Synthesis and micellization properties of new anionic reactive surfactants based on hydrogenated cardanol

Article abstract of DOI:10.1007/s11743-011-1294-z

We report the synthesis, characterization and micellization properties of two anionic reactive surfactants based on 3-pentadecyl phenol obtainable from a renewable resource, cardanol. The synthesis is achieved through simple chemical transformations, first converting the phenol to the acrylate that is sulfonated in a second step. The products were characterized by elemental analysis and spectroscopic techniques. The surfactant properties of the sulfonated acrylates were measured and compared with the standard non-reactive anionic surfactant sodium dodecyl sulfonate. The micellization behavior of aqueous solutions was studied using conductivity, surface tension measurements, and the fluorescence probe technique based on diphenyl hexatriene. Characterization by surface tension measurements facilitated the determination of basic surfactant properties like the critical micelle concentration (CMC), the surface tension at the CMC, surface excess and area per surfactant molecule. The Gibbs free energy of micellization showed a negative value suggesting spontaneous micellization in aqueous solution. The micellization of the surfmer with an ethylene spacer between the phenyl ring and the acrylate group seems to be enhanced as indicated by the lower surface excess and lower free energy. Its CMC was also lower. AOCS 2011.

Full text of DOI:10.1007/s11743-011-1294-z

J Surfact Deterg (2012) 15:207–215
DOI 10.1007/s11743-011-1294-z
ORIGINAL ARTICLE
Synthesis and Micellization Properties of New Anionic Reactive
Surfactants Based on Hydrogenated Cardanol
•
Suresh Kattimuttathu I Gesche Foerst
•
•
Rolf Schubert Eckhard Bartsch
Received: 23 May 2011 / Accepted: 30 July 2011 / Published online: 22 November 2011
Ó AOCS 2011
Abstract We report the synthesis, characterization and
micellization properties of two anionic reactive surfactants
based on 3-pentadecyl phenol obtainable from a renewable
resource, cardanol. The synthesis is achieved through
simple chemical transformations, first converting the phe-
nol to the acrylate that is sulfonated in a second step. The
products were characterized by elemental analysis and
spectroscopic techniques. The surfactant properties of the
sulfonated acrylates were measured and compared with the
standard non-reactive anionic surfactant sodium dodecyl
sulfonate. The micellization behavior of aqueous solutions
was studied using conductivity, surface tension measure-
ments, and the fluorescence probe technique based on
diphenyl hexatriene. Characterization by surface tension
measurements facilitated the determination of basic sur-
factant properties like the critical micelle concentration
(CMC), the surface tension at the CMC, surface excess and
area per surfactant molecule. The Gibbs free energy of
micellization showed a negative value suggesting sponta-
neous micellization in aqueous solution. The micellization
of the surfmer with an ethylene spacer between the phenyl
ring and the acrylate group seems to be enhanced as
indicated by the lower surface excess and lower free
energy. Its CMC was also lower.
Keywords Cardanol ꢀ Reactive surfactant ꢀ Critical
micelle concentration ꢀ Fluorimetry ꢀ Conductance
Introduction
Cashew Nut Shell Liquid (CNSL), a byproduct of the
cashew processing industry, has received the attention of
researchers worldwide as a sustainable raw material for the
development of fine chemicals. Cardanol and anacardic
acid (10 and 63%, respectively) are the major phenolic
constituents present in natural cashew nut shell oil (Ana-
cardium occidentale sp.-natural CNSL) [1, 2]. The main
constituent of technical grade cashew nut shell liquid
obtained by distillation of natural CNSL is cardanol [2, 3].
