Rheologica Acta

, Volume 46, Issue 9, pp 1139–1152 | Cite as

Molecular orientation in sheared molten thermotropic random copolyester

Original Contribution
First Online:
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Accepted:

Abstract

The macromolecular alignment and texture orientation in sheared thermotropic copolyester were investigated using in situ wide-angle X-ray scattering (WAXS) and polarizing optical microscopy (POM). The molecular behavior was correlated with viscoelastic properties. The polymer is a random copolyester based on 60 mol% 1,4-hydroxybenzoic acid (B) and 40 mol% ethylene terephthalate (ET) units. X-ray scattering showed that the molecular chains were aligned along the flow direction. The degree of molecular orientation, \( {\left\langle {P_{2} } \right\rangle } \), is an increasing function of the applied shear rate. However, rheo-optics showed that shear flow could not orient the polydomain texture, i.e., neither defect stretching nor elimination of defects was observed. Instead, shear compressed the microdomains and gave rise to long-range orientation correlations. Rheology showed that the nematic melt is viscoelastic, the loss modulus G″ dominates the elastic modulus G′, and the dynamic viscosity η* is shear thinning. Moreover, the steady shear viscosity, η, also behaved shear thinning, while the first normal stress difference N 1 remained positive. The empirical Cox–Merz rule did not hold, \( \eta ^{ * } > \eta \), within the shear rate range studied. The microscopic and rheological properties suggest that B–ET is a flow-aligning nematic polymer.

Keywords

Thermotropic LCP In situ X-ray scattering Rheo-optics Rheology 
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Notes

Acknowledgment

The in situ X-ray experiments were carried out at the Department of Materials Science and Metallurgy, University of Cambridge; the author gratefully acknowledges the support of Prof. Alan H. Windle, FRS. Thanks to the anonymous referees, the manuscript has benefited from their insightful comments. The financial support of DGAPA–UNAM (PAPIIT project IN107307) is also acknowledged.

