Indian Journa l o f Chemi stry Vol. 45A , June 2006. pp 138 i - 1389

Studies on excess molar volumes and viscosity deviations of binary mixtures of butylamine and N, N-dimethylformamide with some alkyl acetates at 298.15 K

Vikas Kumar Dakua. Bi swajil Sinha & Mahendra Nalh Roy * Department of C he mi stry. Uni vers ity o f North Bengal, Daljeeling 734 013 , India

Email: mahendra roy2002 @yahoo .co .in

Received 26 Decell/ber 2005; revised 2 f April 2006

Densit ies and viscos ities have been measured fo r the binary mi xtures o f buty lamine (B A) and . N-dimethylformamide (DMF) wi th methy l acetate (MA), e thy l ace tate (EA) . buty l acetate (BUA) and iso-amyl ace tate (AA) at 298. 15 K over the entire composition range . From density and viscosity da ta, the values o f excess mo lar volume (VL) and viscos ity dev iat ion

(<">11) have been determined. These results have been fitted to Red li ch~Ki s te r type po lynomi al equ ati ons to estimate the binary coeffi c ien ts and standard e rro rs betwee n the experimental and computed va lues. The de nsity and viscosity data have been analyzed in te rms o f semiempi ri ca l viscosity models and the results have been di scussed in te rms o f mo lecu la r inte rac tio ns and structura l effec ts. The excess properti es are found to be e ither negati ve o r positi ve depending on the molecul ar il1le rac ti ons and the nature of liquid mi xtures.

Studies on thermodynam ic and transport properti es are important in understanding the nature of molecular interact ions in binary liquid mixtures. These properties are extremely useful for des igning many types of transport and process equipment in chemical industries. There has been a recent upsurge of interest l

.2 in the study of thermodynamic properti es

of binary liquid mi xtures. These have been exten­sively used to obtain in fo rmati on on intermolecular interactions and stereochemi cal effects in these systems. BA and DMF are versatile solvents used in the separation of saturated and unsaturated hy0ro­carbons and in pharmaceutical sy nthes is, and serve as solvents for many polymers. 3 In thi s paper, we report experimental data fo r density (p) and viscos ity (1')) of the fo llow ing mixtures at 298. 15 K: butylamine (BA) or N, N-dimethylformamide (DMF) + methy l acetate (MA), ethyl acetate (EA), butyl acetate (BUA), and iso-amyl acetate (AA). Using these data, excess molar volume (VE

), viscosity dev iation (f11'1 ), Grunberg­Ni ssan (d I2), Tamura-Kurata (7d, and Hind (H d interaction parameters have been calculated. These results have been fitted to Redli ch-Ki ster type poly­nomi al equations to estimate the binary coefficients and standard errors between the ex perimental and calculated values .

Materials and Methods Butylamine (S. D. Fine Chem, minimum assay

GLC, 98%) was stored over sodium hydrox ide pellets

for several days and fractionally di stilled twice.4 N, N-dimethylformamide (S . D. Fine Chemicals, AR, purity>99%) was purified by the method described by Zhao et al.s Methyl, ethyl, butyl and iso-amyl acetates (S. D. Fine Chemicals, AR, purity>99%) were used. Methy l acetate was washed with saturated solution of NaCI , dried with anhydrous MgCl 2, and then distill ed. Ethyl acetate was dried over K2CO), filtered, and di stilled, and the first and the las t portions of the di stillate were discarded . The entire middle fraction was then di st illed over P20 s. Butyl acetate and iso-amyl acetate were purified by dryi ng over CaC03 overnight, filtered , and fresh ly distilled. The densiti es and viscosities of the so lvents at 298.15 K were in good agreement with the literature values5

.8

as given in Tab le 1 and the purity of the solvents

Table I-Compari son o f ex perimenta l densiti es and viscositi es o f pure liquids w ith literature values at 298. 15 K

Pure liquids [Ix I 0.3 (kg. m·') 11 ( mPa .s)

Ex p. Lit. Exp. Li t.

