Surface activities, foam properties, HLB, and krafft point of some n-alkanesulfonates (C14-C18) with different isomeric distributions

Article abstract of DOI:10.1007/s11743-012-1335-2

A homologue series of sodium secondary n-alkanesulfonates (C₁₄, C₁₆ and C₁₈) were obtained by photosulfochlorination process with two different reaction conditions. Different length chains with different isomeric distributions of n-alkanesulfonates are expected to present variations in physicochemical properties. In this investigation, the relationships between their isomeric distribution and their chain length and micellar behaviors were thoroughly explored. Their CMC at different temperatures were determined using specific conductivity and surface tension measurements. Through surface tension isotherms, the surface activities (γCMC) were obtained. The surface absorption amounts (C_max) and the molecular areas (A_min) were calculated using Gibb's equation. As expected, these surfactants exhibit good surface properties. It was shown that the CMC values increase with increasing the percentage of secondary isomers, with a surface tension decrease. It was also shown that the CMC values decrease with increasing chain length. The HLB values were calculated for each surfactant and the results obtained suggest that they are O/W emulsifiers. The foam properties of synthesized surfactants were evaluated and compared to those obtained for commercial samples. It was shown that the foamability is influenced both by the length of the hydrophobic moiety and the percentage of secondary isomers. It can be easily concluded that the C₁₄ sulfonates show the best foaming properties independently of their isomeric distribution. The Krafft point values obtained indicate that the micellization and the surfactant solubility mainly depend on the proportion of secondary isomers and the length of hydrophobic moiety. AOCS 2012.

Full text of DOI:10.1007/s11743-012-1335-2

J Surfact Deterg (2012) 15:419–431
DOI 10.1007/s11743-012-1335-2
ORIGINAL ARTICLE
Surface Activities, Foam Properties, HLB, and Krafft Point
of Some n-Alkanesulfonates (C14–C18) with Different Isomeric
Distributions
•
Latifa Fekarcha Amel Tazerouti
Received: 20 October 2011 / Accepted: 17 February 2012 / Published online: 7 March 2012
ꢀ AOCS 2012
Abstract A homologue series of sodium secondary n-al-
kanesulfonates (C14, C16 and C18) were obtained by photo-
sulfochlorination process with two different reaction
conditions. Different length chains with different isomeric
distributions of n-alkanesulfonates are expected to present
variations in physicochemical properties. In this investiga-
tion, the relationships between their isomeric distribution
and their chain length and micellar behaviors were thor-
oughly explored. Their CMC at different temperatures were
determined using specific conductivity and surface tension
measurements. Through surface tension isotherms, the sur-
face activities (cCMC) were obtained. The surface absorption
amounts (Cmax) and the molecular areas (Amin) were calcu-
lated using Gibb’s equation. As expected, these surfactants
exhibit good surface properties. It was shown that the CMC
values increase with increasing the percentage of secondary
isomers, with a surface tension decrease. It was also shown
that the CMC values decrease with increasing chain length.
The HLB values were calculated for each surfactant and the
results obtained suggest that they are O/W emulsifiers. The
foam properties of synthesized surfactants were evaluated
and compared to those obtained for commercial samples. It
was shown that the foamability is influenced both by the
length of the hydrophobic moiety and the percentage of
secondary isomers. It can be easily concluded that the C14
sulfonates show the best foaming properties independently
of their isomeric distribution. The Krafft point values
obtained indicate that the micellization and the surfactant
solubility mainly depend on the proportion of secondary
isomers and the length of hydrophobic moiety.
