Journal of Solution Chemistry, Vol. 27, No. 9, 1998
Solution properties of aqueous mixtures of isomeric butanediols have been investi-gated employing viscosity, surface tension, and index of refraction measurementsas functions of temperature. The deviation of viscosity, surface tension, and molarrefraction from ideal solution behavior is evaluated from the experimental data.The deviation from ideality is discussed in terms of molecular interactions betweenthe components. Surface activity of the diols is evident from the surface tensionmeasurements. It is found that the degree of hydrophobicity of the diols variesin the order 1,2 > 2,3 > 1,3 > 1,4. The strength of interaction of diols with thewater varies in the order 2,3 > 1,4 = 1,3 > 1,2.
KEY WORDS: Viscosity; surface tension; index of refraction; activation parame-ters of viscosity; excess properties; hydrophobicity.
1. INTRODUCTION
Cyclic dimers or higher oligomers are known to exist in the pure stateof alcohols and diols because of hydrogen bonding of the hydroxy groups.In recent years, aqueous solutions of lithium bromide and mixtures of ammo-nia and butanediols have been used as working fluids in heat pumps andrefrigeration equipment.* ° Accurate knowledge of various thermophysicalproperties is thus essential for reliable design/2"4*
Department of Chemistry, St. Francis Xavier University, Antigonish, Nova Scotia, Canada,B2G 2W5.
Viscosity, Surface Tension, and Refractive IndexMeasurements of Mixtures of IsomericButanediols with Water
Brent Hawrylak, Stacey Andrecyk, Carrie-Ellen Gabriel,Kim Gracie, and R. Palepu*
Received July 29, 1997; revised June 23, 1998
8270095-9782/98/0900-0827$ 15.00/0 © 1998 Plenum Publishing Corporation
The thermophysical properties of mixed fluids depend markedly on themanner in which the pure constituents are associated with each other in themixture. The surface tension of mixtures is an important property for thedesign of contacting equipment, which is used to carry out chemical processes,such as, gas absorption.
Although there is much literature on alcohol liquid mixtures, data onviscosities, surface tension, and refractive indices of diol-plus-water systemsare limited. We have measured densities and ultrasonic velocities to obtainimportant thermodynamic properties, such as, partial molar volumes, excessvolumes, and compressibilities.0' This paper reports the viscosity, surfacetension, and refractive index of diol-plus-water systems at five differenttemperatures (from 25-45°C) in order to calculate various excess functionsto gain greater knowledge of the specific interactions between the polargroups of the diols and water. From a fundamental point of view, a study ofisomeric butanediols allows one to examine in detail the influence of thespacing of the hydroxyl groups on the thermophysical properties of thebutanediols.
2. EXPERIMENTAL
Materials were of the same grade used in our earlier studies.(5) Allchemicals were stored over molecular sieves to reduce the water content.Water was of nanopure quality with a conductivity less than 2 (juS-cm"1. Thecomposition of each mixture was obtained with an accuracy of 1 X 10~4 inmole fraction from the measured masses of the components.
For viscosity measurements in the temperature range 25-45°C, modifiedOstwald viscometers of various sizes were employed. A thermostaticallycontrolled oil bath (Koehler Instrumentation) with temperature controlled to± 0.01°C was used for all measurements. The viscometers were calibratedwith aqueous glycerol.(6) Measurements were reproducible to ± 0.005 and± O.OlmPa-s in the lower and higher viscosity values, respectively.
Surface tension measurements were performed using a Fisher surfacetensiometer equipped with a 13-mm diameter Platinum-Iridium Du Nouyring. The solutions were transferred slowly into a double-walled vessel aroundwhich thermostated liquid was circulated to maintain a constant temperature.Adsorption process at the air/aqueous solution interface were generally com-pleted in about 10 min and the repetition rate of individual surface tensionreading was 5 min. The above procedure improved the accuracy of individualsurface tension measurements up to ± 0.20 mN-m"'. The surface tensionvalues 7 were corrected as described in the instrument manual.(7) The surfacetension of water was measured periodically to assure that the technique wasbeing properly carried out.
