All submissions of the EM system will be redirected to Online Manuscript Submission System. Authors are requested to submit articles directly to Online Manuscript Submission System of respective journal.

Dielectric Relaxation Studies of Ternary Liquid Mixtures of Dimethyl Phthalate with Triethylamine in the Microwave Region

A. Mushtaq Ahmed Khan1, M.Subramanian2
  1. Department of Physics, Dr. Zakir Husain College, Ilayangudi, Sivagangai, Tamil Nadu, India
  2. Dean, Fatima Michael College of Engineering and Technology, Madurai, Tamil Nadu, India
Related article at Pubmed, Scholar Google

Visit for more related articles at International Journal of Innovative Research in Science, Engineering and Technology


The molecular structure and molecular forces in liquids and solutions in particular have been investigated by dielectric relaxation studies. The nature and strength of the molecular interactions have been established as the main cause for the chemical behavior of compounds. The dielectric behavior of Triethylamine with Dimethyl Phthalate has been studied at microwave frequency 9.36 GHz at different temperatures 303K, 308K and 313K. Different dielectric quantities like dielectric constant (ε′), dielectric loss (ε″), static dielectric constant (ε0 ) and dielectric constant at optical frequency (εα) have been determined. The relaxation time τ has been calculated by both Higasi’s method and Cole-Cole method. The complex system investigated shows the maximum relaxation time values at temperatures by both Higasi’s method and Cole-Cole method.


Dielectric constant, Dielectric loss, Optical frequency, Higasi’s method, Cole–cole method, Dimethylphthalate, Trimethylamine.


The dielectric relaxation behaviour of mixtures of polar molecules under varying conditions of complexation, temperature and environmental factors has evoked considerable interest. Based on the results, models of relaxation process in liquid mixtures have been formulated. So many researchers [1-6] studied the association of two polar molecules due to hydrogen bonding from the dielectric relaxation measurements at microwave frequencies. Purcell and Smyth [7] were the first to detect solute - solvent interactions through measurements of relaxation time. The dielectric relaxation studies of ternary mixtures of polar solvents in dilute solutions of non-polar liquids provide valuable information about solute-solute and solute-solvent interactions. Molecular association between triethylamine with alcohols in benzene in the microwave region was studied by this dielectric relaxation behaviour by S. Kumar et al [8] using single frequency concentration variation method.
In order to provide the experimental data on ternary mixture, dimethyl Phthalate with triethylamine in benzene at various concentrations were studied at microwave region at different temperatures of 303K, 308K and 313K [9]. The study is expected to provide better understanding of the nature of molecular orientation processes.


Dimethyl Phthalate with triethylamine in benzene was used. The molar concentrations of the ternary mixture of the triethylamine with dimethyl Phthalate in benzene are 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6. The measurement of dielectric constant at an angular frequency ε’ and dielectric loss ε” was carried out in the X band microwave frequency at 9.36 GHz. The static dielectric constant ε0 was measured by heterodyne beat [10] method at three different temperatures 303K, 308K and 313K, using a dipole meter operated at 220 volts. The refractive index was measured by Abbe’s refractometer [11]. The errors in the measurements of density and refractive index (nD) are 0.002g/cc and 0.002 respectively. The temperature of all these measurements was maintained at 303K, 308K and 313K using a water circulating thermostat. The density was measured with a 20ml specific gravity bottle.


