Dissolution of soap scum by surfactant part I: Effects of chelant and type of soap scum

Article abstract of DOI:10.1007/s11743-013-1544-3

The equilibrium solubilities of two model soap scums [calcium stearate and magnesium stearate: Ca(C₁₈)₂ and Mg(C₁₈) ₂] were measured in aqueous solutions containing three different types of surfactants: methyl ester sulfonate (MES) as an anionic; alcohol ethoxylate (EO9) as a nonionic; and dimethyldodecylamine oxide (DDAO) as an amphoteric with and without a chelating agent [disodium ethylenediaminetetraacetate (Na₂EDTA)]. The solubility of calcium soap scum was generally higher than that of magnesium soap scum, the exception being some DDAO systems. The use of the DDAO surfactant with the Na ₂EDTA chelating agent at high pH gives the highest solubilities of both studied soap scums. The soap scum solubility is on the order of 2,000 times that in water at high pH. The DDAO is the most effective surfactant under all conditions. The MES is more effective than the EO9 at low pH with the opposite trend observed at high pH. The synergism from added chelant is generally greater at higher pH and is greatest for DDAO followed by EO9.

Full text of DOI:10.1007/s11743-013-1544-3

J Surfact Deterg
DOI 10.1007/s11743-013-1544-3
ORIGINAL ARTICLE
Dissolution of Soap Scum by Surfactant Part I: Effects of Chelant
and Type of Soap Scum
•
Sawwalak Itsadanont John F. Scamehorn
•
•
•
Sukhwan Soontravanich David A. Sabatini
Sumaeth Chavadej
Received: 5 August 2013 / Accepted: 14 October 2013
Ó AOCS 2013
Abstract The equilibrium solubilities of two model soap
scums [calcium stearate and magnesium stearate: Ca(C18)2
and Mg(C18)2] were measured in aqueous solutions con-
taining three different types of surfactants: methyl ester
sulfonate (MES) as an anionic; alcohol ethoxylate (EO9) as
a nonionic; and dimethyldodecylamine oxide (DDAO) as
an amphoteric with and without a chelating agent [diso-
dium ethylenediaminetetraacetate (Na2EDTA)]. The solu-
bility of calcium soap scum was generally higher than that
of magnesium soap scum, the exception being some
DDAO systems. The use of the DDAO surfactant with the
Na2EDTA chelating agent at high pH gives the highest
solubilities of both studied soap scums. The soap scum
solubility is on the order of 2,000 times that in water at
high pH. The DDAO is the most effective surfactant under
all conditions. The MES is more effective than the EO9 at
low pH with the opposite trend observed at high pH. The
synergism from added chelant is generally greater at higher
pH and is greatest for DDAO followed by EO9.
Introduction
Soap is a salt of a long chain fatty acid consisting of a long
hydrocarbon chain and a carboxylic acid group. In hard
water, soap scum is formed from the reaction between soap
and divalent cations (especially calcium and magnesium
ions), as shown in Eq. 1 for calcium [1], causing a sticky,
visually unpleasant stain. In this work, the model soap
scums studied are calcium stearate (calcium octadecanoic
acid) and magnesium stearate (magnesium octadecanoic
acid).
