Synthesis and characterization of novel surfactants 1,2,3-tri(2- oxypropylsulfonate-3-alkylether-propoxy) propanes

Article abstract of DOI:10.1007/s11743-013-1442-8

A series of trimeric sulfonate surfactants 1,2,3-tri(2-oxypropylsulfonate- 3-alkylether-propoxy) propanes were prepared by the reaction of glycerin triglycidyl ether with long-chain alcohols, followed by sulfonation with 1,3-propane sultone. Glycerin triglycidyl ether was synthesized by the reaction of epichlorohydrin with glycerin. The chemical structures of the prepared compounds were confirmed by FTIR, ¹H NMR and element analysis. Their solution properties were characterized by use of the method of equilibrium and dynamic surface tension, steady-state fluorescence spectroscopy of pyrene and fluorescence quenching. With the increasing length of the carbon chain, the values of their CMC initially decreased. All these trimeric sulfonate surfactants had good water solubility. These compounds were superior in surface active properties to the reference surfactant SDS. The efficiency of adsorption at the water/air interface (pC₂₀) of these surfactants was very high. It is found that the shorter hydrocarbon chain length of the trimeric sulfonate surfactants, the faster the rate of decrease of surface tension, and the bigger the aggregation number of the trimeric sulfonate surfactants.

Full text of DOI:10.1007/s11743-013-1442-8

J Surfact Deterg (2013) 16:665–672
DOI 10.1007/s11743-013-1442-8
ORIGINAL ARTICLE
Synthesis and Characterization of Novel Surfactants
1,2,3-tri(2-oxypropylsulfonate-3-alkylether-propoxy)
Propanes
•
Ming Zhou Jinzhou Zhao Xu Wang
•
•
•
Jiaqiang Jing Lizhi Zhou
Received: 14 October 2012 / Accepted: 2 January 2013 / Published online: 13 March 2013
Ó AOCS 2013
Abstract A series of trimeric sulfonate surfactants 1,2,3-
tri(2-oxypropylsulfonate-3-alkylether-propoxy) propanes
were prepared by the reaction of glycerin triglycidyl ether
with long-chain alcohols, followed by sulfonation with 1,3-
propane sultone. Glycerin triglycidyl ether was synthesized
by the reaction of epichlorohydrin with glycerin. The
chemical structures of the prepared compounds were con-
firmed by FTIR, 1H NMR and element analysis. Their
solution properties were characterized by use of the method
of equilibrium and dynamic surface tension, steady-state
fluorescence spectroscopy of pyrene and fluorescence
quenching. With the increasing length of the carbon chain,
the values of their CMC initially decreased. All these tri-
meric sulfonate surfactants had good water solubility.
These compounds were superior in surface active proper-
ties to the reference surfactant SDS. The efficiency of
adsorption at the water/air interface (pC20) of these sur-
factants was very high. It is found that the shorter hydro-
carbon chain length of the trimeric sulfonate surfactants,
the faster the rate of decrease of surface tension, and the
bigger the aggregation number of the trimeric sulfonate
surfactants.
Keywords Fatty alcohols ꢀ Trimeric surfactants ꢀ 1,2,3-
tri(2-oxypropylsulfonate-3-alkylether-propoxy) propanes ꢀ
Surface-active properties ꢀ Synthesis ꢀ Aggregation
Introduction
In the last twenty years, there has been an increasing
interest in a new type of surfactants called ‘‘gemini’’. These
surface-active compounds have the characteristic of being
composed of a double hydrophobic chain, double hydro-
philic groups and a spacer between them which can be
flexible or rigid. They have better surface-active properties
than conventional ionic surfactants and their dynamic
surface properties differ drastically from those of single-
chain species [1–6]. Gemini surfactants were found to play
an important role in applications to detergents [7–9]. The
design and synthesis of this type of compounds has
recently attracted considerable attention.
Gemini surfactants with two long-chain alkyl groups
and two sulfonate or sulfate groups, which are derived from
ethylene glycol diglycidyl ether, have good water solubility
and excellent surface active properties in water. Glycidyl
compounds have been widely used as valuable intermedi-
ates for the preparation of gemini surfactants [10–13].
However, glycerin triglycidyl ether as valuable intermedi-
ate for the preparation of 1,2,3-tri(2-oxypropylsulfonate-3-
alkylether-propoxy) propane (Schemes 1, 2) has rarely
been reported [14].
