Upload
phamanh
View
220
Download
0
Embed Size (px)
Citation preview
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\
~