Microphase separation kinetics in n-alkane mixtures

Abstract

Using time-resolved small-angle neutron scattering, the kinetics of microphase separation at various quench temperatures between 10 and 43°C in metastable, binary paraffin mixtures C₃₀H(D)₆₂1C₃₆D(H)₇₄ of 4:1, 1:1 and 1:4 composition, and 1:1 mixtures of C_nH_2n+21C₃₆D₇₄ for 28⩽n⩽31, both in the bulk and doped into an exfoliated graphite, have been investigated for up to 6000 minutes at 15 min resolution. The data were fitted to a single exponential relaxation function. Graphite adsorption generally has little effect on the rates, with explicable exceptions. The Q-dependent relaxation times, except for 1:4 C₃₀H₆₂1C₃₆D₇₄, all peak at Qca. 0.07 Å^-1, which together with the shape of the structure function, and the relative trends in the relaxation times, indicate a single demixing process to alternating lamellae. The relaxation time decreases with increasing C₃₆ concentration and has a noticeable H/D isotopic dependence. Increasing chain length mismatch strongly decreases the relaxation times. These observations are all explained by a combination of the interplay of C₃₆ conformational defects and screw motion in the individual alkane chains, together with a void mechanism for mobility. Power-law behaviour of the kinetics is shown to occur over usefully large time domains. The range over which this behaviour is observed increases with decreasing C₃₆ concentration. Our analysis suggests that three broad regions of scattering development can be defined corresponding to linear, power-law and logarithmic growth.