Keywords Secondary alkanesulfonates ꢀ
Photosulfochlorination ꢀ Isomeric distribution ꢀ
LC-ESI/MS ꢀ Surface tension ꢀ CMC ꢀ HLB ꢀ
Krafft point ꢀ Foam properties
Abbreviations
CMC
IR
Critical micelle concentration
Infrared spectroscopy
Cmax
Amin
SAS
SDS
GPC
Surface excess
Minimum area per molecule
Secondary alkanesulfonates
Sodium dodecyl sulphate
Gaz phase chromatography
LC-ESI/MS Liquid chromatography-electrospray
ionisation/tandem mass spectrometry
GC-MS/EI
Gas chromatography coupled to mass
spectrometry using electronic impact mode
Krafft (temperature) point
KT
HLB
Hydrophilic-lipophilic balance
L. Fekarcha ꢀ A. Tazerouti (&)
´
Laboratoire de Chimie Organique Appliquee, Faculte de Chimie,
Universite des Sciences et de la Technologie Houari
´
Introduction
´
Boumediene (USTHB), 16111 Bab Ezzouar,
Algiers, Algeria
e-mail: ameltazerouti@gmail.com; atazerouti@usthb.dz
Anionic surfactants are the most important ingredients used
in laundry and household cleaning products [1, 2]. They are
widely used in pharmaceutical industries as extractants,
emulsifiers, solubilizers, stabilizers agents [3], in coatings
technology [4], textiles, painting, and separation [5]. The
L. Fekarcha
Centre de Recherche Scientifique et Technique en Analyses
Physico-chimiques, BP 248, 16004 Algiers RP, Algeria
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J Surfact Deterg (2012) 15:419–431
efficiency of such agents is conditioned by their amphi-
philic nature. Various structural factors such as (1) struc-
ture and the chain length of the hydrophobic part [6–9], (2)
nature, number and the position of the hydrophilic part
[10], and (3) the hydrophobic-lipophilic balance (HLB) of
certain surfactants have been described. It has been shown
that the variety in the molecular structure of surfactants
leads to variations in their physicochemical properties [11,
12]. The secondary alkanesulfonates (SAS) are frequently
used as active matter in detergent formulations, as emul-
sifying agents and even in flotation. They are regarded as
specific anionic surfactants, because of their high chemical
stability, their better water solubility, their high compati-
bility with electrolytes, and their improved biodegradabil-
ity [13–15]. These surfactants are especially beneficial for
their lower critical micelle concentration (CMC), great
efficiency in lowering surface tension of water, excellent
detersive action and their efficacy to remove particulate
soils [16].
(Cmax) and the minimum molecular areas (Amin) at the air–
water interface were estimated. The hydrophilic-lipophilic
balance (HLB) values for the prepared compounds were
also calculated. The Krafft point, and foaming property
were systematically examined, and the effect of the length
of the hydrophobic part and the proportion of secondary
isomers on these properties were investigated.
Experimental Procedures
As mentioned in the previous work [19], high values of
conversion rate lead to good yields of the sulfochlorination
reaction, and a reduced chlorination molar ratio (RSO2Cl/
RCl). It was also noted that the best results were obtained
at a conversion rate of 80%. Also, the photosulfochlori-
nation of n-alkanes in the presence of aromatic solvent
leads to higher yields and reaction mixtures with high
percentage of secondary sulfochlorinated isomers [19, 20].
It is therefore interesting to apply these conditions set up
for n-tetradecane, n-hexadecane and n-octadecane.
The solubility is represented as a fundamental property,
and the most important attribute of the surfactant system is
its ability to efficiently reduce surface tension. Another
property to be considered is the foam power or foamability,
which is one of the essential characteristics for the for-
mulation of detergents, cosmetics, and similar composi-
tions. In most cases, nice, rich, and creamy foam is a signal
of efficacy [16]. Although, certain surfactants show a bad
foamability and foam stability in spite of their strong sol-
ubility in water, these characteristics are interesting for
applications requiring low foam, e.g. in products for dish-
washing machines. Furthermore, the Krafft point (KT), and
the Hydrophilic-Lipophilic Balance (HLB) are also
important, in order to know the temperature, and the field
of their applications as in solubilization, emulsification,
detergency, dispersion or wetting, respectively [17, 18].
In this paper, a homologue series of sodium salts of
secondary n-alkanesulfonates from n-alkanes with different
length chains (C14, C16 and C18), was prepared by a
photosulfo-chlorination process using sulfuryl chloride
with two different reaction conditions. The positional iso-
mers of n-alkanesulfonyl chlorides were analyzed simul-
taneously by gas phase chromatography (GPC) after
derivatization, and identified by gas chromatography cou-
pled to mass spectrometry using electronic impact mode
(GC-MS/EI). The chemical structures of synthesized sul-
fonates were confirmed by IR, and by liquid chromato-
graphy-electrospray tandem mass spectrometry (LC-ESI/
MS). Various isomeric distributions of these surfactants
having different length chains were obtained. Their critical
micelle concentrations (CMC) in aqueous solutions were
determined using specific conductivity and surface tension
measurements. Through surface tension isotherms, the
surface activity (cCMC), the surface absorption amount
Chemical Products
n-Tetradecane (Fluka, [99% pure), n-hexadecane (Fluka,
[99% pure), n-octadecane (Fluka, [97% pure), 1-chloro-
tetradecane (Aldrich, [98% pure), 1-chlorohexadecane
(Fluka, [98% pure), 1-chlorooctadecane (Fluka, [97%
pure), sulfuryl chloride (Aldrich, [97% pure), chloroben-
zene (Aldrich,[99% pure), pyridine (Fluka,[99.8% pure)
ethanol (Merck, 99.8%), N,N-diethylamine (Aldrich,[99.5%
pure), sodium hydroxide (Sigma-Aldrich, pure) and sodium
dodecylsulfate (Fluka, [98% pure). All others chemicals
were of commercial origin (Fluka), and were used without
further purification. Distilled water was used for preparing
solutions.