2C18H37COONa þ Ca2þ ! ðC18H37COOÞ2Ca #
ð1Þ
þ 2Naþ
Aqueous-based hard surface cleaners targeting soap
scum dissolution commonly use a mixture of surfactants
and chelating agents. At surfactant concentrations above
the critical micelle concentration (CMC), a micelle-
promoting agent [2] or surfactant which co-micellizes
with either a non-ionized stearic acid (at a low solution pH)
or a stearate anion (at a high solution pH), is used [3]. The
chelating agent can disrupt the bond between the divalent
cations (e.g., calcium and magnesium ions) and the stearate
anion of soap scum, to form water soluble complexes of
chelating agent with divalent cations, leading to the
enhancement of soap scum dissolution [4] as shown in
Eq. 2. A study of surfactants with a chelating agent to aid
the soap scum dissolution was carried out systematically by
Soontravanich et al. (2010); A chelant of disodium
ethylenediaminetetraacetate (Na2EDTA) [5] was used
with three different surfactants to dissolve the calcium
soap scum synthesized from a reaction between stearic acid
and calcium hydroxide. The solubility of calcium stearate
in water is very low throughout a wide pH range [6, 7]. The
solubility of the synthesized soap scum was found to
Keywords Anionic surfactants ꢀ Application of
surfactants ꢀ Non-ionic surfactants ꢀ Soap scum
S. Itsadanont ꢀ S. Chavadej (&)
The Petroleum and Petrochemical College, Chulalongkorn
University, 254 Soi Chulalongkorn12, Phayathai Rd., Wangmai,
Patumwan, Bangkok 10330, Thailand
e-mail: sumaeth.c@chula.ac.th
J. F. Scamehorn ꢀ S. Soontravanich ꢀ D. A. Sabatini
Institute for Applied Surfactant Research, University of
Oklahoma, Norman, OK, USA
S. Chavadej
Center of Excellence on Petrochemical and Materials
Technology, Chulalongkorn University, Bangkok, Thailand
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J Surfact Deterg
substantially increase in the presence of Na2EDTA and
dimethyldodecylamine oxide (DDAO). The DDAO yielded
higher solubility of the soap scum compared to an anionic
and a nonionic surfactant [6].
between stearic acid and magnesium chloride (0.9625 g of
stearic acid and 0.1612 g of MgCl2). The stearic acid was
first dissolved in ethanol and then mixed with an aqueous
solution of calcium hydroxide or magnesium chloride for
1 day. The mixture was filtered using 0.2-lm filter paper
and the precipitate was rinsed with water, ethanol, and
acetone to remove the remaining reactants. Finally, the
filtered precipitate was dried in a vacuum oven at 30 °C for
3 h. The synthesized soap scum samples were kept in a
desiccator until use.
ðC18H37COOÞ2Ca þ Na2EDTA ꢀ 2C18H37COOꢁ
ð2Þ
þ 2Naþ þ CaEDTA
To continue the aforementioned research work, the
present study focused on three different surfactants
(anionic, nonionic, and amphoteric) and the equilibrium
solubilities of two model soap scums (calcium stearate and
magnesium stearate) with and without Na2EDTA at various
solution pH levels. In addition, the surface morphology,
crystalline structure, average particle size, and particle size
distribution of the soap scum were measured. In part II of
this series, we will investigate the kinetics of the
dissolution process.
Soap Scum Characterization Techniques
The particle size distribution of soap scum was measured
with a particle size analyzer (Malvern, Mastersizer X).
Surface morphology of soap scum was observed by a
scanning electron microscope or SEM (JSM-5800 LV,
Jeol). The functional groups were identified by FT-IR
(Thermo Nicolet, Nexus 670). Crystalline sizes were
obtained from X-ray diffraction analysis or XRD (PW3710
Based) and calculated by using the Debye–Scherrer equa-
tion [8, 9]:
Experimental
Materials
0:9k
Stearic acid (98.5 ? % purity), calcium hydroxide
(99.995 % purity), and magnesium chloride (99 ? %
purity) were obtained from Sigma-Aldrich (St. Louis, MO,
USA). Methyl ester sulfonate (MES) (88.6 % purity) was
provided by PTT-Chemical Co., Ltd., alcohol ethoxylate
(EO9) (99.95 % purity) was supplied from Thai-Ethoxylate
Co., Ltd., and dimethyldodecylamine oxide (DDAO)
(99 ? % purity) was purchased from Sigma-Aldrich (St.
Louis, MO, USA). Disodium ethylene diamine tetraacetate
(Na2EDTA) (99 % purity) was obtained from Carlo Erba
(Rodano, MI, USA). Absolute ethyl alcohol (99.8 ? %
purity) was purchased from Italmar. Acetone (A.C.S.
grade) was obtained from J.T. Baker (Phillipsburg, NJ,
USA). Sodium hydroxide (98 % purity) was obtained from
J.T. Baker (Phillipsburg, NJ, USA), and HCl (99 % purity)
was obtained from Lab Scan (Phathumwan, BKK). All
chemicals were used as received without further purifica-
tion. Distilled water was used in all experiments.
