User:Shafiyoddin2003/sandbox

=  Dielectric Relaxation Study of Binary Liquid  = 

INTRODUCTION
All the material on earth is in three states-solid, liquid, and gas. The "state" of the matter refers to the group of matter with the same properties. In other words, you group the objects together according to their properties. In solids, since the atoms are closely packed, the particles perform relatively small oscillations about their equilibrium positions governed by the temperature. This explains rigid shape and size of solids. In liquid state; intermolecular interaction are less than solid. As a result of this, the molecules of liquid can move about inside the liquid. From the statistical mechanics, different theories for the equilibrium properties of liquids are developed. Different theories [1-4] have been proposed for various types of liquids.

The substances called insulators which do not have free electrons, the electrons are tightly bound to the atom. When the potential difference is applied to insulator no electron current flows, even then their behavior in fields may change. The insulator whose behavior gets modified in the electric fields is called as dielectrics [5]. When the change in behavior of the dielectric is independent of the direction of applied field, the dielectric called as isotropic, otherwise the change in behavior of the dielectric depends on the direction of the applied field, and the dielectric is called anisotropic.

If we consider a dielectric in an electric field, then the field exerts a force on each charged particle. The positive particles are pushed in one direction (direction of field) while the negative particles in the opposite direction. As a result the positive and negative particles of each molecule are displaced from their equilibrium positions in opposite directions. The overall effect of the charges is called polarization and the dielectric is said to be polarized.

The molecules of dielectrics are classified in to two classes

1.      Polar molecules.

2.      Non-Polar molecules.

In general, polarity refers to the dipole-dipole intermolecular forces between the slightly positively-charged ends of one molecule to the negative end of another or the same molecule. Molecular polarity is dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure.

A molecule with a permanent electric dipole moment is called a polar molecule. When electric field is applied to dielectric, the molecular charges get displaced. The total charge passing through unit area within the dielectric perpendicular to applied field is called polarization. A molecule is polarized when it carries an induced dipole. The physical chemist Peter J. W. Debye [2] was the first scientist to study molecular dipoles extensively, and dipole moments are consequently measured in units named debye in his honor. A permanent electric dipole moment, that is although the total amount of positive and negative charge on the molecule are equal, so that the molecule is electrically neutral, the distribution of two kinds of charges are different, so that the positive and negative charges are centered at points separated by distance of molecular dimensions known as electric dipole. When two centers of gravity coincide in a molecule, the molecule as a whole possesses no result charge and is said to be non-polar.

There are three types of polarization; (i) Orientation polarization, (ii) Electronic polarization, and (iii) Atomic polarization. In electronic polarization the electrons in each atom are displaced from their usual positions, giving each molecule a small dipole moment. Contribution of electronic polarization to the dielectric constant of the liquid is numerically equal to square of refractive index. In atomic polarization there is relative change in the mean positions of the atomic nuclei within the molecules. It occurs at radio frequencies. In the case of orientational polarization, the molecules are partially aligned by the field and contribute heavily to the polarization. The orientational polarization is additional to electronic and atomic polarization for polar molecules. Therefore the polar materials have higher permittivity than non-polar materials. For example, the dielectric constant of a non polar liquid such as hydrocarbon is about 2, which of a weakly polar liquid, such as chloroform or ethyl ether, are about 5, while those of highly polar liquids, such as ethanol and water range from 25 to 80. The orientation polarization falls off rapidly with rising temperature, because the increasing thermal motion reduces the alignment of the permanent dipoles caused by the electric field. For this reason the permittivity of a polar material falls more rapidly with rising temperature.

A dielectric material is one which contains either permanent or induced dipoles which when placed between two electrodes acts as a capacitor, i.e. the material allows charge to be stored and no dc conductivity is observed between the plates. The polarisation of dielectrics arises from the finite displacement of charges or rotation of dipoles in an electric field and should not be confused with conduction which results from translational motion of the charges when the electric field is applied. At the molecular level polarisation involves either the distortion of the distribution of the electron cloud within a molecule or the physical rotation of molecular dipoles.The investigation of dielectric properties provides an important approach to understand the structure of matter.

The permittivity of a material, e, is a property which describes the charge storing ability of that substance irrespective of the sample’s dimensions. The dielectric constant or relative permittivity is the permittivity of the material relative to that of free space. Dielectric studies involve the measurements of dielectric permittivity, dielectric loss at different frequencies and temperature. Understanding of static dielectric constant (low-frequency dielectric constant) is useful in determination of dipole moments of molecules. The measurements of dielectric permittivity and dielectric loss can be used to determine relaxation time and distribution parameters. These parameters then can be used to investigate the molecular motions, which depend on molecular structure, size, shape, and intra molecular forces.