Instruments
IR spectra were recorded on a Perking Elmer Spectrometer
using KBr discs. GPC separations were recorded with a HP
Model 6890 gas chromatograph. A CPsil-5cb capillary
column 60 m 9 0.32 mm I.D, 25 lm film thickness was
used for the analysis with N2 as the carrier gas (0.36 ml/
mn). The gas chromatograph, HP Model 6800 was coupled
to an HP MSD Model 5973 mass spectrometer. The col-
umn used was a HP-INNOWax 60 9 0.25. I.D, 0.25 lm
film thickness with He as the carrier gas (0.7 ml/mn), and
the detection by EI (70 eV). Mass spectrometry was per-
formed in LC-MS/MS Waters ACQUIY (liquid chroma-
tography linked to tandem mass spectrometry) fitted with
an electrospray interface (ESI), and controlled by Mass-
Lynx software. The mass spectrometer was operated in the
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J Surfact Deterg (2012) 15:419–431
421
negative ion mode with MS–MS detection, and by infusing
of compound directly into the mass spectrometer. Typical
interface conditions were optimized for maximum intensity
of the precursor ions as follows: nebulizer and desolvation
(drying gas) N2 flows were set at 50 and 400 l/h, respec-
tively, source block and desolvation temperatures were 150
and 300 ꢁC, respectively.
III
Primary sodium salt of octadecanesulfonate.
IIIa Secondary sodium salts of octadecanesulfonates
obtained in the pure phase.
IIIb Secondary sodium salts of octadecanesulfonates
obtained in the solvent phase.
IR Analysis
Synthesis and Characterizations
The infrared spectra of prepared compounds showed dif-
ferent peaks which are in good correlation with literature
data (Table 1).
n-Tetradecane, n-hexadecane and n-octadecane were con-
verted in pure phase and in the presence of chlorobenzene
(substrate/solvent equal 1:3, by vol), at a conversion rate of
80% into the corresponding n-alkanesulfonyl chlorides by
photosulfochlorination with sulfuryl chloride using pyridine
as catalyst [21]. The primary isomers were obtained from the
corresponding chlorides by a Grignard reaction. As long-
chain n-alkanesulfonyl chlorides can hardly be analyzed
directly by (GPC) because of their instability and their low
volatility, they are transformed into the corresponding sul-
fonamides by addition of N,N-diethylamine [22]. The chem-
ical structures of the resulting sulfonamides was confirmed by
infrared spectroscopy (IR). The positional isomers were ana-
lyzed by (GPC), and identified by (GC-MS/EI). Sodium
alkanesulfonates were prepared by neutralizing the resulting
alkanesulfonyl chlorides with sodium hydroxide. The sulfo-
nates obtained were purified by recrystallization. The chem-
ical structure of these compounds was confirmed by (IR) and
LC-ESI/MS. The sulfonates produced are as follow:
GPC Analysis
All chromatograms of the reaction mixtures of derivatized
n-alkanesulfonyl chlorides reveal the presence of a group of
peaks after that of the solvent, the unreacted n-alkane and the
chlorinated isomers. The group of these peaks correspond to
the n positional isomers of the corresponding sulphona-
mides. The last peak with the higher retention time is that of
the primary isomer identified by cross injection with a
sample obtained by Grignard reaction. The GC analysis of
n-C14H29SO2N(C2H5)2 gives six peaks, as the isomer seven
is not well separated. n-C16H33SO2N(C2H5)2 results in eight
peaks corresponding to each isomer, and n-C18H37SO2N
(C2H5)2 exhibits seven peaks, as isomers eight and nine are
not well separated. The isomeric compositions of these
compounds were well determined by GPC analysis, and are
presented with that of C12H25SO2N(C2H5)2 [20] in Table 2.