It has served as a valuable raw material in the synthesis of
many fine chemicals and monomers for polymer synthesis
[4, 5]. The alkyl chain in the m-position of cardanol makes
it a valuable starting material for the synthesis of surfac-
tants and plasticizers for the polymer industry. The side
chain also carries unsaturation that can be derivatized to
make thermal or photo curable resins [6]. It comprises 41%
of the triene (2-hydroxy-6-pentadeca-8,11,14-trienyl ben-
zoic acid) and 3-pentadeca-8,11,14-trienyl phenol), while
22% are the diene, 34% monoene and the remaining
saturated. Cardanol has been used in many industrial
applications such as paints and varnishes [7], phenol–
formaldehyde resins [8, 9], surface active polymers [10]
and others [11, 12]. Because of their renewable nature and
structural characteristics, anacardic acid and cardanol are
likely candidates for preparing ‘‘green’’ surfactant species
like sulfonates, ethoxylates and cardanol-formaldehyde
S. Kattimuttathu I ꢀ E. Bartsch
Institute for Macromolecular Chemistry,
Stefan-Meier-Straße 31, 79104 Freiburg, Germany
S. Kattimuttathu I (&)
Organic Coatings and Polymers Division,
Indian Institute of Chemical Technology,
Uppal Road, Tarnaka, Hyderabad 500 007, India
e-mail: kisuresh@iict.res.in
G. Foerst ꢀ R. Schubert
Department of Pharmaceutical Technology,
University of Freiburg, Hermann-Herder-Straße 9,
79104 Freiburg, Germany
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J Surfact Deterg (2012) 15:207–215
ethoxylate polymers [13, 14] to replace the petroleum
based nonyl phenol surfactants. They have also been used
in semi-synthetic processes to prepare derivatives with
biological and pharmaceutical applications [15].
further purification. The solvents diethyl ether, chloroeth-
anol, toluene, ethyl acetate, dichloromethane, triethyl
amine were commercial grade (S.D. Fine Chem, Mumbai)
and distilled before use. The product obtained after each
step was characterized by IR, 1H, 13C-NMR and elemental
analysis. The NMR analysis was carried out on a Bruker
400 MHz machine and an EL Vario instrument was used
for elemental analysis. Two surfmers synthesized were
designated as S1 and S2. The synthesis of the surfmer was
carried out using a two step procedure as outlined below.
Cardanol and its saturated analogue, 3-pentadecyl phenol
has been earlier studied for its surface activity and biode-
gradability characteristics by Tymann and Bruce [13]. They
found that cardanol and cardol polyethoxylates derived from
technical cashew nut shell liquid are potential replacement
for synthetic nonyl phenol based surfactants. Scorzza et al.
[16] carboxylated the main phenolic components of cashew
nut shell oil, cardanol and anacardic acids, and tested them
as anionic surfactants. It was observed that these derivatives
lower the surface tension, exhibit a critical micelle concen-
tration, and useful in the preparation of microemulsions
in mixtures with conventional dodecyl sulfate surfactant.
In another work, Dantas et al. [17] reported the synthesis of
2,4-sodium disulfonate-5-n-pentadecylphenol) and studied
the effect of temperature and electrolyte concentration on
micellization of aqueous solutions. The CMC decreased
with increasing electrolyte concentration and temperature. In
terms of biodegradability it was found that the saturated
analogue of cardanol polyethoxylate degraded to the maxi-
mum in comparison to the unsaturated component. The
synthetic t-nonylphenyl polyethoxylate remained substan-
tially undegraded (77%), whereas glucose was almost
completely degraded (5%) [14].
Synthesis of the Acrylate Surfmer (S1)
Step I. Synthesis of 3-pentadecyl phenyl acrylate: The
reaction steps used are summarized in Scheme 1. In the
first step the acrylate was prepared from pentadecyl phenol
[5, 6], followed by its sulfonation and neutralization. In a
typical experiment, a two-necked round-bottom flask fitted
with a mechanical stirrer and dropping funnel was charged
with 15 g (0.05 mol) of 3-pentadecyl phenol, dissolved in
25 mL of toluene along with an equimolar concentration of
triethyl amine (7 mL). The flask was kept in an ice bath,
and the temperature maintained at 0–5 °C. The contents of
the flask were kept stirring and 5 mL (0.05 mol) of acry-
loyl chloride was added through dropping funnel. The
reaction was run for 12 h and the product washed with
excess water till the washings were neutral to litmus.