The distribution of two kinds of charges in molecule is not symmetric; the positive and negative charges are centered at points separated by a distance, forming an electric dipole. In a dielectric material, these charges can’t move freely through the medium but can be displaced. The magnitude of the dipole moment depends on the size and symmetry of the molecule. Molecules having center of charge symmetry are non-polar, while molecules having no center of symmetry, are polar. Thus, the dipole moment indicates electronic structure of molecule. The dipole moment of the molecule influences its permittivity and therefore studies of permittivity can be used to measure the dipole moment of the molecules.

The behavior of dielectric under the influence of high frequency field is different from the static behavior [3, 4, 6, 7]. The frequency of the externally applied alternating field is such that there is an observable lag in the attainment of equilibrium. This lag is commonly referred to as relaxation, which, in general, may be defined as the lag in the response of a system to change in the forces to which it is subjected [8]. Dielectric relaxation is the exponential decay of polarization with time when an externally applied field is removed. The relaxation time may be defined as the time in which this polarization is reduced to 1/e times its original value, e being the natural logarithmic base. Under the influence of ac field, the polar molecules of a system rotate toward an equilibrium distribution in molecular orientation with a corresponding polarization [9]. When the polar molecules are very large in size, or the frequency of the alternating field is very high, or the viscosity of the medium is very great, the rotary motion of the molecules is not sufficiently rapid for the attainment of equilibrium with the field. The dipole moments are not able to orient fast enough to keep in alignment with the applied electric field and the total polarizability falls from at to (at-a0); where at is the total polarizability given by-

at = a0+ae+aa, where, a0 is orientational polarizability;

ae is electronic polarizability;

aa is atomic polarizability.

This fall in polarizability, with its related reduction of permittivity, and the occurrence of energy absorption is referred to as dielectric relaxation, or dispersion. The frequency at which this fall occurs can vary from very low 10-1Hz and below for large hindered macromolecules to frequencies up to 1012Hz for small molecules. In this region, ae and aa, remain unchanged, since the dispersion due to the fall-off of the atomic polarization occurs at frequencies comparable with the natural frequencies of vibration of atoms in a molecule. (i.e. infrared spectrum around 1014 Hz), and that for electronic polarization occurs at still higher frequencies corresponding to electronic transition between different energy levels in the atom (i.e. visible, UV, and X-ray). The frequencies at which electronic and atomic dispersions occur are determined by the internal properties of the molecules or atoms and hence have the form of resonance dispersion [10], because of discrete energy levels. On the other hand, the dipolar orientation process gives rise to relaxation whose both the frequency and shape of the dielectric loss characteristic depend mainly on the immediate environment of the molecular dipole, and the corresponding changes in permittivity are very different from that of the resonance dispersion. The rotational motions of molecules, or molecular group, result in frequency dependent polarization in the radio frequency and microwave region.

From Maxwell’s theory of Electromagnetic waves, the relative permittivity of material is equal to square of its refractive index measured at the same frequency. If the square of refractive index is measured at frequency of the D lines of Sodium, this gives permittivity, a means for finding what proportion of the polarizability is still effective at this frequency. This will be approximately the electronic polarizability. In polar molecules [1], the difference between the static permittivity and permittivity at frequency of D lines is mainly due to the permanent dipole moment.

APPLICATIONS OF DIELECTRIC STUDY

Agriculture:

It is found that the dielectric constant increases with increasing moisture content in the seeds and decreases with increasing frequency. At high moisture level and low frequency range the magnitude of variation in dielectric constant were large. This variation is used to get an idea of the moisture contents in seeds.

Medicine:

The interest of microwaves increased due to biological effects. Exposure to microwaves results in thermal stresses both deep inside the body and also on the surface. Excessive exposure may cause damage but controlled exposure may result in therapy and human comfort. Controlled dose of microwaves can be made useful for medical diagnosis, therapy and human comfort. Physical therapy of microwave radiation has been found effective in curing inflammation, piles, and injury etc. microwave treatment of cancer has also been studied. There has been a surge of interest in the last few years in the use of microwave diathermy for effective cancer treatment. This is expected to burn away the damaged tissues so that the spread of cancer is controlled. Human comfort and physical health depend upon the energy exchange between man and surrounding. Normally heat is generated in the human body by metabolism in the body. Incident microwave energy can help the heat generation metabolism in the body.

