The liquid–liquid critical behaviour of binary solutions for (N-methyl-2-pyrrolidone+cycloalkanes)

Abstract

The critical temperatures and the critical compositions have been measured for binary solutions of {N-methyl-2-pyrrolidone (NMP)+methylcyclohexane}, (NMP+cyclohexane), (NMP+cyclooctane), and (NMP+propylcyclopentane). The dependence of the critical volume fraction on the molar volume of cycloalkanes has been discussed. The coexistence curves of (T, n), (T, x), and (T, φ) (n, x, and φ are refractive index, mole fraction, and volume fraction, respectively) for {NMP+methylcyclohexane} have also been determined within 8 K from the critical temperature by measurements of refractive index and proper conversions of n to x, and x to φ. The critical exponents β deduced from the three types of coexistence curves are consistent with theoretical predictions. The results have been analysed to obtain the critical amplitudes and Wegner-correction terms when β is fixed at the theoretical value. The goodness of the order parameters has been discussed by comparisons of the fits of the diameters of coexistence curves with τ^1-α and τ^2β {τ=(T_c-T)/T_c, where T_c is the critical temperature}. The coexistence curves have been successfully described by a combination of the Wegner equation and the expression for the diameter.

References

1. F. J. Wegner, Phys. Rev. B, 1972, 5, 4529.
2. V. Vani, S. Guha and E. S. R. Gopal, J. Chem. Phys., 1986, 84, 3999.
3. M. B. Ewing, K. A. Johnson and M. L. Mcglashan, J. Chem. Thermodyn., 1988, 20, 49.
4. J. C. Le Guillon and J. Zinn-Justin, Phys. Rev. B, 1980, 21, 3976.
5. S. C. Greer and M. R. Moldover, Annu. Rev. Phys. Chem., 1981, 32, 233.
6. X. An, F. Jiang, C. Chen and W. Shen, Chem. Phys. Lett., 1998, 282, 403.
7. W. Shen, G. R. Smith, C. M. Knobler and R. L. Scott, J. Phys. Chem., 1991, 95, 3376.
8. C. Houessou, P. Guenoun, R. Gastand, F. Perrot and D. Beysens, Phys. Rev. A, 1985, 32, 1818.
9. W. Shen, G. R. Smith, C. M. Knobler and R. L. Scott, J. Phys. Chem., 1990, 94, 7943.
10. X. An, W. Shen, H. Wang and G. Zheng, J. Chem. Thermodyn., 1993, 25, 1373.
11. X. An, H. Zhao, F. Jiang and W. Shen, J. Chem. Thermodyn., 1996, 28, 1221.
12. X. An, X. Liu and W. Shen, J. Chem. Thermodyn., 1997, 29, 669.
13. X. An, H. Zhao, F. Jiang, C. Mao and W. Shen, J. Chem. Thermodyn., 1997, 29, 1047.
14. J. A. Riddick, W. B. Bunger and T. K. Sakano, Organic Solvents, in Techniques of Chemistry, ed. A. Weissderger, Wiley-Interscience, New York, 4th edn., 1986, vol. II.
15. Thermodynamics Research Centre, API 44 Tables, Selected Values of properties of Hydrocarbons and Related Components, 1972, vol. I.
16. D. Z. Alpert, Phys. Rev. B, 1982, 25, 4810.
17. I. C. Sanchez, Macromolecules, 1984, 17, 967.
18. B. Widom, Physica A, 1993, 194, 532.
19. X. An, F. Jiang, C. Chen and W. Shen, Pure Appl. Chem., 1998, 70, 609.