828 Hawrylak et al.
Isomeric Butanediols with Water 829
The index of refraction for the sodium D-Line was measured using theABBE-3L refractometer (Spectronic) thermostated to within ± 0.02°C. Theuncertainty in the measurements was within ± 0.0001 units.
3. RESULTS
3.1. Viscosities
The measured viscosities, refractive indices nD, and surface tensions ofthe pure butanediols at 25°C are presented in Table I together with appropriateliterature data.(8~17) The present data are generally in a good agreement withthe literature values.
Experimental viscosity data for the aqueous binary mixtures of isomericdiols at five different temperatures are presented in Tables II-V. The deviationATI °f viscosity of the measured values from the stipulated additivity ruleswas calculated using the following equation:
where r\, t][, T)2, and X, are viscosities of the mixture and of components 1and 2 and mole fraction of components, respectively.
Table I. Experimental, Viscosity, Index of Refraction, and Surface Tension of PureIsomeric Butanediols at 25°C
Butanediol
1,2-BTD
1,3-BTD
1,4-BTD
2,3-BTD
Viscosity(mPa-s)
52.8052.99"59.61*96.898.3r
110.0"71.171.5rf
71.7"123.8121.0*
Index ofrefraction
.4370.4360*.4390".4382.4389".4390".44474444".4443*.4366.4356rf
124.0° 1.4364"
Surfacetension
(mN-irr1)
31.2
37.137.(X
45.543.8/
32.5
"Ref. 13.*Ref. 9.cRef. 11.rfRef. 10.'Ref. 12.'Ref. 17.
830 Hawrylak et al.
Table II. Experimental Index of Refraction and Viscosity for 1,2-Butanediol
Molefraction
0.00000.09990.20060.30090.40010.50250.59870.70200.80380.89721.0000
25°C 30°C«D
35°C
1.3329 1.3323 1.33161.37731.39951.41151.41871.42421.42851.43201.43401.43501.4370
.3757 1 .3741.3979.4099.4171.4226.4269.4304.4324
.3963.4083.4155.4210.4253.4288.4308
.4334 1.4318.4357 1 .4341
40°C
1.33091.37251 .39471.40671.41391.41941 .42371.42721.42921.43021.4325
45°C
1.33011.37091.39311.40511.41231.41781.42211.42561 .42761.42861.4309
25°C
0.8903.4106.704
10.2714.4919.5425.2831.7638.2745.1252.80
T| (mPa-s)
30°C
0.7982.8555.4898.312
11.5415.4519.3924.0628.8233.4438.71
35°C
0.7192.4454.5866.8879.390
12.4215.5018.9422.4825.7229.48
40°C
0.6532.1383.9075.7597.779
10.1412.5415.1217.7020.1422.86
The viscosity deviation AT) was fitted by a Redlich-Kister (18) equationn
where YE represents the function Air) and a-} represents the polynomial coeffi-cients. The values of a-} were determined by least-squares and are listed inTable VI, along with the standard deviations.
Figure 1 shows the values of ATI as a function of the composition ofthe diol solutions at different temperatures. Figure 2 shows Air) as a functionof the composition for all the diols at 25°C in order to compare the relativestrength of interactions between water and isomeric diols.