Electrochemical supercapacitors [11]:

Resent advertisement in the electro-chemical capacitors have resulted in new type of capacitors known as ‘supercapacitors’ or ‘ultra-capacitors’. These have capacitance (energy capable of being stored) of several hundred farads (generally, the capacitance of normal capacitors is in the range of fractions of a farad). When a metal is brought in contact with a solid or liquid ionic conductor, a charge accumulation is achieved electrostatically on either side of the interface, leading to development of an electrical double layer, which is essentially a molecular dielectric. No charge transfer takes place across the interface and the current observed during this process, is a displacement current due to the rearrangement of charges.

TIME DOMAIN SPECTROSCOPY

Time Domain Spectroscopy (TDS) probes the interaction of a macroscopic sample with a time-dependent electric field. The resulting polarization, either expressed by the frequency-dependent complex permittivity characterizes amplitude and time scale (via the relaxation time) of the charge-density fluctuations within the sample. Such fluctuations generally arise from the reorientation of the permanent dipole moments of individual molecules or from the rotation of dipole moments in flexible molecules, like polymers. The time scale of these fluctuations depends on the sample and on the relevant relaxation mechanism. Relaxation times range from several Picoseconds in low-viscosity liquid, such as water, to hours in the case of glasses [12]. Probably TDS is the technique with the most extensive coverage of dynamical processes. The corresponding measurement frequencies range from 10-4 Hz to 1012 Hz, which requires a variety of instruments for complete coverage. However, it is generally sufficient to concentrate on a smaller frequency range adapted to the sample properties.

In contrast to conventional spectroscopic methods, like NMR spectroscopy, TDS is especially sensitive to intermolecular interactions. TDS includes, Time Domain Reflectometry (TDR) and Time Domain Transmission (TDT) method. TDS is able to monitor cooperative processes and thus provides a link between molecular spectroscopy, which monitors the properties of the individual constituents, and techniques characterizing the bulk properties of the sample, especially the viscoelastic and rheological behavior. The time scales covered by these processes range from milli to picoseconds, so that experiments must be conducted in the range of radio to microwaves. Precise spectra over a broad frequency range are necessary for a meaningful deconvolution. e.g. water peaks at 20 GHz - already in a frequency range difficult to access, such limited investigations do not only forbid a characterization of the solvent response, but also hamper a precise separation of the solute contribution or of specific cooperative relaxation processes [13-15]. TIME DOMAIN REFLECTOMETRY

The Time Domain Reflectometry is a measurement concept having great usefulness in the analysis and synthesis of wide band systems. The development of Time Domain Reflectometry by Cole et. al., [16-19] gives dielectric relaxation study over a wide range of frequency.

The basic TDR system consists of fast rising pulse generator, sampling unit and a wide band, digitizing oscilloscope. A step voltage pulse produced by tunnel diode is detected at the sampler and displayed on the oscilloscope. This voltage pulse is propagated through a coaxial line. The cell, which holds the sample, is placed at the end of coaxial line. When the voltage pulse reaches the air-dielectric interface, a part of pulse is reflected and the rest is transmitted through the dielectric sample. The reflected part is recorded and reflection coefficient is determined. This reflection coefficient, after analysis provides the dielectric parameters. The access to structural changes is through relative changes in dielectric parameters. The relative changes in dielectric parameters over broad range of frequencies and wide range of concentrations at various temperatures can readily be measured using TDR method.