D ¼
ð3Þ
Bcosh
where, D is the crystalline size, k is the X-ray wavelength,
B is the full width half maximum (FWHM) of the dif-
fraction peak measured at 2h, and h is the diffraction angle.
Soap Scum Dissolution Experiments
The equilibrium solubility of the synthesized calcium
stearate or magnesium stearate in a surfactant solution
(MES, EO9, or DDAO) with different concentrations of
Na2EDTA were determined at a constant temperature of
25 °C and different solution pHs. All surfactant solutions
were prepared at pH values in the range of 4–11 by using
HCl and NaOH solutions. Surfactant solutions were pre-
pared at a constant concentration of 3 mM for MES, 2 mM
for EO9, and 0.1 M for DDAO; these concentrations are
consistent with values studied in previous research [6]. An
excess amount of calcium stearate [Ca(C18)2] or magne-
sium stearate [Mg(C18)2] was added into a prepared sur-
factant solution (MES, EO9, or DDAO) with and without
0.1 M Na2EDTA. The mixed solutions in screw-cap vials
were heated to above 70 °C in a water bath. Then, they
were kept in a temperature-controlled water bath at 25 °C
for 3 h. The solutions were further equilibrated for at least
1 week with daily shaking. After that, the solutions were
filtered using a 0.2-lm nylon filter membrane to remove
the remaining soap scum. Finally, the clear solutions were
analyzed by an atomic absorption spectrometer (AAS)
(SpectrAA-300, Varian) for calcium or magnesium
Methods
Synthesis Procedure of Soap Scums
Calcium stearate was synthesized from a stoichiometric
reaction between stearic acid and calcium hydroxide
(0.9375 g of stearic acid in 50 ml of ethanol and 0.1221 g
of Ca(OH)2 in 50 ml of H2O) [6]. The final pH of the
mixed solution was 5.9, suggesting that most Ca(OH)2 was
used to form calcium stearate. In the same way, magnesium
stearate was synthesized from the stoichiometric reaction
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J Surfact Deterg
concentration. Triplicate samples showed less than 1 %
variance.
calcium stearate, the peak at 1,575 cm-1 indicates COO-
stretching from carboxylic acid salts [10]. For magnesium
stearate, the peak at 1,702 cm-1 indicates C=O stretching
from the carboxylic acid ester [10, 11]. This also supports
that calcium or magnesium ions reacted completely with
stearic acid. The peak at 2,990–2,850 cm-1 indicates –CH3
and –CH2– in aliphatic compounds (CH-antisym and CH-
sym stretching) [10].
Results and Discussion
Characteristics of Synthesized Soap Scums
The particle size distribution and average diameter of each
soap scum are shown in Fig. 1. The average particle size of
calcium stearate (10.1 lm) was much lower than that of
magnesium stearate (29.6 lm). Some submicron particles
may have passed through the filter used after synthesis. So,
while a detailed and comprehensive analysis of particle
size distribution is not attempted here, it can be concluded
that the particles of magnesium stearate are broader in size
distribution and larger on average than those of calcium
stearate. Figure 2 shows that the calcium stearate has a
smaller crystalline size (36.9 vs. 57.0 nm, respectively) and
is less crystalline (from Fig. 3) than the magnesium stea-
rate. The SEM images in Fig. 3 show that both calcium
stearate and magnesium stearate have smooth and non-
porous surfaces. The calcium stearate exhibits much
smaller sizes with more uniform particle sizes than the
magnesium stearate from SEM photos, consistent with the
particle size distribution in Fig. 1. The FT-IR spectra in
Fig. 4 indicates that both the calcium stearate and mag-
nesium stearate showed no –OH peak, indicative of the
carboxylic acid group [10], suggesting the stearic acid
completely reacted with calcium or magnesium ions. For
The molar ratios of Ca-to-stearate and Mg-to-stearate of
both synthesized soap scums were found to be 1:1.92 and
1:1.98, respectively which are close to the theoretical molar
ratios of both soap scums.
