On the character of the glass transition in columnar discotics

Glüsen, Andreas; Kettner, A.; Kopitzke, Jörg; Wendorff, Joachim H.

doi:10.1016/s0022-3093(98)00767-4

Cited by 44 publications

(45 citation statements)

References 22 publications

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“…glass transition, manifested by the dielectric a 2 -process, is the most straightforward. Glass forming behavior in columnar discotics has been reported earlier and was attributed to predominantly intracolumnar fluctuations of rotational disorder [6,11,23]. A systematic study of several asymmetrically substituted triphenylenes revealed calorimetric T g in the range from À43 to 8°C [23], which are in good agreement with our findings on the brominated compound.…”

Section: Discussionsupporting

confidence: 91%

“…Glass forming behavior in columnar discotics has been reported earlier and was attributed to predominantly intracolumnar fluctuations of rotational disorder [6,11,23]. A systematic study of several asymmetrically substituted triphenylenes revealed calorimetric T g in the range from À43 to 8°C [23], which are in good agreement with our findings on the brominated compound. Further evidence for the association of the a 2 -process with the columnar glass transition comes from the fact that we did not observe a high-temperature dielectric VFT-process for the symmetric HAT6 molecule.…”

Section: Discussionsupporting

confidence: 91%

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Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Yildirim

Wübbenhorst

Mendes

et al. 2005

Journal of Non-Crystalline Solids

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The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Col h ) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C 10 Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C 10 Br, a Ôhigh temperatureÕ glass transition, manifested by a Vogel-Fulcher-Tammann (VFT) type a 2 -process, was found at À31°C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (a 1 ) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as À100°C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a ÔhinderedÕ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionsupporting

confidence: 91%

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Yildirim

Wübbenhorst

Mendes

et al. 2005

Journal of Non-Crystalline Solids

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“…Notice that these values are comparable to the out-of-plane thermal expansion coefficient of graphite ($2.5 Â 10 À5 K À1 ). [13] The anisotropy in the thermal expansivity of discotic liquid crystals is well known [18,21,22] and it reflects the anisotropy in the molecular interactions (intra-vs. inter-columnar, originating from p-p stacking and van der Waals interactions, respectively).…”

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confidence: 99%

“…Typically, positive linear thermal expansion coefficients were found within the Cr phase with values a a % 1.1 Â 10 À1 K À1 and a c % 2.7 Â 10 À4 K À1 for an adamantanoate compound, [21] whereas for triphenylene derivatives with some ether side chains, a a ¼ a c % 2.8 Â 10 À4 K…”

mentioning

confidence: 99%

Negative Thermal Expansion in Discotic Liquid Crystals of Nanographenes

et al. 2010

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Hexa‐peri‐hexabenzocoronene derivatives show a record high negative volumetric thermal expansion coefficient within the crystalline phase. Responsible for the negative thermal expansion is the increase of the tilt angle and the improved packing of the discotic cores with temperature and this has implications in the design of organic electronic devices as well as in advanced nanocomposites with controlled thermal properties.

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“…[1][2][3][4] All of these states can be frozenin into a corresponding ordered glassy state. [5] The strong orbital overlap existing within the columns gives rise to features such as a rapid transport of charges and optical excitations along their columnar axes. [6][7][8][9] Both theoretical and experimental studies have shown that charge transport takes place via hopping events which in turn are strongly influenced by the degree of supramolecular order in the mesophase.…”

Section: Introductionmentioning

confidence: 99%

Lamellar Nanoconfinements Effects in Discotic Liquid Crystalline Block Copolymers

Stillings

Pettau

Wendorff

et al. 2010

Macro Chemistry & Physics

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We have evaluated the effect of slit‐like nanoconfinements imposed on columnar discotic phases within a discotic block copolymer displaying a lamellar microphase. Findings are that the columns are oriented uniformly along the lamellar normal within the plane of thin films, that a rectangular rather than a hexagonal columnar phase is formed within the discotic regions, that the thermodynamic stability of the columnar phase is strongly reduced relative to the low molar mass model compounds and finally, that the isotropic phase can be unusually strongly supercooled with respect to the columnar phase formation. Slit‐like nanoconfinements allow thus to induce novel types of the intrinsic order and columnar orientations.magnified image

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On the character of the glass transition in columnar discotics

Cited by 44 publications

References 22 publications

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Multiple glass transitions in the plastic crystal phase of triphenylene derivatives

Negative Thermal Expansion in Discotic Liquid Crystals of Nanographenes

Lamellar Nanoconfinements Effects in Discotic Liquid Crystalline Block Copolymers

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