LITERATURE SURVEY

Many research groups to study molecular interactions in liquids have used TDR method. Microwave group at Physics department of Dr. Babasaheb Ambedkar Marathwada University, Aurangabad has developed experimental setup and computer programs required to study dielectric properties of pure liquids as well as binary mixtures using TDR method. We also develop TDR simulation software for analysis of experimental data. Our group to study interactions between various functional groups in organic compounds and biological samples has very effectively used this method. The molecular interactions in aqueous solutions of associative compounds such as Ethylene Glycol [20], Hexamethylphospheramide [21], Dimethylsulfoxide [22], tert Butyl alcohol [23], Acetone and Tetrahydrofuran [24], N,N Dimethylformamide [25], N-Methylformamide [26], Primary alcohols [27-29] was reported earlier. Similarly an aqueous solution of non-associative solute Acetonitrile was reported by Helambe et. al.,[30] The solute solvent interactions between long chain polymeric structures in alcohols with nonpolar molecules such as Benzene and n-Octane [31] and non associative polar solutes such as Aniline [32,33], p-Flourophenylacetonitrile [34], n-nitriles [35],  was studied previously. The dielectric relaxation study of binary mixtures of primary alcohols and polar solutes such as Methyl acetate [36], Dimethylformamide [37], Dimethylsulfoxide [38], Tetrahydrofuran [39] and 2-Nitroacetophenone [40] was reported earlier. The binary mixture of Ethanol, with one –OH group, and Ethylene Glycol, with two –OH groups was reported by S.M. Puranik et. al.,[41]. The binary mixtures of biological samples such as Methanol-Algae [42], Honey-Water [43], Glucose-Water [44], Glycine and Valine-Water [45] were studied by our group. Pure biological samples such as Albumin and Yolk of avian egg [46] and mammalian milk [47] were studied by Lokhande et. al., using TDR technique. The dielectric relaxation study of electrolyte Ca(NO3)2-4H2O in aqueous solution of Urea was reported by S.C. Mehrotra et. al., [48]. The dielectric relaxation study of Chlorobenzene with Dimethylformamide and Dimethylchloride with Ethanol has been reported by V. P. Pawar et. al., [49-50]. The dielectric relaxation study of Ethanol with Nitrobenzene and Nitrotoulene has been reported by Ajay Chaudhari et. al. [51]. N,N-dimethylacetamide with ethanolamine and Formamide with N,N-dimethylaminoethanol has been reported by Prabhakar Undre et. al. [52-53]. Alkyl methacrylate with alcohols has been reported by P. Sivagurunathan et.al [54-60]. Many other research workers in various fields carried out structural dynamics in different type of pure liquids and binary mixtures [61-89] by using different experimental techniques.

INTRODUCTION TO PROBLEM

In Aromatic compounds such as NB, CB and BB the charge distribution is shielded and H-bonds do not appear [90]. Where as in Alkoxyalkanols such as 2-ME, 2-EE, and 2-BE the charge distribution is exposed. In pure NB, CB and BB spatial correlation between molecules may appear only by means of dipole-dipole interactions. When there is an exposed distribution of charges, there may be very strong intermolecular interaction, however in shielded distribution relative contribution to neighbor molecules is absent and hence there may be weak intermolecular interaction between the molecules of the liquids.

Aromatic compound is a large class of chemical compounds whose molecular structure includes one or more planar rings of atoms joined by covalent bonds of two different kinds. Nitrobenzene, Chlorobenzene and Bromobenzene is simple aromatic compounds with only one group attached to the benzene ring [49-51, 83, 91-94].

More specialized applications include the use of nitrobenzene as a precursor to rubber chemicals, pesticides, dyes, and pharmaceuticals. Nitrobenzene is also used in shoe and floor polishes, leather dressings, paint solvents, and other materials to mask unpleasant odors. Redistilled, as oil of mirbane, nitrobenzene has been used as an inexpensive perfume for soaps. A significant merchant market for nitrobenzene is its use in the production of the analgesic paracetamol. Nitrobenzene is also used in Kerr cells, as it has an unusually large Kerr constant.

Chlorobenzene has been used in the manufacture of certain pesticides, most notably DDT by reaction with chloral (trichloroacetaldehyde). It once found use in the production of phenol. Today the major use of chlorobenzene is as an intermediate in the production of nitrochlorobenzenes and diphenyl oxide, which are important in the production of commodities such as herbicides, dyestuffs, and rubber. Chlorobenzene is also used as a high-boiling solvent in organic synthesis as well as many industrial applications.

Bromobenzene can be used to prepare the corresponding Grignard reagent, phenylmagnesium bromide. This can be used in a number of fashions, e.g. the reaction with carbon dioxide to prepare benzoic acid. Bromobenzene is used in the production of drugs.

The dielectric properties of homologous series of liquid molecules of Alkoxyalkanols are of great interest because changes in properties are chiefly related to chain length and molecular size. The dielectric mechanism becomes more complicated with increase in flexibility of the chain. Alkoxyalkanols (2-Methoxyethanol, 2-Ethoxyethanol and 2-Butoxyethanol) have wide range of applications. These are used as industrial solvents, surfactants, detergents and wetting agents. Due to great industrial applications of these molecules, it is interesting to investigate the molecular dynamics of these short-chain molecules with Aromatic compound. These short chain molecules have end –OH group and they can enter either into intra- and intermolecular hydrogen bonding [95-101]. Intermolecular hydrogen bonding in the liquid state plays an important role in relaxation phenomenon. This interaction retards the molecular reorientation since breaking and reforming of hydrogen bonds is required for molecular rotation in an alternating electric field

In the present work an attempt has been made to study the dielectric relaxation behavior of Aromatic compounds with Alkoxyalkanols at different temperatures. All the chemicals used for present investigation are of spectroscopy grade. The systems chosen for the present work are as follows.