References

  1. Alderman NJ, Mackley MR (1985) Optical textures observed during the shearing of thermotropic liquid–crystal polymers. Faraday Discuss Chem Soc 79:149–160CrossRefGoogle Scholar
  2. Andresen EM, Mitchell GR (1998) Orientational behaviour of thermotropic and lyotropic liquid crystal polymer systems under shear flow. Europhys Lett 43:296–301CrossRefGoogle Scholar
  3. Baek SG, Magda JJ, Larson RG, Hudson SD (1994) Rheological differences among liquid crystalline polymers. II. Disappearance of negative N1 in densely packed lyotropes and thermotropes. J Rheol 38:1473–1503CrossRefGoogle Scholar
  4. Bedford SE, Yu K, Windle AH (1992) Influence of chain flexibility on polymer mesogenicity. J Chem Soc Faraday Trans 88:1765–1773CrossRefGoogle Scholar
  5. Beekmans F, Gotsis AD, Norder B (1996) Transient and steady state rheological behavior of the thermotropic liquid crystalline polymer Vectra B950. J Rheol 40:947–966CrossRefGoogle Scholar
  6. Blackwell J, Lieser G, Gutierrez GA (1983) Structure of p-hydroxybenzoate-ethylene terephthalate copolyester fibers. Macromolecules 16:1418–1422CrossRefGoogle Scholar
  7. Burghardt WR (1998) Molecular orientation and rheology in sheared lyotropic liquid crystalline polymers. Macromol Chem Phys 199:471–488CrossRefGoogle Scholar
  8. Calundann GW, Jaffe M (1982) The Robert A. Welch Foundation conferences on chemical research, XXVI. Synthetic polymers, pp 247, Houston, TX, 15–17 Nov. 1982Google Scholar
  9. Calundann GW, Charbonneau LF, Shepard JP (1991) Makromol Chem Macromol Symp 51:147–152Google Scholar
  10. Cinader DK, Burghardt WR (1998) Mixed orientation state induced by expansion flow of a thermotropic liquid crystalline polymer. Macromolecules 31:9099–9102CrossRefGoogle Scholar
  11. Cinader DK, Burghardt WR (1999) X-ray scattering studies of orientation in channel flows of a lyotropic liquid crystalline polymer. Polymer 40:4169–4180CrossRefGoogle Scholar
  12. Cinader DK, Burghardt WR (2000) Molecular orientation in channel flows of main-chain thermotropic liquid crystalline polymers. Rheol Acta 39:247–258CrossRefGoogle Scholar
  13. Colby RH, Gillmor JR, Galli G, Laus M, Ober CK, Hall E (1993) Linear viscoelasticity of side-chain liquid crystal polymers. Liq Cryst 13:233–245CrossRefGoogle Scholar
  14. Cox WP, Merz EH (1958) Correlation of dynamic and steady flow viscosities. J Polym Sci 28:619–622CrossRefGoogle Scholar
  15. de Gennes PG (1982) In: Ciferri AA, Krigbaum WR, Meyer RB (eds) Polymer liquid crystals. Academic, New York, p 115Google Scholar
  16. DeNeve T, Navard P, Kleman M (1993) Shear rheology and shear-induced textures of a thermotropic copolyesteramide. J Rheol 37:515–529CrossRefGoogle Scholar
  17. Deutsch M (1991) Orientational order determination in liquid crystals by X-ray diffraction. Phys Rev A44:8264–8270Google Scholar
  18. Elias F, Clarke SM, Peck R, Terentjev EM (1999) Equilibrium textures in main-chain liquid crystalline polymers. Europhys Lett 47:442CrossRefGoogle Scholar
  19. Elias F, Clarke SM, Peck R, Terentjev EM (2000) Nematic order drives phase separation in polydisperse liquid crystalline polymers. Macromolecules 33:2060–2068CrossRefGoogle Scholar
  20. Ernst B, Denn MM, Pierini P, Rochefort WE (1992) Rheological properties of liquid crystalline solutions of cis-poly(p-phenylenebenzobisoxazole) in polyphosphoric acid (PBO/PPA). J Rheol 36:289–302CrossRefGoogle Scholar
  21. Feijoo JL, Odell J, Keller A (1990) Synchrotron X-ray analysis of disorientation in nematic solutions of poly(1,4-phenylene-2,6 benzo bisthiazole). Polym Commun 31:42–44Google Scholar
  22. Gay P (1984) Introduction to crystal optics. Longman, LondonGoogle Scholar
  23. Gervat L, Mackley MR, Nicholson TM, Windle AH (1995) The effect of shear on thermotropic liquid crystalline polymers. Philos Trans R Soc Lond A350:1–27Google Scholar
  24. Giles DW, Denn MM (1994) The effect of suppression of offgassing on the rheometry of thermotropic liquid crystalline polymers. J Rheol 38:617–637CrossRefGoogle Scholar
  25. Graziano DJ, Mackley MR (1984) Shear induced optical textures and their relaxation behaviour in thermotropic liquid crystalline polymers. Mol Cryst Liq Cryst 106:73–93CrossRefGoogle Scholar