M. Zhou ꢀ J. Zhao (&) ꢀ J. Jing
State Key Laboratory of Oil and Gas Reservoir Geology and
Exploitation, Southwest Petroleum University, Chengdu 610500,
Sichuan, China
e-mail: zhaojz62@163.com
M. Zhou
e-mail: mr.zhouming@163.com
M. Zhou ꢀ X. Wang
School of Material Science and Engineering, Southwest
Petroleum University, Chengdu 610500, Sichuan, China
In the present investigation, five model trimeric sulfo-
nate surfactants 1,2,3-tri(2-oxypropylsulfonate-3-alkyl-
ether-propoxy) propanes (Scheme 2) were prepared from
L. Zhou
Oil and Gas Engineering Institute of Tarim Oilfield,
Xinjiang 841000, China
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laboratory by 1810-B quartz automatic dual distilled water
utensil.
Methods
1H-nuclear Magnetic Resonance (NMR) spectra were
recorded on a Bruker (Wissembourg, France) AR 9 400
spectrometer (400 MHz) with CDCl3 solvent. Infrared (IR)
spectra were obtained on a FTIR-8400S spectrometer
(Shimadzu Corporation, Japan) with a liquid film between
KBr discs. Element analyses were determined by a Costech
ECS 4010 CHNSO analyzer, Italy.
Scheme 1 Trimeric sulfonate surfactants with hydrophilic ionic
groups and three lipophilic alkyl chains
Synthesis
Five model 1,2,3-tri(2-oxypropylsulfonate-3-alkylether-
propoxy) propanes were synthesized through three steps by
following Scheme 3.
A Typical Procedure for the Synthesis of Glycerol
Triglycidyl Ether
Glycerol triglycidyl ether was prepared under phase-trans-
fer catalytic conditions reported previously [11]. According
to the reaction principle, glycerol triglycidyl ether was
prepared by the successive treatment of a mixture of
0.8 mol epichlorohydrin and 0.1 mol glycerol (8:1 molar
ratio) in 40 mL 0. 8 mol/L NaOH aqueous solution at 50 °C
for 10 h with 0.1 molar tetrabutylammonium hydrogen
sulfate as the phase-transfer catalyst, followed by the
addition of 50 mL 4 mol/L NaOH aqueous solution at room
temperature for 20 h. Reaction products were filtered to
remove the solids generated in the system, The filtrate was
then added into the dichloromethane, washed with saturated
salt to pH = 7, glycerol triglycidyl ether was obtained by
distillation under reduced pressure (70–86 % yield).
Scheme 2 The structure of 1,2,3-tri(2-oxypropylsulfonate-3-alky-
lether-propoxy) propane Y = (CH2)3SO3Na R = C8H17, C10H21,
C12H25,C14H29,C16H33
common ingredients, and their structures were character-
1
ized by FTIR and H NMR. The effect of the structure of
the alkyl groups on CMC, cCMC, CMC/C20, pC20, CCMC
,
A
CMC, aggregation number, micropolarity and dynamic
surface tension was investigated.
Experimental
Materials
A Typical Procedure for the Synthesis of 1,2,3-tri
(2-hydroxy-3-alkylether-propoxy) Propane
Octyl, decyl, dodecyl, tetradecyl and hexadecyl alcohols
were purchased from Kelong Ltd., Chengdu, China. Epi-
chlorohydrin, tetrabutylammonium bromide (TBAB:
CH3CH2CH2CH2)4N?-HSO4-), sodium hydroxide, tetra-
hydrofuran (THF), 1,3-propane sultone, potassium, sodium
hydride, dichloromethane, glycerol, anhydrous magnesium
sulfate and sodium dodecylsulfate (SDS: C12H25SO3Na)
were purchased from Changzheng Ltd., Chengdu, China.