Finally, the product was extracted into diethyl ether, dried
over anhydrous sodium sulfate and the solvent evaporated.
The isolated product was further purified by passing
through a basic alumina column, to remove traces of
phenol using toluene as the eluent. Yield 87%.
The synthesis of reactive surfactants (surfmers) based on
3-pentadecyl phenol (hydrogenated cardanol) has not been
reported, to the best of our knowledge. The reactive surfac-
tants (surfmers), unlike conventional non-reactive surfac-
tants, take part in the polymerization with the main monomer
and forms part of the polymer chain. Today, the reactive
surfactants are important additives for emulsion polymers
useful in protective coatings and adhesives, because they
improve the product properties [18, 19]. In this paper the
synthesis and basic surfactant properties of two anionic
surfmers based on 3-pentadecyl phenol are reported. Apart
from structural characterization of the synthesized surfmers
techniques like surface tension measurement, conductivity
and fluorescence probe method were used to measure the
aqueous solution characteristics and CMC behavior of the
synthesized surfactants. The probable micellization mecha-
nism was inferred from the fluorescence probe method.
Step II. Synthesis of sulfonated 3-pentadecyl phenyl
acrylate: The acrylate prepared in the first step was reacted
with chlorosulfonic acid in a 1:1 mol ratio. Typically, 8 g
(0.022 mol) of 3-pentadecyl phenyl acrylate dissolved in
10 mL of dichloromethane was put into a round-bottom flask
and stirred for 15 min to obtain a well mixed solution. To this
solution 2.6 g (0.022 mol) of chlorosulfonic acid, dissolved
in 5 mL of dichloromethane was added drop wise. The
reaction continued for 4 h at room temperature. The product
obtained was neutralized with 10% Na2CO3 solution. The
final product, sulfonated pentadecyl phenyl acrylate (II), was
recovered by freeze-drying process. Yield 65%. Composi-
tion: C21H39SO4; C: obs. 64.9%, calc. 65.1%; H: obs. 10.0%,
calc. 10.07%; S: obs. 8.3%, calc. 8.2%.
Experimental
Synthesis of Acrylate Surfmer (S2)
Materials and Methods
The acrylate surfmer S2 was prepared through the fol-
lowing steps:
3-pentadecyl phenol, acrylic acid, chlorosulfonic acid,
sodium carbonate, chloroethanol and 1,6-diphenyl-1,3,5-
hexatriene were purchased from Aldrich and used without
Step I. Preparation of 3-Pentadecyl (x-hydroxyethoxy)
benzene: The synthetic steps are summarized in Scheme 2.
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J Surfact Deterg (2012) 15:207–215
209
rotoevaporator. The purified product was used in the sec-
ond step to prepare the sulfonated acrylate. For sulfonation,
3 g of pentadecyl (x-hydroxy ethoxy) benzene acrylate
was taken in a round-bottom flask and dissolved in 10 mL
of toluene. The solution was stirred for 15 min to obtain a
well mixed solution. Then, an equimolar amount of (0.8 g)
chloro-sulfonic acid, diluted with 5 mL toluene was added
drop-wise. The reaction was continued for 4 h at room
temperature under stirring. The product was neutralized
with 10% sodium carbonate solution. The neutralized
compound (III, c.f. Scheme 2) was concentrated by using
the freeze-drying process. Product (S2, Scheme 2) yield
was 65%. Composition: C26H41SO6Na; C: obs. 61.85%,
calc. 61.88%; H: obs. 8.08%, calc. 8.11%; S: obs. 6.30%,
calc. 6.35%.