Table III. Experimental Index of Refraction and Viscosity for 1 ,3-Butanediol
Molefraction
0.00000.09960.19820.29910.40360.44890.61180.69890.79860.89711.0000
25°C
1.33291.3755.3985.4119.4203.4230.4305.4334.4355.4369.4382
30°C
1.33231.37421.39721.41061.4190.4217.4292.4321.4342.4356.4376
«n35°C
.3316
.3729
.3959
.4093
.4177.4204.4279.4308.43291.43431.4363
40°C
1.33091.37161.39461.40801.41641.41911.42661.42951.43161.43301.4350
45°C
1.33011.37031.39331.40671.41511.41781.42531.42821.43031.43171.4337
25°C
0.8903.6948.539
15.2723.1628.4847.9056.8067.8582.5696.80
30°C
0.7983.0736.787
11.9418.3023.2835.0242.2751.9262.2070.93
n(mPa-s)
35°C
0.7192.6335.5879.627
14.5217.5727.6833.2738.7846.9553.72
40°C
0.6532.2974.7378.017
11.6313.9221.3825.4229.8035.9240.13
45°C
0.5962.0194.0346.6719.592
11.4017.2220.2423.4027.8731.22
Isomeric Butanediols with Water 831
Table IV. Experimental Index of Refraction and Viscosity for 1,4-Butanediol
Molefraction
0.00000.10000.20010.30070.40060.49770.60020.69820.79930.89691.0000
«D25°C
1.33291.3766.4008. 4 1 5 1.4240.4302.4353.4389.4414.4431.4447
30°C
1.33231.3754.3996.4138.4228.4290.4340.4376.4402.4418.4441
35°C
.3316.3741.3983.4126.4215.4277.4328.4364.4389.4406.4428
40°C
1.33091.3729.3971.4113.4203.4265.4315.4351.4377.4393.4416
45°C
1.33011.37161.39581.41011.41901 .42521 .43031.43391 .43641.43811 .4403
Tl (rnPa-s)
25°C
0.8903.3979.496
13.8221.0029.4238.8547.6656.6563.9071.10
30°C
0.7982.8037.867
11.1616.9123.4130.8938.2044.8148.6550.53
35°C
0.7192.5146.7159.319
13.9919.1625.1230.3036.1840.8045.24
40°C
0.6532.2095.7277.839
11.6015.7820.7724.8829.6333.3937.03
45°C
0.5961.9354.8966.6359.664
13.0917.2120.4924.2427.0630.12
According to the transition state theory,091 the dependence of absoluteviscosity r\ (at constant pressure) on Kelvin temperature T is given by
where r\* is a constant, A//1 is the enthalpy of activation for viscous flow,and ir) is the viscosity of the solution. Values of A//* were obtained fromplots of \n T| vs \IT and are presented in Table VII for the pure diols.
The values of free energy and entropy of activation AG* and AS* ofviscous flow (20) can be estimated using Eqs. (4 and 5).
Table V. Experimental Index of Refraction and Viscosity for 2,3-Butanediol
Molefraction
0.00000.10020.20000.29980.39880.50010.59920.70230.80100.89921.0000
25°C
.3329.3776.3997.4112.4182.42351.42731.42971.43071.43291.4366
30°C
.3323.3761.3982.4098.4168.4221.4259.4282.4293.4314.4402
«D
35°C
1.33161.37471.39681.40831.41531.42061.42441.42681.42781.43001.4388
40°C
1.33091.37321.39531.40691.41391.41921.42301.42531 .42641.42851.4373
45°C
1.33011.37181 .39391.40541.41241.41771.42151 .42391.42491.42711.4359
25°C
0.8903.9819.010
15.0022.0331.0541.4953.0067.2984.27
123.80
30°C
0.7983.3477.179
11.7117.0023.5330.4237.9747.6058.4968.73
n, (mPa-s)
35°C
0.7192.8235.8019.212
13.2217.8222.6427.9434.4941.8849.00
40°C
0.6532.4184.8427.512
10.5313.9917.4321.2523.7831.0034.82
45°C
0.5962.0854.0566.0918.366
10.9913.3516.0719.2122.8125.94
Hawrylak et al.
