Journal of Encapsulation and Adsorption Sciences, 2011, 1, 7-22
doi:10.4236/jeas.2011.11002 Published Online March 2011 (http://www.scirp.org/journal/jeas)
Copyright © 2011 SciRes. JEAS
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Investigation of Swelling/Sorption Characteristics of
Highly Swollen AAm/AMPS Hydrogels and Semi IPNs
with PEG as Biopotential Sorbent
Semiha Kundakci, Erdener Karadağ*, Ömer Barış Üzüm
Adnan Menderes University, Fen-Ede biyat Fac ulty, Department of Chemistry, TR-09010, Aydın, Turkey
E-mail: ekaradag@adu.edu.tr
Received February 20, 2011; revised March 23, 2011; accepted March 30, 2011
Abstract
The aim of this study was to investigate the equilibrium swelling and sorption properties of chemically
crosslinked copolymeric hydrogels as biopotential sorbent consisting of acrylamide (AAm) and 2-acrylamido-2-
methyl-1-propanesulfonic acid (AMPS). Semi-interpenetrating polymer network (semi IPNs) hydrogel,
composed of AAm with AMPS as co-monomer, with poly (ethylene glycol) (PEG) and a multifunctional
crosslinker such as trimethylolpropane triacrylate (TMPTA) was prepared. AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs were synthesized by free radical solution polymerization by using ammonium
persulphate (APS)/N,N,N’,N’-tetramethylethylenediamine (TEMED) as redox initiating pair. Swelling ex-
periments were performed in water, 0.01 M and 0.03 M aqueous urea solutions at 25˚C, gravimetrically. The
hydrogels showed enormous swelling in aqueous urea/water medium and displayed swelling characteristics
that were highly depended on the chemical composition of the hydrogels. FTIR spectroscopy was used to
identify the presence of different repeating units in the semi IPNs. Some swelling and diffusion characteris-
tics were calculated for different semi IPNs and hydrogels prepared under various formulations. For sorption
of cationic dye, Lauths violet into the hydrogels was studied by batch sorption technique at 25˚C. Dye re-
moval capacity, adsorption percentage and partition coefficient of the hydrogels was investigated. Swelling
and dye sorption properties of AAm/AMPS hydrogels and AAm/AMPS/PEG semi IPNs were investigated as
a function of chemical composition of the hydrogels.
Keywords: Swelling, Hydrogel, Interpenetrating Polymer Networks, Acrylamide, 2-acrylamido-2-methyl-1-
propanesulfonic Acid, Urea, Lauths Violet Sorption
1. Introduction
In recent years, polymeric gels are the objects of inten-
sive studies. Highly swollen polymers or copolymers are
highly hydrophilic, three-dimensional crosslinked poly-
meric structures that are able to swell in the aqueous en-
vironment. Hydrogels have found numerous uses ranging
from daily life applications, mainly due to their high wa-
ter absorption capacity to the development of new mate-
rials for many different purposed applications. Hydrogels
are inherently soft, hydrophilic, porous, and elastic
polymeric systems. The use of polymer hydrogels as
biopotential sorbent or carriers for the removal of the
model molecules from aqueous solutions or controlled
release studies of them has been continued to attract con-
siderable attention in recent years. Hydrogels are poly-
mers in three-dimensional network arrangement, which
are able to retain large amount of water. In order to keep
the spatial structure, the polymer chains are usually
physically or chemically crosslinked. Due to their swell-
ing capacity, hydrogels can be easily rinsed to remove
reagents residues. On the other hand, the big water con-
tent that makes hydrogels such a special class of materi-
als. The importance of hydrogels in the biomaterial field
is justified by some unique characteristics: the elas-
tomeric and soft nature of the hydrogels [1-7].
Crosslinked polymers capable of imbibing large vol-
umes of water have found widespread applications in
bioengineering, biomedicine, and food industry and wa-
ter purification and separation process. Due to its swell-
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ing ability in water, hydrophilicity, biocompatibility, and
no toxicity, hydrogels have been utilized in a wide range
of biological, medical, pharmaceutical, environmental
applications [8-18].
The major environmental problem with colorants is
the removal of dyes from effluent waste materials. Un-
treated effluents from dyestuff production and dyeing
mills may be highly colored and thus particularly objec-
tionable if discharged to open waters. Dyeing wastes in
some industrials have high color and organic content.
Colored waters are also objectionable on aesthetic
grounds for drinking and other municipal and agricul-
tural purposes. Effective removal of dyes, in connection
with waste water treatment strategy, still remains a major
topic of present research. Many methods have been pro-
posed for the removal of dyes, heavy metals and other
hazardous materials. Chemical precipitation, membrane
extraction, coagulation, complexing, solvent extraction,
ion change, and adsorption are some of the commonly
used process, but each has its own merits and demerits in
its applications. Adsorption procedures are a way of the
most widely used for pollutants such as dyes and organic
compounds from industrial effluents. Adsorption is a
well-known equilibrium separation process. Recently,
new effective, efficient and economic methods for water
decontamination applications and for separation analyti-
cal purposes have been investigated [2-10].
When hydrogels come in contact with aqueous solu-
tions, they adsorb and retain the dissolved substances.
For this reason, they have been in several studies such as
“for water purification [8], for removal of some dyes
from aqueous solutions [9,11,15-18], for removal of
toxic metal ions with magnetic hydrogels [10], for uptake
of metal ions from aqueous solutions [10,11,13,18], for
uptake of uranyl ions from aqueous solutions [12,18] “as
water purification agents.
