Abstract
The dynamic rheology and accompanying microstructure of a synthetic mesophase pitch (AR-HP) is reported. The loss modulus (G″) was found to be higher than the storage modulus (G′) at all frequencies (∼0.1 to ∼100 rad/s) and temperatures (280–305 °C) tested. The slope of the low-frequency terminal zone for G′ was found to be approximately 0.8, much lower than a value of 2 that is observed for flexible chain polymers. Cross-polarized optical microscopy with full-wave retardation plate confirmed the presence of different textures of mesophase pitch processed under different conditions. While loss moduli remained fairly unchanged, finer textures led to significantly lower storage moduli. Consistent with this trend, coarsening of the microstructure during textural relaxation led to an increase in storage moduli. Therefore, for the discotic mesophase pitch, the viscous component was found to remain unaffected by the microstructure, but the elastic modulus was dependent on the orientation of layer-planes and size of the texture.
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References
Burghardt WR (1991) Oscillatory shear flow of nematic liquid crystals. J Rheol 35(1):49–62 DOI 10.1122/1.550208
Burghardt WR (1998) Molecular orientation and rheology in sheared lyotropic liquid crystalline polymers. Macromol Chem Phys 199(4):471–488
Cato AD (2002) Flow and deformation behavior of mesophase pitch. Ph.D. dissertation, Clemson University
Cato AD, Edie DD, Harrison GM (2005) Steady state and transient rheological behavior of mesophase pitch, part I: experiment. J Rheol 49(1):161–174 DOI 10.1122/1.1835337
Cheung T, Turpin M, Rand B (1996) Controlled stress, oscillatory rheometry of mesophase-pitches. Carbon 34(2):265–271 DOI 10.1016/0008-6223(95)00116-6
De Andrade Lima LRP, Rey AD (2004) Linear viscoelasticity of discotic mesophases. Chem Eng Sci 59:3891–3905 DOI 10.1016/j.ces.2004.06.016
Driscoll P, Masuda T (1991) Rheological properties of homogeneous thermotropic liquid-crystalline polyester: dynamic viscoelastic and interrupted-flow measurements. Macromolecules 24:1567–1574 DOI 10.1021/ma00007a019
Dumont M, Dourges MA, Pailler R, Bourrat X (2003) Mesophase pitches for 3D-carbon fibre preform densification: rheology and processability. Fuel 82:1523–1529 DOI 10.1016/S0016-2361(03)00039-5
Grizzuti N, Moldenaers, Mortier PM, Mewis J (1993) On the time-dependency of the flow-induced dynamic moduli of a liquid crystalline hydroxypropylcellulose solution. Rheol Acta 32(3):218–226 DOI 10.1007/BF00434186
Guskey SM, Winter HH (1991) Transient shear behavior of a thermotropic liquid crystalline polymer in the nematic state. J Rheol 35(6):1191–1207 DOI 10.1122/1.550171
Han CD, Kim SS (1994) Transient rheological behavior of a thermotropic liquid crystalline polymer. II. Intermittent shear flow and evolution of dynamic moduli after cessation of shear flow. J Rheol 38(1):13–30 DOI 10.1122/1.550507
Kim SS, Han CD (1993) Effect of molecular weight on the rheological behavior of thermotropic liquid-crystalline polymer. Macromolecules 26:6633–6642
Kim SS, Han CD (1994) Oscillatory shear flow behavior of a thermotropic liquid-crystalline polymer. Polymer 35(1):93–103 DOI 10.1016/0032-3861(94)90055-8
Kundu S, Ogale AA (2006) Rheostructural studies on a synthetic mesophase pitch during transient shear flow. Carbon 44(11):2224–2235 DOI 10.1016/j.carbon.2006.02.041
Larson RG (1999) The structure and rheology of complex fluids. Oxford University Press, New York
Lee KM, Han CD (2003) Effect of flexible spacer length on the rheology of side-chain liquid-crystalline polymers. Macromolecules 36:8796–8810 DOI 10.1021/ma030303o
Mochida I, Korai Y, Ku CH, Watanabe F, Sakai Y (2000) Chemistry of synthesis, structure, preparation and application of aromatic-derived mesophase pitch. Carbon 38:305–328 DOI 10.1016/S0008-6223(99)00176-1
Moldenaers P, Mewis J (1986) Transient behavior of liquid crystalline solutions of poly(benzylglutamate). J Rheol 30(3):567–584 DOI 10.1122/1.549861
Romo-Uribe A, Lemmon TJ, Windle AH (1997) Structure and linear viscoelastic behavior of main-chain thermotropic liquid crystalline polymers. J Rheol 41:1117–1145 DOI 10.1122/1.550820
Somma E, Nobile MR (2004) The linear viscoelastic behavior of a series of molecular weights of the thermotropic main-chain liquid crystal polymers HBA/HNA 73/27. J Rheol 48(6):1407–1423 DOI 10.1122/1.1795194
Winter HH, Mours M (1997) Rheology of polymers near liquid–solid transitions. Adv Polym Sci 134:165–234
Wissbrun KF, Griffin AC (1982) Rheology of a thermotropic polyester in the nematic and isotropic states. J Polym Sci 20:1835–1845 DOI 10.1002/pol.1982.180201007
Yoon SH, Korai Y, Mochida I, Kato I (1994) The flow properties of mesophase pitches derived from methylnaphthalene and naphthalene in the temperature range of their spinning. Carbon 32(2):273–280 DOI 10.1016/0008-6223(94)90190-2
Acknowledgements
This work was supported by the Engineering Research Centers Program of the National Science Foundation under Award Number EEC-9731680. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect those of the National Science Foundation. The authors would also like to acknowledge Dr. Amit K Naskar for his assistance during the X-ray experiments.
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Kundu, S., Ogale, A.A. Microstructural effects on the dynamic rheology of a discotic mesophase pitch. Rheol Acta 46, 1211–1222 (2007). https://doi.org/10.1007/s00397-007-0209-4
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DOI: https://doi.org/10.1007/s00397-007-0209-4