Measured Soap Scum Solubilities
Figures 5, 6, 7, 8, 9, 10 show the equilibrium solubilities of
both soap scums [Ca(C18)2 and Mg(C18)2] in the presence
and absence of Na2EDTA chelant for all three surfactants
as a function of pH. Also shown are the solubilities of each
soap scum in pH adjusted water only and in the presence
only of the chelant. Table 1 shows the solubilities at the
extreme pH levels (4 and 11) to permit ready comparison
of the effect of different surfactants and of the presence of
the chelant.
All experiments were carried out at a very high sur-
factant concentration (at least one order of magnitude
above the critical micelle concentration or CMC) and an
excess amount of each synthesized soap scum in order to
ensure that most of the added surfactant is in micellar form
and to reach a saturation level of soap scum solubility.
Fig. 1 Particle size distribution
and average diameter of two
soap scums: a calcium stearate,
and b magnesium stearate
Fig. 2 XRD diffraction
patterns and crystalline size of
two soap scums: a calcium
stearate, and b magnesium
stearate
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Fig. 3 SEM images of two soap scums: a, b calcium stearate; and c, d magnesium stearate
Fig. 4 FT-IR spectra of two
soap scums: a calcium stearate,
and b magnesium stearate
Â
Ã
2
KSP ¼ Ca2þ ½C18H37COOꢁꢂ
ð4Þ
Either dissolved calcium or magnesium ions present in the
aqueous phase after the dissolution occurs was measured to
determine soap scum solubility. This analytical technique
is felt to be more accurate than a GC analysis of super-
natant stearate ion concentration after derivatization used
in previous work [6]. The disadvantage of the current
technique is that it does not detect the presence of solidified
protonated stearate which can exist at low pH. There is no
indication that the protonated solidified stearate exists at
even the lowest pH of 4 used here, but systematic verifi-
cation of this was not attempted.
The solubility product can be calculated from the
solubility data at high pH where all the stearate is in
anionic form. At pH 11, KSP is 7.77 9 10-15 M3 for
calcium stearate and 1.94 9 10-15 M3 for magnesium
stearate. Literature values of KSP are 1.58 9 10-15 M3
[13], 3.61 9 10-15 M3 [14], and 1 9 10-12 M3 [15] for the
calcium stearate and 5 9 10-13 M3 [15] for the magnesium
stearate. While there is a large deviation in literature
estimates of KSP values, the KSP values measured here are
in the range of previous measurements. The extremely low
solubilities of the soap scums make these measurements
notoriously difficult. Further, it should be noted that
solubility products are very temperature sensitive.
Discussion of Solubility of Soap Scums without
Surfactant
A concentration-based solubility product or KSP (ignoring
the minor activity coefficient correction needed to give true
thermodynamic solubility products) [12] is defined as:
From Table 1 and Figs. 5 and 6, the solubility of cal-
cium soap scum is higher than that of magnesium soap
scum at all pH levels consistent with the literature
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Fig. 5 Equilibrium solubility of Ca(C18)2 in MES; Na2EDTA; MES/
Na2EDTA solutions; and water
Fig. 7 Equilibrium solubility of Ca(C18)2 in EO9; Na2EDTA; EO9/
Na2EDTA solutions; and water
Fig. 8 Equilibrium solubility of Mg(C18)2 in EO9; Na2EDTA; EO9/
Na2EDTA solutions; and water
Fig. 6 Equilibrium solubility of Mg(C18)2 in MES; Na2EDTA; MES/
Na2EDTA solutions; and water
solubility product values. The solubilities of both soap
scums decrease with increasing pH with the degree of
decline being greater for calcium soap than the magnesium
soap. As pH increases, the fraction of the stearate in
anionic (deprotonated) vs. nonionic (protonated) form
increases [16] so lower cation counterion concentration is
required to achieve the solubility product; therefore, soap
scum solubility decreases.
