Competitive adsorption of

Polyelectrolytes- A size exclusion chromatographic study.

R.Ramachandran and P.Somasundaran,

Henry Krumb School of Hines,

Columbia University,

New York, N.Y. 10027

Abstract

Competitive adsorption of Na-polystyrene sulfonate (PSS), MW 4000

and 1,200,000 hematiteon studied usingwas size exclusion

chromatography. In the absence of electrolyte, short termkinetics led to higher adsorption of 4000 MW. No displacemnteffects observed duewere to electrostatic repulsion between

polymer segments. At 0.1 1,200-,000 PSS displacedadsorbed 4000 PSS leading to isotherms similar to ofthatnonionic polymers."

1

with the Stuart model (3-5~. .

competltlve adsorption ofHowever,

haspolyelectrolytes not been systematically investigated.

Available data (6,7) is restricted to systems where the polymers

of different molecular weights chemicaldifferenthave

compositions which inhibit reliable interpretation. thisIn

work, examine the adsorption of anionic polyelectrolyte-we an

Na-po1ystyrenesu1fonate (MW 4000 and 1,200,000 on hematite under

competitive conditions using size exclusion chromatography..

Materials and Methods:

(PSS) inNa-polystyrenesulfonate obtainedsamples were

monodisperse quantities from Polysciences and Scientific Polymer

BothProducts Inc. characterised by thepolymers were

usingmanufacturers GPC. Polydispersity of the polymers are

in Hematitereported Table 1. samples supplied by Alfawere

surface area of hematite wasproducts Inc. BET 7.5 m2./9 and its

point of zero charge as determined by electrophoresis was 7.9.

Adsorption studied using the 1was depletion technique. gm.

of the solid was conditioned in Scc of triply distilled water or

salt solution for 3 hours. after which 5 of the polymercc

the desired concentration and 7.0 was added.solution at at pH

the case of competitive adsorption studies, theIn two polymers

adjustedpremixed, and the of 7.0pH the towere mixture was

before addition the suspension.to The mineral polymer mixture

time. Solid liquidconditioned for the desired period ofwas

centrifugation andseparation achieved by the supernatantwas

analysed using for isotherms where only polymeruv one was

present) and size exclusion chromatography ( for mixtures).

Size conducted using 2experimentsexclusion columnswere

TSK-SW and in series. The of the presentSHODEX success

chromatographic systematicwork depended partly theon

identification of a suitable mobile pha~e. was usedO.lM Na2S04

A Perkin Elmer seriesthe mobile medium in all experiments.as

400 liquid chromatogram set up was used with CHROM software for

data analysis. Calibration curves for the polymer mixtures were

linear over the concentration range 100 to 900 ppm with a maximum

error of 38 ppm.

Results and Discussion:

Kinetics of adsorption of the 2 4000 and 1,200,000MW PSS was

equilibriumfirst studied, Fig.l. While the 4000 PSg reaches an

to 'reachvalue in less than 2 hours, the 1,200,000 takes 24 hrs.

4

Electrostatic repulsion adjacent polymerbetweenequilibrium.

segments could lead to longer equilibration period of the higher

In all the present experiments 48 hrs.HW PSS. equilibrium time

high affinityused. The polymers, exhibit typicaltwo a

isotherm with value the 4000(Fig.2) higher for PSS.plateaua

in plateau value between the two MW is too smalldifference

to attribute to conformational differences but is consistent with

investigations of Cosgrove and Vincent.(8). Fig.3 shows the

low concentrations.isotherm of At <adsorption the mixture.

adsorptionwhere the number of sites available forppm)

both polymers adsorbexceeds the number of polymer segments

significantly. the concentration is increased a preferentialAs

with the 1,200,000 PSS unab1~ toadsorption of 4000 PSS is seen,

in si9nifica~t quantities. The total adsorption of O~3adsorb

mg/m2 is with the value of the individualconsistent plateau

Based on the kinetics of adsorption of the individualisotherms.

molecular weights, adsorption of 4000 is expected bePSS to

that of 1,200,000 Rapid adsorption of 4000 PSSfaster PSS.than

competitivethe 1,200,000 from adsorbing underprevent PSScan

conditions. is noted effectsIt to be that any displacement

similar to that observed in nonionic polymer systems is prevented

electrostatic repulsion the polymerhere the betweensince

coming closewill the 1,200,000 from tosegments prevent a

adsorbed. thesurface where 4000 PSS has already In present

96study no displacement effects were observed over a period of

5

The electrostatic repulsion contributes a)that to faster

kinetics of 4000 b) absence of bedisplacement effects can

kmol/m3suppressed using indifferent 0.1 NaClan electrolyte.

