Isotropization of nematic liquid crystals by TMDSC

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Temperature-modulated differential scanning calorimetry (TMDSC) and traditional DSC are used to study the transition between the nematic liquid crystalline state and the isotropic liquid for two small molecules [4,4{prime}-azoxyanisole and N,N`-bis(4-n-octyloxybenzal)-1,4-phenylenediamine] and one macromolecule (4,4{prime}-dihydroxy-{alpha}-methylstilbene copolymerized with a 1:1 molar mixture of 1,7-dibromoheptane and 1,9-dibromononane). The DSC measurements with 4,4{prime}-azoxyanisole were used for temperature calibration with varying heating and cooling rates. Quasi-isothermal TMDSC with small temperature amplitude and standard TMDSC with underlying heating and cooling rates were utilized to analyze the breadth of the transitions. It could be verified that the isotropization transition of a nematic liquid crystal is, indeed, ... continued below

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9 p.

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Chen, Wei; Dadmun, M.; Zhang, Ge; Boller, A. & Wunderlich, B. December 1, 1997.

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Description

Temperature-modulated differential scanning calorimetry (TMDSC) and traditional DSC are used to study the transition between the nematic liquid crystalline state and the isotropic liquid for two small molecules [4,4{prime}-azoxyanisole and N,N`-bis(4-n-octyloxybenzal)-1,4-phenylenediamine] and one macromolecule (4,4{prime}-dihydroxy-{alpha}-methylstilbene copolymerized with a 1:1 molar mixture of 1,7-dibromoheptane and 1,9-dibromononane). The DSC measurements with 4,4{prime}-azoxyanisole were used for temperature calibration with varying heating and cooling rates. Quasi-isothermal TMDSC with small temperature amplitude and standard TMDSC with underlying heating and cooling rates were utilized to analyze the breadth of the transitions. It could be verified that the isotropization transition of a nematic liquid crystal is, indeed, reversible for all three molecules. The nature of the transition changes, however, from relatively sharp, for small, rigid molecules, to about three kelvins wide for the small molecule with flexible ends, to as broad as 20 K for the macromolecule. It was also demonstrated that quantitative heats of fusion of sharp transitions can be extracted from TMDSC, but only from the time-domain heat-flow signal.

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9 p.

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OSTI as DE98001071

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  • North American Thermal Analysis Society (NATNAS) meeting, Washington, DC (United States), 7-9 Sep 1997

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  • Other: DE98001071
  • Report No.: ORNL/CP--95019
  • Report No.: CONF-9709121--
  • Grant Number: AC05-96OR22464
  • Office of Scientific & Technical Information Report Number: 552780
  • Archival Resource Key: ark:/67531/metadc694413

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  • December 1, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Aug. 23, 2016, 3:08 p.m.

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Chen, Wei; Dadmun, M.; Zhang, Ge; Boller, A. & Wunderlich, B. Isotropization of nematic liquid crystals by TMDSC, article, December 1, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc694413/: accessed August 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.