Apparent molar volume and viscosity of zirconyl soaps

COLLOIDS AND ELSEVIER

Colloids and Surfaces A: Physicochemicaland EngineeringAspects 122 (1997) 27-32

A

SURFACES

Apparent molar volume and viscosity of zirconyl soaps K.N. Mehrotra, M. Anis Department of Chemistry, Institute of Basic Sciences (Agra University), Khandari Road, Agra-282 002, India Received 1 February 1996; accepted 25 July 1996

Abstract Apparent molar volume and viscometric parameters of zirconyl soaps (hexanoate, octanoate, decanoate and dodecanoate) in a xylene-methanol mixture (xylene : methanol, 4: 1 v/v) were determined from density and viscosity measurements. The viscosity results were explained on the basis of equations proposed by Einstein, by Vand, by Moulik and by Jones and Dole. The values of molar volume calculated from the Einstein and the Vand equations were in close agreement. The contribution of each -CH2 group to the partial molar volume was determined and the results were interpreted in terms of soap-solvent and ion-ion interactions. Keywords: Apparent molar volume; Ion-ion interactions; Ion-solvent interactions; Viscosity; Zirconyl soaps

1. Introduction Recently, metallic soaps are becoming increasingly important in technological as well as in academic fields. The metallic soaps are generally insoluble in water but possess high solubility in non-aqueous solvents and high metal content which lend them unique properties and make them useful in industries. The applications of metal soaps largely depend on their physical state, stability, chemical reactivity and solubility in polar and non-polar solvents. The physicochemical characteristics and structure of soaps can be controlled to some extent by the method and conditions of their preparation and so the studies of soaps are of much significance for their uses in industries under different conditions. K a p o o r and Mehrotra [ 1] prepared tetracarboxylates of zirconium by the reaction of ZrC14 with fatty acids in refluxing benzene. Brainina et al. [2] and Prozorovskaya et al. [3] prepared tetracarboxylates of zirconium by ligand-exchange reaction. Mehrotra [4] and Hughes [5] studied the IR spectra of the solution

of Zr(OOCCF3) 4 and observed the asymmetrical and symmetrical frequencies in the region of 1662 and 1483 cm -1 respectively. The presence of the M - O - M or M2(OH)~ ÷ group or both in zirconium oxyformates was confirmed by Spitsyn et al. [6] by a study of their IR spectra. The use of zirconium soaps (palmitate and stearate) as waterproofing agent was reported by Hirosawa [7]. The present work deals with the measurements of apparent molar volume and viscosity of zirconyl soap solutions in a xylene-methanol mixture (xylene:methanol, 4:1 v/v). The work has been initiated with a view to studying the behaviour of zirconyl soaps in solutions, determining the soapsolvent and soap-soap interactions and testing the validity of well known equations.

2. Experimental details The chemicals used were A R or BDH grade reagents. Zirconyl soaps (hexanoate, octanoate,

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K.N. Mehrotra, M. Anis / Colloids Surfaces A: Physicochem. Eng. Aspects 122 (1997) 2~32

decanoate and dodecanoate) were prepared by direct metathesis of the corresponding potassium soap with the required amount of aqueous solution of zirconium oxychloride under vigorous stirring. The precipitated soaps were washed with distilled water and acetone to remove the excess of metal ions and unreacted fatty acid. The purity of the soap was checked by elemental analysis and the results were found to be in agreement with the theoretically calculated values. The absence of the hydroxyl group in the soap molecules was confirmed by the absence of any absorption maxima in the region 3500-3000 cm 1 in their IR spectra. The reproducibility of the results was checked by preparing two samples of the soap under similar conditions. The density of the solutions were measured with a dilatometer at 40+0.05°C. The volume of the dilatometer was 15 ml and the accuracy of density results was + 0.0001 g m l - 1. An Ostwald-type viscometer was used for measuring the viscosity at 40_+0.05°C and the accuracy of the results was +0.3%.

in terms of the equation due to Root:

The magnitudes of the constants A and B refer to the solute-solvent and solute-solute interactions respectively. The values of the constants A (94.0, 119.5, 145.0 and 169.0) and B (59.5, 100.0, 114.3 and 121.4) for hexanoate, octanoate, decanoate and dodecanoate respectively were obtained from the intercept and slope of the plots of (p-po)/C vs. c t/2 for dilute soap solutions. The results confirm that the soap solvent interaction is larger than the soap-soap interaction in dilute solutions of these soaps. It is concluded that the soap molecules do not show appreciable association in dilute solutions and there is a sudden marked increase in association at a definite concentration of soap. The values of the apparent molar volume ~b~ were evaluated from the density Po of the solvent, the density p of the solution, the molecular mass M of solute and concentration c (mol dm -3) of solution using the equation 1000 (h, =