It is noted that the rate of secondary isomers is higher for the
compounds obtained by photosulfochlorination in the sol-
vent phase, as observed in previous work for n-heptane and
n-dodecane [19, 20].
I
Primary sodium salt of tetradecanesulfonate.
Secondary sodium salts of tetradecanesulfonates
obtained in the pure phase.
Ia
Ib
Secondary sodium salts of tetradecanesulfonates
obtained in the solvent phase.
II
Primary sodium salt of hexadecanesulfonate.
Secondary sodium salts of hexadecanesulfonates
obtained in the pure phase.
IIa
GC-MS/EI
IIb Secondary sodium salts of hexadecanesulfonates
obtained in the solvent phase.
The EI spectra of n-alkanesulfonyl chlorides derivatized
into N,N-diethylsulfonamides reveal the presence of
Table 1 IR characteristic peaks of corresponding sulfonamides, and resulting sodium sulfonates salts
n
14
16
18
Primary
(cm-1
Pure
phase
(cm-1
Solvent
phase
Primary
(cm-1
Pure
phase
(cm-1
Solvent
phase
Primary
(cm-1
Pure
phase
(cm-1
Solvent
phase
(cm-1
)
)
)
)
)
(cm-1
)
)
(cm-1
)
)
CnH2n?1SO2N(C2H5)2
1384
1134
3472
1384
1181
1052
1384
1137
3473
1384
1175
1049
1383
1168
3470
1384
1175
1043
1383
1139
3437
1383
1177
1070
1382
1137
3469
1383
1179
1051
1382
1136
3477
1384
1182
1051
1384
1136
3467
1383
1176
1049
1382
1138
3469
1384
1186
1056
1382
1136
3470
1384
1182
1051
CnH2n?1SO3Na
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Solvent phase
Table 2 Isomeric distribution
of the corresponding
sulfonamides
Pure phase
% Primary
isomer
% Secondary
isomers
% Primary
isomer
% Secondary
isomers
C12H25SO2 N(C2H5)2 [20]
20.36
22.63
21.65
17.81
79.64
77.37
78.35
82.19
7.06
8.38
92.91
91.62
90.31
86.97
C14H29SO2N(C2H5)2
C16H33SO2N(C2H5)2
C18H37SO2N(C2H5)2
9.69
13.03
fragments characterizing the linear hydrocarbon chain, as
those at m/z 29, 43, 57, 71, 85… for all isomers of each alkyl
chain length from C14 to C18, with approximately the same
intensity, respectively. The characteristic fragments of the
N,N-diethylsulfonamide group of each alkyl chain length are
observed at m/z 137, 122, 107, 73, 58, and 43, corresponding
respectively to [HSO2(C2H5)2]?, [HSO2(CH2)(C2H5)]?,
[HSO2(CH2)2]?, [HN(C2H5)2]?, [HN(CH2)(C2H5)]? and
[HN(C2H4)]? fragments. The peak at m/z 73 was present
with an intensity of 100% for all isomers. We note the
presence of the peak characterizing [M–HSO2N(C2H5)2]?
only for the secondary isomers with very low intensity. On
the other hand, the peak characterizing the [M–CH3]?
fragment is present only for the primary isomers.
fragmentation is enhanced, and other peaks are observed
such as m/z 219, 178, 150, 136 and 95 corresponding
respectively to the [M–Na–C4H10]-, [M–Na–C7H15]-,
[M–Na–C9H19]-, [M–Na–C10H21]- and CH3SO3 frag-
-
ments (Fig. 1). The FIA-ESI/MS- spectrum of sodium salt
of 1-hexadecanesulfonate (II) is presented in Fig. 2A, and
reveals the presence of fragments characterizing [M–Na]-
and [2 M–Na]- anions, respectively at m/z 305 and 633.