Poly (ethylene glycol), (PEG) is of great interest in
numerous biomedical applications for several purposes.
PEG is water-soluble and is non-toxic for body immune
system. PEG based hydrogels have good biocompatibility.
PEG based hydrogel systems have been used at many
biotechnological applications [6,19,20].
Some physical properties of hydrogels may be im-
proved by preparing semi-interpenetrating polymer net-
works (semi IPNs), when the hydrogel network is pre-
pared in the presence of a previously made polymer such
as poly (ethylene glycol), polyacrylamide, poly (N-
isopropyl acrylamide), poly (vinyl pyrrolidione), poly
(vinyl alcohol), or poly (acrylic acid), etc. Water sorption
property of hydrogels or semi-interpenetrating polymer
networks (semi IPNs) accounts for a great number of
biomedical and technological applications such as drug
delivery systems, artificial implants, contact lens, en-
zyme immobilization, catheters, wound dressings, bio-
sensors, superabsorbents, and etc, [3,6,21,22].
Hydrogels can be used as a composite membrane for
various enzymes. For example, for immobilization of
Urease enzyme, various composite hydrogel membranes
can be used. Urease is a highly specific enzyme. It cata-
lyzes the hydrolysis of urea to ammonium and carbon
dioxide. It has been immobilized for analytical and
biomedical purposes. One of the major applications of
immobilized Urease is the direct removal from blood
for detoxification, or in the dialysis regeneration sys-
tems of artificial kidney machines. Other applications of
immobilized Urease will be in a bioreactor for the con-
versation of urea present in fertilizer wastewater efflu-
ents to ammonia and carbon dioxide or in the food in-
dustry for the removal of urea from beverages and foods
[4,23-26]. Urea is one of the main toxic wastes in the
dialysate solution from hemodialysis. The most effec-
tive way of removing urea from aqueous solutions is the
utilization of immobilized Urease as no efficient ad-
sorbent is available for urea. On the other hand, urea has
a great importance in biological systems. In our previ-
ously studies, some papers was reported about swelling
characterization of -radiation induced crosslinked
acrylamide/crotonic acid and acrylamide/maleic acid
hydrogels in urea solutions [25,26].
Polyacrylamide based hydrogels have received con-
siderable attention because of their use in many applica-
tions. In our and others previous studies, copolymeric hy-
drogels of acrylamide with some acidic monomers were
prepared by free radical solution polymerization and
used in separation and adsorption of some dye mole-
cules [4,6,17,18,27-29].
AMPS received attention in recent years due to its
strongly ionizable sulfonate group. Increasing number
of ionic groups in the hydrogels is known to increase
their swelling capacity. AMPS dissociate completely in
the overall pH range, and therefore, the hydrogels de-
rived from AMPS exhibit pH independent swelling be-
havior [6,9,13,30,31].
The present paper reports that swelling study in urea
solutions and water, and sorption study of lauths violet
by a novel type of new polymeric adsorbent containing
AAm, AMPS and PEG. The aim of this study is to in-
vestigate the swelling properties and to increase the
water absorption capacity of a series of new interpene-
trating polymeric networks that are crosslinked a
“new” multifunctional crosslinker such as TMPTA and
using a hydrophilic ionic/anionic comonomer such as
AMPS with a polymer such as PEG was selected.
“New” AAm and AMPS based hydrogels and semi
IPNs as potential polymeric adsorbents were prepared
by free radical solution polymerization. It was of inter-
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est to swelling properties of AAm/AMPS hydrogels and
AAm/AMPS/ PEG semi IPNs in urea solutions for new
hydrogels synthesis for urea treatment as new mem-
branes or crosslinked polymeric carriers, or dye sorption
capacity of AAm/AMPS hydrogels and AAm/AMPS/
PEG semi IPNs hydrogels adsorption. Then, swelling
properties and sorption properties of these hydrogel sys-
tems were studied.
2. Experimental
2.1. Preparation of AAm/AMPS Hydrogels and
AAm/AMPS/PEG Semi IPNs
Highly swollen acrylamide (AAm) /2-acrylamido-2-met
hyl-1-propanesulfonic acid (AMPS) hydrogels and
semi-interpenetrating polymer networks, AAm/ AMPS/
PEG hydrogels with 0.25, 0.50, 0.75 and 1.00 g poly
(ethylene glycol) (PEG, Mw = 4600), (Aldrich, Stein-
heim, Germany) (for per 1.00 g AAm) were prepared by
free radical solution polymerization in aqueous solution
of AAm monomer (Aldrich, Steinheim, Germany) with
AMPS (Aldrich, Steinheim, Germany) as co-monomer
and multifunctional crosslinker such as trimethylolpro-
pane triacrylate (TMPTA) (Aldrich, Steinheim, Ger-
many). For this study, the modes of specifications of the
sources of water, the monomers, and other used chemi-
cals were given in our previous study [6]. But, here, it
will be mentioned to the preparation details and condi-
tions of the hydrogels, again. The initiator, ammonium
persulphate (APS) (Merck, Darmstadt, Germany) and
the activator N,N,N’, N’-tetramethylethylenediamine
(TEMED) were also supplied by (Merck Schuchardt,
Germany), and used as the redox initiator pair. All
chemicals were used as received.
