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Materials 2015, 8(6), 3334-3351; doi:10.3390/ma8063334

Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with g-Alumina Nanoparticles

1
Grup de Propietas Físiques dels Materials (GRPFM), Departament de Física i Enginyeria Nuclear, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Diagonal 647, Barcelona 08028, Spain
2
Dielectric Materials Physics Laboratory (DILAB), Departament de Física i Enginyeria Nuclear, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Colom 11, Terrassa 08222, Spain
3
Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV-EHU, Apartado 644, Bilbao 48080, Spain
4
Instituto de Ciencia de Materiales de Aragón (ICMA), Departamento de Química Orgánica-Facultad de Ciencias, Universidad de Zaragoza-CSIC, Zaragoza 50009, Spain
*
Author to whom correspondence should be addressed.
Academic Editor: Klara Hernadi
Received: 14 May 2015 / Revised: 28 May 2015 / Accepted: 1 June 2015 / Published: 8 June 2015
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Abstract

In the present work, the nematic glassy state of the non-symmetric LC dimer α-(4-cyanobiphenyl-4′-yloxy)-ω-(1-pyrenimine-benzylidene-4′-oxy) undecane is studied by means of calorimetric and dielectric measurements. The most striking result of the work is the presence of two different glass transition temperatures: one due to the freezing of the flip-flop motions of the bulkier unit of the dimer and the other, at a lower temperature, related to the freezing of the flip-flop and precessional motions of the cyanobiphenyl unit. This result shows the fact that glass transition is the consequence of the freezing of one or more coupled dynamic disorders and not of the disordered phase itself. In order to avoid crystallization when the bulk sample is cooled down, the LC dimer has been confined via the dispersion of γ-alumina nanoparticles, in several concentrations. View Full-Text
Keywords: liquid crystal; dimer; glass transition; confinement; nanoparticles; modulated differential scanning calorimetry (MDSC); dielectric spectroscopy; thermally stimulated depolarization currents (TSDC) liquid crystal; dimer; glass transition; confinement; nanoparticles; modulated differential scanning calorimetry (MDSC); dielectric spectroscopy; thermally stimulated depolarization currents (TSDC)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Diez-Berart, S.; López, D.O.; Salud, J.; Diego, J.A.; Sellarès, J.; Robles-Hernández, B.; de la Fuente, M.R.; Ros, M.B. Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with g-Alumina Nanoparticles. Materials 2015, 8, 3334-3351.

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