The Na2EDTA alone has little effect on soap scum
solubility at low pH, but improves solubility as pH
increases due to the increased effectiveness of the com-
plexation between the chelant and calcium or magnesium
ions. In the presence of chelant, there are five forms of
chelant that depends on solution pH (H4Y, H3Y-, H2Y2-
,
HY3-, and Y4-) [6]. The most effective form to bind with
metal ions (calcium and magnesium ions) is Y4- which
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Table 1 Equilibrium solubilities of calcium stearate and magnesium
stearate at extreme pH levels (data from Figs. 5, 6, 7, 8, 9, 10)
Systems
Equilibrium solubility (M)
Calcium stearate
Magnesium stearate
pH 4
pH 11
pH 4
pH 11
MES
0.000823
0.000299
0.017477
0.001123
0.000474
0.011259
0.000274
0.000274
0.002894
0.000274
0.001048
0.023578
0.000494
0.000103
0.007199
0.000658
0.000165
0.011518
0.000074
0.000123
0.003085
0.000123
0.000267
0.019416
EO9
DDAO
MES/Na2EDTA
EO9/Na2EDTA
DDAO/
Na2EDTA
Na2EDTA
H2O
0.0000332 0.0000329 0.0000247 0.0000309
0.0000634 0.0000125 0.0000264 0.0000079
½MLꢂ
KMY
¼
ð5Þ
½Mꢂ½L]
where, [ML], [M], and [L] are concentrations of metal–
ligand complex, metal, and ligand, respectively [17].
The value of KMY could not be calculated from the
solubility data here because at the highest pH value used
(11), only about 85 % of the EDTA is in Y4- form [18].
From the literature, the complexation constant for EDTA/
calcium is 5.0 9 1010 and is 4.9 9 108 for EDTA/mag-
nesium [18, 19]. The KMY for Na2EDTA increases with
increasing pH [20], explaining why soap scum solubilities
increase with increasing pH in the presence of a ligand.
From Table 1, at pH 11, the chelant alone without sur-
factant can increase soap scum solubility by a factor of 3
for calcium stearate and 4 for magnesium stearate at a
Na2EDTA concentration of 0.1 M. At pH 11, the calcium
stearate is more soluble than the magnesium stearate in the
presence of the Na2EDTA, consistent with the KMY values.
In interpreting solubilities in the presence of surfactants
with and without chelant in the next section, the surfactant-
free results have demonstrated that the solubility of the
soap scum in water decreases with increasing pH and that
with chelant present increases with increasing pH.
Fig. 9 Equilibrium solubility of Ca(C18)2 in DDAO; Na2EDTA;
DDAO/Na2EDTA solutions; and water
Discussion of Solubility of Soap Scums with Surfactant
Fig. 10 Equilibrium solubility of Mg(C18)2 in DDAO; Na2EDTA;
DDAO/Na2EDTA solutions; and water
From Figs. 5, 6, 7, 8, 9, 10 and Table 1, all three surfac-
tants studied substantially increase soap scum solubility
either in the presence or absence of ligand (EDTA). The
relative improvement and the synergism between surfac-
tant and ligand are very dependent on surfactant type and
pH. The model amphoteric surfactant DDAO is clearly the
most effective in dissolving the soap scum under all con-
ditions as also found in our previous study [6].
exists at a very high solution pH. The solubility improve-
ment due to the chelant is greater for the less soluble
magnesium soap than the calcium soap. If all of the EDTA
is in Y4- form, the complexation constant for Na2EDTA
with a divalent metal is given by:
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J Surfact Deterg
Table 2 Forms of soap scum, DDAO, ability of Na2EDTA to complex cation, and solubility of soap scum in surfactant/chelant system at
different pH levels
pH
Dominant form of soap scum
Dominant charge of Ability of Na2EDTA to
DDAO
Solubility of soap scum in
surfactant/chelant system
complex cation
MES
EO9
DDAO
Low
Protonated stearic acid (nonionic)
Cationic
Low
Medium Low
High
Intermediate Protonated stearic acid (nonionic) and
Stearate (anionic)
Cationic and
Zwitterionic
Medium
Medium Medium High
High
Stearate (anionic)
Zwitterionic
High
Low
Medium Very
high
The simultaneous complexation of calcium or magne-
sium by the chelant and the formation of mixed micelles
between the stearate and the added surfactant cause the
most effective soap scum dissolution [4]. Table 2 sum-
marizes the charge on the soap scum, charge on the DDAO,
ability of Na2EDTA to complex calcium or magnesium,
and the qualitative ability of each of the three surfactants to
dissolve soap scum in the presence of chelant, all as a
function of pH. Table 2 will be referred to in our inter-
pretation of equilibrium solubilities of soap scums. Syn-
ergism in mixed micelle formation between the
carboxylated soap and the added surfactant will be key in
understanding trends in solubility of soap scum overlaying
the solubility of the pure soap scum in water and the ability
of the chelant to complex metal cations already discussed.