Aromatic Compound + Alkoxyalkanol Binary Mixtures under study

1.      2-Methoxyethanol                  +         Nitrobenzene

2.      2-Ethoxyethanol                    +          Nitrobenzene

3.      2-Butoxyethanol                    +          Nitrobenzene

4.      2-Methoxyethanol                  +         Chlorobenzene

5.      2-Ethoxyethanol                    +          Chlorobenzene

6.      2-Butoxyethanol                    +          Chlorobenzene

7.      2-Methoxyethanol                  +         Bromobenzene

8.      2-Ethoxyethanol                    +          Bromobenzene

9.      2-Butoxyethanol                    +          Bromobenzene

All above binary systems are studied for 11 different concentrations over the frequency range of 10 MHz to 20 GHz. Temperature dependent variations in dielectric parameters for four different temperatures are also reported for all the systems. The dielectric parameters i.e. dielectric constant and relaxation time have been determined. The static permittivity and relaxation time have been used to obtain the excess dielectric parameters, which give information related to molecular interaction. The Kirkwood correlation factor and Bruggeman factor for all systems have been determined. The obtained results are discussed on the basis of excess permittivity, excess inverse relaxation time, Kirkwood correlation factor, Bruggeman factor, enthalpy and entropy.

Physical Constant of Pure Liquids:

a D. R. Lide, Handbook of Chemistry and Physics 87 th edition, CRC Press, 2006-2007

b R. J. Sengwa et. al., Physics and Chemistry of Liquids 44(6) 2006, 637

c Digest of Literature on Dielectrics, Vol 39, National Academy of Sciences; Washington DC, 1975

Molecular Structures of Pure Liquids:

REFERENCES

[1]           N. E. Hill, W. E. Vaughan, A. H Price, and M. Davis, Dielectric Properties and Molecular Behavior, Van Nostrand, London, 1969.

[2]           P. Debye, Polar Molecule, Chemical Catalog, Dover, NY, 1929.
[3]           A. R. Von Hippel, “Dielectric Materials and Applications”, John Willy and Sons Inc. NY, 1954.

[4]           C. P. Smyth, Dielectric Behavior and Structure, McGraw-Hill Book Comp., NY, 1955.

[5]           S. L. Gupta, V. Kumar and S. P. Singh, “Electrodynamics”, Pragati Prakashan, Meerut 1995.
[6]           H. Frolhich, Theory of Dielectric, Oxford University Press, London, 1967.

[7]           V. V. Daniel, Dielectric Relaxation, Academic Press, London, 1967.

[8]           W. Kauzmann, ''Revs. Mod. Phy.,'' 14, 12, 1942.

[9]           CJF Bottcher, Theory of Electric Polarization, Elsevier Pub. Comp. Inc. Amsterdam, 1952.
[10]           Ronald Pethig, Dielectric and Electronic Properties of Biological Materials, John Willy and Sons, Chichester, 1979

[11]           A. K. Shukla, S. Sampath and K. Vijayamohanan, Current Science, 79 (12), 1656-1661,  2000.

[12]           C. C. Ku and R. Liepins, Electrical Properties of Polymers, Hanser, Munchan, 1987.

[13]           R. Buchner and J. Barthel, Dielectric Relaxation in Solutions, Annu. Rep. Prog. Chem., Sect. C, 91, 71-106, (1994); 97, 349-382, 2001.

[14]           U. Kaatze, ''J. Sol. Chem''., 26, 1049-1112, 1997.

[15]           J. Barthel et. al, ''J. Mol. Liq''., 78, 82-109, 1998.

[16]           T. Skomoto, H. Nakamura, H. Udedira, and A. Wada, ''J. Phys. Chem''., 93, 357, 1989.

[17]           R. H. Cole, ''Ann. Rev. Chem''., 28, 283, 1977.

[18]           R. H. Cole, ''IEEE Trans. Instrum. Meas. IM-''32, 42, 1983.

[19]           R. H. Cole, J. G. Berberion, S. Mashimo, G. Chryssikos, A. Burns, and E. Tombari, ''J. Appl. Phys'', 66, 793, 1989.