To prepare highly swollen AAm/AMPS hydrogel sys-
tems, AAm weighing 1.0 g (14.07 mmol) was dissolved in
1.0 mL water. Then 0 mg, 60 mg/0.29 mmol, 120 mg/
0.58 mmol, 180 mg/0.87 mmol, 240 mg/1.16 mmol, 300
mg/1.45 mmol of AMPS were added to each AAm solu-
tions, respectively. After these additions, for the synthe-
sis, 0.25 mL/0.0093 mmol of 1% concentration of
TMPTA and 0.20 mL/0.044 mmol aqueous solutions of
APS (5.0 g APS/0.022 mol/100 mL water) and 0.25
mL/0.017 mmol 1% concentration of TEMED were
added these aqueous solutions. The solutions were
placed in PVC straws of 3 mm diameter, then, they were
waited for gelation time in an oven at 40˚C. Fresh hy-
drogels obtained in long cylindrical shapes were cut into
pieces of 3 mm - 4 mm in length.
After gelation, they were washed and thoroughly
rinsed with distilled water, blot dried with filter paper,
dried in air and vacuum, and stored for swelling and
sorption studies.
2.2. Measurement of Swelling in Water and
Aqueous Urea
For swelling studies, AAm/AMPS hydrogels and AAm/
AMPS/PEG semi IPNs were accurately weighted and
transferred into water or aqueous 0.01 M/0.03 M urea
solutions. Urea was provided from Merck, Darmstadt,
Germany. Dry gels were weighed and then immersed in
distilled water, or aqueous 0.01 M or 0.03 M urea solu-
tions at 25 ± 0.1˚C. Swollen gels were removed from
water or aqueous solutions at predetermined times, blot-
ted dry, and weighed in air. The measurements were
conducted at 25 ± 0.1˚C in a water bath.
2.3. Dye Sorption Equilibrium Experimental
Batch sorption studies were applied in all sorption ex-
periments. Cationic dye, Lauths violet, (Thionin, LV),
used in sorption studies and some properties of LV were
given in Table 1. Cationic dye, Lauths violet was pur-
chased from Aldrich, Milwauke, USA.
Solutions of LV concentration range 1.00 x 10-6 M -
20.0 x 10-6 M in distilled water were prepared. Aam
/AMPS hydrogels and AAm/AMPS/PEG semi IPNs
containing 180 mg AMPS was used in a known volume
of dye solution until equilibrium was reached. For
AMPS effect on the dye sorption, aqueous solution of
concentration of 20.0 x 10-6 M of LV was used.
After sorption, dye solution was separated by decan-
tation from the hydrogels. Spectrophotometric method
was applied to dye solutions for determining of the con-
centrations of the hydrogel systems. Spectrophotometric
measurements were carried out using a SHIMADZU
UV 1601 model UV-VIS spectrophotometer at ambient
temperature. The absorbances of these solutions were
read at 598 nm for LV [32]. Distilled water was chosen
as the reference. The equilibrium concentrations of the
cationic dye solutions were determined by means of
precalibrated scales.
3. Results and Discussion
Semi-interpenetrating network (semi IPNs) hydrogel,
composed of acrylamide (AAm) with 2-acrylamido-2-
methyl-1-propanesulfonic acid (AMPS) as co-monomer,
with poly (ethylene glycol) (PEG) and a multifunctional
crosslinker such as trimethylolpropane triacrylate
(TMPTA) was prepared. AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs were synthesized by free
radical solution polymerization (Figure 1).
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Table 1. Some properties of lauths violet.
Name Chemical formula
mak(nm) Color Index No
Lauths violet
(LV)
(Thionin)
+
S
N
NH2
H2NCl-
598 52000
Acrylamide (AAm) 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS)
Acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid (AAm/AMPS)
Figure 1. Representative chemical structures of monomers and AAm/AMPS hydrogel.
0
2000
4000
6000
8000
10000
12000
14000
0 500 1000 1500200
t (min)
S%
0
300 AMPS
240 AMPS
180 AMPS
120 AMPS
60 AMPS
00 AMPS
Figure 2. Swelling isotherms of AAm/AMPS hydrogels crosslinked in aqueous 0.01 M urea solutions.
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0
2000
4000
6000
8000
10000
12000
14000
16000
0 5001000 15002000
t (min)
S%
300 AMPS
240 AMPS
180 AMPS
120 AMPS
60 AMPS
00 AMPS
Figure 3. Swelling isotherms of AAm/AMPS hydrogels crosslinked in aqueous 0.03 M urea solutions.
3.1. Equilibrium Swelling Studies
Swelling experiments were performed in water at 25˚C,
gravimetrically. Some swelling and diffusion parameters
of AAm/AMPS hydrogels and AAm/AMPS/PEG semi
IPNs in water were reported previously by our group [6].
A fundamental relationship exists between the swell-
ing of a polymer in a solvent and the nature of the poly-
mer and the solvent. The percentage swelling (S%) of the
hydrogels in distilled water was calculated from the fol-
lowing relation,
%
to
o
mm
Sm
100 (1)
where m
t
is the mass of the swollen gel at time t and mo is
the mass of the dry gel at time 0.
The water intake of initially dry hydrogels was fol-
lowed for AAm/AMPS hydrogels and AAm/AMPS/PEG
semi IPNs crosslinked by TMPTA in water, and swelling
isotherms of AAm/AMPS hydrogels and AAm/AMPS/
PEG semi IPNs crosslinked by TMPTA were presented
in our published study [6].
Swelling studies have been repeated in aqueous 0.01
M and 0.03 M urea solutions for AAm/AMPS hydrogels
and AAm/AMPS/PEG semi IPNs crosslinked by TMPTA.
