Gore, Periodic Coagulation in the Mutual Coagulation o/ Sols 27

From the Chemical Laboratory, Mahakoshal Mahavidyalaya, Jabalpur, M. P. (India)

Periodic Coagulation in the Mutual Coagulation of Sols

I n the m u t u a l coagu l a t i on of colloids c a r r y i n g oppos i t e charges, a colloid was m i x e d w i t h v a r i o u s c o n c e n t r a t i o n s of an - o the r colloid h a v i n g a n oppos i te charge a n d t he m i x t u r e was t r a n s f e r r e d i m m e d i a t e l y i n n a r r o w glass t u b i n g s of 4 m . m . d i ame te r . B a n d e d c o a g u l a t i o n was o b s e r v e d for a p a r t i c u l a r c o n c e n t r a t i o n .

S imi l a r ly As2S a sol was first t r e a t e d w i t h d i f fe ren t c o n c e n t r a t i o n of agar -agar , s t a r c h a n d Fe(OH)3 sol of d i f fe ren t c o n c e n t r a t i o n s was s lowly p o u r e d on t he t op of the a b o v e m i x t u r e in t e s t - t ubes . R h y t h m i c a l s t r u c t u r e s were o b t a i n e d in some cases.

T h e resu l t s were e x p l a i n e d b y a c o a g u l a t i o n t h e o r y p roposed b y t he au tho r .

Introduction I n t he p r ev ious p u b l i c a t i o n s (2) t he a u t h o r

has r e m a r k e d t h a t t he f o r m a t i o n of Liesegang r ings a m o u n t s to a p r o b l e m of per iod ic c o a g u l a t i o n or s e p a r a t i o n of so lva t ed h y d r o - p h o b i c colloids u n d e r su i t ab l e cond i t ions , or t he p h e n o m e n o n is a n o u t c o m e of t he pro- t e c t i ve a c t i o n of t h e lyosphere a n d t he e l ec t ro ly te coagu la t ion .

Th i s p a p e r embod ie s the resu l t s o b t a i n e d w h e n h y d r o p h o b i c colloids, such as Fe(OH)3 a n d As2S 3 are c o a g u l a t e d b y colloids h a v i n g oppos i t e charges .

Experimental The experiments were carried out (a) in the presence,

and (b) in the absence of starch and agar-agar jellies. The sols of Fe(OH)3, As,Sa, starch and agar-agar were prepared as usual.

Table I

Set A (In the absence of jellies and in small spaces)

The s conditions were kept constant throughout these experiments: Diameter of the tube 4 m.m. Volume of the sol 5 c. c. Volume of the coagulator sol 1 c. c. Concentration of As2Sa 1.98 per litre Concentration of Fe(OH)3 2.52 gm. Fe20a per litre.

By V. Gore

With 2 tables (Received April 14, 1958)

5 c.c. of the As2Sa sol was taken in different tubes and covered slowly in each case with 1 c.c. of Fe(OH)3 sol of various concentrations. The coagulator sol floated on the As~Sa sol in the tubes. There was flocculation at the junction. There was no diffusion.

Set B 5 c.c. of the As2Sa sol was mixed with 1 e.c. of Fe(OH)8

sol of various concentrations in separate tubes and the mixture in each case was transferred to the narrow glass tubes by means of a pipette, x indicates the concentration of Fe~08 in grams per litre.

No. As~S3 sol 1 c.c. of Fe(OH)3 sol Results

1 As2S3 sol x/16:0.1575 gm No coagulation 2 ,, x/8:0.315 gm Partial coagulation 3 ,, x/4: 0.630 gm Banded coagulation

6 bands 4 ,, x/2 : 1.26 gm Banded coagulation

9 bands 5 ,, x: 2.52 gm Complete coagulation

Table 2 These experiments were carried out in test tubes, and

in the presence of starch and agar-agar of different concentrations. The hydrophobic sols used were the same. 5 c.c. of the As2S a sol was mixed with 5 e.c. of starch sol and 1 c.c. of Fe(OH)a sol in a test tube.

Set A

N 5c.c. of 5c.c. of lc.c. o. As~S3 sol 0.2% starch Fe(OH)s Results

1 5c.c. of 5c.c. of As2S3 sol 0.2 ~o starch x/16 : 0.1575 gln

J 2 5e.c. of 5c.c. of No AszS8 sol 0.2% starch x/8:0.315 gm coagulation

3 5c.c. of 5e.c. of As~Ss sol 0.2~o starch x/4:0.630 gm

4 5c.e. of 5c.c. of ] As2Sa sol 0.2 ~o starch x/2 : 1.26 gm [ Partial

5 5 c.c: of 5 c.c. of | coagulation As2Sasol0.2O/o starch x :2.52 gm J

Set B Experiments were carried out by using the same

hydrophobie sols but with different concentrations of starch solution. 5 c.c. of 0.5, 1, 2 and 4% of starch solutions were used. There was no coagulation, both the hydrophobic sols were solvated by the lyo- philie starch solution. Semi-liquid jellies were obtained. This shows that the increased concentration of the lyophilic structure has exerted its protective action on the hydrophobic colloidal particles and there is no coagulation.