[20]           A. C. Kumbharkhane, S. M. Puranik, S. C. Mehrotra, ''J. Sol. Chem''., 21, 201-212, 1992.

[21]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Chem. Phys.,'' 21, 201-212, 1993.

[22]           S. M. Puranik, A. C. Kumbharkhane and S. C. Mehrotra, ''J. Chem. Soc. Faraday Trans''., 88 (3), 433-435, 1992

[23]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Chem. Soc., Faraday Trans''., 87, 1569-1773, 1991a

[24]           A. C. Kumbharkhane, S. N. Helambe, M. P. Lokhande and S. C. Mehrotra, ''Pramana-J. Phy''., 46 (2), 91-98, 1996

[25]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Sol. Chem.,'' 22 (3), 219-228, 1992

[26]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Mol. Liq.,'' 51, 261-277, 1992

[27]           S. M. Puranik, A. C. Kumbharkhane and S. C. Mehrotra, ''Proc. Nat. Acad. Sci., India,'' 63 (A), II, 1993

[28]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Pure and Appl. Phys''., 4 (2), 62, 1992.

[29]           S. M. Puranik, A. C. Kumbharkhane and S. C. Mehrotra, ''Proc. Nat. Acad. Sci., India'', 63 (A), II, 415-426, 1993.

[30]           S. N. Helambe, M. P. Lokhande, A. C. Kumbharkhane, S. C. Mehrotra and S. Doraiswamy, Praman J. Phy., 44 (5), 405-410, 1995.

[31]           S. C. Mehrotra, B. Gestblom and J. Sjoblom, ''Finn. Chem. Lett''., 1985.

[32]           R. H. Fattepur, M. T. Hosamani, D. K. Deshpande and S. C. Mehrotra, ''J. Chem. Phys.'', 101, 9556, 1994.

[33]           S. P. Patil, A. S. Chaudhary, M. P. Lokhande, A. G. Shankarwar, S. N. Helambe, B. R. Arbad and S. C. Mehrotra, ''J. Chem. Eng. Data'', 44, 875-878, 1999.

[34]           M. T. Hosamani, R. H. Fattepur, D. K. Deshpande and S. C. Mehrotra, ''J. Chem. Soc., Faraday Trans.,'' 91(4), 623-626, 1995.

[35]           S. N. Helambe, A. S. Chaudhari and S. C. Mehrotra, ''J. Mol. Liq''., 84, 325-244, 2000.

[36]           R. M. Shirke, A. S. Chaudhari, N. M. More and P. B. Patil'', J. Chem. Eng. Data'', 2-8, 2000.

[37]           P. W. Khirade, A. S. Chaudhari, J. B. Shinde, S. N. Helambe and S. C. Mehrotra, ''J. Sol. Chem''., 28(8), 1031-1043, 1999.

[38]           P. W. Khirade, Ajay Chaudhari, J. B. Shinde, S. N. Helambe and S. C. Mehrotra, ''J. Chem. Eng. Data'', 44, 879-881, 1999.

[39]           A. S. Chaudhari, P. Khirade, R. Singh, S. N. Helambe, N. K. Narin and S. C. Mehrotra, ''J. Mol. Liq.,'' 82, 245-253, 1999.

[40]           A. C. Kumbharkhane, S. M. Puranik and S. C. Mehrotra, ''J. Mol. Liq.,'' 51, 307-319, 1992.

[41]           S. M. Puranik, A. C. Kumbharkhane and S. C. Mehrotra, Indian J. Phys., 67 (1), 9-13, 1993.

[42]           A. C. Kumbharkhane, M. U. Patil and S. C. Mehrotra'', Nat. Acad. Sci. Lett''. 19 (1 and 2), 19-23, 1996.

[43]           S. M. Puranik, A. C. Kumbharkhane and S. C. Mehrotra, J. Microwave power and EM energy, 26, 196-201, 1991b.

[44]           D. V. Jahagirdar, B. R. Arbad, M. P. Lokhande and S. C. Mehrotra, ''Ind. J. Chem.'', 34 (A), 462-465, 1995.

[45]           M.P. Lokhande, S. Mujumdar and S.C. Mehrotra, ''Indian J. of Biochem. and Biophy''. 34, 385-390, 1997.

[46]           M.P. Lokhande, B.R. Arbad, M.G. Lande and S.C. Mehrotra, ''Indian J. of Biochem. and Biophys''. 33, 156-158, 1996.

[47]           M.P. Lokhande, B.R. Arbad, M.G. Lande and S.C. Mehrotra, Indian J. of Dairy Sci. 48, 11, 1995.