Swelling isotherms of AAm/AMPS hydrogels in aqueous
0.01 M urea solutions was presented at Figure 2, and
swelling isotherms of AAm/AMPS hydrogels in aqueous
0.03 M urea solutions at Figure 3. Figure 2 and Figure
3 show that swelling increases with time up to certain
level, then levels off. This value of swelling may be
called as the equilibrium percent swelling (Seq%). Seq%
of AAm/AMPS hydrogels and AAm/AMPS/PEG semi
IPNs is used for the calculation of swelling characteriza-
tion parameters. Seq% AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs are given in Table 2.
Table 2 shows that the values of Seq% of AAm hy-
drogels are 900%, but Seq% of AAm/AMPS hydrogels
are 4850% - 12750% with the incorporation of AMPS
groups into AAm chains crosslinked by TMPTA for wa-
ter. Table 2 shows that the values of Seq% of AAm hy-
drogels are 900 and 950%, but Seq% of AAm/AMPS hy-
drogels are 4100% - 13450% with the incorporation of
AMPS groups into AAm chains crosslinked by TMPTA
in aqueous 0.01 M and 0.03 M ures solutions.
In Table 2, Seq% of the hydrogels increased with the
AMPS content in the copolymers. Seq% of AAm/AMPS
hydrogels is higher than Seq% of AAm hydrogels. The
reason of this is the hydrophilic groups on the AMPS.
AMPS has got strongly ionizable sulfonate group. The
more hydrophilic groups in the AAm/AMPS get the
more the swelling of the AAm/AMPS hydrogels. This is
an expected result about swelling of AAm/AMPS hy-
drogel systems. Hydrophilicity of AAm/AMPS copoly-
mers becomes greater than that of AAm, so, the swelling
of AAm/AMPS copolymers is greater than the swelling
of AAm hydrogels [6].
Effect of the content of AMPS and concentration of
aqueous urea solutions onto swelling of AAm/AMPS
hydrogels crosslinked by TMPTA in water, in aqueous
0.01 M urea solutions and in aqueous 0.03 M urea solu-
tions are presented at Figure 4.
The values of Seq% of AAm/AMPS hydrogels swollen
in water are generally smaller than the hydrogels swollen
in urea solutions. The reason of this different behavior is
the hydrophilic character of urea molecules. Urea mole-
cule has got more hydrophilic sites, as NH2 and C=O.
When, urea molecules have interacted with much water,
so, there has been much swelling than swelling values in
water, also. That’s way, urea molecules have got hydro-
philic groups, more swelling values have been observed
when the hydrogels swollen in aqueous urea solutions.
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Table 2. Values of the equilibrium percentage swelling (Seq%) and equilibrium water contents (EWC) or equilibrium
urea/water contents (EUWC) of AAm/AMPS hydrogels and AAm/AMPS/PEG (containing 0.50 g PEG) semi IPNs systems.
water 0.01 M urea 0.03 M urea
AMPS / mg Equilibrium percentage swelling, (Seq%)
0 900 900 950
60 4850 4100 4500
120 7250 8500 9100
180 10400 10300 10600
240 11150 11750 12550
300 12750 13100 13450
AMPS/PEG mg
0 550 500 500
60 1100 1350 1350
120 2100 2100 2050
180 2650 3250 3250
240 2950 3400 3400
300 4400 3600 3650
AMPS/mg Equilibrium water content, (EWC)/Equilibrium urea/water content, (EUWC)
0 0.8995 0.9011 0.9042
60 0.9798 0.9763 0.9784
120 0.9864 0.9883 0.9891
180 0.9905 0.9904 0.9906
240 0.9911 0.9915 0.9921
300 0.9922 0.9924 0.9926
AMPS/PEG mg
0 0.8422 0.8366 0.8385
60 0.9163 0.9315 0.9317
120 0.9542 0.9541 0.9532
180 0.9639 0.9703 0.9700
240 0.9674 0.9832 0.9716
300 0.9777 0.9947 0.9734
Here main characteristic effects are the hydrophilic char-
acter of urea molecules. So, the more hydrophilic groups
in the aqueous urea solutions get the more the swelling
of AAm/AMPS hydrogels and AAm/AMPS/PEG semi
IPNs.
3.2. Equilibrium Water or Urea/Water Content
The water (or with together urea,) absorbed by AAm
/AMPS hydrogels and AAm/AMPS/PEG semi IPNs is
quantitatively represented by Equilibrium water content
(EWC), or Equilibrium urea/water content (EUWC), by
using below equation [33,34]
EWC
s
o
s
mm
m
(2)
Here, ms is the mass of the swollen gel at time t (equi-
librium), and mo is the mass of the dry gel at time 0.
The EWC (or EUWC) values of AAm/AMPS hydrogels
and AAm/AMPS/PEG semi IPNs were calculated. The
EWC (or EUWC) values of the hydrogels are tabulated
in Table 2. Generally, it was seen that the EWC (or
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0
4000
8000
12000
16000
0
60120180 240 300
AMPS contents (mg)
Water
0.01 M Urea
0.03 M Urea
S
eq
%
Figure 4. Effect of the content of AMPS onto swelling of AAm/AMPS hydrogels in water, in aque-
ous 0.01 M urea solutions and in aqueous 0.03 M urea solutions.