28 Kolloid-Zeitschri/t, Band 160 �9 Heft I

Table 2 (continued) Set C

The above experiments were repeated by using As2S8 as the coagulator sol, under identical conditions. There was no coagulation. Both the sols were solva~ed. Semi-liquid jellies were obtained. The eolour of the jelly in which As,Sa sol is in excess varies from greenish yellow to orange yellow. Similarly, the eolour of the jelly in which Fe(OH)~ sol is in excess varies from brown red to dark red.

Set D In the following experiments agar-agar was used

as a protective colloid.

5 c.e. 5 c . c . 1 c.c. Fc(OH)8 sol Results

No. As~Sa o f a g a r a b c d e

1 5c.c. 0.2% x x x x x There was no eo- As2S s 16 8 4 2 0 agulat ion in a, b, c

and d. In e, there was partial coagu- lation. The super- natant unaffected sol was full of discharg- ed particles, which could not settle due to the protective action of the agar sol.

2 5 c.e. 0.5% x x x Partial coagulation As2Ss 4 2 0 in all the three cases,

i. e., in c, d and e. Assemblage of dis- charged particles was observed in the supernatant un- affected sol.

3 5 e.c. 1% x x x Rhythmic or banded As~S a 4 2 0 structures in all the

three cases. The structures are quite stable. These are clearly seen when viewed against light as a background

4 5 c.e. 2% x x x No rhythmic struc- As~S8 4 2 0 tures, no coagulation,

stiff jellies are form- ed.

Set E The experiments were carried out as above. The

eoagulator sol, in these eases, is As~Sa; y ~ the con- centration of As~Sa in gms per litre -~ 1.98 gins. As~S3 per litre.

5 c.e. 1 e.c. of No. Fe(OH)a 5 e.e. of As~S~ Results

sol agar a b c

1 5c.e. 0.5% y y y In all three cases, Fe(0H)a 4 4 2 there was periodic

sol coagulation. The ex- periment No. 1 e gave good rhythmic struc- ture. There was com- plete coagulation in the three cases after five days.

Table 2 (continued)

5c.c. 5 c.c. of 1 e.e. of No. Fe (OH)~ AsaSa Results

sol agar a b e

2 5c.c. 1% y y y In a and b there was Fe(OH)s 4 2 0 rhythmic structure or

periodic coagulation. In c, both the sols were solvated. A jelly was formed.

3 5 e.c. 2% y y y There was no coagu- Fe(Ott)s 4 2 0 lation, no band for-

sol marion. Stiff jellies were obtained.

D i s c u s s i o n

T h e r e s u l t s c a n be s u m m a r i s e d as fo l lows : F o r c e r t a i n c o n c e n t r a t i o n s o f t h e l y o p h i l i c

sols a n d t h e c o a g u l a t o r co l lo id , t h e r e is f r a c t i o n a l c o a g u l a t i o n . H e r e i n , t h e con- c e n t r a t i o n o f t h e l y o p h i l i c sols is low. As t h e c o n c e n t r a t i o n o f t h e s e sols is i n c r e a s e d , b o t h t h e h y d r o p h o b i c co l lo ids g e t s o l v a t e d , c l ea r ie l l ies a r e f o r m e d in t h e s e cases. F o r a p a r t i c u l a r c o n c e n t r a t i o n o f t h e s t a r c h a n d a g a r a n d t h a t o f t h e c o a g u l a t o r co l lo id t h e r e a r e r h y t h m i c a l s t r u c t u r e s . I t is t h e r i g h t k i n d o f p r o t e c t i v e a c t i o n w h i c h s o l v a t e s as wel l as h e l p s t h e b a n d f o r m a t i o n (v ide t a b l e 2, se ts B a n d D a n d se t D No. 3 a n d se t E N o . 2). T h i s e x p l a i n s t h e d i f f e r en t r e s u l t s o b s e r v e d b y v a r i o u s w o r k e r s b y us ing d i f f e r en t t y p e s o f j e l l i es [cf. Hatschek (3)]. I n t h e t h e o r y p r o p o s e d b y D h a r a n d Chatter i j (1), t h e r i n g f o r m a t i o n is e x p l a i n e d b y t h e a s s u m p t i o n t h a t i t is due to t h e a d s o r p t i o n o f co l l o ida l p a r t i c l e s b y t h e c o a g u l u m , w h i c h f o r m s t h e r ing . T h e r e m u s t be a d i f fus ing e l e c t r o l y t e w h i c h m u s t p r o c e e d f u r t h e r to c o a g u l a t e a n o t h e r p o r t i o n o f t h e sol a n d t h u s f o r m a f r e sh c o a g u l u m . B u t in t h e e x p e r i m e n t s d e s c r i b e d a b o v e , t h e c o a g u l a t o r a g e n t is a co l lo id a n d n o t a d i f fus ing e l e c t r o l y t e . B a n d f o r m a t i o n is a lso o b s e r v e d in t h e a b s e n c e o f je l l ies (v ide E x p . No . 3, 4 se t B, t a b l e 1). T h e h y d r o p h o b i c sols u s e d in t h e a b o v e e x p e r i m e n t s we re p u r i f i e d as f a r as poss ib le .