Silica gel for column chromatography (60–120 mesh) was
purchased from Huideyi Ltd., Beijing, China. All the
chemicals were of reagent grade and used directly without
further purification. Distilled water was prepared in our
1,2,3-tri(2-hydroxy-3-alkylether-propoxy) propanes (R =
C8H17, C10H21, C12H25, C14H29, C16H33) were obtained by
the ring opening reaction of glycerol triglycidyl ether with
long-chain fatty alcohols in the presence of potassium at
60 °C for 8 h. The molar ratio of glycerol triglycidyl ether
to long-chain fatty alcohols and potassium was 1:8:2. The
organic layer was dried with anhydrous magnesium sulfate,
and then distilled to remove the solvent methylene chlo-
ride. Finally, purification of 1,2,3-tri(2-hydroxy-3-alky-
lether-propyl) propane was carried out by silica gel column
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667
Scheme 3 Preparation of
CH2
CH
O
CH2
CH2
CH2
HC
CH2
CH2 OH
CH OH
CH2 OH
trimeric sulfonate surfactants
1,2,3-tri(2-oxypropylsulfonate-
3-alkylether-propoxy) propane
O
phase-transfercatalyzer
NaOH
k
+
3H2C
CH CH2
Cl
O
HC
CH2
O
O
(R-C8H17, C10H21, C12H25
,
HC
CH2
CH2
O
C14H29, or C16H31). a glycerol
triglycidyl ether (Yield: about
70–86 %). b 1,2,3-tri(2-
hydroxy-3-alkylether-propoxy)
propane (Yield: about
71–75 %). c 1,2,3-tri(2-
oxypropylsulfonate-3-
alkylether-propoxy) propane
(Yield: about 72–80 %)
O
(a) glycerol triglycidyl ether (Yield: about 70 86%)
CH2
CH
O
CH2 CH CH2
O R
CH2
CH
O
CH2 CH CH2
O
R
R
O
O
O
S
OH
O(CH2)3SO3Na
CH2 CH CH2
NaH
THF
O
CH2 CH CH2
O R +
O
O
R
OH
O(CH2)3SO3Na
CH2 CH CH2
CH2
O
CH2 CH CH2
O R
CH2
O
O
OH
O(CH2)3SO3Na
(b) 1, 2, 3-tri᧤2-hydroxy-3-alkylether- propoxy᧥ (c)1, 2, 3-tri(2-oxoypropylsulfonate-3-alkylether
propane (Yield: about71ᨺ75%) -propoxy᧥propane (Yield:about72 80%)
chromatography with a hexane:ethanol (2:1, v/v) eluent
(71–75 % yield).
Measurements
Equilibrium Surface Tension
A Typical Procedure for the Preparation of 1,2,3-tri
(2-oxypropylsulfonate-3-alkylether-propoxy) Propanes
The surface tensions of surfactants were measured with a
K100 tensiometer (Kru¨ss Corporation, Germany) by the
Wilhelmy plate technique at 20 °C. A series of measure-
ments to obtain equilibrium surface tension were taken
until the change in surface tension was less than
0.05 mN m-1 for 10 min. The surface tension of each
surfactant is an averaged value of three measurements only
when the deviation of three measurement values was less
than 1 %. The critical micelle concentration (CMC) and
surface tension at the CMC (cCMC) were determined from
the breakpoint of the surface tension and logarithm of
concentration curve. The solutions of the trimeric sulfonate
surfactants with concentrations above the CMC reached
equilibrium within 1 h, whereas those below the CMC
reached equilibrium within several hours. The adsorption
amount of surfactant (C) (in mol m-2) for trimeric sulfo-
nate surfactants can be calculated by applying the follow-
ing Gibbs adsorption isotherm equation [15],
The target compounds 1,2,3-tri(2-oxypropylsulfonate-3-
alkylether-propoxy) propanes (R = C8H17, C10H21,
C12H25, C14H29, C16H33) were synthesized by sulfonation
of corresponding 1,2,3-tri(2-hydroxy-3-alkylether-pro-
poxy) propane with 1,3-propanesultone and sodium
hydride in dry THF at 60 °C for 12 h. The molar ratio of
1,2,3-tri(2-oxypropylsulfonate-3-alkylether-propyl)
pro-
panes to THF, 1,3-propane sultone and sodium hydride was
1:20:8:6. Methanol was added to the products to remove
unreacted sodium hydride, distilled to remove THF, and
then the remaining solution was dissolved in an n-butanol
and water solution (molar ratio 3:1). The organic phase was
dried with anhydrous magnesium sulfate, and distilled to
remove the butanol. Finally, purification of 1,2,3-tri
(2-oxypropylsulfonate-3-alkylether-propoxy) propanes was
carried out as white waxy product by silica gel column
chromatography with a hexane:ethanol (2:1, v/v) eluent
(72–80 % yield).
