Solid phases in cycloheptanol: Dynamic disorder and glass transitions

Salud, J.; López, David; Diez‐Berart, S.; Pérez‐Jubindo, M. A.; Fuente, M. R. de la; Rute, M.A.; Puertas, R.

doi:10.1016/j.jnoncrysol.2009.09.007

Cited by 5 publications

(5 citation statements)

References 40 publications

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“…Could it be that different disorders give rise to different glass transition temperatures? If we are dealing with structural (SG) and orientational glasses (OG), the dynamic disorder is governed by the so-called α-dielectric relaxation, which embeds the different disorders present in the vitrified phase and, therefore, there is just one glass transition temperature [ 3 , 4 , 5 , 6 , 7 ]. The main dynamic disorders represented by the α-relaxation are translational and orientational in the SG and orientational in the OG.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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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.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…In our case, we obtained 119 for poly2‐4 and 151 for poly2‐6. The lower limit of m is assigned to 16, the strongest materials 35, 36. On the other hand, the most fragile glass‐forming materials have values of m up to 200 or even more.…”

Section: Resultsmentioning

confidence: 99%

Electric modulus and polarization studies on piezoelectric polyimides

Gonzalo¹,

Vilas²,

Sebastián³

et al. 2011

J of Applied Polymer Sci

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The piezoelectric polymeric sensors and actuators are widely valued because of their low density, availability to obtain complex shapes, and easy processing among other characteristics. However, there are not many useful piezoelectric polymers. Aromatic polyimides are high‐performance polymeric materials characterized by thermal stability, chemical resistance, and excellent mechanical properties. Besides, some of these polymers have been reported as candidates to present piezoelectric properties. Our research focuses in the electric characterization of three piezoelectric amorphous aromatic polyimides, containing CN groups in different number and positions. The piezoelectricity in amorphous polymers is mainly due to the orientation polarization of the molecular dipoles, which is induced by the application of an external electrical field to a temperature over their glass transition temperature (Tg). Polyimides are measured by thermally stimulated depolarization currents and dielectric spectroscopy and the analysis of the dielectric data has been performed using the electric modulus formalism to separate conductive and dipolar processes. These measurements have evidenced that the frozen‐in polarization is mainly due to the dipole orientation of the dipolar CN groups, allowing us to understand in depth the mechanism of polarization that contributes to the piezoelectric properties. This will facilitate the obtention of materials with the best possible piezoelectric properties, comparable to those currently available but with higher mechanical and thermal performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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“…As for cC7‐ol, in addition to the α ‐relaxation, it only shows one secondary process ascribed to the axial and equatorial orientations of the –OH group and, by analogy with cC8‐ol is called γ ‐relaxation 11. It should be mentioned that some authors argued the existence of a β ‐relaxation also for cC7‐ol 22.…”

Section: Introductionmentioning

confidence: 81%

Secondary relaxations of orientationally disordered mixed crystals at temperatures lower than the glass transition temperature

García

Tamarit

Pardo

et al. 2011

Physica Status Solidi (a)

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Low‐molecular weight cyclic alcohols as cycloheptanol (C7H14O, hereinafter referred to as cC7‐ol) and cyclooctanol (C8H16O, cC8‐ol) are prototypical materials displaying OD phases which, under fast cooling give rise to orientational glasses (OG). In addition to the ubiquitous α‐relaxation of canonical glasses, several secondary relaxations appear for the mentioned systems (β and γ for cC8‐ol and β for cC7‐ol). The intramolecular character of these secondary relaxations for these materials as well as their mixed crystals was highlighted at temperatures close but above the glass transition. For lower temperatures the low values of dielectric strength makes difficult to account for the relaxation times obtained from the permittivity losses and, thus in this work we present a data analysis based on the Kramers–Kronig relations which connect the real and imaginary parts of dielectric permittivity and shows up a new method to make evident the existence of such secondary relaxations as well as to avoid phenomenological equations for determining the relaxation time.

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Solid phases in cycloheptanol: Dynamic disorder and glass transitions

Cited by 5 publications

References 40 publications

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

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

Electric modulus and polarization studies on piezoelectric polyimides

Secondary relaxations of orientationally disordered mixed crystals at temperatures lower than the glass transition temperature

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