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Molecular orientation of a commercial thermotropic liquid crystalline polymer in simple shear and complex flow

Burghardt, Wesley R. and Brown, Eric F. and Auad, Maria Lujan and Kornfield, Julia A. (2005) Molecular orientation of a commercial thermotropic liquid crystalline polymer in simple shear and complex flow. Rheologica Acta, 44 (5). pp. 446-456. ISSN 0035-4511.

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In-situ X-ray scattering methods have been used to measure the average degree of molecular orientation in the commercial thermotropic copolyesteramide, Vectra B. Experiments were conducted in both homogeneous shear flow and in extrusion-fed channel flows that provided mixed shear/extensional deformations. In the channel flows, extension has a dramatic effect on the average orientation state in the vicinity of stagnation points or expansions/contractions in cross-sectional area. Of particular note, a temporary increase and subsequent decay in orientation observed in a 4:1 slit-contraction flow provides additional indirect evidence supporting the hypothesis that Vectra B exhibits director tumbling. This is consistent with results from other fully aromatic copolyesters but contrasts with findings in “model” thermotropes incorporating flexible spacers. Thus, it seems that the stiffer backbone of commercial main chain LCPs is the main feature which, apparently, leads to tumbling. Measurements of average molecular orientation in transient shear flows show some connections with the corresponding mechanical response, but fail to show the distinctive characteristics that have previously been associated with either tumbling or aligning in LCPs using similar procedures. These experiments might be adversely affected by the comparatively slow rate of data acquisition, which leads to lengthy experiments in which the sample is more prone to degradation.

Item Type:Article
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Kornfield, Julia A.0000-0001-6746-8634
Additional Information:© Springer-Verlag 2004. Received: 15 June 2004. Accepted: 14 October 2004. Published online: 2 December 2004. This work was funded by the Air Force Office of Scientific Research MURI on liquid crystals (Grant F49620-97) and by NSF grant DMI-0099542. We gratefully thank A.D. Gotsis for providing the Vectra B polymer. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) Synchrotron Research Center located at Sector 5 of the Advanced Photon Source. DND-CAT is supported by E.I. DuPont de Nemours & Co., the Dow Chemical Company, the National Science Foundation through Grant DMR-9304725, and the State of Illinois through Department of Commerce and Board of Higher Education Grant IBHE HECA NWU 96. Use of the Advanced Photon Source was supported by the US Department of Energy, Basic Energy Sciences, Office of Energy Research, under Contract No. W-31-102-Eng-38.
Funding AgencyGrant Number
Air Force Office of Scientific Research (AFOSR)F49620-97
E. I. DuPont de Nemours and Company, Inc.UNSPECIFIED
Dow Chemical CompanyUNSPECIFIED
Illinois Department of CommerceIBHE HECA NWU 96
Illinois Board of Higher EducationUNSPECIFIED
Department of Energy (DOE)W-31-102-Eng-38
Subject Keywords:Shear Rate, Molecular Orientation, Liquid Crystalline Polymer, Normal Stress Difference, Anisotropy Factor
Issue or Number:5
Record Number:CaltechAUTHORS:20200723-174403394
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Official Citation:Burghardt, W.R., Brown, E.F., Auad, M.L. et al. Molecular orientation of a commercial thermotropic liquid crystalline polymer in simple shear and complex flow. Rheol Acta 44, 446–456 (2005).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104551
Deposited By: Rebecca Minjarez
Deposited On:28 Jul 2020 15:55
Last Modified:28 Jul 2020 15:55

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