4.0
3.0
2.0
1.0
0.0
1.52.53.54.55.56.5
ln t
ln F
00 AMPS
60 AMPS
120 AMPS
180 AMPS
240 AMPS
300 AMPS
Figure 5. Plots of lnF versus lnt for AAm/AMPS hydrogels in aqueous 0.01 M urea solutions.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1.52.0 2.53.03.54.0 4.55.0
ln t
ln F
00 AMPS/PEG
60 AMPS/PEG
120 AMPS/PEG
180 AMPS/PEG
240 AMPS/PEG
300 AMPS/PEG
Figure 6. Plots of lnF versus lnt for AAm/AMPS/PEG hydrogels in aqueous 0.01 M urea solutions.
Copyright © 2011 SciRes. JEAS
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14
EUWC) values of the hydrogels are increased by the
adding of AMPS molecules. Here, the main effect is the
hydrophilic character of AMPS.
It is well known that the swelling of a hydrogel is in-
duced by electrostatic repulsion of the ionic charges of
its network. The ionic charge content is important.
AMPS contain many strongly ionizable sulfonate group.
The swelling increase is due to an increase in the anionic
units. The hydrophilic group numbers of Aam /AMPS
hydrogels and AAm/AMPS/PEG semi IPNs are higher
than those of AAm, and so the swelling values of AAm/
AMPS hydrogels and AAm/AMPS/PEG semi IPNs are
greater than that of AAm swelling values.
3.3. Diffusion
When a glassy hydrogel is brought into contact with wa-
ter, water diffuses into the hydrogel and the network ex-
pands resulting in swelling of the hydrogel. Diffusion in-
volves migration of water into pre-existing or dynami-
cally formed spaces between hydrogel chains. Swelling
of the hydrogel involves larger segmental motion result-
ing, ultimately, in increased separation between hydrogel
chains.
Analysis of the mechanisms of water diffusion into
swellable polymeric systems has received considerable
attention in recent years, because of important applica-
tions of swellable polymers in biomedical, pharmaceuti-
cal, environmental, and agricultural engineering.
The following equation is used to determine the nature
of diffusion of water into hydrogels [33,35].
n
t
s
M
F
kt
M
 (3)
Here, F is the fractional uptake at time t, Mt and Ms
are the mass uptake of the solvent at time t and the equi-
librium, respectively. Eq. 3 is valid for the first 60% of
the fractional uptake. Fickian diffusion and Case II
transport are defined by n values of 0.5 and 1.0, respec-
tively. Anomalous transport behavior (non-Fickian diffu-
sion) is intermediate between Fickian and Case II. That
is reflected by n between 0.5 and 1.0 [33,35]. The values
of (n) and (k) were calculated from the slope and the in-
tercept of the plot of lnF against lnt, respectively.
For AAm/AMPS hydrogels and AAm/AMPS/PEG
semi IPNs, lnF vs. lnt graphs are plotted and representa-
tive results are shown in Figure 5 and Figure 6. Diffu-
sional exponents, (n) and diffusion constant, (k) are cal-
culated and listed in Table 3.
Table 3 shows that the number determining the type
of diffusion (n) is over 0.50. Hence the diffusion of water
into the super water-retainer hydrogels is generally found
to have a non-Fickian character. When the diffusion type
is anomalous behavior, the relaxation and diffusion time
are of the same order of magnitude. As solvent diffuses
into the hydrogel, rearrangement of chains does not oc-
cur immediately.
The study of diffusion phenomena of water in hy-
drogels is of value in that it clarifies polymer behavior.
For hydrogel characterization, the diffusion coefficients
can be calculated by various methods. The diffusion co-
efficient, D of the water was calculated using the fol-
lowing equation [33,36,37].
1/
2
π 4
n
k
r
D


(4)
Here, D is in cm2 min–1, r is the radius of a cylindrical
polymer sample, (n) is the diffusional exponent and (k)
is a constant incorporating characteristic of the macro-
molecular network system and the penetrant. The values
of diffusion coefficient determined for AAm/AMPS
hydrogels and AAm/AMPS/PEG semi IPNs are listed in
Table 3. Table 3 shows that the values of the diffusion
coefficient of AAm/AMPS hydrogels and AAm/AMPS
/PEG semi IPNs vary from 0.11 × 10–3 cm2min–1 to
112.53 × 10–3 cm2 min–1. It was seen that an increasing
of the values of the diffusion coefficient of Aam /AMPS
hydrogels and AAm/AMPS/PEG semi IPNs by increas-
ing of AMPS content. Hydrophilicity of AAm/AMPS
hydrogels and AAm/AMPS/PEG semi IPNs becomes
greater than that of AAm, so, the diffusion of water of
AAm/AMPS hydrogels and AAm/AMPS/PEG semi
IPNs is greater than the diffusion of water of AAm hy-
drogels.
3.4. PEG Effect on the Swelling and Diffusion
For investigation of the effect of mass/content of PEG
on the swelling properties of AAm/AMPS/PEG semi
IPNs, the related swelling isotherms of AAm/AMPS
/PEG hydrogels were constructed and representative
swelling isotherms, and lnF vs. lnt graphs are plotted
and representative results are shown in Figure 7, Fig-
ure 8 and Figure 9. PEG effect on some swelling and
diffusion parameters of AAm/AMPS/PEG semi IPN
systems containing 180 mg AMPS are tabulated in Ta-
ble 4.