Scheme 1 Schematic of the reactions used for the synthesis of
surfmers S1 starting from 3-pentadecyl phenol
Critical Micelle Concentration (CMC) Measurements
To assess the surfactant properties and CMC of the syn-
thesized surfmers different method were used as outlined
below.
In the first step a three-neck round-bottom flask fitted with
a mechanical stirrer and water condenser was charged with
15 g of hydrogenated cardanol dissolved in 10 mL of
ethanol. The flask was kept in an oil bath and the tem-
perature maintained at 70 °C. To this equimolar amount of
NaOH dissolved in water was added slowly along with
50 mg of sodium iodide through a dropping funnel. Finally,
equimolar amount of 2-chloroethanol was added, main-
taining the reaction temperature. The reaction was contin-
ued for 24 h to achieve maximum conversion.
Fluorescence Method
The fluorescence measurements were performed at 25 °C
using a Perkin Elmer LS 5B luminescence spectrometer in
the single read mode. A stock solution of the fluorescent
probe DPH was prepared in THF at a concentration
0.005 mM. To exclude solvent effects 20 lL of this stock
solution is pipetted with a Hamilton syringe into a spike test
tube and solvent was evaporated. Then 1 mL of Millipore
water is added and the sample is dispersed with a spike and
again diluted with de-ionized water so as to achieve a con-
centration of 16.7 lM. From this solution a constant volume
of DPH was added to all the sample tubes containing the
surfmer and filled up to a fixed volume of 3.0 mL.
The reaction product was washed with water to remove
water soluble impurities and then extracted into tetrahy-
drofuran. The product was dried over anhydrous sodium
sulfate and the solvent evaporated on a rotoevaporator. The
residue was further purified by preparative column chro-
matography on a basic alumina column using toluene as the
eluent. The product (I) yield was 86%.
Step II. Preparation of 3-pentadecyl (x-hydroxyalkoxy)
benzene acrylate: In this reaction 3-pentadecyl (x-
hydroxyalkoxy) benzene and acrylic acid were reacted in a
1:1 mol ratio. A two-neck round-bottom flask fitted with
Dean–Stark trap and stirrer, containing 7.5 g of 3-penta-
decyl (x-hydroxy ethoxy) benzene dissolved in 10 mL of
toluene was charged with 50 mg of hydroquinone, 1 g of p-
toluene sulfonic acid (PTSA). The flask was kept in an oil
bath under reflux conditions. To this solution 1:1 ratio of
acrylic acid was added using an addition funnel, and the
water that evolved during the reaction was removed from
the Dean–Stark trap. The reaction was continued for about
6 h. The reaction product was washed with water and
extracted in tetrahydrofuran.
The solutions, while protected from light, were allowed
to stand overnight and equilibrated in a water bath at 25 °C
for 1 h before measurements. A plot of measured intensity
versus conc. of solute was made. From the intersection
points, the CMC was calculated.
Tensiometry
The surface tension measurements were carried out on a
Kru¨ss K-100 Tensiometer in plate mode according to
ASTM D-1331 56. An aqueous solution of the surfmer was
prepared at a concentration of 0.5 wt%.
Conductivity Measurements
The product was further purified on a 60–120 mesh
silica gel column using toluene and ethyl acetate. The
different fractions were collected and concentrated on a
For conductivity measurements aqueous solutions were
prepared at different dilutions and the conductivity was
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Scheme 2 Schematic of the
Reactions used for the synthesis
of surfmers S2 starting from
3-pentadecyl phenol
measured after successive dilution of the samples starting
with a concentration of 0.5 mg/mL. The electrolytic con-
ductivity of the solutions was directly measured using a
WTW conductometer. To control the temperature within
0.1 °C, a water thermostated Haake NK22 water bath was
used.
