Mathur, A

Sahni, N

Saxena, C

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Indian 91-94 (1976)A ctivation  energ ies  and  tim es of re laxation  for b inary  m ix tu res  in d ilu te  so lu tionN. S a h n i , a . Mathttb a n d  M. C. S a x b n a  Physics Department, Lucknow University, Lucknow {Received 19 September 1974, revised 11 December 1974)TJie dielectric relaxation times have been evaluated for six binary mixtures of anilines and xylenes in dilute solutions of benzene in the 3 cm microwave region. The relaxation times of each of the mixtures have been found to be nearly the average of the relaxation times of its two components. The various energy parameters have also been evaluated and discussed.1. I n t r o d u c t io nTlio dipole orientation in polar liquids in dilute solutions cannot be treated as ail isolated molecular motion (Bauer & Magat 1938). The dielectric relaxa- l ion in liquids is a cooj3erative process involving the relaxation of a number of molecules around any particular individual. In his study of binary mixtures of polar liquids, Schallamach (1946) found that the curve of the dielectric constant as a function of temperature showed a single maximum^ The two polar media ap])(^ ar to have merged to provide a single local environment in the liquid, liabiida (1958), Forest & Smyth (1965) observed that for some mixtures two relaxation times wore obtained. This was interpreted by Schallamach as a result of the mixtures being not microscopically homogeneous, such as a mixture of an associated and a nonassociated liquid.Keeping in view the involvement of a single relaxation time for a micro­scopically homogeneous mixture, the authors have investigated the relaxation times of several binary mixtures of substituted aniline and xylene molecules in dilute solutions in benzene. These values are then compared with those of the components of the mixtures reported earlier by Srivastava (1960), Mehrotra Saxena (1966). The energy parameters for the dielectric relaxation and for the viscous flow of the solvent have also been obtained for the dipolar mixtures.2. E x p e r im e n t a l  P b o o b d u b bA 3 cm microwave bench has been used for the measurement of the dielectric constant e' and the loss factor e", utilising the technique of Roberts & Von Hippel (^946), described by Mehrotra el al (1967). The varying concentration method91d 2 K. Salmi, A. Hathur and M. C. Sazenaof Gopala Krislxoa (1957) has been used for the determination of the relaxation time r using the following relationsand_  6 '»+e"»+e'-2 _  3e"(e '+ 2)*+e'« ’ (e '+ 2)*+e"*T =2ttc ' dx'The thormodynamioal parameters were evaluated using the Eyring’s theory of rate process (Glasstone et al 1941).The chemicals used were of the purest available quality, obtained from Aldrich Chemicals. The AR grade benzene was obtained from B.D.H. Ltd., England and was distilled before use.3* R e su l t s  a n d  D isc u ssio n sThe relaxation times of six binary mixtures and their thermodynamical parameters at varying temperatures have been reported in table 1 . The relaxa­tion times of the component molecules in solutions are also stated for comparison. The relaxation times of all mixtures are found to decrease with an increase in temperature as in the case of individual molecules. The relaxation times of investigated mixtures and those of their component liquids, on comparison reveal that the former are nearly the average of the latter values. This has been inter­preted by the fact that the relaxation of liquid mixtures is a cooperative process, involving the relaxation of the structure around any pai ticular molecule. Similar results have boon obtained by Dhar k, Saxena (1972).The relaxation time for the mixture : 3-nitro-o-xylene+N-N'-dimethyl-4- mothyl aniline in mixture, and is slightly greater than the average relaxation times of its component molecules, showing that the