It was shown that a decreasing of the equilibrium
swelling percent (Seq%), and equilibrium water contents
(EWC/EUWC) of AAm/AMPS/PEG semi IPN systems
when PEG has been added to the hydrogel systems. In-
corporation of PEG into the copolymer network leads to
lower degrees of swelling. It was seen that diffusion of
water or urea/water mixture onto AAm/AMPS/PEG
semi IPN systems has shown “non-Fickian” character
from Table 4. Value of diffusion exponent of Aam
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Table 3. Some diffusion parameters of AAm/AMPS hydrogels and AAm/AMPS/PEG (containing 0.50 g PEG) semi IPNs systems.
water 0.01 M urea 0.03 M urea
AMPS / mg Diffusion exponent, (n)
0 0.59 0.60 0.66
60 0.81 0.78 0.80
120 0.82 0.97 0.88
180 0.91 0.93 0.88
240 0.90 0.90 0.90
300 0.92 0.93 0.89
AMPS / PEG mg
0 0.73 0.79 0.76
60 0.84 0.87 0.88
120 0.78 0.85 0.83
180 0.80 0.85 0.90
240 0.75 0.78 0.82
300 0.74 0.81 0.84
AMPS / mg Diffusion constant, (k x 103)
0 32.68 35.35 24.45
60 7.62 9.13 7.71
120 6.21 4.06 5.19
180 4.23 3.95 5.83
240 6.25 5.76 4.65
300 6.87 6.38 4.30
AMPS/PEG mg
0 31.65 23.12 26.92
60 15.54 12.79 16.68
120 16.22 15.88 17.40
180 17.60 14.21 12.40
240 21.08 19.04 16.66
300 19.56 18.63 20.94
AMPS / mg Diffusion coefficient, D x 103
0 3.42 0.11 0.17
60 16.58 0.63 0.59
120 20.50 1.45 0.93
180 47.00 1.18 1.36
240 78.84 1.40 1.40
300 112.53 1.74 1.31
AMPS / PEG mg
0 14.57 0.42 0.53
60 34.95 0.68 1.26
120 27.07 1.18 0.91
180 44.65 1.74 2.17
240 41.85 1.19 1.66
300 41.64 1.26 1.83
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0
1000
2000
3000
4000
5000
050010001500 200
0
t
(
mi n
)
S%
0.25 PEG
0.50 PEG
0.75 PEG
1.00 PEG
Figure 7. Effect of the content of PEG in swelling isotherms for AAm/AMPS/PEG hydrogels in aqueous
0.03 M urea solutions.
0
1000
2000
3000
4000
5000
0 60120180240300
AMPS/PEG contents (mg)
S
eq
%
Wa ter
0.01 M Urea
0.03 M Urea
Figure 8. Effect of the content of AMPS onto swelling of AAm/AMPS/PEG hydrogels in water, in aqueous
0.01 M urea solutions and in aqueous 0.03 M urea solutions.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1.52 2.53 3.54 4.55
ln t
0,25 PEG
0,50 PEG
0,75 PEG
1,00 PEG
ln F
Figure 9. Effect of the content of PEG in swelling kinetics curves for AAm/AMPS/PEG hydrogels in aque-
ous 0.03 M urea solutions.
Copyright © 2011 SciRes. JEAS
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Table 4. Some swelling and diffusion parameters of AAm/AMPS/PEG semi IPNs systems containing 180 mg AMPS.
PEG/g 0.25 0.50 0.75 1.00
Equilibrium percentage swelling, (Seq%)
water 3150 2650 2000 1500
0.01 M urea 4350 3250 2250 1750
0.03 M urea 4400 3250 2900 1800
Equilibrium water content, (EWC)/Equilibrium urea-water content, (EUWC)
water 0.9694 0.9639 0.9527 0.9370
0.01 M urea 0.9774 0.9703 0.9570 0.9432
0.03 M urea 0.9777 0.9700 0.9666 0.9469
Diffusion exponent, n
water 0.74 0.80 0.70 0.81
0.01 M urea 0.74 0.85 0.77 0.75
0.03 M urea 0.79 0.90 0.83 0.76
Diffusion constant, k × 103
water 19.56 17.60 29.77 25.09
0.01 M urea 16.59 14.21 20.06 19.73
0.03 M urea 14.96 12.40 18.21 25.46
Diffusion coefficient, D × 103
water 34.44 44.65 29.79 48.96
0.01 M urea 0.88 1.74 0.52 0.66
0.03 M urea 1.12 2.16 1.71 1.02
Table 5. Some adsorption parameters of AAm/AMPS hydrogels and AAm/AMPS/PEG (containing 0.5 g PEG) semi -IPNs
systems in aqueous solutions of 20.0 x 10-6 M LV solutions.
AMPS, mg 60 120 180 240 300
Dye removal capacity, q × 105 (mol g–1)
1.25 1.23 1.35 1.28 1.06
Adsorption percentage, Ads%
71.75 82.79 89.01 90.09 92.66
Partition coefficient, Kd
2.54 4.81 8.10 9.09 12.63
AMPS/PEG, mg 60 120 180 240 300
Dye removal capacity, q × 105 (mol g–1)
1.12 1.23 0.94 1.30 1.22
Adsorption percentage, Ads%
88.27 92.02 93.20 96.09 96.31
Partition coefficient, Kd
7.52 11.53 13.70 24.61 26.10
Table 6. PEG affects on some adsorption parameters of AAm/AMPS/PEG semi IPNs systems crosslinked by TMPTA con-
taining 180 mg AMPS in aqueous solutions of 20.0 x 10-6 M LV solutions.
PEG/g 0.25 0.50 0.75 1.00
Dye removal capacity, q × 105 (mol g-1)
1.08 0.94 1.00 0.94
Adsorption percentage, Ads%
90.30 93.20 93.84 94.70
Partition coefficient, Kd
9.31 13.70 15.24 17.87
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/AMPS/PEG semi IPN systems are between 0.70 - 0.90.