M (Po-P)+

Cpo

3. Results and discussion 3.1. A p p a r e n t molar volume ~Pv

The density p of the solutions of zirconyl soaps (hexanoate, octanoate, decanoate and dodecanoate) in xylene-methanol mixture (xylene: methanol, 4:1 v/v) increases with increasing concentration and chain length of the soap (Table 1). The plots of density p vs. soap concentration c are characterized by an intersection of two straight lines at a definite soap concentration (hexanoate, 0.050 M; octanoate, 0.047 M; decanoate, 0.043 M; dodecanoate, 0.040 M) which correspond to the concentration for onset of association for these soaps in solutions. The plots of p vs. c for dilute solutions were extrapolated to zero soap concentration and the extrapolated values Po of density were found to be in agreement with the experimental value of the density of the solvent mixture (839.7 kg m 3). The density results were explained

(1)

P = Po + A C - BC3/z

-Po

(2)

The values of ~ were found to be positive and increase with increasing chain length of the soap (Table 1), which suggests that there is an increase in solvation with increasing size of the anion in the soap molecules. The values of apparent molar volume ~b~ (m a mo1-1) increase at first and then decrease with increasing soap concentration (Fig. 1). The validity of the Root equation (Eq. (1)justifies the use of the Masson equation

~, =~bvo+ Svc1/2

(3)

for the estimation of limiting apparent molar volume or partial molar volume q%o of solute. In Eq. (3) ~b° is a measure of the soap-solvent interaction and the magnitude of Sv represents the variation in apparent molar volume ~b~, with concentration c. The increase in the values of ~b° (292 x 10 -6, 330 x 10 -6, 368 x 10 - 6 and 406 x lO-6m3mol -x) with increasing chain length of soap suggests that there is an increase in solvation of soap and the positive values of

K.N. Mehrotra, M. Anis / Colloids Surfaces A: Physicochem. Eng. Aspects 122 (1997)27-32

29

Table 1 Apparent molar volume and viscosity parameters of zirconyl soaps in xylene-methanol mixture (40+0.05°C) Sample

Hexanoate 1 2 3 4 5 6 7 8 9 10 Octanoate 1 2 3 4 5 6 7 8 9 10 Decanoate 1 2 3 4 5 6 7 8 9 10 Dodecanoate 1 2 3 4 5 6 7 8 9 10

Concentration c (tool dm -a)

Density p (kg m 3)

Apparent molar volume 0v x 106 (m3 mol l)

Viscosity t/x 103 (Pa s)

Specific viscosity ~/spx 102

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

840.6 841.4 842.2 842.9 843.7 844.8 846.0 847.5 848.8 850.1

294.75 300.70 302.96 306.66 306.66 300.70 294.75 285.82 281.52 278.08

0.4800 0.4891 0.4984 0.5072 0.5160 0.5419 0.5681 0.5950 0.6218 0.6479

2.76 4.71 6.70 8.58 10.47 16.04 21.62 27.38 33.12 38.71

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

840.8 841.8 842.8 843.9 845.1 846.5 847.8 849.5 851.1 852.4

337.29 343.24 345.23 343.24 339.67 333.32 330.48 322.40 317.44 317.04

0.4832 0.4940 0.5058 0.5170 0.5353 0.5695 0.6031 0.6370 0.6698 0.7039

3.45 5.76 8.29 10.68 14.60 21.92 29.12 36.37 43.39 50.69

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

841.0 842.2 843.4 844.6 846.1 847.8 849.5 851.0 852.7 854.4

380.16 386.11 388.09 389.09 382.54 374.21 368.25 366.76 362.96 359.91

0.4860 0.4997 0.5132 0.5271 0.5609 0.6010 0.6389 0.6782 0.7164 0.7560

4.05 6.98 9.84 12.84 20.08 28.68 36.78 45.19 53.37 61.85

0.01 0.02 0.03 0.04 0,05 0,06 0,07 0,08 0,09 0.10

841.3 842.8 844.1 845.7 847.3 849.6 851.9 853.9 856.0 858.1

417.12 417.08 427.00 423.03 420.65 405.17 394.11 390.28 385.98 382.54

0.4886 0.5043 0.5200 0.5360 0.5900 0.6437 0.6960 0.7496 0.8021 0.8580

4.60 7.96 11.33 14.75 26.31 37.81 49.00 60.48 71.72 83.69

Sv (57.14 × 10 -6, 71.43 × 10 -6, 114.29 x 10 -6 and 128.57 × 10 - 6 ) confirm strong ion-ion interactions. The differences between the values of ~bvO for hexanoate and octanoate ( 3 8 . 0 m l m o l -~) bet-

ween octanoate and decanoate ( 3 8 . 0 m l m o l -~) and between decanoate and dodecanoate (38.0 ml mo1-1) indicate that the contribution of each - C H 2 group to partial molar volume is about