used in this study for this Fig.4 shows thepurpose.

kinetics of adsorption in the of O.lM NaCl. Thepresence

1,200,OOO'PSS again, takes longer time than the 4000 PSS to reach

its equilibrium value. However the adsorption isotherms, (Fig-

5 show significantly higher adsorption of 1,200,000. Coiling of

polymer under high salt conditions enables andbetter packing

leads to higher adsorption. Interestingly, competitve adsorption

in the presence of salt show opposite effects than that observed

(Fig.in triply distilled water, low concentrations6). While at

400-500 ppm) both polymers adsorb, concentration isas

increased, 1,200,000 PSS adsorbs in significantly higher amounts

of the weight.at The presence ofthe expense lower molecular

in this case. Fig. 7salt enables displacement effects to occur

the results of systematic investigation of thegives a

phenomenon functiondisplacement of time initialatas a an

concentration of 1000 of each polymer Initially bothppm

1,200,000 PSS and 4000 PSS adsorb 4 hours); but after 24 hours,

displacement of the adsorbed 4000 PSS by the 1,200,000 PSS can be

to take place. The displacement phenomenon mostlyseen occurs

during the initial 36 hrs. Thus, only when the ionic strength is

6

does a charged polymer displaceincreased NaClto a

(even thoughlower molecular weight from thecomponent surface

the double layer ~s not completely suppressed).

Conclusions:

Competitive adsorption of monodisperse polyelectrolytes on

surfaces exhibit markedly behavioroppositely charged different

from that of nonionic polymers. In the absence of electrolytes,

4000 MW PSS adsorbed more strongly than 1,200,000 primarily

to faster adsorption kinetics. No displacement was observed-due

to the electrostatic repulsion between adjacent segments. At

M NaCl, 1,200,000 PSS adsorbed more strongly and was also able to

is clearthe adsorbed 4000 PSS. It thatMW sizedisplace

exclusion chromatography can be successfully used to monitor

polydispersity effect on the adsorption of polyelectrolytes.

Acknowledgements:

the National science Foundationauthors wish to acknowledgeThe

7

REFERENCES

1. Scheutjens, J.H.H.H.,and Fleer, G.J.,Cohen Stuart, M.A.,

J. Polymer Sci., Polymer Phy. edition, v.18, 559-573

(1980).

2. van der Schee, H.A., and Fleer, G.J., J.Papenhuijzen, J.,

ColI. Interf. Sci., v.104, 2, 540-553, April 1985.

3. Felter, and Ray L.N. , J. Colle Interf.R.E., Jr., Sci.,

v.32, 2, 349-360, Feb. 1970.

4 Howard, G.J., and Woods, S.J., J. polym. Sci., part A-2,

v.10, 1023-1028,1972.

5. Vander Linden c., and Van Leemput, ColleJ. Interf.R. ,Sci., 67,63, 1978.

6. Adam S. Unus, and Robb D. Ian, J. Chern. Soc. Faraday Trans,

1,79,2745-2753,1983

7 Bain, Cafe,D., Robb, 1.0., and Williams, P., J.H.C.,Colle Interf. Sci., 88,467,1982.

8. Cosgrove, J. and Vincent, E.D., J. Colt. Interf. Sci., 111,

2,409-419, June 1986.

Table 1

Code Supplier ~w/Mn

4000 PSS Polysciences Inc.

1,200,000PSS

Scientific PolymerProducts, Mass.

(/)(/)a..J~~000V"0C000000(\I

-

-...0c0.--a.'-0tit"0oC

t

...0titU.--Q)

c.-~

a> I

000~A

D r]

I 1.0.I00o.00IN

.-

I

(,0 ~

~w

/ 5w U

! J xat .

C\I

0

0(0 0CX

)

00-0C\I

0

In'-~0.r.c.-Q)

E.-01-V

, C

/)I

C/)

c.

"oW0CI

0

'-IoJ

. a....

I 0IIJ

.

ooQl

, 10""'>

.

~f'"40

~.&oJ

IIJ tJ

tJ Q

I

f'"4

.4.JQI

QI

c~

-0~

QI

00 tJ

f'"4C0 Q

I

~IIJ

.Qr.;.ca

~~0... '0cfO ccc,

cCN, Q

J.C

o,4.J

C-

~~00000N.

--CC0000..;..Q)

-'t-

00

c0

E~

... ~

Q)u>

.c- Q

)g

cH

C

)...

c >

.0-

0- II)

--

>.