Table VI. Redlich-Kister Parameters for Excess Viscosities of Butanediols
System
1,2-BTD
1,3-BTD
1,4-BTD
2,3-BTD
Coefficients"
«oa,«2
«3
«4
afl0
a\a-i0)
«4
aaa
a\02
03«4
a«oa\a2
«3
«4
CT
25°C
12.70-13.51- 5.42
13.42- 7.28
0.1920.79
-28.42-14.82
28.75- 6.30
0.7921.83
-27.92-11.18
27.80- 10.70
0.1721.92
-27.66- 6.46
27.01-15.46
0.72
30°C
9.77- 9.29- 5.36
9.24- 4.42
0.1815.02
-19.87- 9.93
19.93- 5.42
0.2817.12
-21.71- 8.86
21.62- 8.28
0.1915.97
-18.08- 6.64
17.56- 9.26
0.47
35°C
7.75- 6.85- 4.71
6.83- 3.05
0.1811.73
-15.46- 7.50
15.51- 4.51
0.4513.79
-16.78- 7.97
16.74- 5.85
0.1912.00
-11.24- 8.79
11.36- 3.42
0.41
40°C
6.23- 5.03- 4.18
5.02- 2.06
0.178.98
-10.32- 7.48
10.28- 1.62
0.4711.15
-12.99- 7.13
12.99- 4.04
0.189.12
- 8.00- 6.60
7.98- 2.59
0.18
45°C
7.09- 7.71- 6.01
7.59- 1.14
0.819.06
-10.13- 6.20
10.16- 2.91
0.187.06
- 5.98- 4.79
5.86- 2.24
0.38
"Units: mPa-s.
832
where Vis the molar volume and N and h are Avogadro's number and Planck'sconstant, respectively. The values of AG* and AS* are also included for purediols in Table VII. The values of A//* of viscous flow for the diols follothe order 2,3 > 1,3 > 1,2 > 1,4. The values of A//* reflect the relativdegree of association in the liquid state.
The excess activation parameters Y*E were calculated according tothe equation
where Y*,Yf, and Kf are specific properties of the mixture and of the
Isomeric Butanediols with Water 833
pure components 1 and 2, respectively. The excess Gibbs free energy, enthalpy,and entropy of activation for viscous flow are presented in Table VIII.
3.2. Surface Tension
Experimental values of surface tension for aqueous binary selections ofisomeric butanediols are presented in Table IX. Plots of surface tension at25°C vs. concentration for diols and water system are presented in Fig. 3.Initially the surface tension decreases rapidly for 1,2- and 2,3-diols comparedto the 1,3 and 1,4 systems. The surface tension changes very slowly at higherconcentrations of the diols.
The continuous curves in Fig. 3 were generated by fitting the experimen-tal data by the Connors and Wright equation'2"
Fig. 1. Plot of At) vs. mole fraction of diol at different temperatures.
834 Hawrylak et at.
-5 I I
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Mole FractionFig. 2. Plot of At) vs. mole fraction of diol at 25°C.
Table VII. Calculated Gibbs Energies, Enthalpies, and Entropies of Activation of ViscousFlow for Pure Diols at 25°C
Compound AG*" AW*° AS**
1,2-BTD1,3-BTD1,4-BTD2,3-BTD
"k J-moP1."J-K-'-mor1.
23.8925.3224.3225.50
41.6343.8431.6253.41
59.5362.1224.4893.64
Isomeric Butanediols with Water 835
Table VIII. Excess Gibbs Energies, Enthalpies, and Entropies of Activation for ViscousFlow at 25°C
System
1,2-Butanediol
1,3-Butanediol
1,4-ButanedioI
2,3-Butanediol
^diol
0.09980.20060.30090.40010.50250.59870.70200.80380.89721.000000.09960.19820.29900.40350.44890.61170.69890.79860.89701.000000.09990.20010.30070.40050.49760.60010.69810.79930.89691.000000.10010.19990.29970.39880.50010.59910.70230.80100.89901.0000
(AC*)6"
02.893.843.883.863.513.062.421.650.91002.964.174.574.404.373.602.881.981.12002.854.624.594.584.323.823.132.301.36003.114.244.454.263.863.312.541.790.990
(AW*)6"
05.656.695.895.534.534.103.492.201.56005.047.978.217.828.577.105.154.121.93004.126.928.158.278.066.646.524.833.04005.948.058.337.276.326.204.574.561.600
(AS*)6*
09.259.576.745.594.433.613.502.151.83007.00
11.4512.2412.7314.0811.737.607.192.72004.257.72
11.9412.3712.5311.409.488.505.64009.49
12.8013.0310.109.728.266.799.292.050
"kJ-mor1.'J-K-'-mor1.