As summarized in Table 2, the soap transitions from
nonionic (protonated) at low pH to anionic (stearate anion)
at high pH. The DDAO is cationic (protonated) at low pH
and zwitterionic at high pH. So, as pH increases, the mixed
micelle between the carboxylate soap and the added sur-
factant goes from nonionic/anionic to anionic/anionic for
MES; from nonionic/nonionic to anionic/nonionic for EO9;
and from nonionic/cationic to anionic/zwitterionic for
DDAO. The synergism of mixed micelle formation can be
quantified by the variable b; the more negative the value of
b, the greater the synergism. Micelle formation synergism
increases in the order anionic/anionic (0) = nonionic/non-
ionic (0) \ nonionic/cationic (-2.5) \ nonionic/anionic
(-3.5) \ anionic/zwitterionic (-7) [21–23] with typical
b values given in parentheses.
From Figs. 7 and 8, in the case of model nonionic sur-
factant EO9, the equilibrium solubility of each soap scum
changes little with pH in the absence of a chelant, but
increases with pH in the presence of a chelant. At low pH,
the chelant has little effect on solubility, but increases it by
as much as 200 % at pH 11. The calcium soap has higher
solubility than the magnesium soap. At high pH, the che-
lant improves solubility modestly, from an average of
111 % for the calcium soap to 71 % for the magnesium
soap. In the absence of a chelant, the greater synergism of
the anionic/nonionic mixed micelles at high pH is probably
offset by the decreasing water solubility of the soap scum.
From Figs. 9 and 10, in the case of the model ampho-
teric surfactant DDAO, the equilibrium solubility of each
soap scum decreases modestly with increasing pH without
chelant and increases modestly with increasing pH with
chelant. Without chelant, the increasing synergism in
mixed micelle formation with increasing pH is more than
offset by the decreasing solubility of the raw soap scum
itself. The calcium soap has a similar solubility to the
magnesium soap. The chelant improves solubility sub-
stantially, particularly at high pH; for calcium soap at pH
11 by a factor of 8, and by a factor of 6 for magnesium soap
at pH 11.
From Figs. 5, 6, 7, 8, 9, 10 and Table 1, the solubility of
Ca(C18)2 is significantly higher than that of Mg(C18)2 in all
systems except the DDAO system at low pH in the pre-
sence of chelant or marginally at high pH in the absence of
chelant. There is no apparent explanation for these DDAO
results.
From Figs. 5 and 6, in the case of model anionic sur-
factant MES, the equilibrium solubility of each soap scum
decreases with increasing solution pH, with or without
chelant. The calcium soap has higher solubility than the
magnesium soap. The chelant improves solubility mod-
estly, from an average of 27 % for the calcium soap to
64 % for the magnesium soap. The limiting factor with
MES is formation of mixed micelles with the greater
synergism of the anionic/nonionic mixed micelles yielding
high solubilities at low pH than the anionic/anionic mixed
micelles at high pH.