References

1. E. P. Gilbert, P. A. Reynolds, A. S. Brown and J. W. White, Chem. Phys. Lett., 1996, 255, 373.
2. E. P. Gilbert, P. A. Reynolds and J. W. White, J. Phys. Chem., 1996, 100, 18201.
3. E. P. Gilbert, PhD Thesis, Australian National University, 1997.
4. Z.-Y. Wang, P. A. Reynolds, E. P. Gilbert and J. W. White, Mol. Phys., 1996, 91, 1025.
5. R. G. Snyder, V. J. P. Srivatsavoy, D. A. Cates, H. L. Strauss, J. W. White and D. L. Dorset, J. Phys. Chem., 1994, 98, 674.
6. J. E. Epperson, J. W. White and D. G. Wozniak, Mat. Res. Soc. Symp. Proc., 1992, 205, 159.
7. P. W. Zhu, PhD Thesis, Australian National University, 1993.
8. J. W. White, P.-W. Zhu, J. E. Epperson and R. G. Snyder, Mol. Phys., 1997, 91, 1039.
9. J. W. White, P.-W. Zhu, J. E. Epperson, D. Wozniak and R. G. Snyder, Mol. Phys., 1997, 91, 1017.
10. E. P. Gilbert, Phys. Chem. Chem. Phys., 1999, 1, 1517.
11. D. L. Dorset and R. G. Snyder, Macromolecules, 1995, 28, 8412.
12. D. L. Dorset and R. G. Snyder, J. Phys. Chem., 1996, 100, 9848.
13. R. G. Snyder, M. C. Goh, V. J. P. Srivatsavoy, H. L. Strauss and D. L. Dorset, J. Phys. Chem., 1992, 96, 10008.
14. R. G. Snyder, G. Conti, H. L. Strauss and D. L. Dorset, J. Phys. Chem., 1993, 97, 7342.
15. J. D. Gunton, M. San Miguel and P. S. Sahni, in Phase Transitions and Critical Phenomena, ed. C. Domb and J. L. Lebowitz, Academic Press, London, 1983, vol. 8, p. 267.
16. G. Kostorz, in Modern Aspects of Small-Angle Scattering, ed. H. Brumberger, Kluwer, Dordrecht, 1995, p. 255.
17. C. K. Haas and J. M. Torkelson, Phys. Rev. Lett., 1995, 75, 3134.
18. K. Oki, H. Sagane and T. Eguchi, J. Phys. Paris, 1977, C7, 414.
19. R. G. Snyder, G. Conti, H. L. Strauss and D. L. Dorset, J. Phys. Chem., 1993, 97, 7342.
20. R. G. Snyder, M. C. Goh, V. J. P. Srivatsavoy, H. L. Strauss and D. L. Dorset, J. Phys. Chem., 1992, 96, 10008.
21. B. Ditchek and L. H. Schwartz, Ann. Rev. Mater. Sci., 1979, 9, 219.
22. J. W. White, P.-W. Zhu and J. E. Epperson, J. Phys. Chem., 1996, 100, 19967.
23. J. W. White, D. L. Dorset, J. E. Epperson and R. Snyder, Chem. Phys. Lett., 1990, 166, 560.
24. Papyex is a product of Le Carbone-Lorraine, 4. Rue Jean Jaures, F-92231 Gennevilliers, France.
25. P. Thiyagarajan, J. E. Epperson, R. K. Crawford, J. M. Carpenter, T. E. Klippert and D. G. Wozniak, J. Appl. Cryst., 1997, 30, 280.
26. J. E. Epperson, P. Thiyagarajan, J. M. Carpenter, R. K. Crawford and D. G. Wozniak, in IPNS Progress Report 10th Anniversary Edition, ed. F. J. Rotella, Argonne National Laboratory, Argonne, IL, 1991, p. 76.
27. R. K. Heenan and S. M. King, in International Seminar on Structural Investigations at Pulsed Neutron Sources; Joint Institute for Nuclear Research(Report number: E3-93-65), Dubna, Russia, 1993, p. 176.
28. R. Heenan and S. King, in ISIS User Guide, ed. B. Boland and S. Whapham, ISIS, Rutherford Appleton Laboratory, Didcot, 1992.
29. H. Homma and R. Clarke, Phys. Rev. Lett., 1984, 52, 629.
30. J. Marro, J. L. Lebowitz and M. K. Kalos, Phys. Rev. Lett., 1979, 43, 282.
31. G. Porod, in Small Angle X-Ray Scattering, ed. O. Glatter and O. Kratky, Academic Press, London, 1982, p. 17.
32. O. Glatter, in International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer Academic, Dordrecht, 1992, vol. C, p. 89.
33. M. Schuler and B. Stühn, Macromolecules, 1993, 26, 112.
34. B. Chu, T. Gao, Y. Li, J. Wang, C. R. Desper and C. A. Byrne, Macromolecules, 1992, 25, 5724.
35. C. G. Vonk, J. Appl. Cryst., 1973, 6, 81.
36. W. Ruland, Colloid Polym. Sci., 1977, 255, 417.
37. H. L. Snyder and P. Meakin, J. Chem. Phys., 1983, 79, 5588.
38. A. Milchev, D. W. Heermann and K. Binder, Acta Metall., 1988, 36, 377.
39. S. R. Craig, G. P. Hastie, K. J. Roberts and J. N. Sherwood, J. Mater. Chem., 1994, 4, 977.
40. S. C. Nyburg and J. A. Potworowski, Acta Cryst., 1973, B29, 347.
41. A. Putnis and J. D. C. McConnell, in Principles of Mineral Behaviour, Blackwell Scientific Publications, Oxford, 1980.
42. M. Maroncelli, H. L. Strauss and R. G. Snyder, J. Phys. Chem., 1985, 89, 5260.
43. I. Basson and E. C. Reynhardt, J. Chem. Phys., 1991, 95, 1215.
44. D. L. Dorset, Macromolecules, 1985, 18, 2158.
45. I. Basson and E. C. Reynhardt, J. Chem. Phys., 1990, 93, 3604.
46. D. L. Dorset, Macromolecules, 1991, 24, 6521.
47. M. G. Broadhurst, J. Res. Nat. Bur. Stand., 1962, A66, 241.
48. J. Marro, A. B. Bortz, M. H. Kalos and J. L. Lebowitz, Phys. Rev. B, 1975, 12, 2000.
49. O. G. Mouritsen and P. J. Shah, Phys. Rev. B, 1989, 40, 11445.
50. P. J. Shah and O. G. Mouritsen, Phys. Rev. B, 1990, 41, 7003.