836 Hawrylak et al.
Table IX. Surface Tension of Butanediol + Water Solutions at 25°C"
1,2-Buta
Molefraction
0.00000.00990.01910.02980.03980.06000.09790.14900.19990.24960.29910.39930.50060.59680.69280.79910.89141.0000
mediol
"If
71.9759.8053.5849.0946.2942.6739.1236.7835.4834.6634.0733.2632.7032.2931.9631.6531.4131.16
1,3-Buta
Molefraction
0.00000.00090.00460.00810.01810.02940.03520.06490.10820.15990.24870.42480.49950.64730.71540.80970.89191.0000
nediol
•y
71.9771.2667.9065.3060.1256.3554.9350.3747.1645.1343.1841.0640.4139.3138.8538.2437.7337.09
1,4-Buta
Molefraction
0.00000.01000.06000.08980.10970.15990.19840.22940.29900.36000.39800.42840.49910.59740.69900.80010.90091.0000
nediol
•y71.9766.2656.6955.2054.3152.5451.6551.1649.9949.3149.0248.7348.1547.3846.8146.3345.9545.47
2,3-Buta
Molefraction
0.00000.00990.03000.05000.06990.10000.13000.14990.17020.20020.25000.30160.39860.49120.59960.73150.89931.0000
nediol
~i
71.9765.8556.0149.7446.4343.7341.7140.6639.7038.4737.5236.3935.3634.7034.0533.3133.0332.47
"Units: mN-nT1.
where a and b are adjustable parameters obtained by nonlinear least-squares.The binding constant K representing the binding of organic component tothe surface region is calculated as
The values of K can be used as a measure of the relative hydrophobicity ofthe organic molecules.
3.3. Index of Refraction
The index of refraction data for the aqueous diol systems at five differenttemperatures is presented in Tables II-V.
The Lorentz-Lorentz molar refraction R is related to electronic polariz-ability a of molecules by the expression:
Isomeric Butanedlols with Water 837
where nD, M, p, N are index of refraction, average molar mass, density ofsolution, and Avogadro's number, respectively. Density data required for thecalculation of R are taken from our previous studies.(5) The excess molarrefraction A/? is calculated based on volume-fraction additivity as follows
where
R\, R2, <PI, and <p2 represent molar refraction and volume fraction of waterand diol, respectively.
Fig. 3. Plot of surface tension of diol at 25°C.
838 Hawrylak et al.
In the calculation of /?ideai. it is a common practice_in the literature todefine the volume fraction <PJ on a partial molar volume (V?) basis at infinitedilution of component i
The partial molar volume data were taken from our previous studies/5'Plots of A/? vs. volume fraction for all isomers at 25°C are presented in Fig. 4.