On the other hand, also, it is seen that an increasing of
diffusion constant (k) of AAm/AMPS/PEG hydrogels
with increasing content of PEG in hydrogel systems from
Table 4. Here, it was said that PEG chains was placed in
the crosslinked polymeric systems, in stead of cross-
linked AAm and AMPS molecules, it was seen that de-
creasing of the value of the equilibrium swelling percent
and related parameters, because of decreasing of hydro-
philic character at crosslinked polymeric systems. In ad-
dition of this phenomenon, the PEG chains are located in
the free space of crosslinked polymer networks; water
diffusion is prevented by the PEG chains. This is also
caused of decreasing of the equilibrium swelling percent
and related parameters.
3.5. Equilibrium Sorption Studies
For sorption of cationic dye, Lauths violet (LV) into the
hydrogels, AAm/AMPS hydrogels and AAm/AMPS/PEG
semi IPNs were placed in aqueous LV solutions and al-
lowed to equilibrate for four days at 25˚C. At the end of
this period AAm/AMPS hydrogels and AAm/AMPS
/PEG semi IPNs in aqueous LV solutions showed the
dark coloration. But acrylamide hydrogel did not sorb
any dye from solution.
For equilibrium sorption studies, the dye removal ca-
pacity (q) (mass amount as “mol” of sorption per unit
mass (as gram)) of the adsorbent, adsorption percentage
(Ads%), and partition coefficient (Kd) can be investi-
gated.
The dye removal capacity, (q) of AAm/AMPS hy-
drogels and AAm/AMPS/PEG semi IPNs were evaluated
by using the following equation.
(oCCv
qm
)
(5)
Where q, is the dye removal capacity of AAm/AMPS
hydrogels and AAm/AMPS/PEG semi IPNs (mol g–1),
Co and C are the concentration of aqueous LV solutions
in the initial solution and the aqueous phase after treat-
ment for a certain period time, respectively (mol L–1), v
is the volume of the aqueous phase (L) and m is the
amount of dry AAm/AMPS hydrogels and AAm
/AMPS/PEG semi IPNs (g).
Uptake of dye was measured effects of contents of
AMPS. The dye removal capacity, the amount of dyes
sorbed onto unit dry mass of the gel was calculated for
uptake of dye within the hydrogel in 20.0 x 10–6 mol LV
in L of aqueous solutions, and presented in Table 5. Ta-
ble 5 presents that the dye removal capacity of Aam
/AMPS hydrogels and AAm/AMPS/PEG semi IPNs
(0.94 x 10–5 – 1.35 x 10–5 mol g–1).
Equilibrium LV adsorption isotherm of AAm/AMPS
hydrogels and AAm/AMPS/PEG semi IPNs is pre-
sented in Figure 10 and Figure 11. To Figure 10 and
Figure 11, the dye removal capacity (mol amount of
sorption LV per unit mass) of the hydrogels is increased
with the increasing concentration LV sorbed onto unit
dry mass of the gel, q of the hydrogels increased with
PEG in the copolymers. The reason of this is the hydro-
philic effect and dye sorption capability of PEG.
Adsorption percentage (Ads%) of AAm/AMPS hy-
drogels and AAm/AMPS/PEG semi IPNs was calcu-
lated by following equation.
%
o
o
CC
Ads C
100
(6)
Here Co and C were defined earlier.
Table 5 presents that adsorption percentage of them
(71.75% - 96.31%) is increased with increased with the
increasing of content of AMPS. The dye removal capac-
ity and adsorption percentage of AAm/AMPS hydrogels
and AAm/AMPS/PEG semi IPNs gradually increased
with the increase of content of AMPS in hydrogels and
semi IPNs.
Partitioning of dissolved constituents between an
aqueous phase and adsorbents in waters and sediments
has commonly been described by an empirical partition
coefficient that simply relates the total concentration of
a dissolved species to the total concentration of the ad-
sorbed species [38,39].
()o
dCC
KC
(7)
Here; Kd is empirical partition coefficient at equilib-
rium. Co and C were defined earlier. Partition coeffi-
cients of LV between dye solution and hydrogels were
calculated, and are shown in Table 5. In Table 5, Kd
values of AAm/AMPS hydrogels is 2.54 - 12.63, but Kd
values of AAm/AMPS/PEG semi IPNs is 7.52 - 26.10
with the incorporation of PEG groups into the hydrogels.
Here, Kd values of AAm/AMPS hydrogels and Aam
/AMPS/PEG semi IPNs are higher than 1.0. So, it can
be said that synthesized crosslinked AAm/AMPS hy-
drogels and AAm/AMPS/PEG semi IPNs could be used
as potential water adsorbent [38,39].
The ionic charge content in the polymeric structure is
important. AMPS contain ionic units. The swelling de-
grees of the hydrogels increase due to increasing of the
hydrophilic units on hydrogel structure (Figure 1).
Therefore AAm/AMPS hydrogels and AAm/AMPS
/PEG semi IPNs have many ionic groups that can in-
crease interaction between the cationic dye molecules
and anionic groups of hydrogels. The results of swelling
studies are parallel character to the results of sorption
Copyright © 2011 SciRes. JEAS
S. KUNDAKCI
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0.
0
2.
0
4.
0
6
.
0
8.
0
10. 0
12. 0
14.
0
0.
5
1.
0
1. 5 2.0 2.5 3.0 3.
