NotesElectrokinetic Studies on Ion-exchange.

Membranes-Electroosmosis & ElectrophoresisStudies with Amberlite IRe-50 in Different

Ionic Forms

KEHAR SINGH* & RAM SHABD

Chemistry Department, University of GorakhpurGorakhpur 273001

Received 23 April 1978; revised 11 August 1978accepted 26 September 1978

Electroosmosis of methanol-water mixtures usingAmberlite IRe-50 in varlous ionic forms has beenstudied. Electrophoretic velocity of the ion-exchangerparticles dispersed in methanol-water mixtures hasalso been measured. Form of transport equationsneeded for the description of the experimental datahas been ascertained. Dependence of phenomeno-logical coefficients-on composition of the mixture hasalso been examined. Zeta potentials using electro-osmotic flux data and electrophoretic velocity datahave been estimated and compared.

ELECTROOSMOSIS of alcohol-water mixturesthrough a Zeokarb 226 (H+ form) membrane

has earlier shown- that in certain cases the directionin which permeation occurs undergoes reversal whenelectrical potentials beyond a certain magnitudeare applied. Electrophoretic velocities also exhibitreversal under comparable conditions. No suchunusual electrokinetic behaviour has, however, beenobserved- when Zeokarb 225 (Na+ form) mem-branes were used. There is a need to investigatethe electrokinetic behaviour of other weak ion-exchange and strong ion-exchange membranes.: Inthe present paper electroosmotic permeation andelectrophoretic migration through the weak ion-exchanger (Amberlite IRC-50) in different ionicforms using methanol-water mixtures are reported.Validity of non-linear equations used earlier hasbeen ascertained. Dependence of the phenomeno-logical coefficients on composition has also beenexamined. Zeta potentials from electroosmotic andelectrophoretic data have been estimated andcompared.

Amberlite IRC-50 (Rohm Haas, Philadelphia,USA), methyl alcohol (BDH) and conductivity waterwere used. Ion-exchanger indifferent ionic formswas prepared by repeatedly equilibrating the resinwith one molar solution of a suitable electrolyte over12 hr. Electroosmotic permeability" and electro-phoretic velocity measurements were carried outas described elsewhere'.

Rates of electroosmotic permeation and electro-phoretic migration have been found to dependnon-linearly on the applied electrical potential (Figs. 1

(

and 2) and the data on electroosmosis and electro-phoresi~ are descr~bed by non-li~ear Eqs. (1) and (2)respectively when ion-exchanger III Hr-form is used.

I,~L12 (i) + ~L122 (iY (1)

Ve = L~2(1l4» + tLi122(1l4»2 (2)Equations (1) and (2) have also been found to beapplicable for Na", Ba2+ and AP+, forms of theion-exchanger. Sign reversal during electroosmosisand electrophoresis occurs when composition isvaried. Sign reversal is not observed when theion-exchanger in other forms is used.

Eq. (1) predicts that:

L12 [L12] [L12]T - T 'x",+ T w'x", ._.(3)

and

L122 [L122] 2 [L122] 2T2 = T2. ,,; x'" + T2 w' Xw .•. (4)

The symbols m and w affixed to the coefficientsdenote respectively their values when methyl alcoholand water alone are used. Xm and Xw denote themas~ fractions of meth~nol and water respectively.

Snvastava et al.4 studied electroosmosis of acetone-water mixtures through a pyrex membrane andfound that Eq. (3) holds good. Strictly speaking

---...3·0 G'>

Iv .•..•.•...••

"<IIIt)

iu 1·0'-"

\O~ ---><

~~ 1·0

> --.--.:>

0 10 200 ~oo 00A~ ( Vott~)

-,.0

Fig. 1 - Test of the validity of Eq. (1) for Amberlite IRe-50(H+ form)jmethanol-water system [-0 -Xw = 0; .:.... -Xw

= 0'11; -,i-xw = 0'19; - X -Xw = 0·27; -A-Xw = 0·36;-0 -Xw = 0'44; and -. -Xw = 0'57J