are given in Table 1. The characteristic peaks in IR, 1H- and
13C-NMR of hydrogenated cardanol and the final products
S1 and S2 are tabulated in Table 1. The formation of S1 is
confirmed by characteristic bands due to the acrylate group
at 1,745 cm-1 of the ester carbonyl and at 1,194 and
1,160 cm-1 due to SO3 stretch. The corresponding peaks
1
due to acrylate protons appear at 5.94–6.62 ppm in H-
NMR and in 13C-NMR spectra and the additional peak due
to the carbonyl carbon appears at 162.98 ppm. Similarly,
for S2 the IR spectrum shows bands at 1,728 cm-1 and S=O
stretch at 1,150–1,200 cm-1. The spectral data in combi-
nation with the elemental analysis results support the
assigned structure of S1 and S2. However, it must be noted
that some ortho isomer will be formed in this type of
reaction and no attempt was made to separate the different
isomers in the present work. The presence of the different
isomers may also influence the micellization of the surf-
mers. For simplicity of analysis and interpretation the
structure of the para isomer is shown in Table 1. As seen
Results and Discussion
Surfmer Synthesis and Characterization
In this work, we report the synthesis of two novel anionic
reactive surfactants starting from 3-pentadecyl phenol
(hydrogenated cardanol). The synthesized surfmers were
labelled as S1 and S2 (cf. Schemes 1, 2). The structural
characterization of the synthesized surfmer was carried out
using spectroscopic techniques. Important spectral charac-
teristics along with the structure of the synthesized surfmers
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211
Table 1 Reaction yield and spectroscopic data of the products
1
Compound
Yield (%)
65
Chemical shifts H, 13C (d, ppm)
IR (cm-1
)
1H = 0.8 (t, CH3), 1.25 (m, CH2), 1.61
(–CH2–CH2–Ar), 2.60 (–CH2–Ar),
5.94–6.62 (m, –CH2, m, –CH of
acrylate), 6.91–7.24 (m, arom).
7.94–8.17 ppm
1,745 cm-1 carbonyl stretch
2,925; 2,853 cm-1. Aliphatic C–H
stretch, 1,226 cm-1, 1,194 cm-1 and
1,160 cm-1 SO3 stretch
O
O
13C: 162.98, 153.63 (phenolic, carbonyl)
139–127.33 (alkene, aroma) 14–36
(aliphatic)
C15H31
NaO3S
O
S1
82
0.927, t, CH3; 1.292, m, CH2; 1.614, m,
CH2CH2Ar; 2.55, m, CH2–Ar; 4.21,
m–CH2–OCOR; 5.8–6.3, m, acrylate;
6.40–7.30, m, aroma
3,000–3,100 cm-1 arom-C–H
2,800–3,000 cm-1 aliph. C–H stretch
1,728 cm-1 ester C=O stretch
O
O
1,590 cm-1, 1,459–1,485 cm-1 C=C ring
1,370 cm-1 C–H bend,
1,150–1,200 cm-1, S=O stretch
13C: 162.98, 153.63 (phenolic, carbonyl);
139–127.33 (alkene, aromatic); 62,69
–CH2CH2–; 14–36 (aliphatic)
C15H31
NaO3S
S2
–
0.8 (t, CH3), 1.25 (m, CH2),
1.61(–CH2–CH2–Ar), 2.60 (–CH2–Ar)
O—H stretch, 3350; C—H stretch, arom,
3010; C—H stretch, meth 2930, 2830;
C==C ring stretch, arom
a
OH
6.91–7.24 (m, arom)
13C: 14–36, m, aliphatic C; 112–145, m,
aromatic; 155, s, phenolic carbon
1590, 1450. C–O; stretch, 1150
C–H bend, methylene, 780, 700
C15H31
SO3Na
a
Values taken from Ref. [20]
from Table 1, the main difference between these surfmers is
that in S2, there is an ethylene spacer between the poly-
merizable acrylate group and the phenolic ring. This is
expected to influence the reactivity of the acrylate group
and hence its incorporation efficiency during emulsion
polymerization [18]. It is anticipated that S1 reactivity will
be higher than that of S2, because the acrylate group is
conjugated to the electron withdrawing effect of the sulfo-
nate group and phenolic nuclei [20]. The reactivity of S2
may be comparable to that of ordinary acrylates, as the
acrylate group is isolated from the electron withdrawing
effect of phenolic ring and sulfonate group.