From Figs. 5, 6, 7, 8, 9, 10, changes in solubility were
fairly monotonic, so in comparing different surfactants,
we will focus on the results at extreme pH values of 4
and 11 in Table 1. In the absence of chelant, at pH 4, the
order of dissolution effectiveness is DDAO [ MES
[ EO9 for both calcium and magnesium and at pH 11, is
DDAO [ EO9 & MES for calcium and DDAO [
EO9 [ MES for magnesium. In the presence of chelant,
at pH 4, the order of dissolution effectiveness is
DDAO [ MES [ EO9 for both calcium and magnesium
and at pH 11, is DDAO [ EO9 [ MES for calcium and
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J Surfact Deterg
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Acknowledgments Financial support for this work was provided by
The Thailand Research Fund (TRF)-The Royal Golden Jubilee Ph.D.
Program (RGJ); Center of Excellence on Petrochemical and Materials
Technology, Thailand; The Petroleum and Petrochemical College,
Chulalongkorn University; The industrial sponsors of the Institute for
Applied Surfactant Research at the University of Oklahoma including
CESI Chemical Research, Church and Dwight, Clorox, ConocoPhil-
lips, Ecolab, GSK (GlaxoSmithKline), Haliburton, Huntsman, InVia-
Westvaco, Novus, Sasol North America, S. C. Johnson and Son, and
Shell Chemical. We thank Dr. Piyawat, from The University of
Oklahoma for assistance. We thank David Scheuing for introducing
us to this research topic.
23. Soontravanich S, Munoz JA, Scamehorn JF, Harwell JH, Sabatini
DA (2008) Interaction between an anionic and an amphoteric
surfactant: part I. Monomer-micelle equilibrium. J Surf Deterg
11:251–261
References
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Mixtures. In: Abe M, Scamehorn JF (eds) Mixed Surfactant
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Sawwalak Itsadanont received her B.Eng. (2007) in petrochemicals
and polymeric materials from the Faculty of Engineering and
Industrial Technology, Silpakorn University. She is currently a
Ph.D. candidate in the Petrochemical Technology Program at The
Petroleum and Petrochemical College, Chulalongkorn University,
Thailand.
4. Martell AE, Motekaitis RJ (1992) Determination and Use of
Stability Constants, 2nd edn. VCH Publishers, New York
5. Tai LHT (2000) Formulating Detergents and Personal Care
Products. A Complete Guide to Product Development. AOCS
Press, Champaign
John Scamehorn is Emeritus Director of the Institute for Applied
Surfactant Research at the University of Oklahoma. He received his
B.Sc. and M.Sc. at the University of Nebraska and his Ph.D. at the
University of Texas, all in chemical engineering. He has worked for
Shell, Conoco, and DuPont. His research interests include surfactant
properties important in consumer product formulation and thermo-
dynamics of surfactant aggregation processes.
6. Soontravanich S, Lopez HE, Scamehorn JF, Sabatini DA, David
R (2010) Dissolution study of salt of long chain fatty acids (soap
123

J Surfact Deterg
Sukhwan Soontravanich received a B.Sc. in Chemical Engineering
and an M.Sc. in petroleum engineering from Chulalongkorn Univer-
sity in Bangkok, Thailand, and a Ph.D. in chemical engineering from
the University of Oklahoma in the USA. She is a principal chemist at
the technology center (SEA/India), Ecolab, Thailand.
technologies, advanced microemulsion systems for vegetable oil
extraction, biofuel production and cleaning systems, and sustainable
technologies for drinking water treatment in developing countries.
Sumaeth Chavadej is a professor at the Petroleum and Petrochemical
College, Chulalongkorn University, Bangkok, Thailand. He received
his B.Sc. in chemical engineering from Chulalongkorn University
(1971), his M.Sc. in public health engineering from the University of
Newcastle upon Tyne UK (1978), and his Ph.D. in chemical
engineering from Monash University, Australia (1985). His research
focuses on the areas of applied surfactants, plasma for chemical
conversion, biohydrogen, and photocatalysis.
David A. Sabatini is a professor of civil engineering and environ-
mental science, and is Associate Director of the Institute for Applied
Surfactant Research, and Director of the WaTER Center at the
University of Oklahoma, Norman. He received his B.Sc. from the
University of Illinois (1981), his M.Sc. from Memphis State
University (1985), and his Ph.D. from Iowa State University
(1989). His research focuses on surfactant-based environmental
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