Microdeformation of a polydomain, smectic liquid crystalline thermoset
Source abstract
Abstract
The microdeformation and fracture mechanisms of a densely crosslinked, polydomain, smectic liquid crystalline thermoset (LCT) were investigated in order to gain some insight into its interesting mechanical properties (e.g. improved fracture toughness). A difunctional LC epoxy monomer, diglycidyl ether of 4,4′-dihydroxy-α-methylstilbene (DGDHMS), was crosslinked with the tetrafunctional, aromatic crosslinker, 4,4′-methylene dianiline (MDA) to produce the LCT. Thermoset films (30 μm in thickness) were bonded to copper grids, strained in tension, and observed under the polarizing optical microscope. A new type of microdeformation and fracture mechanism was observed for the smectic LCT. At small strains, numerous microcracks formed which were oriented at various angles to the straining direction. Many smaller isolated and interconnected defects (of the order of a single LC domain, ∼1 μm in size) surrounded and emanated from the crack tips. At larger strains, the microcracks propagated slowly and stably until reaching a critical size of ∼250 μm, at which time they began to widen and change direction, indicative of plastic deformation which extended over many LC domains. Film failure occurred through microcrack interconnection. A fracture mechanism for the LCT is proposed based on microscopic voiding near the crack tip through the failure of individual LC domains.
Source: openaire · Quality: candidate unverified · Source record ↗
Research context
OpenAlex topics: Liquid Crystal Research Advancements · Epoxy Resin Curing Processes · Polymer crystallization and properties
SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.
References (46)
Show source-provided references
1. H.-J. Sue, J. D. Earls and R. E. Hefner, JR., in Proceedings of the 10th Annual International Conference of the Institute of Materials; Deformation, Yield, and Fracture of Polymers, Churchill College, Cambridge, UK, April 7-10th, 1997, (Chameleon Press Ltd, 1997) p. 129.
2. M. Laus, R. Pernozzoli, H. Koerner and C. K. Ober, in XII convegno italiano di scienza e tecnologia delle macromolecole, Palermo, Italy, 1995, p. 661.
3. J. D. Earls and R. E. Hefner, JR., European Patent Appl. #0-379-057A2, assigned to the Dow Chemical Company, 1990.
4. S. Jahromi, W. A. G. Kuipers, B. Norder and W. J. Mijs, Macromolecules 28 (1995) 2201.10.1021/ma00111a014 ↗
5. R. A. M. Hikmet and D. J. Broer, Polymer 32 (1991) 1627.10.1016/0032-3861(91)90398-3 ↗
6. C. Carfagna, E. Amendola and M. Giamberini, Composite Struct. 127 (1994) 37–43.10.1016/0263-8223(94)90064-7 ↗
7. E. Amendola and M. Giamberini Idem., in Proceedings of the InternationalWorkshop on Liquid Crystalline Polymers, Capri, Italy, June 1-4, 1993, edited by C. Carfagna (Pergamon Press, Oxford, UK, 1994) p. 69.
8. W.-F. A. Su, J. Polym. Sci.: Part A: Polym. Chem. 31 (1993) 3251–3256.10.1002/pola.1993.080311312 ↗
9. A. Shiota and C. K. Ober, J. Polym. Sci.: Polym. Phys. Ed. 36 (1998) 31–38.10.1002/(SICI)1099-0488(19980115)36:1<31::AID-POLB4>3.0.CO;2-X ↗
10. M. H. Litt, W.-T. Whang, K.-T. Yen and X.-J. Qian, J. Polym. Sci: Part A: Polym. Chem. 31 (1993) 183–191.10.1002/pola.1993.080310122 ↗
11. A. P. Melissaris and M. H. Litt, Macromolecules 127 (1994) 2675–2684.10.1021/ma00088a005 ↗
12. A. P. Melissaris, J. K. Sutter, M. H. Litt, D. H. Scheiman and M. Scheiman, ibid. 128 (1995) 860–865.10.1021/ma00108a009 ↗
13. G. G. Barclay, S. G. Mcnamee, C. K. Ober, K. I. Papathomas and D. W. Wang, J. Polym. Sci.: Part A: Polym. Chem. 30 (1992) 1843–1853.
14. C. Ortiz, R. Kim, E. Rodighiero, C. K. Ober and E. J. Kramer, Macromolecules 31(13) (1998) 4074–4088.10.1021/ma971439n ↗
15. G. Barclay, S. G. Mcnamee, C. K. Ober, K. I. Papathomas and D. W. Wang, J. Polym. Sci.: Part A: Polym. Chem. 30 (1992) 1831–1843.10.1002/pola.1992.080300906 ↗
16. P. G. De Gennes, “The Physics of Liquid Crystals,” (Claredon Press, Oxford, 1974).
17. W. H. De Jeu, “Physical Properties of Liquid Crystalline Materials,” (Gordon and Breach Scientific Publishers, 1980).