In analogy to the micellization phenomena of conven-
tional surfactants it may be assumed that very dilute sur-
factant solutions contain only monomeric surfactant
molecules [17]. As the concentration is increased, a point
reached at which the individual surfactant molecules start
to aggregate and form micelle structures called CMC. The
CMC of the developed surfactant was obtained in water as
0.5% w/v solutions using the Wilhelmy plate method.
Here, the relative surface tension of water is measured
continuously as the surfactant solution is added in small
increments. The reduction in surface tension as a function
of surfmer S1 concentration is presented in Fig. 1.
As shown in Fig. 1 the surface tension starts to decrease
and once the CMC is reached the value levels off. From the
plot of surface tension versus concentration of added sur-
factant, the CMC is calculated as the intercept of the two
straight lines (c.f. Fig. 1). This plot shows that the acrylate
surfmer based on hydrogenated cardanol exhibit a reduction
in surface tension with a low CMC value reported in the
literature [20] for other derivatives. For example, 0.5% w/v
solution of cardanol sulfonate was reported to possess a
surface tension of 32.25 mN/m with a CMC value of
0.372 mol/L. In the present work we obtained surface ten-
sion value of 35.52 mN/m for S1 with a corresponding
CMC value of 40.11 mg/L (8.7 9 10-5 mol/L). The surf-
mer S2 showed a lower value of 31.61 mN/m for the surface
tension and a CMC value of 8.8 mg/L (1.7 9 10-5 mol/L)
Critical Micelle Concentration (CMC) Measurements
The surfactant properties may be assessed in various ways.
The CMC determination is generally based on localization
of the position of a break in concentration dependence of a
selected physical or chemical property of the surfactant
solution. The reduction in surface tension of water by
dilute solution of the reactive surfmer was used in this
study to determine the optimal efficiency. The study of
surfactant properties of aqueous solutions are important
because the performance of the surfactant in many indus-
trial processes like enhanced oil recovery as corrosion
inhibitors depend on its concentration and orientation at the
interface.
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and a surface area per molecule 25.13°A2. All other
parameters obtained for S1 & S2 are tabulated in Table 2.
The surfmer samples exhibit, a constant high surface
tension region at low concentrations followed by a
decreasing surface tension with increasing concentration.
Ionic surfactants in general show a decrease in CMC value
with any factor, like addition of salt or increase of tem-
perature by which the interactions between the charged
hydrophilic groups are weakened, and micelle formation is
favoured [20]. A surfactant with sulfonate groups in the
ortho position with respect to the alkyl chain exhibit higher
surface tension and solubility in water.
The Gibbs free energy of micelle formation is another
parameter that can be calculated from the CMC value. The
appropriate relation depends upon the nature of the sur-
factant. Ionic surfactants are represented as dissociated
molecules in solution but not completely and necessarily at
the surface or in the form of micelles. The observed surface
tension is low and CMC lower when compared with
commercial surfactant like SDS (2.8 g/L). As shown by
earlier researchers this may be attributed to the fact that a
surfactant with the sulfonate group in the ortho position
with respect to the alkyl chain had lower optimal salinity,
higher surface tension and lower solubility in water than
surfactants with the sulfonate group in the para or meta
position [21, 22].
Analyzing the free energy of micellization of S1 and S2
(cf. Table 2), based on CMC data it may be concluded that
the micellization process was spontaneous as indicated by
the negative value of DmicG (DmicG \ 0) for both surfmers.