0""1

e-O

N0

Q.

LLQ)

CI)

,

-C

0 c

<tZ

O

CD

000.v

I c9~~

0 00a070C'!.

-

[]

\\,(D

v

ZW

/ 6w

ul

J)( 0\

N .

0 8too..

0g 00<D

Ea..a..c.-

°c00~;

c'--c~uc00ourt>

-c~'a-II)~a:

8N00-0

0QQ,

QQN,

c Q)

.c+J

~

~0e~Q)

.c.&oJ

0U)

.Q)

.&oJ

c>.

0'6-~~

.&oJ

o.u~

Q

)0,...U

) Q

)

'0I

~~

0..

, N

Q

)\

. u

O'C

Q)

rz.U).cC

O

000...

'0C10

t11t110.

Adsorption of 2 MW: 4,000 and 1.200.000No-Polystyrene Sulfonate on Fe203

pH 7.1f: 0.17.0

9.0 - -~

8.0

7.0 -

6.0 ~c3.0 ~

.-=-t\I

E

E 5.0

c

4.0-~><0-

i ~\ 0 1. 200,000 ~0, .0

00 800200 400 600

Initial Concentration of each Polymer

Fig.3: Adsorption isotherm under competitive conditions of 4000and 1,200,000 PSS- no electrolyte.

E0'

5.0 Ec-~

:4.0 x0-

'3::~00o.00C

\I--"'CCC000.v..

-.,..~C

c-C

cU0

0 D

--""Z+

--Q

.~~

'-(/),c0

-."

~

.

"CcO

ct~+

-'-

0-.,..~O

+-

rt)

CI)

." ~

Q.

u -

,~.-

0 ~

+-a.LL

Q)

I

~

D

C~

ZO

000.00Na

- .a0- cc

000..

V-C

X)

CD

11ft'

-Zw

/6w

U! J )(ot

C\J

.000

jt):el

-'..-l U)

'-~.,g,I

C-

0c0-.I.JQ

,W0fIJ

~IV0fIJU-.I.JQ

I .

c -

0'" u

~

10Z

.."'M.

E0\"""

0'" -

rr.. 0E~

~.c.,co{J){J)C

o

CCC~

CCN~

~'0cco

c00..

~~000~

00N~

-"0C0000~..

--~

000-

E~

(.),---0«)-z

~=

(/)~0«)-II)

c .

.-1«)0'--c~

o0-

0- II)

It)0

-~o

0..- ~

'- 0

N0

a.. I~II)

I w

. ~

"OO

c 0..

~Z

O

(\J- .80-00(\J--0

00r- 0

.

000-

V

«>

CD

~w

/ 5w

U

! J xotv

N

000-~

IIEa..a..I

0.50

I

CO

8.-..c...

..'c.,Co)

c0U

0 -'

0 c

'4t' ~'C-~~Q:

N

0

c0~0.~0

.U

2 ~

'0 U

-C

111'

Z..~M.

etJI

~

rz.. 0e~

e~Q)

.c+J0(/]

.~ 0 000... '0cco 000~

00N~

~ CI2

~Q,

~IU ...t.0

9.0 10.5",E

'"0

9.5 ~,

)(~

8.5 -0-0

-p ...

Adsorption of 2 MW:4,000 and 1,200,000No-Polystyrene Sul-fonate on Fe2030.1 M NaCIpH 7. 0 :t 0.1

d"'"'1~ D.~!~~ ~8.0

7.0

~

.,-.6.

6.0N

5.0

4.0

3.0

...2.0

1.0

00 200 400 600 800

Initial Concentration of each Polymer900

Fig.6: Adsorption isotherm under competitive conditions of 40003and 1,200,000 PSS- 0.1 kmol/m .

E"'"0Ec-

~X~

..~-

~(.)

NO

~ZO~

cOr-;

;00.-'-

00~C

/)<

XC

/) 0

a..

~O

:;:0-.;:0«>

-

o.VE

P

":0"'g0(.)

0 +

1~

OO

00 .

V)O

~u

-..,..=

O~

«>00.

.~

N~

--m .

0

m

0 00Q00N-

-

')to- ().~~~\,

<D

It)

v

~w

lOW

U

I J XQ

\

~N

00-0V 0CD

0U)

0'"0

CI)

1

~0.c.

c-~E.-.-

.CI1

C/)

c-o00~

00N~

~>.

,QCI1

C/)

C-

O00..1604

0+JCOJ

eOJ

Qft30.U)

'C1604

0U)

Q.&J

OJ

C~..

r-...

0\

~