[48]           S.C. Mehrotra, A.C. Kumbharkhane, S.N. Helambe, B.R. Arbad and D.V. Jahagirdar, Ind. J. of Chem., 35A, 878-883, 1996.

[49]           V. P. Pawar and S. C. Mehrotra, ''J Mol. Liq''., 95, 63-74, 2002.

[50]           V. P. Pawar and S. C. Mehrotra'', J Mol. Liq''., 108/1-3, 95-105, 2003.

[51]           Ajay Chaudhari, Anita Das, G. Raju, Harish Chaudhari, Prakash Khirade, N. K. Narain and S. C. ''Proc. Natl. Sci. Counc. ROC(A),'' 25(2001) 205 210.

[52]           Prabhakar Undre, S.N.Helambe, S.B. Jagdale, P. W. Khirade, S. C. Mehrotra J''. Mol. Liqs,'' 137 (2008) 147

[53]           Prabhakar Undre, S.N.Helambe, S.B. Jagdale, P. W. Khirade, S. C. Mehrotra. ''Pramana-J. Phy,'' 68 (5) 851,2007.

[54]           P. Sivagunathan, K. Dharmalingam, K. Ramchandran, B. Prabhakar Undre, P. W. Khirade, S. C. Mehrotra, Philosophical Magazine Letters, 86(5), 291,2006.

[55]           P. Sivagurunathan, K. Dharmalingam, K. Ramachandran, B Prabhakar Undre, P.W.Khirade and S.C.Mehrotra. Physica B, 387, 203,2007.

[56]           P. Sivagurunathan, K. Dharmalingam, K. Ramachandran, B. Prabhakar Undre, P.W.Khirade and S.C.Mehrotra. J. Mol Liq., 133, 139,2007.

[57]           P. Sivagurunathan; K. Dharmalingam; K. Ramachandran; Prabhakar B Undre; P.W. Khirade and S.C Mehrotra; Main Group Chemistry, 2005,4(3),235.

[58]           K. Dharmalingam P. Sivagurunathan; K. Ramachandran; Prabhakar B Undre; P.W. Khirade and S.C Mehrotra; ''Mol. Phys''. 2006,104,2835.

[59]           P. Sivagurunathan; K. Dharmalingam; K. Ramachandran; Prabhakar B Undre; P.W. Khirade and S.C Mehrotra; Lithuanian J. Physics. 46(4) 2006, 441-445

[60]           K. Dharmalingam K. Ramachandran; P. Sivagurunathan; B. Prabhakar Undre; P.W. Khirade and S.C Mehrotra; ''Bull. Korean Chem. Soc''. 2006, 27 (12) 2040

[61]           J. B. Hasted, Dielectric and related molecular Process Vol. 1. (London : The Chemical Society), 121-162, 1972 b.

[62]           J. Crossely, Can. J. of Chem. (Canada), 49, 712, 1971.

[63]           S. S. N. Murthy, Molecular Phys. Vol. 87, 3691-709, 1996

[64]           Josef Barthel, Richard Buchener and Bernhard Wurm, ''J. Mol. Liq''., 98-99,51-69, 2002

[65]           S. F. Al-Azzawl, A. M. Awwad, A. M. Al-Dujaili and M. K. Al-Noori, ''J. Chem. Engg. Data.,'' 35, 463, 1990.

[66]           M. I. Aralaguppi, T. M. Aminabhavi, R. H. Balundgi and S. S. Joshi, ''J. Phys. Chem.,'' 95, 5299, 1991.

[67]           V. Satheesh, M. Jeyaraj and J. Sobhanadri, ''J. Mol. Liq.,'' 64,247-261, 1995.

[68]           A. K. Lyashchenko, A. S. Lileev, V. S. Kharkin, V. S. Goncharov and A. F. Borina Mendeleev Communications Electronic Version Issue 5, 169-212, 1997.

[69]           I. V. Ermolina, V. D. Fedotov and Yu. D. Feldman, Physica A, 249, 347-352, 1998.

[70]           U Becker and M. Stockhausen ''J. Mol. Liq''., 81, 89-100, 1999.

[71]           Shugin Li, Xingen Hu, Ruisen Lin and Hanxing Zong Thermochimica Acta, 342,1-6, 1999.

[72]           K. E. Gibbons, M. O. Jones, S.J. Blundell, A.I. Mihut, Ian Gameson, P.P. Edwards, Y. Miyazaki, N.C. Hyatt and A. Porch ''Chem. Commun.,'' 159-160, 2000.