N. N-D imethylfo rmamide 0 .9442 0.9440" 0.801 6 0.802"

Buty lamine 0.73 19 0.733 Ih 0.4934 0.496'

Me thy l acetate 0.9261 0.9268" 0.3798 0.384"

Ethyl acetate 0.8941 0.894" 0.4233 0.428"

Buty l acetate 0.8744 0.8762" 0.6684 0.674"

Iso- amy l acetate 0. 8660 0.8662d 0.7822 0. 78 1d

"Re f. 5 ; bRe I'. 6; ' Re f. 7 and "Re f. 8.

1382 I DIAN J CHEM. SEC A, JUNE 2006

used in the present study is expected to be about 99.5 %.

Densiti es (p) at 298. 15 K were measured with an Ostwald-Sprcngel type pycnometer having a bulb volu me of' about 25 cm.1 and capi llary of internal diameter of about I mm. The measurements were done in a thermostated bath controlled to ± 0.1 K. The vi scos ity was measu red by means of a suspended Ubbelohde type viscometer, calibrated at 298.15 K with triply distilled water and purified methanol using densi ty and viscosity va lues from the literature. The flow ti mes were accurate to ±O. I s, and the uncertai nty in the viscosity measurements, based on our work on several pure liquids, was ±2x lO-4 mPa.s. The detail s of the methods and techniques have been described

I· ~- I I Th . db' . ear ler . e mixtures were prepare y ml xll1g known vol u mes of pure liquids in airti ght-stoppered bottles. The reproduci bi Ii ty in mole fraction was with­in ±0.0002 units. The mass measurements accurate to ±O.O Img were made on a digital electroni c analytical balance (Mett ler, AG 285, Switzerland). The preci­sion of density measurements was ±3x I 0-4 g cm-3.

Calculations F The excess molar volumes (V ' ) were ca lculated

using the eq uati on,

... ( I )

where P is the density of the mixture and Mi. Xi and Pi are the molecular weight , mole fraction and density of ith component in the mixture, respect ively. The values of excess molar volume (0) have been presented in Table 2. The es timated uncertainty fo r excess molar volumes (VE) is ± 0.005 cm' .mor l

.

The deviation in viscos ities (Lrrl ) can be computed using the relationship,

j

1'1 1] = 17 - L (x/7;) ... (2) i = 1

where 11 is the dynamic viscos iti es of the mi xture and Xi, 11 i are the mole fraction and viscosity of it" component in the mixture, respectively. The es timated uncertainty for viscosity deviation (Ml ) is ±0.004 mPa.s.

Several semiempiri cal models have been proposed to estimate the dynamic viscosity (11 ) of the binary liquid mixtures in terms of pure-componen t data I 2

.1] .

Some of these that we examined are as follows:

Grunberg and Nissan 14 have suggested the following logarithmic relation between the viscosity of the binary mixtures and the pure components:

... (3)

where d l 2 is a constant proportional to the interchange energy. J t maybe regarded as an approx i mate measure of the strength of molecu lar interactions between the mixing components.

Tamura- K urata 15 put forward the followi ng eq uation for the viscosi ty of the binary liquid mi x tures:

i j I

17 = L'X'; ¢Ji 17i + 2~ 2 TI [Xi ¢Ji F (4) ;= 1

where TI 2 is the interaction parameter and <Pi is the volume fraction of ith pure componen t ill the mi xture.

Molecular interactions may al so be interpreted by the fo llowing viscosity mode l of Hind e l al.16

:

j i

1] = '" X C lJ. + 2H lo TIx. L.J I I _ I ... (5)

;=1 ; = 1

where HI 2 is Hind interaction parameter, whi ch may be attributed to unlike pair interacti on. 17

The excess properties (VE and 1'111) were fitted to the Red li ch-Kister polynomial eq uation,

K

y'" = X I X2 L (I i (XI - Xc )i .. . (6) i = l

where y E refers to excess properties and XI and X2 are the mole fraction BA or DMF and other component,

respectively. The coeffi cients, C1 j , were obtained by

fitting Eq.6 to ex perimental results using a least­sq uares regress ion method. In each case, the opt imal number of coefficients was ascerta ined from an approximation of the variation in the standard

deviation (a ). The calculated values of ai along with

the tabulated standard deviations (0) are listed in Table 3. The standard dev iat ion (0) was calculated uSing,

I

[

( y E y E )2]2 CJ = cx p cal

(11- Ill ) . .. (7)

where n is the number of data points and m IS the number of coefficients.