1
dc
nRT d ln C
C ¼ ꢁ
ð1Þ
where c is the equilibrium surface tension in mN m-1, C is
the saturation adsorbed amount in mol/1,000 m2, R is the
gas constant (8.314 J mol-1 K-1), T is the absolute
temperature, C is the surfactant concentration, and
(dc/dlnC) is the slope in the surface tension isotherm
when the concentration is near the CMC. The value of n
(the number of species at the interface whose concentration
1
FTIR, H NMR and Element Analysis
The structure of 1,2,3-tri(2-oxypropylsulfonate-3-alky-
lether-propoxy) propanes was confirmed by its FTIR, NMR
and element analysis. NMR and element analysis is showed
in Table 1. The FTIR, 1H NMR and element analysis show
that the synthetic products are target products.
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Table 1 Preparation and properties of 1,2,3-tri(2-oxypropyl sulfonation-3-alkylether-propoxy) propane
R
Yield (%)
80
1H NMR (CDCl3) (d)
Anal. found (calc.)
C8H17
0.81–0.88 (m, 9H, 1.18–1.51 (m, 36H), 1.93–2.18
(m, 6H, 2.86–3.13 (m, 6H, 3.16–3.81 (m, 32H)
C, 49.98 (49.91); S, 8.79 (8.87); H, 8.20 (8.22);
O, 26.48 (26.62)
C10H21
76
78
72
74
0.81–0.88 (m, 9H, 1.15–1.55 (m, 48H), 1.88–2.19
(m, 6H, 2.89–3.15 (m, 6H, 3.11–3.91 (m, 32H)
C, 52.51 (52.49); S, 8.11 (8.23) H, 8.53 (8.66);
O, 25.87 (25.94)
C
12H25
14H29
0.81–0.88 (m, 9H, 1.17–1.59 (m, 60H), 1.82–2.33
(m, 6H, 2.78–3.06 (m, 6H, 3.22–3.85 (m, 32H)
C, 54.72 (54.56); S, 7.68 (7.83) H, 9.04 (9.12);
O, 22.46 (23.04)
C
0.81–0.88 (m, 9H, 1.20–1.68 (m, 72H), 1.88–2.28
(m, 6H, 2.72–3.10 (m, 6H, 3.25–3.92 (m, 32H)
C, 59.65 (59.15); S, 7.42 (7.51) H, 9.95 (9.78);
O, 22.32 (22.54)
C16H33
0.81–0.90 (m, 9H, 1.28–1.61 (m, 84H), 1.95–2.24
(m, 6H, 2.83–3.03 (m, 6H, 3.30–3.89 (m, 32H)
C, 64.21 (63.40); S, 7.23 (7.35) H, 10.64 (10.49);
O, 21.83 (22.05)
The FTIR spectrum in the range 3,000–700 cm-1 of 1,2,3-tri(2-oxypropylsulfonate-3-dodecylether-propoxy) propanes was as follows. The
absorption peak at 2,933.25 cm-1 corresponds to the –CH3 asymmetric stretching vibration. The spectrum band at 2,851.15 cm-1 contributes to
the symmetric stretching vibration peak of –CH2. Further, the spectrum also has a peak at 1,461.75 cm-1 contributing to the deformation
vibration of –CH2–, 1,212.90 cm-1, the stretching vibration of the ether bond (C–O–C). Peaks at 1,199.42, 1,121.23 and 1,034.56 cm-1
correspond to the symmetrical and asymmetrical peaks of –SO3-, 719.35 cm-1, the vibration peak of long-chain –CH2–
changes with the surfactant concentration) is taken as 2 for
lnðI0=IÞ ¼ ½Qꢂ=½ðC ꢁ CMCÞ=Nꢂ
where I0 and I are the fluorescence intensities without and
with quencher, respectively, and [Q] is the concentration of
quencher.
ð3Þ
an equimolar ratio of surfactant anion and counteraction at
interface in the absence of extra electrolyte. In order to
extract the minimum surface area occupied by a surfactant
molecule, ACMC (nm2), at the air–water interface when the
surface adsorption was saturated, Eq. (2) was used,
Dynamic Surface Tension
1
ACMC ¼ ꢁ
ð2Þ
NCCMC
The dynamic surface tension was measured using a Kru¨ss
bubble pressure tensiometer BP2, a method which involves
measuring the maximum pressure necessary to blow a
bubble in a liquid from the top of a capillary. The mea-
surements were conducted with effective surface ages from
1 ms to several seconds.
where N is Avogadro’s number. When CCMC is in
mol cm-2, ACMC is in nm2.