[73]           F. F. Hanna, A. L.G. Saad, M.H. Youssef and A. Soliman ''J. Mol. Liq''. 89, 57-79, 2000.

[74]           Ruisen Lin, Xingen Hu, and Xiaoling Ren Thermochimica Acta, 352-353, 31-37, 2003

[75]           F. F. Hanna, Bo Gestblom and A. Soliman ''Phys. Chem. Chem Phys''., 2, 5071-5075, 2000

[76]           R. J. Cava, J. Mater. Chem., 11, 54-62, 2001.

[77]           S. Sudo, N. Shinyashiki and S. Yagihara, ''J. Mol. Liq.,'' 90, 113-120,  2001

[78]           A. K. Lyashchenko, T.A. Novskova and V. I. Gaiduk, ''J. Mol. Liq''., 94, 1-16, 2000

[79]           Qingwang Liu, Xingen Hu, Ruisen Lin, Shugin Li, and Wenqiang Sang Thermochimica Acta, 369,31-37, 2001

[80]           Li Yu, Xingen Hu, Ruisen Lin, Shuang Shao and Honglin Zhang Thermochimica Acta, 378,1-8, 2001

[81]           T. Sato, A. Chiba and R. Nozaki, ''J. Mol. Liq''., 96-97, 327-339, 2002

[82]           E. N. Tsurko, T. M. Shihova and N. V. Bondarev, ''J. Mol. Liq.,'' 96-97, 425-437, 2002

[83]           AKL. M. Awwad, A. H. Al-Dujaili, and S. R. Syriagh., ''J. Mol. Liq.,'' 100/2, 129-141, 2002.

[84]           T. Sato, A. Chiba and R. Nozaki, ''J. Mol. Liq''., 101/1-3, 99-111, 2002.

[85]           V. A. Rana and A.D. Vyas, ''J. Mol. Liq''., 102/1-3, 379-391, 2002.

[86]           F.F. Hanna, Bo Gestblom and A. Soliman,  ''J. Mol. Liq''., 95, 27-40, 2002.

[87]           S. L. Abd-El-Messieh, ''J. Mol. Liq''., 95, 167-182, 2002.

[88]           R. L. Smith, C. Saito, S. Suzuki, Sung-Bong Lee H. Inomata, and K. Arai Fluid Phase Equilibria, 194-197,869-877, 2002.

[89]           R. J. Sengwa, R. Chaudhary and S. C. Mehrotra, Molecular Phys., 99, 21, 1805-1812, 2001.

[90]           Gerald Oster and J. G. Kirkwood in “Dielectric –Intermolecular forces-Optical Rotation” Ed. R.H. Cole, Gordon and Breach Science Publishers, N.Y., London, Paris, (1965) pages 81-87.

[91]           E. A. Nicol and N. E. Hill, ''J. Phys. C. Solid St. Phys''., 3 1970, 2207-2215

[92]           V.P. Pawar, G. S. Raju and S.C. Mehrotra, Pramana, 59/4 (2002) 693 699.

[93]           C. Gabriel, S. Gabriel, E. H. Grant, B. S. J. Halstead and D. M. P. Mingos, ''Chem. Soc. Rev.'' 27, 213 (1998).

[94]           M. B. R. Murthy, B. S. Dyasagar and R. L. Patil, Pramana, 61 (4) 2003, 725-727.

[95]           R. J. Sengwa, Madhvi and Sonu Sankhla, Physics and Chemistry of Liquids, 44 (6) 2006, 637-653

[96]           R. J. Sengwa, Madhvi, Sonu Sankhla, and Shobha Sharma, ''Bull. Korean Chem. Soc''. 27 (5) 2006,

[97]           R. J. Sengwa and Kulvinder Kaur ''J. Mol. Liq''. 82-231-243, 1999.

[98]           R.J. Sengwa, R. Chaudhary and S. C. Mehrotra, Polymer, 43, 1467-1471, 2002

[99]           H. D. Purohit and R. J. Sengwa, ''J. Mol. Liqs,'' 39, 1988 43-52.

[100]           H. D. Purohit and R. J. Sengwa, ''J. Mol. Liqs,'' 47, 1990 53-62.

[101]           Sayyad Shafiyoddin, Pravin Yannewar, S. S. Patil, P. W. Khirade and S. C. Mehrotra, ''Frontiers of Microwaves and Optoelectronics, Proc. ICMO'' 2007, 699-705.