DAKUA 1'1 al.: EXCESS PROPERTIES OF SOME 13 1 ARY MIXTURES 1383

Table 2- Valucs of density (p). viscosity (11). excess molar volume (V'), viscosity dcviation (L'> ll ) ror the binary mixtures or I3A or DMF (I) wit h some alkyl acetates (2) at 298. 15 K

Mo le fraction p x IO-J 11 VE x l06

Ll 11 (Xl) (kg. m--') (mPa.s) (n1"' . mo l-I) (mPa. s)

I3A ( I) + MA (2)

0 0.9261 0.3798 0 0 0.1011 0.9032 0.3847 -0.090 -0.007 0.2020 0.8827 0.3889 -0.308 -0.0 14 0.3027 0.8653 0.3942 -0.740 -0.020 0.403 1 0.850 I 0.4024 - 1.330 -0.023 0.5032 0.8352 0.4109 - 1.894 -0.026 0.6031 0.8 191 0.42 11 -2.270 -0.027 0.7027 0.7998 0.4359 -2.200 -0.024 0.8020 0.7776 0.45 16 - 1.685 -0.0 19 0.9011 0.7535 0.470 1 -0.770 -0.0 12

0.73 19 0.4934 0 0

I3A( I)+EA(2)

0 0.8941 0.4233 0 0 0. 11 80 0.874 1 0.4059 0.070 -0.026 0.23 15 0.8546 0.3973 0. 18 1 -0.042 0.3405 0.8364 0.3923 0.240 -0.055 0.4454 0.8188 0.3929 0.300 -0.062 0.5464 0.8015 0.3967 0.431 -0.065 0.6437 0.7860 0.407 1 0.403 -0.06 1 0.7376 0.7720 0.4192 0.259 -0.056 0.8281 0.7588 0.4353 0.09 1 -0.046 0.9 156 0.7454 0.459 1 0.0 10 -0.028

0.73 19 0.4934 0 0

I3A ( I) + BUA (2)

0 0.8744 0.6684 0 0 0. 1500 0.8570 0.6056 0. 10 1 -0.036 0.2842 0.8398 0.56 18 0.269 -0.057 0.4050 0.8235 0.5299 0.389 -0.068 0.5 143 0.8080 0.508 1 0.469 -0.070 0.6136 0.793 1 0.4887 0.530 -0.072 0.7043 0.7802 0.4786 0.39 1 -0066 0.7875 0.7680 0.47 15 0.2 11 -0.059 0.8640 0.7558 0.47 14 0. 100 -0.046 0.9346 0.7439 0.4753 0.020 -0.029

0.7319 0.4934 0 0

BA ( I) + AA (2)

0 0.8660 0.7822 0 0 0.1651 0.8493 0.6901 0.18 1 -0.044 0.3080 0.8329 0.6290 0.400 -0.064 0.4327 0.8 17 1 0.5855 0.590 -0.072 0.5427 0.8024 0.551 2 0.680 -0.074 0.6403 0.7885 0.5200 0.730 -0.077 0.7275 0.7766 0.5003 0.539 -0.072 0.8059 0.7650 0.4865 0.371 -0.063 0.8768 0.7538 0.4778 0.2 10 -0.051 0.9412 0.7428 0.4780 0.090 -0.032

0.7319 0.4934 0 0 CIJllId

1384 INDI AN J CHEM, SEC A, JUNE 2006

Table 2 (Contd)--Values of density (p). viscosity (11 ). excess molar volume (V"), viscosity dev iat ion (tlll) for the binary mixtures of BA or DMF ( I) with so me alky l acetates (2) at 298. 15 K

Mole frac ti on p x lO" 11 V,,' x I06 ,1 '7 (X I) (kg. m" ) (mPa.s) (m] mol' l) (mPa.s)

DMF ( I) + MA (2)