4. DISCUSSION
Many properties of binary liquid mixtures are not additive with respectto the pure components. This phenomenon may arise as a result of mutualinteractions. The extent to which real solutions deviate from ideality is bestexpressed through the use of thermodynamic excess functions. The plots ofAt] show a positive deviation with a well-defined maximum for all diols.This behavior is indicative of strong interactions between the diols and water.The deviation decreases with increasing temperature (Fig. 1) for all of thediols. The maximum value of deviation for the diols follows the order 2,3> 1,3 - 1,4 > 1,2 (Fig. 2) at 25°C. This order is reflected in the relativepositions of the hydroxyl groups on each isomer and their ability to form
Fig. 4. Plots of A/f vs. mole fraction for diols at 25°C.
hydrogen bonds with water. The unsymmetrical nature of the curves indicatesthat the energy necessary to break hydrogen bonds in the pure liquids is notcompensated for by the mixing process. The positive values of the activationparameters A//* (Table VII) normally reflect the degree of association in thepure liquid state. The positive value of AS* can be explained by noting thatthe formation of the activated complex of flow requires the breaking of themore ordered hydrogen-bonded network, thereby decreasing the molecularorder in the solution.
The excess enthalpies (A//*)E and entropies (AS*)E of activation of flowfor aqueous mixtures of isomeric diols are positive for the entire compositionrange. The values reach a maximum at a mole fraction of 0.2 for 1,2-, 0.3for 1,3- and 2,3-, and 0.4 for 1,4-diols.
The positive values of (A//* )E indicate that the association and dipoleinteractions vary in the order 2,3- > 1,4- — 1,3- > 1,2-diol. It can beconcluded from the positive values of (AS*)E, that the formation of theactivated complex in each case involves less order. This is probably due tothe destruction of hydrogen bonds.
The sign of (AC*)6 provides a quantitative interpretation of the natureof the interactions/2*"235 Positive values can be seen in binary mixtures,where specific interactions like dipole-dipole and hydrogen bonds betweenmolecules are prevalant. The values of (AG*)E also take into account thevolume changes on mixing. From the value of the maxima, one can concludethat the strength of the interactions varies in the order 1,4 > 1,3 — 2,3 >1,2. The change in the order from (A/f*)E and viscosity maxima can beexplained on the basis that the excess volume V* for 2,3-diol is more negativethan the value for l,4-diol.(5)
4.1. Surface Tension
One can conclude from the surface tension plots (Fig. 3) that the hydro-phobicity of the diols follows the order 1,2- > 2,3- > 1,3- > 1,4-diol.The relative degree of hydrophobicity of the diol molecules can be furthersubstantiated from the value of K obtained from the Connors and Wrightequation. The values are found to be 44.0 for 1,2-, 40.0 for 2,3-, 37 for1,3-, and 34 for 1,4-diol, respectively. The degree of hydrophobicity of thediol molecules can be interpreted on the basis of the relative positions of thehydroxyl groups.
4.2. Molar Refraction
The excess molar refraction A/? represents the electronic perturbationdue to orbital mixing of the molecules and has been discussed extensivelyin the literature.'24"301 It has been shown that A/? is an indication of the
Isomeric Butanediols with Water 839
modification of the electronic polarization of the mixtures and, in most cases,allows one to draw some conclusions concerning the inter- and intramolecularforces operating. Values of A/? follow the order 2,3- > 1,3- «* 1,2- > 1,4-diol (Fig. 4). Incidentally the volume contraction VE for these systems alsofollows the same pattern leading(5) to an order of modification of the electronpolarizability as depicted in A/? plots.
5. CONCLUSIONS
From the viscosity and (A//*)E data, the strength of interactions withwater varies in the order 2,3 > 1,4 — 1,3 > 1,2. The surface tension dataindicate that relative hydrophobicities of the diols vary in the order 1,2 >2,3 > 1,3 > 1,4 in water. Nashikawa and Mashima (3n also concluded that1,2-BTD is more hydrophobic than 1,4-diol from their ultrasonic relaxationstudies in aqueous media.
ACKNOWLEDGMENTS
The authors are grateful to the financial support by the Natural Sciencesand Engineering Research Council of Canada in the form of an operatinggrant. B. H. and C. E. G. are grateful to NSERC for undergraduate summerresearch awards.
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840 Hawrylak et al.
Isomeric Butanediols with Water
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