The Effect of Polar Head and Chain Length on the Physicochemical Properties of Micellization and Adsorption of Amino Alcohol-Based Surfactants

Article abstract of DOI:10.1002/jsde.12241

In this work, we have synthesized a series of quaternary ammonium from amino alcohols and n-bromoalkanes. The compounds are referred to as C_nEtOH, C_nPrOH, and C_niPrOH (where n = 12 and 14 carbons, EtOH = ethanol, PrOH = propanol, iPrOH = iso-propanol). Their structures were checked using the usual spectroscopic methods [¹H, ¹³C nuclear magnetic resonance (NMR) and infrared (IR)]. Their physicochemical properties in aqueous solution were studied using conductivity, surface tension, and ultra violet (UV)–visible absorption spectroscopy measurements. This study was conducted to show the effect of the linear hydrophobic chain and the location of the OH polar group with respect to the N⁺ quaternary ammonium on the physicochemical properties of the surfactants. The comparison between the physicochemical properties of the surfactants studied shows a distinct effect of the position of the OH group on the critical micelle concentration (CMC), the ionization degree (a), the area occupied at the interface (A_min), the free energy of adsorption (ΔG⁰_ad), and the free energy of micellization (ΔG⁰_M). The intermolecular interaction between the synthetic surfactants and the methyl orange (OM) dye is related to the degree of hydration of the micelle, proven by the hypsochromic displacement of OM wavelength (?_max) and ionization (a) of the micelles. The CMC, the degree of ionization, and the degree of hydration of the micelle follow the same trend.

Full text of DOI:10.1002/jsde.12241

J Surfact Deterg (2018)
DOI 10.1002/jsde.12241
ORIGINAL ARTICLE
The Effect of Polar Head and Chain Length on the
Physicochemical Properties of Micellization and Adsorption
of Amino Alcohol-Based Surfactants
1
1
Zakaria Hafidi · Mohammed El Achouri
Received: 30 April 2018 / Revised: 10 October 2018 / Accepted: 19 November 2018
2018 AOCS
©
In this work, we have synthesized a series of quaternary
ammonium from amino alcohols and n-bromoalkanes.
The compounds are referred to as C EtOH, C PrOH, and
Keywords Surfactants ꢀ Quaternary ammonium ꢀ Polar
head group ꢀ Critical micelle concentration ꢀ Degree of
ionization ꢀ Surface excess concentration ꢀ Amino alcohol
n
n
C iPrOH (where n = 12 and 14 carbons, EtOH = ethanol,
n
PrOH = propanol, iPrOH = iso-propanol). Their structures
were checked using the usual spectroscopic methods
J Surfact Deterg (2018).
1
13
[ H, C nuclear magnetic resonance (NMR) and infrared
IR)]. Their physicochemical properties in aqueous solution
(
Introduction
were studied using conductivity, surface tension, and ultra
violet (UV)–visible absorption spectroscopy measurements.
This study was conducted to show the effect of the linear
hydrophobic chain and the location of the OH polar group
Cationic surfactants have attracted the attention of many
researchers for a long time because of their wide applica-
tions, they are used as softeners, cosmetic or coating ingredi-
ents (Akram et al., 2015), antimicrobial agents (Gotmukle
and Bhagwat, 2013; Migahed et al., 2016), and also in the
mining and papermaking industries (Nilsson et al., 2008).
The aggregation of surfactants in micellar structures is a
phenomenon that depends on the molecular structure of the
surfactant and the conditions of the surfactant solution
(Akram et al., 2015; Grillo et al., 2009; Lv et al., 2014; Pan
et al., 2012; Phani Kumar et al., 2011, 2018; Prameela et al.,
+
with respect to the N quaternary ammonium on the physi-
cochemical properties of the surfactants. The comparison
between the physicochemical properties of the surfactants
studied shows a distinct effect of the position of the OH
group on the critical micelle concentration (CMC), the ioni-
zation degree (α), the area occupied at the interface (Amin),
0
the free energy of adsorption (ΔG ), and the free energy of
ad
0
M
micellization (ΔG ). The intermolecular interaction
between the synthetic surfactants and the methyl orange
2013, 2015, 2017; Wattebled and Laschewsky, 2007). The
(OM) dye is related to the degree of hydration of the
formation of micelles for ionic surfactants in solution is
mainly controlled by the equilibrium between two opposing
forces such as the attractive interaction between the linear
hydrophobic chains and the electrostatic repulsion between
the ionic groups (Akram et al., 2014; Maiti et al., 2009).