0 0.926 1 0.3798 0 0

0. 1012 0.9292 0.4 148 -0. 11 2 -0.008

0.2022 0.9320 0.4504 -0. 193 -0.0 15

0.3028 0.9347 0.4858 -0.275 -0.022

0.4032 0.9372 0.5236 -0.33 1 -0.026

0.5034 0.9393 0.5636 -0.349 -0.028

0.6032 0.94 12 0.6045 -0.357 -0.030

0.7028 0.9425 0.6504 -0.3 12 -0.026

0.802 1 0.9435 0.6976 -0.242 -0.020

0.90 12 0.9438 0.7482 -0. 11 7 -0.0 12

0.9442 0.80 16 0 0

DMF ( I) + EA (2)

0 0.894 1 0.4233 0 0

0. 118 1 0.8998 0.4567 -0. 100 -0.0 11

0.23 16 0.9056 0.4896 -0. 198 -0.021

0.3406 0.9 11 3 0.5232 -0.267 -0.029

0.4456 0.9 168 0.559 1 -0.3 15 -0.033

0.5466 0.9220 0.5955 -0.330 -0.035

0.6439 0.':1269 0.6339 -0.308 -0.033

0.7377 0.93 16 0.6737 -0.264 -0.029

0.82R2 0.9359 0.7 153 -0.1 83 -0.021

0.9 156 0.9400 0.7573 -0.086 -0.0 12

0.9442 0.80 16 0 0

DMF ( 1)+ BUA (2)

0 0.8744 0.6684 0 0

0. 150 1 0.88 16 0.6705 -0.09 1 -0.0 18

0.2843 0.889 1 0.676 1 -0.206 -0.030

0.405 1 0.8963 0.6849 -0.258 -0.037

0.5 144 0.9035 0.6955 -0.282 -0.04 1

0.6 138 0.9 107 0.7082 -0.296 -0.042

0.7045 0.9 177 0.7247 -0.272 -0.Q37

0.7876 0.9243 0.743 1 -0.2 13 -0.030

0.864 1 0.93 11 0.76 12 -0. 156 -0.022

0.9346 0.9375 0.7797 -0.070 -0.01 3

0.9442 0.80 16 0 0

DMF ( 1)+ BUA (2)

0 0.8660 0.7822 0 0

0. 1652 0.8738 0.7649 -0.086 -0.020

0.308 1 0.88 19 0.753 1 -0. 192 -0.035

0.4329 0.8898 0.7483 -0.233 -0.042

0.5429 0.8977 0.7469 -0.247 -0.046

0.6404 0.9054 0.7481 -0.228 -0.046

0.7277 0.9 133 0.7548 -0.2 13 -0.041

0.806 1 0.92 10 0.7648 -0. 172 -0.033

0.8769 0.9287 0.7750 -0.11 8 -0.024

0.94 13 0.9363 0.7869 -0.046 -0.014

0.9442 0.80 16 0 0

DAKUA el af .: EXCESS PRO PERT IES OF SOME BINA RY MI XT URES 1385

Table 3-Values o f coeffic ients ai

of Eq. 6 and standard deviati ons (a) for the excess properties V'o' x I 0(' (m-'. mol-I ) and

6 11 (mPa s) for the binary mi xlUres o f BA or DMF ( I) + so me alkyl acetates (2) at 298. 15 K

Binary lll ixlU re Excess properly ao

S A+MA V" x I06 -7.536

il l? -0 .1 04

S A + EA Vl:x lOc. 1.535

il l1 -0 .255

S A + I3UA v,: x I oc. 1.940

611 -0.283

BA + AA V'o· x IOC. 2.685

il l1 -0 .297

DM F + MA V'o' x I oc. - 1.425

il l? -0. 11 6

DM F + EA V"x 106 -1.30 I

il l? -0. 136

DMF +BUA V" x 106 - 1. 162

il l1 -0 . 164

DM F+AA V/' x I06 -0 .984

il l? -0 . 182

Results and Discussion The ex peri menta l viscos iti es, densities, excess

vo lumes ( VE), viscos ity dev iati o ns (~11 ) fo r the binary mi xtures studi ed at 298. 15 K are presented in Tabl e 2. The va lues o f G run berg-Ni ssan interact ion parameter (d I2), the va lues of inte ract io n parameters TI 2 and H I2

have been calcul ated as a functi on of the compositi o n of the binary mi xtures of BA and DMF with MA , EA, B UA and AA, and were presented in Tab le 4 .