Other peaks appear at higher cone voltage such m/z 290,
276, 219, 206, 179, 150, 136, 107 and 80, resulting from a
successive elimination of a methylene moiety from
[M–Na]- anion. The spectra of n-C16H33SO3Na (IIa and
IIb)) reveal also the presence of fragments characterizing
[M–Na]-, [2M–Na]-, and [SO3]- anions (Fig. 2B). The
molecular ion at m/z 328 has been observed by the
expanded view of the m/z 758 daughter ion region
(Fig. 2C). Figure 3 shows the FIA-ESI/MS- spectra of
sodium salts of octadecanesulfonates. The peaks charac-
terizing [M–Na]- and [SO3]- anions are observed
respectively, in the two spectra (Fig. 3A, B). The mass
spectra of III (Fig. 3A) show a presence of a major peak at
m/z 305 characterizing a [M–Na–C2H5]- fragment. The
successive elimination of a methylene moiety from this at
ESI/MS
The ESI mass spectrum of sodium salts of tetradecane-
sulfonates (I, Ia, and Ib) acquired in negative ion mode with
a direct infusion analysis spectrum (FIA-ESI/MS)- reveal
the presence of peaks at m/z 277, 577 and 80 corresponding
to [M–Na]-, [2M–Na]- and [SO3]- fragments, respec-
tively. However, at different ESI conditions, the
Fig. 1 FIA-ESI/MS- spectra of sodium salts of n-tetradecanesulfonates
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423
last leads to the following peaks at m/z 290, 249, 220, 205
and 165. The molecular ion has been observed by an
expanded view of the m/z 612 daughter ion region.
Results and Discussion
Surface Properties
The surface tension isotherms of the synthesized sulfonates
are shown in Fig. 4. They are similar to those obtained for
surfactants in general. The surface tension decreases as the
concentration increases. Surfactant molecules first adsorb
at the liquid/air interface until the surface of the solution is
saturated; the excess molecules tend to self-aggregate in
the bulk to form micelles and a clear break in the slope was
observed. The critical micelle concentration (CMC) and
the surface tension at the CMC (cCMC) were determined
from the intersection points in the c versus log C curves
and are given in Table 3. It can be noticed that the increase
in the length chain leads to lowering surfactant solubility as
expected. This is the case of IIIa, where its surface prop-
erties are not determined at 40 ꢁC, but at temperatures
close or higher than 50 ꢁC. The CMC values were also
determined by conductivity, to confirm the results obtained
by the tensiometry method. Figure 5 illustrates the specific
conductivity against concentration of synthesized second-
ary alkanesulfonates at different temperatures. It shows the
presence of two linear segments; the specific conductivity
of surfactant solution quickly rises by increasing the con-
centration because of the ion species. After the CMC, the
slower increase is due to the micelles formed preventing
the mobility of the ion species. CMC values of prepared
surfactants were taken at the intersection of the two straight
line trends and are illustrated in Table 3. They are in
general close to those obtained by the tensiometry method.
CMC values tend to increase with rising temperature.
However, a temperature increase also causes disruption of
the structured water surrounding the hydrophobic chain, an
effect that disfavors micellization [32]. It can be due to the
fact that it requires more surfactant molecules to aggregate
and be able to form micelles, which lead to high CMC
values [16]. It is also noted that there is an increase in the
CMC values accompanied by a reduction in the cCMC when
the percentage of secondary isomers increases. A minimum
is exhibited in the region of the CMC, probably due to the
presence of highly surface active impurities. In the surface
tension isotherms of Ib, IIb and IIIb, makes it difficult to
make a determination of an accurate CMC value by the
tensiometry method, whereas the conductivity method
leads to more accurate values because it is less sensitive.
The CMC values decrease with increasing numbers of
methylene groups in the hydrophobic moiety, obeying a
linear relationship. An increase in the length of hydro-
phobic carbon chain will lead to an increase in the repul-
sion force, and should be attributed to the weaker
interaction between hydrocarbon chains due to the
presence of two hydrophobic tails in the molecule, as these
Physicochemical Characterization
Surface Tension Measurements
The surface tension of synthesized sodium alkanesulfo-
nates was measured with a Wilhelmy tensiometer (Prolabo
TD 2000) using a series of aqueous solutions at various
concentrations. Doubly distilled water exhibiting a surface
tension of 72 mN/m-1 at 25 ꢁC was used to prepare all
solutions. Measurements of secondary alkanesulfonates
were carried at 40, 50 and 65 ꢁC, but those of primary
isomers were realized at 65 ꢁC. The CMC and cCMC values
were taken from the plots of the surface tension against the
logarithm of the concentration.
Conductance Measurements
The specific conductance method was also used for deter-
mining CMC values. The specific conductivity data were
collected with an electrical conductometer (Tacussel CD
61) using a platinum electrode with a cell constant of
62.82 m-1. The CMCs were determined as the concentra-
tion at the intersection of two lines obtained by plotting
specific conductance against concentration [23–25].