The modification of the molecular structures of the sur-
factants and the modification of the conditions of the sur-
factant solution affect the two antagonistic forces, thus
influencing the micellization and also the adsorption of the
ionic surfactants (Kabir-ud-Din et al., 2008; Moreira and
Firoozabadi, 2009; Shah et al., 2016).
micelle, proven by the hypsochromic displacement of OM
wavelength (λmax) and ionization (α) of the micelles. The
CMC, the degree of ionization, and the degree of hydration
of the micelle follow the same trend.
*
Mohammed El Achouri
achmedens@yahoo.fr
1
Mohammed V University in Rabat, Laboratoire de physico-
chimie des matériaux inorganiques et organiques, Centre des
Sciences des Matériaux, Ecole Normale supérieure-Rabat,
Morocco
In the literature, there are numerous reports on the effects
of the alkyl chain length on the micellization of surfactants
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containing a single hydrophilic group. On the other hand,
only a limited number of publications have been devoted to
bifunctional species and the effect of the polar head on micel-
lization. The influence of the size of the hydrophilic part of a
quaternary ammonium surfactant on its ability to adsorb at
the air/water interface and to form micelles in aqueous media
has been reported by many researchers (Dahanayake and
Rosen, 1984; Kabir-ud-Din et al., 2008; Moreira and Firooza-
badi, 2009; Omar and Abdel-Khalek, 1998; Shah et al.,
1-(dimethyl amino) propan-2-ol (>99%), and 2-(dimethyl
amino) ethan-1-ol (>99%) were purchased from Fluka, Swiss,
1-Bromododecane (>97%), 1-Bromotetradecane (>97%),
methyl orange (Helianthin), Acetonitrile, Dichloromethane,
Methanol, and Sodium bromide were from Sigma-Aldrich,
Germany.
Synthesis
2016; Venable and Nauman, 1964), but the study of the
N-(hydroxyalkyl)-N,N- dimethyl n-alkyl ammonium bromides
effect of the localization of a polar group with respect to qua-
ternary nitrogen, N , has not been widely reported. Let us
(Scheme 1), referred to as C EtOH, C PrOH, and C iPrOH
n
n
n
+
(n = 12 and 14, EtOH = ethanol, PrOH = propanol, and
iPrOH = iso-propanol) were synthesized using a simple
alkylation of the amino alcohol (3-(dimethyl amino) propan-
1-ol, 1-(dimethyl amino) propan-2-ol, or 2-(dimethyl amino)
ethan-1-ol)) with alkyl bromide (1-Bromododecane or
1-Bromotetradecane) in acetonitrile: a mixture of bromoalk-
ane (25 mmol) and amino alcohol (20 mmol) in acetonitrile
(20 mL) was heated for 24 h. The excess of amine was elim-
inated by vacuum evaporation. The products obtained were
washed three times with a mixture of ether and hexane for
purification. The yield of the reaction was about 70%.
The purity of the compounds was determined by chro-
matography, using a thin layer chromatography (TLC) plate
on silica gel immersed in a solution of 8% of NaBr pre-
pared in methanol. The eluent used was methanol/dichloro-
methane (1:9, by vol); the examination of the spots on the
plate was done by the ultra violet (UV) light (245 nm)
using bismuth nitrate as a revelator.
cite, for example, the work of Chevalier et al. (1991), who
studied the effect of the distance between the positive group
N and the carboxylate group on the physicochemical param-
eters, such as the maximum surface excess Γm and critical
micelle concentration (CMC) of zwitterionic surfactants and
also the work in which Hajji et al. (1990) showed the effect
of the polar head of 2-(decyldimethylammonio) alkanol bro-
mide surfactants on physiochemical parameters such as the
degree of ionization, α, and CMC.
+
The present article deals with surfactants prepared from
amino alcohols, whose polar heads contain two incorporated
+
functional groups: ammonium, N , and alcohol, OH. The
aim of this work is to detect micelle formation and investi-
gate the effect of the polar head on the properties accompa-
nying the micellization using different techniques, such as
conductivity and surface tension measurements. The interac-
tions of those cationic surfactants with an anionic dye,
methyl orange (OM), will also be used to understand the
behavior of surfactants studied in aqueous solution better.
Structural Characterization
1
The structure of the pure component was verified by H
1
3
Experimental
Reagents
and C nuclear magnetic resonance (NMR), using a Var-
1
ian spectrometer at 499.8 MHz ( H) and 125.23 MHz
13
( C), using the signal of deuterium of the solvent as the
lock. Infrared spectra were recorded on a Spectrophotome-
ter ALPHA II FTIR.