From Table 2, it is observed that excess mo lar vo lumes (VE) for all the BA systems, except for that in vo lving MA, are pos iti ve over the entire range of co mpos itio n. The posi ti ve values of excess vo lumes

E . (V -) fo r the three systems fo ll ow the order:

BA + AA > BA + BUA > BA + EA

The excess molar vo lumes (VE) for all the DM F systems are negati ve and thei r negat ive va lues fo ll ow the order:

DM F+MA> DM F+ EA> DM F + BUA>D M F + AA

The negati ve va lues of excess mo lar vo lume eVE) sugges t specif ic inte ractions 's.

,'! be tween the unl ike

molecules in the sys tems while its pos iti ve va lues d · fd" f '8 1'! b suggest omlll ance 0 Isperston orees' e tween

a l a2 aJ a

- 10.229 2.90 1 8.387 0.0 11

-0.03 1 0.000

1.1 44 - 1.694 -2.644 0.034

-0.04 1 -0.0 17 -0.043 0.00 1

1.047 -2. 13 1 - 1.934 0.030

-0.035 -0. 109 -0 084 0.00 1

1.678 - 1.98 1 -2.086 0.029

-0.044 -0. 184 -0.095 0.002

-0.335 0. 199 0.355 0 .007

-0.030 -0.0 14 0.000

-0.275 0.1 63 0.203 0.002

-0.027 -0.263 0.000

-0.376 0 .264 0.009

-0.037 -0.069 -0.08 1 0 .00 1

-0.268 0.245 0 .009

-0.054 0.00 1

the m. Treszczanow iez ef al .20 suggested th at VE is the result of contribu tions from several oppos ing e ffects . These may be d iv ided a rbitra ril y into three types, name ly , physical , chemical, and structural. Phys ical contributio ns contribute a positi ve te rm to V

E. T he

chemi cal o r specific intermo lecul ar inte ract io ns resul t in a vo lume decrease and contribute nega ti ve values to VE

. The structura l contributi ons are mos tl y negati ve and ari se from severa l effects, espec ia lly from interstiti a l accommodati on and changes in the free vo lume . The actua l vo lume change, the refore, depe nds on the re lative strength o f these effects. The negative va lues of excess mo lar vo lume (Vi,) fo r all the mi xtures studi ed may be attributed to d ipole­induced dipole interactions between the unlike mo lecules in the binary mi xtures through hydrogen bo nding. The plo ts o f excess mo lar vo lume (V")

versus mo le frac tio n (XI) of BA or DM F for the binary mi xtures are presented in Figs I and 2. It is evident fro m the va l ues of VE th at for both the bi nary systems, the degree of specific inte rmo lecul ar interactions between unlike mo lecules in the binary mixtures decreases as the chain length of the a lky l acetate inc reases . The excess entha lpy va lues dete rmi ned by Venkatesu ef at? fo r DMF + EA and DM F + BUA mixtures report simil ar results.

1386 INDIAN J CHEM, SEC A, JUNE 2006

4 • 0,5

° "0 ~ -0,5

'" E '"-'

'" 0

)< -1 [J.J

> -1.5

-2

-2.5 -'------- ---- - ---------------------'

Fig. I- Plots of excess molar vo lume (VE) versus mole fracti on of SA (XI) at 298. 15K for binary mixtures of I3A wi th I. MA ( A ): 2. EA (i':. ); 3, SUA (0 ) : ancl4, AA (e).

-0.1

,-.,

0 E ~ g -0.2 "'0

><: Ul

> -0.25

-0.3

-0.4 L-_ ____________________ _ __ --'

Fig. 2-Plots of excess molar vo lu me (vE) versus mole fraction of DMF (Xl ) at 298. 15K for binary mixtures of DMF with I . MA ( A ): 2, EA (i':. ); 3, SUA (0 ); Jncl4, AA (e).