283

-,\\

INDIAN J. CHEM., VOL. 17A, MARCH 1979

.., no~,.~~ 8·0

~4·0

----~~'-:::O-=::?::~

----0-- . " A..-

------- --

Fig. 2 - Test of the validity of Eq. (2) for Amberlite IRC-50(H+ form)/methanol-water system [-0 -Xw = 0; - x -Xw= 0·11; -. -Xw = 0·19; - •• -Xw = 0'27; -/1-xw = 0·36;-8-xw = 0·44; -. -XfJI = 0·57; and -0 -Xw = 0'67]

these relationship apply when components of themixtures migrate independently. Our results showthat Eqs. (3) and (4) are not obeyed. This clearlyshows that methanol and water interact significantlyand do not undergo permeation independently.Existence of strong interaction in the case ofmethanol and water has been established on the

basis of thermodynamic studies. Ion-exchangemembrane undergoes swelling when equilibrated.The extent of swelling, however, depends on thecomposition of the equilibrating mixtures. Thepermeation characteristics of the membrane, there-fore, undergo change as a result of which applicabilityof the relations (3) and (4) is further affected.

It has been found that composition dependenceof L'12 and L'122 cannot be expressed by Eqs. (5)and (6): .L~2=[L~2]1n·X",+[L~2]W'XW (5)L;22= [L~22]",·X;.+[L~22]W'X! (6)as required by Eq. (2) because of interactionsbetw~en constituents of th~ mixture and swellingto different extents when ion-exchanger particlesare dispersed in different mixtures.

Electrokinetic phenomena even in the case ofion-exchanger membranes occur on account of theformation of an electrical double layer endowedwith electric potential,.~. The rate of volumetricflux during electroosmosis is expressed in termsof zeta potential by Eq. (7):

] v = nDr2~ f1c/>41)1

where n = total number of capillary channels,r = average pore radius of the capillary channels,l = length of the capillary channel, D = dielectricconstant of the medium and 1) = coefficient ofviscosity of the medium.

Eq. (7) has <l: re~tri~ted range .of applicabilitybecause of the simplifying assumption upon whichit is based". Polarization of the electrical doublelayer and surface conductivity effects are also not

... (7)

Xw

TABLE 1 - ZETA POTENTIALFROMELECTROOSMOTICAND ELECTROPHORETICDATA

H+ form Na+ form Ba2+ form A13+form

i;EO i;EP i;EO i;EP i;EO i;EOmV mV mV mV mV mV

4·48 27·48 -1'39 ~12'40 9'92 6·357·19 22·78 -6,36 -20·31 2·38· 4·335·87 13-49 -13-77 -29·49 2·11 8'945·00 15·35 -18'44 -36·82 1·87 2·424'56 11·782'08 3·65

-4·32 -3-65

0·000'110·190·270·360·440'57

i;EO = Zeta potentials obtained from electroosmosis data.i;EP = Zeta potentials obtained from electrophoresis data.

TABLE 2 - VALUESOF 'I), D, K OF METHANOLWATER MIXTUREAND R OF AMBERLITEIRC-50 INVARIOUSIONIC FORMS

Kx10' R (ohms)mho cm-'1

H+ form Na+ form Ba2+ form Als+ formx 10-5 X 10-· X 10-5 X 10-5

1'210 0'830 0'160 3'000 1·9504·420 0·420 0·110 0'595 0·5554·300 0·330 0·200 0·800 0'8004·855 0·650 0'135 0·870 0·6656·330 0·2056'300 0·1956·500 0·165

XfJI 'I) X 103

poiseD

0·000·110·190·270·360·440'57

4·666·667'738'839·80

10·8011·87

34·038'040·543·547·050·157'5

284

(

r

considered. These complicating effects can, how-ever, be ignored if tl.<fJ-+0 so that equilibriumundeformed state of electrical double layer may bepostulated. Under these conditions Eq. (7) andEq. (1) retaining only first order term may becompared so that

Ll2 = nDr2 C, ... (8)T 4'l)1

The resistance R of the membrane equilibratedwith the permeant, is given by Eq. (9)

R = _1_ . ... l9)K'l)7tr2

where K is specific conductance of the permeant.It, therefore, follows that

L12 DC,T = 4RK7t~

or

c, = 4'l);KR (L;2) X 9 X 104 volts ... (10)

Zeta potentials estimated using Eq. (10) are giv~nin Table 1 for Amberlite IRC-50 membrane mvarious ionic forms when alcohol-water mixturesof different compositions are used. The valuesof R, K, D and n used in the calculations are summa-rized in Table 2.