Fig. 1 Typical plot showing the variation in surface tension of
surfmer S1 measured using the Wilhelmy plate method (For actual
values refer to Table 2)
Table 2 Physico-chemical properties of the prepared reactive surfactants (surfmers)
Compound
Surface tension
at CMC (mN/m)
CMC (mol L-1), method
Surface area per
molecule am (°A2)
DGmax
kJ/mol
Tensiometry
Conductivity
Fluorescence
35.52
8.7 9 10-5
(40.11 mg/L)
7.2 9 10-6
(3.32 mg/L)
9.76 9 10-5
(44.9 mg/L)
16.39
-33.4
O
O
C15H31
NaO3S
O
S1
31.61
32.25
1.7 9 10-5
(8.8 mg/L)
2.89 9 10-5
(14.3 mg/L)
3.81 9 10-7
(0.188 mg/L)
25.13
-37.11
O
O
C15H31
NaO3S
S2
0.37
–
–
–
–
a
OH
C15H31
SO3Na
SDS-area per surfactant molecule = 5.4 9 10-19 m2 (5.4°A2)
Values taken from Ref. [20]
a
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213
The fact that the value is larger for S1 indicates that here
the sulfonate group is preferably in the o-position of the
alkyl group.
long chain (15 C atoms) makes the formation of monolayer
difficult [16].
Fluorimetry
Adsorption Behavior
To supplement the micellization behavior of the studied
surfmer and to determine the critical micelle concentration
another commonly used fluorescence probe method
employing 1,6-diphenyl-3,5,6-hexatriene (DPH) as probe
molecule was used. It has already been shown to be useful
to investigate the micellization of Pluronics [26] and var-
ious other surfactants [27]. The hydrophobic DPH exhibits
negligible fluorescence in hydrophilic environment,
whereas it is highly fluorescent in hydrophobic compart-
ments. A rise in fluorescence intensity upon increasing the
surfmer concentration indicates solubilization of the probe
in the formed micelles. Since fluorescence intensity of
DPH is known to be temperature sensitive [23], all mea-
surements were carried out at 25 °C. The CMC was
determined as the point of intersection of two extrapolated
straight lines when plotting the fluorescence intensity
against the log concentration of the surfactant. A typical
plot obtained for surfmer S1 using the fluorescence probe
method is shown in Fig. 2.
The relationship between surface adsorption and surfactant
concentration in solution for an anionic surfactant is
expressed on the basis of the Frumkin adsorption equation
[17, 23].
C
KFC expðꢁAhÞ
U ¼
¼
;
C
max;F 1 þ KFC expðꢁAhÞ
where C is the surface excess and h is the surface layer
coverage, KF is the adsorption equilibrium constant and
A is the parameter accounting for lateral interaction. The
Frumkin equation is reduced to the Langmuir equation for
A = 0. If A [ 0, a decrease in the effective adsorption
constant occurs that is caused by the repulsive interactions
between the adsorbed surfactant monolayer and the mole-
cules into the bulk solution. When A \ 0, there is high
compatibility between the bulk solution and the adsorbed
monolayer. The affinity for micelle formation of these
surfmers is also indicated by the negative surface excess
values.
It can be seen from Table 2 that the values obtained are
comparable to that of phenolic lipids reported in the liter-
ature. The phenolic lipids are reported to have very low
CMC values about 0.5–5 lM [15], quite comparable to the
value obtained in the present work. Another feature of the
studied system, seen from Fig. 2, is that the fluorescence
intensity decreases with decreasing concentration but never
becomes a constant or zero as reported earlier for other
systems [26]. This could be because very diluted surfactant
solutions contain only monomeric surfactant molecules and
The difference in surface excess of S1 and S2 is further
indicative of a change in micellar structure [17]. For S2
surface excess was 6.61 9 10-12 mol/mm2 as compared to
1.01 9 10-11 mol/mm2 for S1, i.e. a reduction in surface
excess on going from S1 to S2. This also suggests a change
in micelle formation. Dantas et al. [17] while studying
micellization of 2,4-sodium disulfonate-5-n-pentadecyl-
phenol have observed a similar effect on the addition of
electrolyte. The micellar structure of aqueous solutions of
phenolic lipids has been widely studied [24] and it was
suggested that they can form spherical, cylindrical or
lamellar shaped micelles, the fact directly dependent on the
geometry of the monomeric units and their molecular
environment. According to Rosen and Dhanayake [25] the
cross sectional area occupied by the hydrophilic group at
the interface often varies with the molecular environment
like pH, ionic strength, temperature, concentration of sur-
factant, temperature etc. For example, in ionic surfactants,
the cross sectional area decreases with increasing surfac-
tant concentration or temp or ionic strength allowing
formation of more complex structures.