  26. Guskey SM, Winter HH (1991) Transient shear behaviour of a thermotropic liquid crystalline polymer in the nematic state. J Rheol 35:1191–1207CrossRefGoogle Scholar
  27. Hanna S, Romo-Uribe A, Windle AH (1993) Sequence segregation in molten liquid crystalline random copolymers. Nature 366:546–549CrossRefGoogle Scholar
  28. Hashimoto T, Nakai A, Shiwaku T, Hasegawa H, Rojstaczer S, Stein RS (1989) Small-angle light scattering from nematic liquid crystals: fluctuations of director field due to many-body interactions of disclinations. Macromolecules 22:422–429CrossRefGoogle Scholar
  29. Jackson WJ, Kuhfuss H (1976) Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters. J Polym Sci Polym Chem Ed 14:2043–2058CrossRefGoogle Scholar
  30. Jerman RE, Baird DG (1981) Rheological properties of copolyester liquid crystalline melts. I. Capillary rheometry. J Rheol 25:275–292CrossRefGoogle Scholar
  31. Kadoma IA, Ylitalo C, van Egmond JW (1997) Structural transitions in wormlike micelles. Rheol Acta 36:1–12CrossRefGoogle Scholar
  32. Kalika DS, Nuel L, Denn MM (1989) Gap dependence of the viscosity of a thermotropic liquid crystalline copolymer. J Rheol 33:1059–1070CrossRefGoogle Scholar
  33. Keates P, Mitchell G, Peuvrel-Disdier E, Navard P (1993) In situ X-ray scattering study of anisotropic solutions of hydroxypropylcellulose subjected to shear flow. Polymer 34:1316–1319CrossRefGoogle Scholar
  34. Keller A, Warner M, Windle AH (eds) (1994) Self-order and form in polymeric materials. Philos Trans R Soc Lond A 348Google Scholar
  35. Larson RG (1999) The structure and rheology of complex fluids. Oxford University Press, New YorkGoogle Scholar
  36. Larson RG, Mead DW (1992) Development of orientation and texture during shearing of liquid–crystalline polymers. Liq Cryst 12:751–768CrossRefGoogle Scholar
  37. Larson RG, Mead DW (1993) The Ericksen number and Deborah number cascades in sheared polymeric nematics. Liq Cryst 15:151–169CrossRefGoogle Scholar
  38. Leadbetter AJ (1979) Structural studies of nematic, smectic A and smectic C phases. In: Luckhurst GR, Gray GW (eds) The molecular physics of liquid crystals. Academic, London, pp 285–316Google Scholar
  39. Leadbetter AJ, Norris EK (1979) Distribution functions in three liquid crystals from X-ray diffraction measurements. Mol Phys 38:669–686CrossRefGoogle Scholar
  40. Li MH, Brulet A, Davidson P, Keller P, Cotton JP (1993) Observation of hairpin defects in a nematic main-chain polyester. Phys Rev Lett 70:2297–2300CrossRefGoogle Scholar
  41. Luckhurst GR,Gray GW (eds) (1979) The molecular physics of liquid crystals. Academic, LondonGoogle Scholar
  42. Mackley MR, Pinaud P, Siekmann G (1981) Observation of disclinations and optical anisotropy in a mesomorphic copolyester. Polymer 22:437–446CrossRefGoogle Scholar
  43. Meesiri W, Menczel J, Gaur U, Wunderlich B (1982) J Polym Sci Polym Phys 20:719CrossRefGoogle Scholar
  44. Menczel J, Wunderlich B (1980) J Polym Sci Polym Phys 18:1433CrossRefGoogle Scholar
  45. Ober CK, McNamee S, Delvin A, Colby RH (1990) Chemical heterogeneity in liquid crystalline polyesters. In: Weiss RA, Ober CK (eds) Liquid crystalline polymers. ACS symp. series 435, Washington DC, pp 220–240Google Scholar
  46. Picken SJ, Noirez L, Luckhurst GR (1998) Molecular conformation of a polyaramid in nematic solution from small angle neutron scattering and comparison with theory. J Chem Phys 109:7612–7617CrossRefGoogle Scholar
  47. Picken SJ, Aerts J, Visser R, Northolt MG (1990) Structure and rheology of aramid solutions: X-ray scattering measurements. Macromolecules 23:3849–3854CrossRefGoogle Scholar
  48. Picken SJ, Aerts J, Doppert HL, Reuvers AJ, Northolt MG (1991) Structure and rheology of aramid solutions: transient rheological and rheooptical measurements. Macromolecules 24:1366–1375CrossRefGoogle Scholar
  49. Picken SJ, van Wijk RJ, Lichtenbelt JWTh, Westerink JB, van Klink PJ (1995) Measurement of the domain growth kinetics in multidomain nematic liquid crystal polymers by means of the worm-like path model for multiple scattering. Mol Cryst Liq Cryst 261:535–547CrossRefGoogle Scholar