Steady-State Fluorescence
The fluorescence measurements were performed using a
SENS-9000 fluorescence spectrophotometer. The spectra
were recorded between 185 and 900 nm with the excitation
wavelength at 350 nm, where the concentration of pyrene
was 1 9 10-5 mol L-1 for each solution. The fluorescence
intensity ratio of the first (373 nm) to the third (384 nm)
vibronic peaks, I1/I3, depends on the environment of the
pyrene molecules [16, 17]. The environment of the pyrene
is more hydrophobic when the I1/I3 ratio decreases. The
I1/I3 ratio is influenced not only by the solvent polarity but
also by the aggregation number and core cavity [18].
Results and Discussion
Equilibrium Surface Tension
The CMC values and surface tension at the CMC (cCMC) of
trimeric sulfonate surfactants with n of 8, 10, 12, 14 and 16
were determined using Wilhelmy tensiometry. The results of
these measurements are showed in Table 2. These results
indicate that the CMC values of trimeric sulfonate surfac-
tants are about one or two orders of magnitude lower than
those of the corresponding monomeric surfactants, which
suggests that the trimeric sulfonate surfactants make it easy
to form micelles in the bulk solution. The CMC of the con-
ventional ionic surfactant is known to decrease with
increasing number of carbon atoms in the hydrophobic
groups. In this work, the CMC of trimeric sulfonate surfac-
tant decrease from 3.16 9 10-4 to 1.80 9 10-6 mol L-1
when increasing the carbon atom of hydrocarbon chain from
8 to 16, which is similar to those common surfactants in a
Fluorescence Quenching
The micelle aggregation numbers were obtained by the
quenching method, with pyrene as the fluorescence probe
and cetylpyridinium chloride as the quencher of the pyrene
fluorescence. Pyrene was excited at 350 nm and its emission
recorded at 384 nm. The probe concentration in the surfac-
tant solution was 1 9 10-5 mol L-1. The aggregation
number (N) can be calculated from the equation [19, 20],
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Table 2 Surface chemical properties of 1,2,3-tri(2-oxypropylsulfonate-3-alkylether-propoxy) propane (20 °C)
Alkyl chain
CMC (910-4mol L-1
)
cCMC (mN m-1
)
pC20
CMC/C20
106CCMC (mol m-2
)
A )
CMC, nm2 (molecule-1
C8H17
3.160
0.800
0.330
0.040
0.018
82.00
29.5
26.8
23.3
24.8
26.2
32.5
4.64
5.52
6.05
6.74
7.02
2.50
13.79
26.49
37.03
21.98
18.84
2.60
2.45
2.30
2.72
2.47
2.34
3.16
0.678
0.722
0.611
0.672
0.710
0.526
C10H21
C12H25
C14H29
C16H33
SDS
homologous compound, as may result from the conformation
of the surfactants at interface or the curling of the three
hydrophobic chains during dissolution. The formation of the
micelle is the joint result of the hydrophobic effect and
intermolecular force between surfactants. In view of the
conformation of trimeric sulfonate surfactants, three
hydrophobic chains are not parallel due to the presence of
several oxygen atoms in ether bonds.
Trimeric sulfonate surfactants exhibited clear solutions
and displayed a sharp break in the surface tension versus
concentration (on a log scale) curves and a final plateau
indicating a well-defined CMC and surface tension at the
CMC (cCMC), as showed in Fig. 1. The surface tension
decreases with increasing concentration and then clearly
reaches a breakpoint. It can be seen from Fig. 1 that when
the length of hydrophobic chain increases, the CMC of the
surfactants decrease.
Fig. 1 Surface tension versus logarithm of the aqueous molar
concentration (log C) of synthesized 1,2,3-tri(2-oxypropyl sulfo-
nate-3-alkylether-propoxy) propane: (circles) n = 8, (multiplication
signs) 10, (triangles) 12, (squares) 14, (diamonds) 16
1.0E+4
1.0E+3
1.0E+2
1.0E+1
1.0E+0
1.0E-1
1.0E-2
Figure 2 shows the relationship between the logarithm
of CMC and the total carbon number in the hydrophobic
groups for trimeric sulfonate surfactants with the chain
length of 8–16; the plot of trimeric sulfonate surfactants
shows a linear decrease. In general, the relationship
between the CMC and the number of carbon atoms n in the
hydrophobic chain for homologous straight–chain ionic
surfactants can be written in the following form [21, 25],
where A and B are constants.
