May 2017, accepted on 03 Jul 2017 and first published on 05 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP03630B
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    On the microscopic mechanism behind the purely orientational disorder–disorder transition in the plastic phase of 1-chloroadamantane

    A. Vispa, D. Monserrat, G. J. Cuello, F. Fernandez-Alonso, S. Mukhopadhyay, F. Demmel, J. Ll. Tamarit and L. C. Pardo, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP03630B

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