  50. Pople JA, Mitchell GR, Chai CK (1996) In situ time-resolving wide-angle X-ray scattering study of crystallization from sheared polyethylene melts. Polymer 37:4187–4191CrossRefGoogle Scholar
  51. Riti JB, Cidade MT, Godinho MH, Martins AF, Navard P (1997) Shear induced textures of thermotropic acetoxypropylcellulose. J Rheol 41:1247–1260CrossRefGoogle Scholar
  52. Romo-Uribe A (2001a) On the molecular orientation and viscoelastic behaviour of liquid crystalline polymers. The influence of macromolecular architecture. Proc R Soc Lond A457:207–229Google Scholar
  53. Romo-Uribe A (2001b) Smectic-like order in the log-rolling flow of thermotropic random copolymers. A time-resolved wide-angle X-ray scattering study. Proc R Soc Lond A 457:1327–1342CrossRefGoogle Scholar
  54. Romo-Uribe A (2006) Shear-induced long-range spatial correlation and banded texture in thermotropic copolyester. In-situ light and X-ray scattering. Europhys Lett 76:609–615CrossRefGoogle Scholar
  55. Romo-Uribe A (2007) Long-range orientation correlations and molecular alignment in sheared thermotropic copolyester. In-situ light and X-ray scattering. Polym Adv Technol (in press). DOI  10.1002/pat.878
  56. Romo-Uribe A, Windle AH (1993) Flow-induced orientational transition in thermotropic random copolyesters. Macromolecules 26:7100–7102CrossRefGoogle Scholar
  57. Romo-Uribe A, Windle AH (1996) Log-rolling alignment in main-chain thermotropic liquid crystalline polymers: an in-situ WAXS study. Macromolecules 29:6246–6255CrossRefGoogle Scholar
  58. Romo-Uribe A, Windle AH (1999) A rheo-optical and dynamic X-ray scattering study of flow-induced textures in main-chain thermotropic liquid crystalline polymers: the influence of molecular weight. Proc R Soc Lond A 455:1175–1201Google Scholar
  59. Romo-Uribe A, Lemmon TJ, Windle AH (1997a) Structure and linear viscoelastic behaviour of main-chain thermotropic liquid crystalline polymers. J Rheol 41:1117–1141CrossRefGoogle Scholar
  60. Romo-Uribe A, Mather PT, Chaffee KP, Han CD (1997b) Molecular and textural ordering of thermotropic polymers in shear flow. MRS Symp Proc 465:63–68Google Scholar
  61. Sawyer LC, Jaffe M (1986) The structure of thermotropic copolyesters. J Mater Sci 21:1897–1913CrossRefGoogle Scholar
  62. Sawyer LC, Linstid HC, Romer M (1998) Emerging applications for neat LCPs. Plast Eng 54:37–41Google Scholar
  63. 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 48:1407–1423CrossRefGoogle Scholar
  64. Viney C, Windle AH (1982) Phase transformations in the thermotropic liquid crystal polymer: 60/40 PABA/PET. J Mater Sci 17:2661–2670CrossRefGoogle Scholar
  65. Viney C, Mitchell GR, Windle AH (1983) Optical microstructure of oriented liquid crystal polymers. Polym Commun 24:145–147Google Scholar
  66. Wang XJ, Warner M (1992) Theory of main chain nematic polymers with spacers of varying degree of flexibility. Liq Cryst 12:385–401CrossRefGoogle Scholar
  67. Wilson TS, Baird DG (1992) Transient elongational flow behaviour of thermotropic liquid crystalline polymers. J Non-Newton Fluid Mech 44:85–112CrossRefGoogle Scholar
  68. Windle AH, Viney C, Golombok R, Donald AM, Mitchell GR (1985) Molecular correlation in thermotropic copolyesters. Faraday Discuss Chem Soc 79:55–78CrossRefGoogle Scholar
  69. Wissbrun KF (1981) Rheology of rod-like polymers in the liquid crystalline state. J Rheol 25:619–662CrossRefGoogle Scholar
  70. Wunderlich B (1973) Macromolecular physics, vol I. Academic, New YorkGoogle Scholar
  71. Yoon HN, Charbonneau LF, Calundann GW (1992) Adv Mater 4:206CrossRefGoogle Scholar
  72. Zhou WJ, Kornfield JA, Ugaz VM, Burghardt WR, Link DR, Clark NA (1999) Dynamics and shear orientation behavior of a main-chain thermotropic liquid crystalline polymer. Macromolecules 32:5581–5593CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Laboratorio de Nanopolímeros y Coloides, Instituto de Ciencias FísicasUniversidad Nacional Autónoma de México, Av. Universidad s/nCuernavacaMexico

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