0
10
20
30
40
50
total carbon number
Fig. 2 Variation of the CMC with the number of total hydrocarbon
chains for trimeric sulfonate surfactants (triangle) and CnH2n?1-
SO3Na (diamond)
log CMC ¼ A ꢁ Bn
ð4Þ
The linear relationships between log CMC and n for tri-
meric sulfonate surfactants and CnH2n?1SO3Na deduced
from Fig. 2 are as follows:
increase of chain length for the trimeric sulfonate surfac-
tants is smaller than in the case of monomeric surfactants.
This trend is consistent with the data on carboxylate
gemini surfactants [22] and quaternary ammonium type
trimeric surfactants [23]. Thus, it is clarified that the effect
of the chain length on the CMC for trimeric sulfonate
surfactants is smaller in comparison with monomeric
surfactants.
Trimeric sulfonate surfactants:
log CMC ¼ 2:8296 ꢁ 0:0965nðR2 ¼ 0:982Þ
CnH2n?1SO3Na:
log CMC ¼ 6:5868 ꢁ 0:3103nðR2 ¼ 0:9923Þ
The surface tensions at the CMC of trimeric sulfonate
surfactants with n of 8–16 are lower than those of the
monomeric surfactants. This shows that the gemini sur-
factants adsorb strongly at the air/water interface, and
orient themselves to cause effective surface activities.
From the slope of the straight line, the values of B are
determined to be 0.0965 for the trimeric sulfonate surfac-
tant. The value of B of trimeric sulfonate surfactants is
smaller than that of the conventional surfactants SDS
(0.3038); it indicates that the decrease in the CMC with an
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Among these trimeric surfactants, those with hydrocarbon
chain length of 12 and 14 provide especially great effi-
ciency in lowering the surface tension. The compact
micelles of these surfactants can be formed due to strong
hydrophobic interactions between multiple hydrocarbon
chains. The increase in the hydrocarbon chain length from
14 to 16 renders them slightly less surface active, probably
due to a strong cohesion by three long hydrocarbon chains.
Information on the orientation and the packing degree of
surfactant molecule adsorbed at the air/water interface can
be obtained by the occupied area per molecule. From the
data of Table 2, it can be seen that the occupied areas of the
trimeric sulfonate surfactants are smaller than the con-
ventional monomeric surfactants. The trimeric sulfonate
surfactant with chain length 12 has an extremely small
occupied area in comparison with those with chain length
8, 10, 14 and 16, and it is not possible to normally adsorb
for the values at the interface. The reasons might be the
effect of the formation of a film at the interface by
hydrocarbon chains on small area.
probably reflects the difficulty if packing two hydrophobic
groups in micelle [24].
Micropolarity
The micropolarity and micellization of the trimeric sulfo-
nate surfactants with chain lengths of 8–16 were investi-
gated by a pyrene fluorescence probe. Figure 3 shows the
variations of the pyrene polarity ratio I1/I3 with the change
of the surfactant concentration. The curve of the trimeric
sulfonate surfactants with chain length 8 could not be
obtained above the concentration of 0.5 mol L-1 in this
study due to its limitation in solubility. With increasing the
surfactant concentration, the I1/I3 ratio of the trimeric
sulfonate surfactants with chain length 10–16 decreases.
With increasing further concentration, the I1/I3 ratio of
trimeric sulfonate surfactants reaches constant values of
approximately 1.2. In addition, the final I1/I3 ratio of the
trimeric sulfonate surfactants is almost the same values as
that of a conventional anionic surfactant such as SDS,
which indicates that the micropolarity of trimeric sulfonate
surfactant micelles is very low.
The efficiency and effectiveness can be characterized by
the value of cologarithm of the surfactant concentration
C20 at which the surface tension of water is reduced by
20 mN m-1 and by the value of CMC/C20, respectively.
The values of pC20 and CMC/C20 for the trimeric sulfonate
Aggregation Number
surfactants are also listed in Table 2. The pC20 (pC20
=
The aggregation number of micelles for the trimeric sul-
fonate surfactants was determined by a steady-state fluo-
rescence quenching method. As it is clear from the
equation of the experimental section, the aggregation
number N can be obtained from constant surfactant con-
centration C with the quencher concentration Q [22].