relaxation process of mixtures is influenced more by the molecule having a higher relaxation time. This is in agreement with the investigations of Ritson (1946).The free energy of activation is maximum for that set of mixturewhich has got the highest relaxation time and it increases with increasing tempera­ture. The free energy of activation due to viscous flow of the solvent (AJ’i-), is always greater than that due to dielectric relaxation (AJ’a) indicating greater interference by neighbours to the viscous flow than to the dielectric relaxation. The enthalpy of activation (A//j) is found to bo less than that for viscous flow (AH„), because the latter involves both the rotational and translational motion (Petro & Smyth 1957). The negative value of the entropy of activation indicatesBetaxation for binary mixtures 93Table 1. Relaxation times and energy parameters for binary mixtures at A =  3.10 cm.Mixture 210Rr x l 0 »SocAi?’eKcal/molKcal/molAHeKcal/molAH„Kcal/molCal/molA^,Cal/mol2-nitro-m-xylene “ 298 15.65 2.71 4.27 1.68 2.62 - 3 .4 6 - 6 .8 8304 14.63 2.74 4.31 1.68 2.52 - 3 .4 9 - 6 .9 0ni-ohloroaniline*' 310 13.64 2.76 4.36 1.68 2.62 - 3 .4 8 - 5 .9 23-nifcro-m-xyleiio^^ 298 16.06 2.76 4.27 1.83 2.62 - 3 .1 2 - 6 .8 8304 16.82 2.78 4.31 1.83 2.62 - 3 .1 3 - 6 .9 0N -N'-dimo thy 1 - 4 - ^  methylaniline310 14.36 2.79 4.36 1.83 2.52 - 3 .1 0 - 6 .9 22*nitro-m-xylene" 298 14.03 2.66 4,27 0.71 2.62 -6 .6 1 - 6 .8 8"f 304 13.69 2.69 4.31 0.71 2.62 -6 .6 1 - 6 .9 0N-N'-diethyl-4-“aminoaniline310 13.06 2.73 4.36 0,71 2.52 - 6 .6 2 - 6 .9 23-nitro-o-xylene^ 298 20.39 2.87 4.27 1.96 2.62 - 3 .0 9 - 6 .8 84" 304 19.74 2.91 4.31 1.06 2.62 - 3 .1 6 - 6 .9 0N-N'-diraethyl'4-cmethylaniline310 17.61 2.92 4.36 1.96 2.62 - 3 .1 3 - 6 .9 23-nitro-o-xyleno^ 298 18.26 2.80 4.27 2.06 2.62 - 2 .4 8 - 6 .8 8+ 304 16.31 2.81 4.31 2.06 2.52 - 2 .4 7 - 6 .9 0m-ohloroaniline*' 310 14.84 2.82 4.30 2.06 2.62 - 2 .4 6 - 5 .9 2m*(3liloroanilino*» 298 11.41 2.63 4.27 0.51 2.62 - 6 .7 8 - 6 .8 8304 11.16 2.67 4.31 0.61 2.62 - 6 .7 8 - 6 .9 0N-N'-dimethyl-4 mothylanilino310 10.76 2.62 4.30 0.61 2.62 -6 .8 1 - 6 .9 2**295 18.26 from the data of Mehrotra & Saxona (I960) ‘’303 9.10 from the data of Srivastava (1960)^303 13.59“303 10.20 from author’s unpublished data •298 21.90the possibility of fewer configurations in the activated state and for these con­figurations the activated state is more ordered than the normal state. Similar results were obtained for single molecules by Shukla et al (1969).A c k n o w le d g m en tThe authors express their thanks to Professor B. G. Gokhalo, Head of the Ph3rsics Department for providing the necessary facilities and to Dr. J . P. Shukla for his interest in the work. ^N. Sahai, A. Mathur and M. C, 8axenaB b f b b x n o b sBauer E. & Magat M. 1938 J. Ph/ys. Radium. 9, 319.Dhar K. h. &> Saxena M. C. 1972 Z. Phyaik. Chem. Ncue. Polge. 81, 189.Forest. E. & Smyth C. P. 1965 J, Phya. Otem, 69, 1302.Glasstono 8., Laldlor K. J. & Eyring H. 1941 The theory of rate proceasy MoGraw Hill Book Co.,New York.Gopala Krishna K. V. 1967 Tratia. Faraday S o d . 53, 767.Kadaba P, K. 1968 J. Phya. Chem. 62, 887.Mehrotra N. K. & Saxena M. C. 1966 Ind. J. Pure & AppL Phya. 4, 438.Mehrntra N. K., Shukla J. P. & Saxena M. C. 1967 Ind. J. Pure & Appl. Phya. 5, 61.Pebro A. J. & Smyth C. P. 1957 J. Amer. Chem. Soc. 79. 6142.Kitspn D. M. 1946 Trcma. Faraday Soo. 42A, 193.Boberts 8. & Von Hippel A. 1946 Trane. Faraday Soc. 17, 60.Schallamaoh A. 1946 Trana. Faraday Soc. 42A, 180.Shukla J. P., Shukla 1). D. & Saxena M. C. 1969 J. Phya. Chem, 73, 2187.Srivaatava H. N. I960 Tnd. J. Sci. Industrial Res. B19, 149.

Activation Energies and Times of Relaxation for Binary Mixtures in Dilute Solution

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Activation Energies and Times of Relaxation for Binary Mixtures in Dilute Solution

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