Zeta potentials can also be estiJ?ate~ uS!ngelectrophoretic mobility data. Keeping m v~ewthe simplifying assumption refer~ed. to. earlier,it is possible to express electrophoretIc velocity as":

DV. = 47tYJ1' tl.<fJ ... (11)

and

so that

~= 47tYJ1' L~2'9 X 104 volts ... (12)DC,l' = distance between two electrodes. In our e~ec-trophoretic cell 1'= 12·5 em. ~he zeta .potentialscalculated using Eq. (12) are also mcluded in Table 1.It is seen that zeta potentials c~culated from theelectroosmotic and electrophoretIc data do notagree. There is agreement, however, when wate:-rich alcoholic mixtures are used for e~ectroos~ot~cstudies. In water rich alcoholic ~Ixtures lO?IC

concentration will be relatively high. At highionic concentration agreement bet~een zeta poten-tials obtained from electroosmotic and elect~o-phoretic mobility data has also been reported earlierin some cases=". . .

Ram Shabd is thankful to the CSIR, Ne~ Delhi,for the award of a senior research fellowship.

References1. RASTOGI, R. P., SINGH, K. & SINGH, J., J. phys. Chem.,

79 (1975), 2574.2. RASTOGI, R. P., SINGH, K., KUMAR, R. & SHABD, R.,

J. memb. Sci., 2 (1977), 317.3. RASTOGI, R. P., SINGH, K. & SINGH, S. N., J. pbys, cu«;

73 (1969), 1593.

(

NOTES

4. SRIVASTAVA, R. C. & ABRAHAM, M. G., J. chem, Soc.Faraday I, 72 (1976), 2631.

5. KRUYT, H. R., Colloid science, Vol.I (Elsevier, Amsterdam),1952.

6. WHITE, H. L. & MONAGHAN, E., J. phys. Chem., 39 (1935),925.

7. MONAGHAN, B. & WHITE, H. L., J. phys. Chem., 39 (1935),935.

Viscosities of Dioxane-water Mixtures &Their Solutions with Tetra-n-butylammonium

Iodide

N. ISLAM*, M. R. ISLAM & R. AHMAD

Department of ChemistryAligarh Muslim University,' Aligarh 202001

Received 15 May 1978; revised 18 September 1978accepted 13 October 1978

Viscosities of dioxane-water mixtures containing10, 20, 30, 40 and 50% by weight of dioxane and thoseof their solutions with tetra-n-butylammonium iodide(TBAI) have been measured as functions of tempera-ture and composition. The concentration dependenceof viscosities of the electrolytic solutions is explainedby least-squares fitting the data in Jones-Dole andthe Thomas equations. The values of the effectiveflowing volume, Ve have also been computed. Anincrease in the value of Ve with solute concentration isattributed to the rupture of hydrated (C.H.).N+ ionsresulting in an increase in the number of free watermolecules.

THE viscosities of pure solvents and their dilutesolutions with tetraalkylammonium salts as well

as with alkali halides enabled':" the correlation ofthe transport behaviour with the solute-solventinteractions. The concentration dependence of visco-sity for dilute electrolytic solutions was successfullyexplained by the Jones-Dole equationt'<-,

[(-'1/-rJo)-lJ/v'C = A+Bv'c ... (1)

in which 'l), YJo' and C stand for the viscosity ofthe solution, the viscosity of the solvent, and theconcentration in mol/litre, respectively and A and Bare the empirical parameters. However, this equa-tion shows limited applicability to such solutionsin the concentration range 0·002 to 0·2M. Night-ingale-", Miller and Doranw, on the other hand,employed the Eyring's14,15 treatment of viscosityto investigate the behaviour of concentrated electro-lytic solutions. On the basis of Eyring's conceptThomas's described the viscosities of such solutionsby Eq. (2),'1)s/'1)o = 1+k1<fJ+k2<fJ2 •• ,. (2)where 'l)s/'1)o is the relative viscosity and <fJ is thevolume fraction of the solute. Recently, Breslauand Miller? employed the above equation to explainthe viscosity of concentrated aqueous solutions oftetraalkylammonium halides on the basis of Ve.

The present investigation was, therefore, undertaken with a view to understanding the transportbehaviour in relation to the solute-solvent inter-

285