5
C
×
10
6
180 AMPS
q×106
Figure 10. Equilibrium sorption isotherms of AAm/AMPS hydrogels in aqueous LV solutions.
0
.
0
2
.
0
4
.
0
6.
0
8.
0
10.
0
0
.
7
1.
2
1.7 2.2 2.7 3.2 3.
7
C×10
6
q×10
6
180 AMPS/PEG
Figure 11. Equilibrium sorption isotherms of AAm/AMPS/PEG hydrogels in aqueous LV solutions.
studies. Both of them, it can be seen that swelling or
sorption capability of AAm/AMPS hydrogels and Aam
/AMPS/PEG semi IPNs are increased with increasing
AMPS content in copolymeric structure. The most im-
portant effect is hydrophilicity of copolymeric gels. Hy-
drophilicity of AAm/AMPS and AAm/AMPSA/PEG co-
polymers becomes greater than that of AAm, when addi-
tion of AMPS to the copolymeric structure.
There can be many reasons for non-covalent interac-
tions in the binding of LV by AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs. The main interactions be-
tween the hydrogel and the monovalent cationic dye may
be hydrophobic and hydrogen bonding. Specially, hy-
drogen bonding will be expected to occur between amine
groups and nitrogen atoms on the dye molecules and the
amine and carbonyl groups on the monomer unit of
crosslinked polymer. Hydrophobic effects are especially
aqueous solutions interactions which in the present case
will involve those aromatic rings on the dye molecules
and the methine and methyl groups on the gel. There
can be some other interactions such as dipole-dipole and
dipole-induced dipole interactions between the dye
molecules and the hydrogel chains.
3.6. PEG Effect on the Sorption of LV
For investigation of the effect of mass/content of PEG
on the sorption properties of AAm/AMPS/PEG semi
IPNs, some sorption parameters such as dye removal
capacity, adsorption percentage and partition coefficient
of AAm/AMPS/PEG semi IPN systems containing 180
mg AMPS are tabulated in Table 6.
It was shown that a increasing of adsorption percent-
age (90.30% - 94.70%) and partition coefficient (9.31 -
17.87) of AAm/AMPS/PEG semi IPN systems when
PEG has been added to the hydrogel systems. Incorpo-
Copyright © 2011 SciRes. JEAS
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ration of PEG into the copolymer network leads to higher
values of adsorption percentage and partition coefficient
of AAm/AMPS/PEG semi IPN systems. Here, Kd values
of AAm/AMPS/PEG semi IPNs are higher than 1.0. So,
it can be said that synthesized crosslinked AAm/AMPS
/PEG semi IPNs could be used as potential water adsorb-
ent [38,39]. On the other hand, it can be said that there is
no important chancing of the dye removal capacity of
AAm/AMPS/PEG semi IPN systems when PEG has
been added to the hydrogel systems (0.94 × 10–5 – 1.08 ×
10–5 mol g–1). Here, it was said that PEG chains was
placed in the crosslinked polymeric systems, in stead of
crosslinked AAm and AMPS molecules, it was seen that
increasing of the adsorption percentage, because of in-
creasing of hydrophilic character at crosslinked poly-
meric systems.
4. Conclusion
Incorporation of hydrophilic group containing chemicals
such as AMPS and a polymer such as PEG in AAm hy-
drogels can be obtained successively by free radical solu-
tion polymerization method. Multifunctional cros-
slinker such as TMPTA used at the polymerization proc-
ess. AAm/AMPS hydrogels and AAm/AMPS/ PEG semi
IPNs showed high water absorbency. The equilibrium
percentage swelling ranges are 900% - 13450% for
AAm/AMPS hydrogels and 500% - 4400% for AAm
/AMPS/PEG semi IPNs. It was seen that swelling of
AAm/AMPS hydrogels and AAm/AMPS/ PEG semi
IPNs increased with the increasing of content of AMPS.
But, it was seen that a decreasing of values of Seq%
from 3150% to 1500% when the adding of PEG for con-
taining of 180 mg of AMPS. It was seen that swelling
values of AAm/AMPS hydrogels and AAm/AMPS/PEG
semi IPNs with increasing in aqueous 0.01 M/0.03 M
urea solutions. Also, it was seen that a increasing of val-
ues of Seq% from 3150% (for water) to 4350% - 4440%
when the adding of PEG for containing of 180 mg of
AMPS. Here, again, the main effect is the hydrophilic
character of AMPS and urea molecules.
The present work has given the quantitative inform-
ation on the sorption characteristic of LV with AAm
/AMPS hydrogels and AAm/AMPS/PEG semi IPNs. In
this study, it has shown that AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs have sorbed the monova-
lent cationic dyes such as LV, while AAm do not. The
amount of LV sorbed onto unit dry mass of the gel is in-
creased with the content of AMPS. The values of adsorp-
tion percentage (Ads%) for LV of AAm/AMPS hy-
drogels and AAm/AMPS/PEG semi IPNs are changed
among 71.75% - 96.31%. Here, all Kd value of AAm
/AMPS hydrogels and AAm/AMPS/PEG semi IPNs is
higher than 1.0. So, it can be said that synthesized
crosslinked AAm/AMPS hydrogels and AAm/AMPS
/PEG semi IPNs could be used as potential highly water
adsorbent. Consequently, AAm/AMPS hydrogels and
AAm/AMPS/PEG semi IPNs developed in this study
may serve as a potential device for water and dye sor-
bent. The utilization of these types of materials, in
pharmaceuticals, agriculture, biotechnology, environ-
ment, separation, purification and immobilization
makes hydrogels more popular.
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