Hydrophilic-Lipophilic Balance (HLB)
The HLB values of sodium alkanesulfonates were calcu-
lated using Davies’s estimation formulas [26–28].
Krafft Point
Conductance against temperature of the aqueous surfactant
solutions containing the suspended solid was determined
and plotted against the reciprocal of the absolute temper-
ature (1/T). The Krafft points were determined as the
temperature at the intersection of two straight line fittings
[29].
Foaming
Foam measurements were done using the Bartsch
(Shaking) method [30, 31]. Aqueous solutions of sodium
alkanesulfonates and a commercial surfactant were pre-
pared close to their CMC. A certain amount of solution was
vigorously shaken in a closed cylinder. The foam evolution
versus the time was measured for all surfactants over a
concentration range.
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425
Fig. 2 FIA-ESI/MS- spectra of sodium salts of hexadecanesulfonate.
A Full scan mass spectrum of II; B full scan mass spectrum of IIa;
C expanded view of the m/z = 758 daughter ion region
in the absence of any other solutes, Cmax is calculated from
the following relation:
b
ꢀ
ꢁ
1
oc
Cmax ¼ ꢁ
ð1Þ
4:606 RT o Log C
samples are a mixture of secondary isomers. This leads to
the migration of the surfactant molecules to the air/water
interface and, consequently, reduces the surface tension.
This behavior has been confirmed for all sodium alkane-
sulfonates synthesized with a chain length varying from 12
to 18, and with different isomeric distributions, as shown in
Fig. 6. This behavior is the same at other temperatures.
Values of maximum surface excess (Cmax) can be
obtained from the slope of the plot of c versus Log C using
Gibbs’s equation [32]. For a solution of 1:1 ionic surfactant
where c is the tension (mN m-1), T is the absolute
temperature, R = 8.31 jmol-1 K-1, and Cmax is the
adsorption (mol cm-2). The area per molecule at the
interface (Amin) is expressed in square angstroms as
calculated from Eq. 2:
1016
Amin
¼
ð2Þ
N Cmax
where N is Avogadro’s constant and Cmax is in mol cm-2
.
Fig. 3 FIA-ESI/MS- spectra of sodium salts of octadecanesulfonate. A Full scan mass spectrum of III; B full scan mass spectrum of IIIa
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Fig. 4 Variation of surface
tension versus logarithm of
concentration of secondary
sulfonates at different
temperatures
The resulting values are presented in Table 3. There is a
increases with an increase in temperature, as a result of
increased molecular motion, which causes poorer packing
of adsorbed molecules [32].
significant increase of concentration at the interface (Cmax
)
with an increasing length of the hydrophobic moiety, which
becomes more important. Therefore, it increases the
amount of the saturation of adsorption at the air/water
interface, and so reduces Amin values. We also note that as
the hydrophilic group is moved from a terminal position to
an internal position, an increase of Cmax values is shown
which has been attributed to the fact that the internal iso-
mers occupy a larger area at the interface, versus terminal
isomers. The increased spatial demand of split hydrophobic
parts has a negative influence on the packing of the mol-
ecules at the interface [16]. An increase in temperature has
also a negative impact on the Cmax, which leads to a
reduction of its values for all surfactants. However, the
minimum area per molecule at the interface air/water
Hydrophilic-Lipophilic Balance (HLB)
The physico-chemical properties of ionic surfactants are
intimately associated with the balance between the polarity
of the head group and non polarity of the hydrocarbon
chain. This property is closely affected by various struc-
tural factors such as chain length, structure of the hydro-
phobic group, nature of hydrophilic group and its position
in the molecule, etc. The changes can be described and
explained in terms of the hydrophilic-lipophilic balance
(HLB). Its knowledge facilitates the choice of the best
surfactant in such processes as detergency, emulsification,
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Table 3 CMC, cCMC, and
surface parameters of resulting
surfactants in water at different
temperatures
T (ꢁC)
CMCa
(m mol/l)
CMCb
(m mol/l)
cCMC
(m N/m)
Cmax 9 1010
Amin
(A0)2
(mol/cm2)
I
40
50
65
40
50
65
40
50
65
40
50
65
40
50
65
40
50
65
40
50
65
40
50
65
40
50
65
–
–
–
–
–
–
–
–
–
–
1.82
2.09
1.20
1.95
2.70
–
1.80
2.45
1.51
2.54
3.77
–
31.79
32.46
31.00
28.66
31.83
–
1.28
1.50
1.23
1.15
1.24
–
129.71
110.68
134.98
144.37
133.89
–
Ia
Ib
2.88
–
4.73
–
30.36
–
1.22
–
136.1
–
II
–
–
–
–
–
0.371
0.588
–
0.327
0.368
0.377
0.386
0.345
0.427
0.385
–
32.81
33.5
–
1.32
1.47