Figure 4 shows the relationship between [Q]/(C-CMC)
and ln (I0/I) for the trimeric sulfonate surfactants with n of
-logC20) value measures the efficiency of adsorption of
surfactant at the air/water interface; the larger the value of
pC20, the greater the tendency of the surfactant to adsorb at
the air/water interface, relative to its tendency to form
micelles and its ability for reduce the surface tension. The
value of CMC/C20 is a convenient way of measuring
effectiveness which can be correlated with structural fac-
tors on the micellization and adsorption processes; the
larger the values of the CMC/C20, the greater the tendency
of the surfactant to adsorb at the air/water interface, rela-
tive to its tendency to form micelles. The values of pC20 of
trimeric sulfonate surfactants increase with increasing
hydrocarbon chain length from 8 to 16. This result suggests
that the longer the hydrocarbon chains of the trimeric
sulfonate surfactants, the stronger its adsorption at the air/
water interface. Compared with the monomeric surfactants
SDS, pC20 of the trimeric sulfonate surfactants with the
n of 8–16 are much larger. This indicates that the trimeric
sulfonate surfactants are superior to the monomeric sur-
factants in their efficiency at reducing surface tension. The
values of CMC/C20 of trimeric sulfonate surfactants
increase with increasing hydrocarbon chain length from 8
to 12 and decrease with increasing hydrocarbon chain
length from 12 to 16, but they are much larger than those
corresponding to the monomeric surfactants. This indicates
that the trimeric sulfonate surfactants make it easy to
adsorb at the air/water interface. The larger CMC/C20 ratio
8–16. The concentrations used are 4.5 9 10-4, 1.2 9 10-4
,
0.8 9 10-4, 0.2 9 10-4 and 0.1 9 10-4 mol L-1 for the
trimeric sulfonate surfactants with n of 8, 10, 12, 14 and 16,
respectively. The chart give straight lines in all the cases
1.8
1.7
1.6
1.5
1.4
1.3
1.2
0.001
0.01
0.1
1
10
concentration(×10-4mol.L-1)
Fig. 3 Variation of the pyrene intensity ratio I1/I3 with the surfactant
concentration for the trimeric sulfonate surfactants with n = 8–16 at
25 °C: (circles) n = 8, (multiplication signs) 10, (triangles) 12,
(squares) 14, (diamonds) 16
123

J Surfact Deterg (2013) 16:665–672
671
10
9
8
7
6
5
4
3
2
1
0
70
65
60
55
50
45
40
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0
0.4
0.8
1.2
1.6
2
[Q]/(concentration-cmc)
time(second)
Fig. 4 Relationship between ln (I0/I) and [Q]/(C - CMC) from
fluorescence quenching method: (circles) n = 8, (multiplication
signs) 10, (triangles) 12, (squares) 14, (diamonds) 16
Fig. 5 Variation of the dynamic surface tension with the time for the
trimeric sulfonate surfactants with n = 8–16 at 25 °C: (circles)
n = 8, (multiplication signs) 10, (triangles) 12, (squares) 14,
(diamonds) 16
and the values of N are obtained from the slope of each
straight line. The aggregation numbers of trimeric sulfonate
surfactants with n of 8, 10, 12, 14 and 16, are found to be 7,
14 1, 20 1, 24 1 and 33 2, respectively. The
aggregation number of trimeric sulfonate surfactants with
n of 8 is very small in comparison with those with n of
10–16. Further, the aggregation numbers of the present
trimeric sulfonate surfactants are also smaller than those of
the conventional anionic surfactants [25]. It is likely that
the small aggregation number of the trimeric sulfonate
surfactants micelles is due to the electrostatic repulsion
between sulfonate groups, as well as the steric hindrance of
the multiple hydrocarbon chains. This might be caused by
close distance of three ether bonds connected by glycerin
monomer unit as spacer group.
adsorption rate of the trimeric sulfonate surfactants might
be slow because they possess a larger structure, in com-
parison with the monomeric surfactant.
Acknowledgments This research was supported by the National
Natural Science Foundation of China (Projects No. 51074133 and
51074136) and Major Special Technological Programmes Concerning
China Petroleum (NO.2008ZX05049-004-007HZ).
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