All solvents were of reagent grade and used without further
purification, 3-(dimethyl amino) propan-1-ol (>99%),
C PrOH (Scheme 2).
n
Scheme 1 Synthesis of N-(n-hydroxyalkyl)-N,N-dimethyl n-alkyl ammonium bromides
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1
13
n
Scheme 2 The spectral characteristics— H and C NMR spectra of N-(3-hydroxypropyl)-N,N-dimethyl n-alkyl ammonium bromide(C PrOH)
1
H NMR: (a) 0.89 ppm(t;3H); (b) 1.24–1.28 ppm
m;22H or 18H); (c) 1.59 ppm (p;2H); (d) 3.55 ppm
m;2H); (e) 3.34 ppm (s;6H); (f) 3.64 ppm (t;2H);
g) 1.88 ppm (p;2H); (h) 3.76 ppm (td;2H); and
i) 5.51 ppm (t;1H).
3,15–3.65 ppm
(dd;2H);
(g)
4.29 ppm
(m;1H);
(
(
(
(
(h) 1.42 ppm (d;3H); and (i”) 5.23 ppm (d;1H).
13
C NMR: (a) 14.09 ppm, (b; c; d) 22.71–66.05 ppm,
(e) 53.11 ppm, (f ) 68.1 ppm, (g) 61.75 ppm, and
(h) 20.81 ppm.
IR: υ(O H)
1
3
3741.26–3877.08 cm−1;
C NMR: (a) 14.09 ppm, (b; c; d) 22.71–65.04 ppm,
=
υ
=
(C H)
−1
−
1
(
(
e) 51.62 ppm, (f ) 62.04 ppm, (g) 27.95 ppm, and
h) 58.28 ppm.
3009.2–3387 cm ; and υ
= 685.6–1591.2 cm .
C C)
(
−
1
IR: υ
= 3746.4–3746.6 cm ; υ
C C)
= 3000-3210
(
O H)
(C H)
−1
Conductivity Measurements
−
1
cm ; and υ
= 740.8–1560.71 cm .
(
C EtOH (Scheme 3).
H NMR: (a) 0.89 ppm (t;3H); (b) 1.24–1.28 ppm
m;22H or 18H); (c) 1.59 ppm (p;2H); ; (d;f) 3.58-
.60ppm (dt;4H); (e) 3.34 ppm (s;6H); (g) 3.89 ppm
n
Conductivity measurements for the different concentrations
of prepared surfactants are taken using Thermo Scientific
Orion Star A212 Benchtop Conductivity Meter of a cell
1
(
3
(
−
1
constant K equal to 0.4750 cm . The aqueous solutions of
surfactants were prepared with ultrapure water having a
conductivity value of about 2 μS cm− at 298.15 K.
q;2H); and (i’) 4.93 ppm (t;1H).
1
3
1
C NMR: (a) 14.09 ppm, (b; c; d) 22.71–65,56 ppm,
e) 51.81 ppm, (f ) 66.58 ppm, and (g) 55.67 ppm.
(
−
1
IR: υ(O H −) = 3734.2–3752.24 cm ; υ
= 3009.
(C H)
−1
Surface Tension Measurements
1
2
–3205.4 cm ; and υ
= 739.4–1561.2 cm .
(C C)
C iPrOH (Scheme 4).
n
The measurement of the surface tension (γ) for the solu-
tions of different surfactant concentration was made by the
plate method using a Lauda TD1 tensiometer with an accu-
racy of ꢁ0.2 mN m . The surface tension of the ultrapure
1
H NMR: (a) 0.89 ppm (t;3H); (b) 1.24–1.28 ppm
m;22H or 18H); (c) 1.52–1.53 ppm (m;2H); (d) 3.45–-
.49 ppm (hept;2H); (e) 3.43 ppm (s;6H); (f)
(
3
−1
1
13
n
Scheme 3 The spectral characteristics— H and C NMR spectra of N-(2-hydroxyethyl)-N,N-dimethyl n-alkyl ammonium bromide(C EtOH)
1
13
Scheme 4 The spectral characteristics— H and C NMR spectra of N-(2-hydroxyisopropyl)-N,N-dimethyl n-alkyl ammonium bromide
CniPrOH)
(
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−
1
water γW was 73.1 ꢁ 0.2 mN m at 298.15 K. Before
experimental values of the conductivity before and after the
each measurement, the aqueous solutions of surfactants in a
CMC (κ < CMC, κ > CMC).
C
C
−
6
−1
−1
concentration range from 1 × 10 to 1 × 10 mol L
were filtered on filter paper having a porosity of 0.45 μm.