--­[/)

-0.02

DAKUA el 01. : EXCESS PROPERTIES OF SOME BINARY M IXTURES

cci -0.04 g I=" -0.05 <1

-0.06

-0.07

-0.08

-0.09 L-__________________ -------'

1387

Fig. }--Plots of viscos ity dev iati on (t.ll) ve rsus mole fracti on of BA (XI) at 298.15 K for binary mi xtures of BA with I. MA ( "' ): 2. EA (~) : 3, BUA (D) : and 4. AA ( e ).

-0.005

-0.01

-0.015 ·

r-- -0.02 Ul

~

] -0.025 '-' ~

<I -0.03 ·

-0.035

-0.04

-0.045 ·

-005 ··L------------------ ------

Fig. 4--Plots of viscosity dev iation (t.11) versus mole fracti on of DMF (XI) at 298 .1 SK for binary mi xtures of DMF with I , MA ( "' ): 2. EA (f:J. )::1. BUA (D); Jnd 4. AA ( e ).

1388 INDIAN J CHEM . SEC A. JUNE 2006

Tab le 4--Grunberg-N issan interact ion parailleter (dd. Taillura-Kurata parailleter (1'1 2)' and Hind parameter (1-1 '1 ) for the binary mi xtun.!s of BA or DMF ( I) witl, sO llle alkyl acetates (2) at 298. 15 K

XI dl ~ 1'1 2 I-I I ~ XI cl I2 TI ~ 1-1 12

BA ( I) + MA (2) DMF ( I) + MA (2)

0.101 1 -0. I 503 0.3997 0.4003 0. 10 12 0.1379 0.5514 0.5484

0.2020 -0. 1803 0.3927 0.3938 0.2022 0.1 204 0.5482 0.5451

0.3027 -0.1992 0.3874 0.3892 0.3028 0.0949 0.5425 0.5393

0.4031 -0.1983 0.3855 0.3884 0.4032 0.0825 0.5394 0.5361

0.5032 -0.2113 0.3806 0.3846 0.5034 0.0749 0.5372 0.5337

0.603 1 -0.2274 0.3746 0. ]799 0.6032 0.0595 0.5324 0.5286

0.7027 -0.2204 0.37:13 0.]799 0.7028 0.0617 05327 0.5287

0.8020 -0.23 11 0.3677 0.]758 0.802 1 0.0560 0.5303 05261

0.90 11 -0.25 II 0.3591 0. ]692 0.90 12 0.055 1 0.5294 0.5250

BA ( I) + EA (2) DMF ( I) + EA (2)

0. 11 80 -0.5774 0.3354 0.3]49 0. 11 8 1 0.0046 0.5802 0.5582

0.2315 -0.5554 0.3399 0.3]97 0.23 16 -0.0 133 0.5756 0.5526

0.3405 -0.57 15 0.336 1 (U]61 0.3406 -0.0254 0.5723 0.5479

0.4454 -0.577S 0.]]]5 (U]36 0.4456 -0.0257 0.572 1 0.5461

0.5464 -0.5996 (U27 I (U274 0.5466 -0.03 13 0.5703 0.5427

0.6437 -0.600 I 0.]242 (U247 0.6439 -0.0321 0.5698 0.5405

0.7376 -0.6343 0.3135 0.3142 0.7:177 -0.0330 05694 0.5]83

0.828 1 -0.6945 0.2957 0.2967 0.8282 -0.0295 0.5704 0.5376

0.9156 -0.762] 0.2740 0.2753 0.9156 -0.0388 0.5671 0.5322

BA ( I) + BUA (2) DMF(I ) +BUA (2)