Higasi Method



The values of the dielectric constants at high frequency (ε’), the dielectric loss (ε’’), the distribution parameter (α), the most probable relaxation time (τ), the relaxation time for overall rotation of the molecule (�� 1 ), the relaxation time for group rotation ( �� 2 ) and the excess dipole moment for the system benzene + dimethyl phthalate + triethylamine at temperatures 303 k, 308k, and 313k are reported in Table 1.
The static dielectric constant, the dielectric constant at optical frequency, the dielectric constant and dielectric loss at microwave frequency decrease with the increase of concentration of the mixture. The variation of the dielectric constant with concentration indicates the hetro junction between the components [15 ].
Higasi’s parameters were calculated using equation (2) and (3). The relaxation time (τ) and the distribution parameter (α) were also determined by the Cole-Cole method using equation (2). Davidson [16] showed that the relaxation process for any system can be resolved into inter molecular relaxation time τ(1), and intra molecular relaxation time τ(2) components only if the ratio of the relaxation time τ(1) τ(2) is greater than 6. In our present investigation, no such resolution is found to occur owing to the increased overlap of the nearby equal regions. The different sizes of the relaxing units give rise to a changed environment, but not to a distinguishable change in the multimeric unit responsible for different relaxation times. Our results are consistent with the interpretation that there is a progressive change in the n-mer and no abrupt change on the dilution.
The decrease in τ (1) and τ(2) wit h dilution is assigned to the red uction in t he sizes of the n-mer s due to the intervention caused by the solvent . The coupling between the dipoles is also reduced by the solvent, enabling the dipoles to rotate more freely. Similar results were reported by the Dannhauser et al. [17] and Cambell et al[18].
The τ values obtained from the Cole –Cole plot are higher than the values obtained by Higasi’s method. This may be attributed to the rigid behavior of solute molecules. Similar results were reported by S. Krishnan et al. in the studies of alcohols and triethylamine [19].
For all the concentrations and temperatures studied, the free energy of activation (ΔFτ) is less than the corresponding values of the viscous flow (ΔFη). This is in agreement with the fact [20-21] that the process of viscous flow involves greater interference by neighbours than does dielectric relaxation as the latter takes place by rotation only whereas the viscous flow involves both the rotational and translational forms of motion.
The excess dipole moment is a qualitative index for the presence of a hydrogen bond in the ternary system. The excess dipole moment of the mixture is calculated using the following equation
Δμ= μab - μa - μb (10)
The excess dipole moment may be attributed to the proton - transfer in this bond. Similar results were reported by Thenappan [22] for the mixture of amines and alcohols in benzene and by Subramainian [23] for the mixtures of alcohols and nitriles in benzene /1,4 dioxane . The values of relaxation times, distribution parameters, activation free energies and excess dipole moments at various temperatures are reported in Table 2.
The values of Δμ are found to be negative for all the concentrations and temperatures . This shows the absence of ionic structures[24, 25]. The negative value of Δμ also indicates the presence of hydrogen bonds between the partners.


The authors express their sincere thanks to the College Managing Board of Sree Sevugan Annamalai College, Devakottai and Dr.Zakir Husain College, Ilayangudi for their constant encouragement and providing research facilities. The authors express their heartfelt thanks to the UGC for utilizing the instruments purchased from the Major research funding provided to one of the authors.


1. Gupta, K. K., Banshal A. K., Singh P. J., and Sharma,K. S., “Temperature dependence of dielectric relaxation of rigid polar molecules acetophenone, pyridine and their mixtures in dilute solutions of benzene”, Indian Journal of Pure and Applied Physics, Vol. 41, pp. 57–63, 2003.

2. Madhurima, V., Murthy,V.R.K., & Sobhanadri, J, “Investigations on binary mixtures of propan-2-ol with methyl benzoate and ethyl benzoate”, Indian Journal of Pure and Applied Physics, Vol.41 , pp.57, 2003.

3. Thakur, N. & Sharma, D. R., “N,N-dimethylacetamide in benzene solutions have been calculated at different temperatures”, Indian Journal of Pure and Applied Physics, Vol.38, pp.328, 2003

4. Hill,N. E., Vaughan,W. E., Price,A. H. and Davies,M., “ Dielectric Properties and Molecular Behavior”, Northland Reinhold Company, London, UK, 1968.

5. Higasi, K., “ Dielectric Relaxation and Molecular Structure II, Notes on Analyhsing Dielectric data on Dilute Solution “, Bulletin of the Chemical Society of Japan, Vol. 39, pp. 2157, 1966.

6. Thenappan,T. and Sankar, U., “Study of correlation factors and dipolar excess free energies of esters in benzene,” Journal of Molecular Liquids, Vol. 126, No. 1–3, pp. 23–28, 2006.

7. Purcell,W.P. & Smyth,C.P., “Dielectric Properties and Molecular Behavior”, Journal of American Chemical Society. Vol. 86, pp.152, 1963.