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K.N. Mehrotra, M. Anis / Colloids Surfaces A. Physicochem. Eng. Aspects 122 (1997)27-32 430

I

~

, ~

A A

DODECANOATE DECANOATE

410

%

×> 390

J o

370

< o

x

350

~ <

330

310

290

.0

0.i0

0.20

0 30

i 0.40

SQUARE ROOT OF CONCENTRATION,c I/2

Fig. 1. Apparent molar volumevs. square root of concentration.

9.5 ml mol-*. The value is slightly lower than the result (15mlmo1-1 at 25°C) reported [8] for aqueous solutions of sodium salts of lower fatty acids (formate, acetate, propionate, butyrate and valerate). The difference in -CH2 contribution to ~bvomay be due to the size of anions, the nature of cation, the composition of the solvent mixture and the extent of solvation. 3.2. Viscosity q

The viscosity is considered to be an important rheological parameter. The viscosity q and specific viscosity qsp of solutions of zirconyl soaps in the xylene-methanol mixture (xylene:methanol, 4:1 v/v) increase with increasing concentration and chain length of the soap (Table 1). The increase in viscosity with increasing chain length of the soap may be due to the increasing solvation of

anions and association in solutions. The association is mainly caused by the energy change due to dipole-dipole interactions. The plots of viscosity ~/ vs. soap concentration, c (Fig. 2) and specific viscosity qsp vs. c are characterized by the intersection of two straight lines at a definite soap concentration (hexanoate, 0.050 M; octanoate, 0.047 M; deconate, 0.042 M; dodecanoate, 0.040 M) which correspond to the concentration for onset of association for these soaps in solutions. The plots of vs. c for dilute soap solutions were extrapolated to zero soap concentration and the extrapolated values q of viscosity were found to be in agreement with the experimental value of the viscosity of the solvent mixture (0.4671 Pa s). The viscosity results were explained in terms of the following equations:Einstein [9]

n,p =2.5Pc

(4)

K.N. Mehrotra, M. Anis / Colloids Surfaces A: Physicochem. Eng. Aspects 122 (1997)27-32

31

0.8600

0.8200

0.7800

•

DODECANOATE

A

DECANOATE

•

OCTANOATE

O

HEXANOATE

0.7400

I

0.7000

0.6600

0.6200

0.5800

0.5400

0.5000

I

0.0

0.02

I

0.04

0.06

I

0.08

l

0.i0

C(~JCENTRAT] 0~I,c _ _ ~

Fig. 2. Viscosityvs. concentration.

Vand [ 10]

l (~)

-1

c

1 log(q/go)

(5)

Moulik [ 11 ] (6) Jones and Dole [12] qse + A + Bc 1/z

C1/2

(7)

where V (1 mol-1), c (mol dm-3), ~b, q (Pa s), ~/o (Pa s) and qsp are the molar volume, concentration, interaction coefficient, viscosity of solution, viscosity of solvent and specific viscosity respectively. M and K are the Moulik constants and the constants A and B of the Jones-Dole equation refer to soap-soap and soap-solvent interactions respectively. The plots of qsp vs. c with intercept almost equal to zero are linear for dilute solutions which suggests that the Einstein equation (Eq. (4) is applicable to these dilute solutions of zirconyl soaps. The values of moldr volume V were evaluated from the