In the light of earlier studies on cardanol based surfac-
tants and the reduced surface excess of S2 when compared
with S1 in water we assume lateral interaction between
–CH2 groups present in the side chain of the molecules is
operating. Such interactions, when compared with repul-
sive interaction caused by the polar hydrophilic group, are
greatly relevant for micelle formation because the extended
Fig. 2 Fluorescence data for the 3-pentadecyl phenol based poly-
merizable surfactant S1 determined in distilled water with DPH at
25 °C
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conductivity method gave slightly higher values of the
CMC for S2 than S1. The discrepancy may be because the
conductivity method depends on ion concentration in
the bulk of the solution compared with surface tension
measurement. The change of observed surface excess from
surface tension measurements further indicates a change in
micelle aggregation. The surface area per molecule of the
surfmers is larger than that of SDS due to increased
molecular size. The evaluation of the synthesized surfmer
in the emulsion polymerization and its influence on the film
formation and film properties will be reported in forth-
coming publications.
Acknowledgments This research was supported by a Marie Curie
International Incoming Fellowship to Dr. K. I. Suresh within the 7th
European Community Framework Programme (FP-7).
Fig. 3 Conductance of surfmer S2 in water at successive dilutions
(c.f. Refer Table 2 for CMC values)
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Author Biographies
Suresh Kattimuttathu I received his M.Sc. (1990) in Polymer
Chemistry from Mahatma Gandhi University Kottayam, and M.Tech.
(1993) (Polymer Technology) from the Cochin University of Science
& Technology, India. He completed his Ph.D. (2005) in Applied
Chemistry under CSIR (India)–DAAD (Germany) Sandwich model
fellowship. He is currently principal scientist at the Organic Coatings
& Polymers Division of the Indian Institute of Chemical Technology,
Hyderabad, India. His research interests focus on emulsion polymer-
ization, morphology control during emulsion polymerization, poly-
mers and monomers from renewable resources, atom transfer radical
polymerization and structure property correlation studies, as well as
adhesives and coatings.
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2008 from the University of Freiburg. She is currently a Ph.D. student
in the group of Prof. Schubert at the Department of Pharmaceutical
Technology and Biopharmacy at the University of Freiburg Germany,
working on model membranes.
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Rolf Schubert is a professor and head of the Department of
Pharmaceutical Technology and Biopharmacy at the University of
Freiburg. He received his Ph.D. in biochemistry from the University
of Tu¨bingen in 1981. The main fields of his research are model
systems for biological membranes and nanocarriers as drug delivery
systems, especially liposomes.
Eckhard Bartsch is a professor at the Institute of Macromolecular
Chemistry at the Faculty of Chemistry, Pharmacy and Earth Sciences
at the University of Freiburg, Germany. He received his Ph.D. (1987)
from the Julius-Maximilians-University at Wu¨rzburg. He then joined
the group of Prof. Hans Sillescu at the Institute of Physical Chemistry,
University of Mainz, as a researcher and a lecturer. Since 2004 he has
been an associate professor in physical and macromolecular chem-
istry at the University of Freiburg. His research focuses on
fundamental and applied characteristics of concentrated colloidal
dispersions, colloid synthesis and characterization, latex film forma-
tion and scattering techniques for microstructural characterization of
colloidal systems.
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