Double primary relaxation in a highly anisotropic orientational glass-former with low-dimensional disorder
The freezing of the cooperative reorientational motions in orientationally disordered (OD) molecular crystals marks the so-called \glassy" transition, which may be considered a lower-dimensional version of the structural glass transition. While structural glasses display both positional and ori...
| Autores: | , , , , , |
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| Formato: | artículo |
| Fecha de publicación: | 2016 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/88403 |
| Acesso em linha: | https://hdl.handle.net/2117/88403 https://dx.doi.org/10.1021/acs.jpcc.5b12747 |
| Access Level: | acceso abierto |
| Palavra-chave: | Glass manufacture--Chemistry Chloronitrobenzenes hexa-substitued benzenes goldstein beta-relaxation discotic liquid-crystals plastic crystals transition phenomena dielectric loss supercooled liquids dynamic properties alpha relaxation Vidre -- Fabricació -- Química Benzè Àrees temàtiques de la UPC::Física Àrees temàtiques de la UPC::Enginyeria química::Química física |
| Resumo: | The freezing of the cooperative reorientational motions in orientationally disordered (OD) molecular crystals marks the so-called \glassy" transition, which may be considered a lower-dimensional version of the structural glass transition. While structural glasses display both positional and orientational disorder, in fact, in orientational glasses the disorder involves exclusively the orientational degrees of freedom of the constituent molecules, while the molecular centres of mass form an ordered lattice. We report here on a glass-forming system with even less degrees of freedom, namely the OD phase of a dipolar benzene derivative, pentachloronitrobenzene (C6Cl5NO2). We probe the orientational dynamics of PCNB as a function of temperature and pressure by means of dielectric spectroscopy at normal and high pressure and high-pressure density measurements, and show that the system exhibits a double primary relaxation feature associated with two distinct motions of the molecular dipole moment. After ruling out an interpretation in terms of primitive or intramolecular relaxations, we discuss an assignment of the double relaxation feature based on the material's anisotropy and on the comparison with discotic liquid crystals. |
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