–
125.78
112.94
–
IIa
IIb
III
IIIa
IIIb
0.758
0.355
0.446
0.400
–
31.38
30.79
29.56
28.91
–
1.25
1.33
1.15
1.26
–
132.82
124.83
144.37
131.77
–
–
–
–
–
–
0.186
–
0.071
–
33.46
–
1.58
–
105.08
–
0.132
0.182
0.093
0.102
0.105
0.186
0.230
0.0984
0.273
0.281
32.05
30.76
31.36
30.41
29.54
1.43
1.38
1.48
1.30
1.32
116.10
120.31
112.18
127.71
125.78
CMCa, CMCb: critical micelle
concentrations determined by
surface tension and by
conductivity measurements,
respectively
flotation, flocculation, foam separation, and corrosion inhi-
bition. It is also useful in interpretation of interfacial phe-
nomena as the reduction in surface tension, adsorption,
micellization, etc. HLB values of surfactants can be calcu-
lated by applying the Davies’ equation [26]. The HLB values
of the prepared sodium alkanesulfonates are given in
Table 4. The data reveal that the HLB values decrease by
increasing the length of the alkyl chain, and suggest that
these surfactants are direct-emulsion (O/W) emulsifiers.
This result is in good correlation with the fact that the
commercial SAS are well known as emulsifying agents [33].
lization. Micelle formation evidently becomes possible at
this point, beyond which there is a rapid increase in the
solubility of the surfactant in the micelles. KT values of
these sodium alkanesulfonates were determined and pre-
sented with those of primary alkanesulfonates taken from
the literature in Table 4 [34]. The results clearly show that
KT values increase as usual with an increase in the number
of methylene groups in the alkyl chain. The increase in
length of hydrophobic chain makes the molecules aggre-
gate in the bulk, thereby causing a reduction in surfactant
solubility and, consequently an increase in the KT value
[35]. The Krafft point follows a linear relationship based on
the number of carbons in the hydrocarbon chains (Fig. 7),
according to the general equation given by Gu [36], as
shown in the following equations (R2 is the correction
factor):
Krafft Point Temperature (KT)
The Krafft point is a temperature below which the solu-
bility of surfactant is quite low and insufficient for micel-
123

428
J Surfact Deterg (2012) 15:419–431
Primary alkanesulfonates
Secondary alkanesulfonates obtained in pure phase
Secondary alkanesulfonates obtained in solvent phase KT ¼ 4:05n ꢁ 28:00 R2 ¼ 0:9990
KT ¼ 4:62n ꢁ 18:16 R2 ¼ 0:9995
KT ¼ 4:72n ꢁ 32:96 R2 ¼ 0:9902
It is interesting to highlight the differences in KT values
related to the SAS obtained in the pure phase, commercial
SAS and SAS obtained by photosulfochlorination in the
presence of an aromatic solvent. Indeed, KT values
decrease as expected with an increase in the rate of sec-
ondary isomers for SAS obtained in the presence of an
aromatic solvent. This seems to be an interesting result, and
can be explained by increasing surfactant solubility, in
contrast to the primary surfactants which have a higher KT
with low solubility.
Foam Properties
This section reports on the study of the effect of the chain
length and isomeric distribution respectively on foaming
power and foam stability of synthesized sodium
Fig. 5 Plots of specific
conductivity of secondary
sulfonates solutions at various
temperatures as a function of
concentration
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J Surfact Deterg (2012) 15:419–431
429
Fig. 6 Linear relationship of log CMC versus carbon number of
secondary sulfonates at 40 ꢁC and primary sulfonates at 65 ꢁC
Fig. 7 Linear relationship of KT versus carbon number
alkanesulfonates. In general, the foams formed have rather
similar appearance after agitation, a mixture of large bub-
bles and very small ones, especially for Ia, Ib and IIa. The
foam evolution versus the time was measured for all sur-
factants over a concentration range. So, the initial foam
heights produced (h0) were read immediately after the last
agitation, and these are plotted against concentration in
Fig. 8. It can be seen from this figure that foam heights
increase gradually as a function of concentration, even
beyond the CMCs. The lower values of initial foam height
below CMCs are more pronounced, and this can be
explained by the fact that the air/water interfaces do not
contain sufficient amounts of surfactant to stabilize the
foam. The results obtained are comparable to those
obtained for sodium salts of commercial SAS [37]. The
initial foam height at the CMC becomes increasingly low
with an increase in the chain length of surfactants. This can
be explained by the reduction in their solubility, as for
C18H37SO3Na, which possess a low solubility. This can be
rationalized by the slow rate adsorption of these surfactants
at the air/water interfaces.