Haze l a n d M c q u e e n (4) a t t r i b u t e t h e m u t u a l c o a g u l a t i o n of t h e sols p r i m a r i l y t o t h e m u t u a l a d s o r p t i o n o f o p p o s i t e l y c h a r g e d p a r t i c l e s w i t h a n u n e q u a l d i s t r i b u t i o n o f t h e t e r m charges . W h e n b o t h t h e sols a re m i x e d , t h e c o a g u l a t o r co l lo id h a v i n g a c o n c e n t r a t i o n w h i c h a p p r o a c h e s t h e f i oc c u l a t i on v a l u e for t h e p a r t i c u l a r sol n e u t r a l i z e s t h e c ha rge s o n t h e p a r t i c l e s o f t h e sols b e a r i n g a n o p p o s i t e c h a r g e . T h e p a r t i c l e s a r e p a r t i a l l y d e p r i v e d

o f t h e i r cha rges . T h e d i s c h a r g e d p a r t i c l e s a s s e m b l e t o g e t h e r . T h e g r o u p s a r e f o r m e d l e a v i n g t h e u n a f f e c t e d sols b e c a u s e t h e

Gore, Periodic Coagulation in the Mutual Coagulation o/Sols 29

coarse particles do not form centres of coagulation for all smaller particles as these break lose from the aggregates due to their thermal movements; at the same time part of the dispersion medium is released due to the shrinkage in the number of particles. The band formation in these cases can also be explained by the coagulation theory as pro- posed by the author (2) or as follows:

The banded coagulation takes place at the isoelectric point but above ~-potential when the particles are not yet fully discharged (as the concentration of the coagulant is not sufficient for rapid coagulation, i. e., for neutralization of the charges as well for the desolvation), and are also surrounded by a more or less thick solvated shell on the assumption that the ~-potential is not uniformly lowered over the surface of the particles. The coalescence of the particles takes place at the point of lower S-potential forming agglomerates, and as a result of this, the parts with high potential are turned outside. The like sign of S-potential on the similarly charged large coarse particles exert a repelling force which keep them apart.

Thus the separation of groups or bands takes place. The space between the bands is occupied by the released dispersion media and the unaffected portion of the diluted sols. The dispersion medium is held between another assemblage of the discharged par- ticles. The band formation in these cases can also be explained by the coagulation theory as proposed by the author. The band formation or the periodic coagulation can only be effected by keeping down the concentration of the coagulator solution, which approaches a flocculation value within a definite time for the particular concentration of the reactant colloid. The jellies offer their solvated shell or lyosphere as the protection for the hydrophobic particles of the sols formed during the growth of the precipitate.

The coagulator agent might be a diffusing electrolyte, a sol having opposite electric charges, radiant energy, thermal energy or

any coagulant, When a right kind of pro- tective action of the lyosphere is available for the colloidal particles they interplay with the suitable concentration of the coagulator colloid and the band formation results. The results recorded herein also suggest that the formation of Liesegang rings is an outcome of the protective action of the lyosphere and the slow coagulation caused by different coagulator agents. The presence of the jellies affects the lyosphere of the lyosols and makes them suitably solvated and thus helps or retards the ring formations (vide table 2, Ex. No. 3, 4, set A, B, C and set D, 3, set E 2).

Summary 1. Experiments are described in which periodic

coagulation is produced in As~Sa and Fe(OH)a sols by colloids having opposite charges.

2. The effect of different lyophilic structures is studied. The function of the jellies is to offer their solvated shells or lyosphere for the protection of the hydrophobic particles of the sols.

3, The results can be explained by the coagulation theory as proposed by the author.

4. These and other results described in the various publications show that the formation of Liesegang rings is a special case of periodic coagulation wherein the coagulants are electrolytes.

Zusammen/assung 1. Experimente werden beschrieben, in denen

periodische Koagulation in As~Sa- und Fe(OH)a-Solen durch Kolloide erzeugt wird, die entgegengesetzte Ladungen besitzen.

2. Die Wirkung yon verschiedenen lyophilen Struk- turen wird untersucht. Die Funktion der Gele ist es, ihre Solvatationshfillen oder Lyosph~ren zum Schutz der hydrophoben Teilchen der Sole anzubieten.

3. Die Ergebnisse kSnnen durch die vom Autor vor- geschlagene Koagulationstheorie erkl~rt werden.

4. Diese und andere in verschiedenen Ver6ffent- liehungen beschriebene Ergebnisse zeigen, dab die Bil- dung yon Liesegang-Ringen ein besonderer Fall periodi- seher Koagulation ist, bei der die koagulierenden Substanzen Elektrolyte sind.

Re/erences 1) Dhar and Chatter]i, Kolloid-Z. 31, 15 (1922);

49, 97 (1926). 2) Gore, Kolloid-Z. 82, 79, 203 (1938). 3) Hatschek, Kolloid-Z. 38, 151 (1926). 4) Hazel and Mcqueen, J. Phys. Chem. 37, 533, 571

(1933).