18. D. Demus and L. Richter, “Textures of Liquid Crystals,” (VCH Publications, 1978).
19. H. Kelker and R. Hatz, “Handbook of Liquid Crystals,” (Verlag Chemie, 1980).
20. E. B. Priestley, P. J. Wojtowicz and P. Sheng (eds.), “Introduction to Liquid Crystals,” (Plenum Press, 1974).10.1007/978-1-4684-2175-0 ↗
21. G. Vertogen and W. H. De Jeu, “Thermotropic Liquid Crystals: Fundamentals,” (Springer-Verlag, 1988).10.1007/978-3-642-83133-1 ↗
22. P. J. Collings, “Liquid Crystals: Nature's Delicate Phase of Matter,” (Princeton University Press, 1990).
23. A. M. Donald and A. H. Windle, “Liquid Crystalline Polymers,” (Cambridge University Press: Cambridge, UK, 1992).
24. R. A. Gledhill, A. J. Kinloch, S. Yamini and R. J. Young, Polymer 19 (1978) 574.10.1016/0032-3861(78)90285-9 ↗
25. G. Pritchard and G. V. Rhodes, Matls. Sci. Eng. 28 (1976) 1.
26. R. J. Young, “Developments in Polymer Fracture-1,” edited by E. H. Andrews (Applied Science: London, 1979) Ch. 6.
27. M. D. Glad, PhD thesis, Department of Materials Science and Engineering, Cornell University, Ithaca, N.Y., 1990.
28. B. D. Lauterwasser and E. J. Kramer, Phil. Mag. 39A (1979) 469.10.1080/01418617908239285 ↗
29. G. Wisanrakkit and J. K. Wisanrakkit, J. Appl. Polym. Sci. 41 (1990) 2885–2929.10.1002/app.1990.070411129 ↗
30. A. M. Donald and E. J. Kramer, J. Matls. Sci. 16 (1981) 2967–2976.10.1007/BF00540301 ↗
31. E. J. Kramer Idem., ibid. 16 (1981) 2977–2987.10.1007/BF00540302 ↗
32. E. J. Kramer Idem., ibid. 17 (1982) 1871–1879.10.1007/BF00540402 ↗
33. E. J. Kramer Idem., J. Polym. Sci.: Polym. Phys. Ed. 20 (1982) 899–909.
34. E. J. Kramer Idem., Polymer 23 (1982) 1183.10.1016/0032-3861(82)90376-7 ↗
35. C. Henkee and E. J. Kramer, J. Polym. Sci.: Polym. Phys. Ed. 22 (1984) 721–737.
36. P. Miller and E. J. Kramer E. J., J. Matls. Sci. 25 (1990) 1751.10.1007/BF01045380 ↗
37. A. C.-M. Yang, Matls. Chem. Phys. 41 (1995) 295–298.10.1016/0254-0584(95)01542-6 ↗
38. L. L. Berger and E. J. Kramer, J. Matls. Sci. 22 (1987) 2739–2750.10.1007/BF01086466 ↗
39. C. J. G. Plummer, J. L. Hedrick, H.-H. Kausch and J. G. Hilborn, J. Polym. Sci.: Part B Polym. Phys. 33 (1995) 1813–1820.10.1002/polb.1995.090331211 ↗
40. G. Wisanrakkit and J. K. Gillham, J. Appl. Polym. Sci. 41 (1990) 2885–2929.10.1002/app.1990.070411129 ↗
41. M. M. Leven (ed.), “Photoelasticity,” (Pergamon Press, 1941).
42. C. Ortiz, M. Wagner, N. Bhargava, C. K. Ober and E. J. Kramer, Macromolecules 38 (1998) 8531–8539.10.1021/ma971423x ↗
43. It has been shown that oriented polymers exhibit much lower moduli when strained perpendicular to the direction of orientation. (I. M. Ward (ed.), “Structure and Properties of Oriented Polymers,” (Applied Science Publishers, Ltd.: London, 1975) Ch. 7.)
44. It is thought that the main toughening mechanism in rubber-modified thermosets comes from rubber particles which debond and cavitate under stress, thus generating a series of voids which can relieve triaxial stresses in the matrix and promote the energy-absorbing process of shear yielding. (Y.HUANGand A. J.KINLOCH,Polymer 33 (1992) 1330
45. F. J. GUILD and A. J. KINLOCH, J. Mater. Sci. 30 (1995) 1689.)10.1007/BF00351597 ↗
46. G. E. Dieter, JR., “Mechanical Metallurgy,” (McGraw-Hill Book Company, Inc.: New York, 1961) p. 202.