where (h5) is the residual foam height measured after
5 min.
These data were used to estimatethe foamability and foam
stability of each surfactant [38, 39]. Foam with R5 higher
than 50% can be considered as metastable, while lower
values of R5 indicate foams of low stability. Figure 9A, B
shows foam stability of the SAS obtained by photosulfo-
chlorination in the pure phase and in the presence of solvent
respectively. It is seen that the R5 = f(C) plots have a similar
character. There is a transition from a region of low foam
stability to that of high stability (meta stability). This tran-
sition occurs within a narrow concentration range and is
followed by a plateau at concentrations above the CMC. The
results obtained are similar to those obtained for a com-
mercial sample of sodium dodecylsulfate (SDS) used as
reference for anionic surfactants. It is noted that the abilities
of foaming and foam stability of Ia and IIa are much higher
than that of IIIa, and a reduction of foam stability was
observed when the rate of the secondary isomers increases
(IIb and IIIb). This study indicates that the best foaming
property is observed for primary and secondary sodium salts
of tetradecanesulfonates independently of their isomeric
distribution. This result is in good correlation with that
already shown for commercial SAS for the same length chain
[40], and in recent works related to glycine based surfactants
The residual foam ratio (R5%) was calculated as
follows:
h0
R5 ¼ ꢂ 100
ð3Þ
h5
Table 4 Krafft temperatures
and HLB values
KT (ꢁC)
HLB
Primary
Pure phase
Solvent phase
Experimental
Calculated
C14H29SO3Na
46.5
55.3
64.8
48 [34]
48 [35]
59 [35]
70 [35]
32.8
43.4
51.7
28.2
36.6
44.4
11.35
10.4
9.45
C
16H33SO3Na
18H37SO3Na
57 [34]
70 [34]
C
123

430
J Surfact Deterg (2012) 15:419–431
Fig. 8 Variation of the initial
foam values as a function of
Log C of synthesized
surfactants. A Pure phase,
B solvent phase
Fig. 9 Variation of the R5
parameter values as a function
of Log C different surfactants
A pure phase, B solvent phase
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12. El-Sukkary MMA, Sayed NA, Aiad I, Al-Azab WIM (2008)
Synthesis and characterization of some alkyl polyglycosides
surfactants. J Surf Deterg 11:129–137
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Author Biographies
Latifa Fekarcha earned her master’s degree in macromolecular
chemistry from the University of Sciences and Technology Houari
Boumediene (USTHB), Algiers, Algeria in 2004. She is currently a
Ph.D. student at the same university, and a permanent researcher at
the ‘‘Centre de Recherche Scientifique et Technique en Analyses
Physico-chimiques’’ (CRAPC), Algiers. Her research interests are in
anionic surfactants–their synthesis, properties and applications.
Amel Tazerouti received her master’s degree in organic chemistry
(1988) and her Ph.D. in organic chemistry (1994) from the University
´
of Sciences and Technology Houari Boumediene (USTHB), Algiers,
Algeria. During her doctorate, she joined the department of chemistry,
Catholic University of Louvain, Belgium, on a Belgium fellowship
for one year. She is currently a professor and director of the
Laboratory of Applied Organic Chemistry, Faculty of Chemistry,
University of Sciences and Technology Houari Boumediene (US-
THB), Algiers, Algeria. Her main research fields are synthesis and
properties of surfactants.
34. Weil JK, Smith FD, Stirton AJ, Bistline JR (1963) Long chain
alkanesulfonates and 1-hydroxy-2-alkanesulfonates: structure and
properties. J Am Oil Chem Soc 4:538–544
35. Nong L, Xiao C, Zhong Z (2011) Physicochemical properties of
novel phosphobetaine zwitterionic surfactant and mixed systems
with an anionic surfactant. J Surf Deterg 14:433–438
123