8. Kumar S, Ph. D Thesis, Annamalai University, Chidambaram, 2001.

9. Madhu Mohan,T., Sreehari S and Murthy V.R.K., “Microwave dielectric relaxation, thermodynamic and conformational studies of hydrogen bonded binary mixtures of propan-1-ol with methyl benzoate and ethyl benzoate”, Indian Journal of Pure and Applied Physics. Vol.48, pp.668-675, 2010.

10. Kalaivani,T.,and Krishnan,S., “Dielectric relaxation studies of ternary liquid mixtures of aniline and substituted anilines with acrylonitrile in the microwave region,” Indian Journal of Pure and Applied Physics, Vol. 47, No. 12, pp. 880–882, 2009.

11. Thenappan,T., “Studies on molecular interactions and fluid structure of anisole with 2-ethyl-1-hexanol and decyl alcohol Journal of Molecular Liquids”, Vol. 133 , pp.1, 2007.

12. Higasi,K. A., Koga,Y., and Nakamura,M., “Dielectric relaxation and molecular structure Application of the single frequency method to systems with two debye dispersions,” Bulletin of the Chemical Society of Japan, Vol. 44, pp.988, 1971.

13. Khameshara,S.M.,and Sisodia,M.L., “Dielectric relaxation study of some substituted anilines in benzene solutions at different temperatures and Advances in Molecular Relaxation process”, Vol.15, pp.213, 1979.

14. Eyring H, Cernuschi F., “An Elementary Theory of Condensation Journal of Chemical Physics”, Vol. 7 , pp.547, 1939.

15. Parthipan,G., and Thenappan,T., “Dielectric and thermodynamic behavior of binary mixture of anisole with morpholine and aniline at different temperaturesJournal of Molecular Liquids”, Vol. 138, pp.20, 2008.

16. Davidson,D.W., “Dielectric relaxation of butyl acrylate-alcohol mixtures”, Canadian Journal Chemistry, Vol. 39 , pp.57, 1961.

17. Dannhauser,W., Guering,R., and Flueckinger, A.F., “ Effect of temperature on the dielectric relaxation in solvent mixtures at microwave frequencies”, Journal of Chemical Physics. Vol. 52 , pp.6443, 1970.

18. Campbell,C., Crossley,J., and Glasser,L., “Dielectric relaxation of some alcohols in solution and Advances in Molecular Relaxation process”, Vol.9, pp.63,1976.

19. Kalaivani,T., Kumar,S., & Krishnan,S., “Dielectric relaxation studies of ternary liquid mixtures of alcohols with triethylamine in the microwave region” , Indian Journal of Chemistry, Vol. 43A, pp,.291, 2004.

20. Kalaivani,T., and Krishnan,S., “Dielectric relaxation studies of ternary liquid mixtures of aniline and substituted anilines with acrylonitrile in the microwave region” , Indian Journal of Pure and Applied Physics, Vol.47, pp.383-385, 2009.

21. Malathi,M., Sabesan,R., Krishnan,S., “Dielectric relaxation studies of N,N-dimethyl formamide and N,N-dimethyl acetamide on complexation with phenols”, Material Science and Engineering – B, Vol. 100, pp. 318-322, 2003.

22. Thenappan, T., “Studies on the fluid structure and molecular interactions of monoalcohols and monolayers of fatty alcohols”, Ph.D Thesis, Alagappa University, 1994

23. Thenappan,T., and Subramainan,M., “Dielectric studies of hydrogen bonded complexes of alcohols with nitriles”, Material Science and Engineering – B, Vol. 86 , pp.7, 2001. Material Science and Engineering – B, Vol. 86 pp.7 , 2001.

24. Parthipan,G., Aswthaman,H., Sankar,U., “The dielectric studies of hydrogen-bonded complexes of anisole with alcohols” Journal of Molecular Liquids. Vol. 140 pp.1, 2008.

25. Parthipan,G., Arivazhagan,G., and Thenappan,T., “Dielectric and thermodynamic studies on a binary mixture of anisole with butyric or caprylic acid”, Philosophical Magazine Letters, Vol. 88, No. 2, pp. 125–136, 2008.