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K.N. Mehrotra, M. Anis / Colloids Surfaces A: Physicochem. Eng. Aspects 122 (1997) 27-32

slope of the plots of risp VS. C for dilute solutions and were found to be 0.7761mol 1, 0.964 1 mo1-1, 1.172 1 mo1-1 and 1.390 1 m o l i for zirconyl hexanoate, octanoate, decanoate and dodecanoate respectively. The differences in the values of molar volume P for these soaps (hexanoate and octanoate, 0.1881 mol-1; octanoate and decanoate, 0.2081mol 1; decanoate and dodecanoate, 0.2181mol -1) suggest that each - C H 2 group makes a definite contribution to the molar volume of soaps and the contribution of each - C H 2 group to molar volume is about 0.094-0.109 1 mol - 1. The plots (Vand 1/c vs. 1/log(q/rio); Moulik, (q/ri0) 2 vs. c2; Jones-Dole, ri~p/C1/2 vs. c 1/2) are also characterized by an intersection of two straight lines at concentrations which correspond to the concentration for onset of association for these soaps in solutions. The evaluated values of molar volume V from the slope of the Vand plots (1/c vs. 1/log(Urlo)) for dilute solutions (hexanoate, 0.7651mo1-1; octanoate, 0.903 1 mol-1; decanoate, 1.001 1 m o l - 1 ; dodecanoate, 1.3421mo1-1) were found to be in agreement with those obtained from the Einstein plots. The values of interaction coefficient ~b evaluated from the intercept of the Vand plots were -16.99, -15.56, - 1 3 . 4 8 and - 8 . 9 4 for hexanoate, octanoate, decanoate and dodecanoate respectively. The values of the Moulik constant M (1.06, 1.07, 1.10 and 1.10 for hexanoate, octanoate, decanoate and dodecanoate respectively) obtained from the intercepts of the plots of (ri/rio) 2 vs. c a are almost constant while those of K (68.9, 88.8, 107.5 and 125.9) evaluated from the slope of the Moulik plots increase with increasing chain length of the soap. The values of the Jones-Dole constants A (0.11, 0.16, 0.16 and 0.18) and B (1.52, 1.82, 2.25 and 2.26) for hexanoate, octanoate, decanoate and dodecanoate respectively were evaluated from the intercept and slope of the plots of ri~p/c 1/2 vs. e 1/2 for dilute soap solutions. The values of the constant B (soap-solvent interaction) are larger than those of A ( s o a p - s o a p interaction), which confirms that the soap molecules do not associate appreciably in dilute solutions and there is a sudden change in association at a definite concentration of these soaps.

The values of intrinsic viscosity ri obtained from the plots of risp/C vs. c decrease with the increasing chain length of the soap molecule (hexanoate, 4.25 dm 3 tool - 1; octanoate, 3.70 dm 3 tool - 1; decanoate, 3.10 dm 3 m o l - 1 ; dodecanoate, 1.35 dm 3 m o l - 1). The values of the proportionality factor K and the slope factor a of the M a r k H o u w i n L S t a u d i n g e r equation were obtained from the plots of log ri vs. log M for zirconyl soap solutions in a xylene-methanol mixture. The value of the shape factor ~ (1.05) suggests that the soap molecules behave like stiff rods. The value of the proportionality factor K was found to be equal to 4.45. The viscosity measurements show that the equations proposed by Einstein, by Vand, by Moulik and by Jones and Dole are applicable to dilute solutions of zirconyl soaps. The results explain the bulk and association behaviour of zirconyl soaps in mixed organic solvents.

Acknowledgment The authors are grateful to the University Grants Commission, N e w Delhi, for providing financial support to the research project.

References [1] R.N. Kapoor and R.C. Mehrotra, J. Chem. Soc., 422 (1959); Chem. Abstr., 53 (1959) 9043a. [2] E.M. Brainina, R.Kh. Freidlina and A.N. Nesmeyov,Bull. Acad. Sci., USSR, Div. Chem. Sci., No. 4 (1961) 560. [3] Z.N. Prozorovskaya, L.N. Komissarova and V.I. Spitsyn, Russ. J. Inorg. Chem., 13 (1968) 369. [4l R.C. Mehrotra, Nature, 172 (1953) 74. [5] B. Hughes, MSc Thesis, University of Manchester, 1971. [6] V.I. Spitsyn, L.N. Komissarova, Z.N. Prozorovskaya and V.F. Churaev, Russ. J. Inorg. Chem., 12 (1967) 785. [7] S. Hirosawa, Jpn. Pat. 7,241,048, 1974; Chem. Abstr., 80 (1974) 30208t. [8] R.K. Mohanty, I. Basumallick,A.K, Das and S. Bhowmik, J. Indian Chem. Soc., 63 (1980) 30l. [9] A. Einstein, Ann. Phys., 19 (1906) 289. [101 V. Vand, J. Phys. Colloid, Chem., 52 (1948) 277. [11] S.P. Moulik, J. Phys. Chem., 72 (1968) 4682. [12] J. Jones and M. Dole, J. Am. Chem. Soc., 51 (1929) 2950.