0. 1500 -0.4148 0.4158 0.438 1 0.150 1 -0.1893 0.6940 0.6648

0.2842 -0.4302 0.4244 0.4410 0.284] -0. 1978 0.6945 0.6608

0.4050 -0.4532 0.4288 0.4406 0.405 I -0.2045 0.6955 06572

0.514] -0.4726 0.4327 0.4402 0.5144 -0.21 SO 0.6949 0.652 I

0.6 136 -0.5349 0.4252 0.4284 0.6 138 -0.2268 0.6938 0.6464

0.7043 -0.5768 0.422] 0.42 12 0.7045 -0.2262 0.6969 0.6449

0.7875 -0.6569 0.4104 0.404] O.7X76 -0.2222 0.7008 06447

08640 -0.7:195 0.3977 0.3860 0.8641 -0.2300 0.7007 0.6401

0.9346 -0.9348 0.3605 0. 3396 0.9]46 -0.2591 0.6938 0.6270

BA ( I) + AA (2) DMF (I) + AA (2)

0.165 1 -0.3566 0.4]49 0.4 768 0. 1652 -0. 1914 0.7440 0.7 176

0.3080 -0.3572 0.4555 0.4869 0.]08 1 -0.2134 0.74 16 0.7096

0.4327 -0.3674 0.4683 0.4918 0.4]29 -0.2237 0.7444 0.7058

0.5427 -0.4026 0.471 3 0.4882 0.5429 -0.2395 0.7445 0.6996

0.6403 -0.4918 0.4598 0.4700 0.6404 -0.26 16 0.7422 0.6909

0.7275 -0.5633 0.4535 0.4567 0.7277 -0.2697 0.7448 0.6872

0.8059 -0.66 12 0.44 14 (J4367 0.806 1 -0.2699 0.7496 0.6864

0.8768 -0.8218 0.4165 0.4012 0.8769 -0.2846 0.7494 06798

0.94 12 -1.0605 0.3763 0.3457 0.94 13 -0.3097 0.7460 0.6689

OAK UA et 01.: EXCESS PROPERTIES OF SOM E BINARY MI XTUR ES 1389

A perusal of Table 2 shows that the va lues of viscosity devi ati on (Ll11) are negati ve over the entire co mposition range fo r all the binary mi xtures studi ed and the negati ve values increase as the chain length of the alky l acetates increases. It is observed in many systems that there is no simple correlation between the strength of the interacti ons and the observed properties. Rastogi el a/.22 therefore, suggested that the observed excess property is a combination of an interaction and a non-i nteraction part. The non­interaction part in the form of size effect can be comparable to the interaction part and may be suffic ient to reverse the trend set by the latter. In general, the negati ve va lues imply the presence of di spersion forces23 in these mi xtures; while positi ve va lues may be attributed to the presence of specific interac ti ons23

. The plots of viscosity dev iation (Llll ) versus mole fracti on (x,) fo r the di fferent binary mi xtures of BA and DM F have been presented in Figs 3 and 4, respecti vely. The Llll values for all the binary mi xtures studi ed supported the results obtained from the va lues of VE di scussed earlier.

From Table 4, it is seen that the values of d l2 are negati ve fo r all the binary systems studi ed, except for the mi xtures of DMF + MA. The negati ve values of d l 2 ind icate the presence of di spersive forces23 or weak speci fic interacti on while its positi ve values indicate the presence of strong specifi c interactions23

between the unlike molecules in the binary mixtures. Also for a given binary mi xture, it has been observed that the values of TI 2 and H I2 do not di ffe r appreciably from each other. Thi s is in agreement with the view put forward by Fort and MooreD in regard to the nature of parameter T I2 and H12 . From Table 3, it is observed that the fits were good as presented by the small values of standard dev iation (rr).

In the eight binary mi xtt.;res studied, it is really in teresting to note that VE and Ll11 have maxima! minima in the mole fraction range xI =0.5 to 0.7 (Table 2). Thi s indicates th at specific interaction between the component molecules is predo minated by hydrogen bonding. The maximum/minimum points are clear indications of the hi ghest point of interacti on between the component molecules in the binary mi xtures.

Acknowledgements The authors are grateful to the Departmental

Special Assistance Scheme under the Uni versity Grants Commission, New Delhi (No. 540/6/ DRS/ 2002, SAP-I ) fo r financial support. One of the authors (VKD) is also grateful to C.S.I.R. (New Delhi) under Uni versity of North Bengal, Dalj eeling for sanctioning of a Junior Research Fellowship and providing fin ancial aid in support of thi s research work.

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