The degree of ionization of a micelle (α) is defined as the
fraction of counterion not associated with the micelle; in
others terms, α quantifies the proportion of counterions that
are completely hydrated away from the micelles compared
to the counterion set. α can then be obtained by making the
ratio of the slopes of the conductivity curve as a function of
the concentration of surfactant before and after the CMC
according to the following relation:
Absorbance Measurements
The absorbance spectra of OM solutions at different con-
centrations were made using a Jasco V-630 UV–VIS Spec-
trophotometer with quartz cups. The change of the
absorbance value in the range 300–600 nm in the presence
of a surfactant was determined using water as a reference.
All tests were conducted at ambient temperature and
neutral pH.
S2
α ¼
ð1Þ
S1
where S is the post-CMC slope and S is the pre-CMC
1
2
slope. The value of α also reflects a partial binding between
−
the amphiphile molecules and the Br counterion and pro-
vides the net charge of the micelles. α can also be used to
predict the degree of hydration of micelles (Soldi
et al., 2000).
The free energy of micellization of a monovalent ionic
amphiphile can be obtained from the CMC and the degree
of ionization α (Nakagaki and Handa, 1984; Zana, 1996):
Results
Conductivity Measurements
The plots obtained from the conductivity as a function of
surfactant concentrations are presented in Fig. 1 for the C14
series. The same trend was observed for the C12 series.
These conductometry diagrams allow calculation of the
physicochemical parameters, such as CMC, degree of ioni-
zation, α, and free energy of micellization, ΔG .
ꢀ
ꢁ
CMC
0
M
ΔG ¼ ð2 + αÞRTln
ð2Þ
ω
where ω is the number of moles of water per liter (ω = 55.5
0
M
−1
mol L at 298.15). The results obtained from conductivity
The hypothesis of an aggregation of molecules in clus-
ters beyond a threshold concentration was first suggested
by McBain in 1913 (Holmberg, 2002). In water, the cat-
ionic surfactant molecules form micelles in which the
hydrophobic parts assemble and are protected from contact
with water by an envelope of polar heads. The CMC is fre-
quently determined to be the concentration at the inter-
section of the two straight lines extrapolated from the
measurements are summarized in Table 1.
Surface Tension Measurements
Figure 2 shows the variation of the surface tension as a func-
tion of the concentration of surfactants. To determine the num-
ber of molecules adsorbed at the interface, we have used the
method based on the measurement of the surface tension, γ, as
a function of the concentration of surfactant according to the
Gibbs adsorption equation (Rosen and Kunjappu, 2012):
X
dγ ¼
Γ dμ
i
ð3Þ
i
i
where Γ can be assimilated to the number of moles of each
i
species, i per unit area at the interface (Holmberg, 2002),
and μ is the chemical potential for each species, i.
i
X
dγ ¼ −RT
iΓidlnCi
ð4Þ
where R is the gas constant in J mol− L , T the tempera-
1
−1
−
1
ture in K, and C the concentration in mol L . For ionic
i
surfactants of the AB
Z
type such that A is the surfactants
j Aj
jZBj
of the charge Z and B the counterion of opposite charge
Fig. 1 Specific conductivity (κ) as a function of concentration of
A
C
14EtOH, C14PrOH, and C14iPrOH at 298.15 K
ZB, the equation is written in the following way:
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Table 1 Conductivity parameters of surfactants at 298.15 K: Critical micelle concentration (CMC), ionization degree α, and free energy of micel-
0
lization ΔGM
C
12PrOH
C
12EtOH
C
12iPrOH
C
14PrOH
C
14EtOH
C
14iPrOH
CMC (mmol L−
1
)
15.2
0.51
14.6
0.47
13.7
0.45
5.1
4.2
3.5
α
0.33
0.32
0.29
ΔG (kJ mol−1)
0
−30.28
−31.25
−31.89
−38.43
−39.54
−40.95
M
1
016
Amin ¼
ð8Þ
N:Γm
−
2
where N = Avogadro’s number and Γ (mol cm ) is the
m
maximum surface excess concentration at the CMC.
The efficiency pC20 is the negative logarithm (pC20 = −
log(C )) of the concentration of the surfactant in the bulk
2
0
−
1
phase necessary to produce a 20 mN m reduction in the
surface tension of the solvent.
Surface pressure, ПCMC, is calculated by the difference
between the value of the surface tension of the water, γw,
and that of the surfactant solution at the CMC, γCMC
,
according to the following relation:
ПCMC ¼ γ −γCMC:
ð9Þ
w
The standard free energy of adsorption was calculated
using to Eq. 10:
Fig. 2 Variation of the surface tension γ with surfactant concentration
log(C) for C
98.15 K
n
PrOH, C
n
EtOH, and C
n
iPrOH (n = 12 and14) at
2
ꢀ
ꢁ
CMC
П
Γm
0
ΔG ¼ ð2−αÞRTLn
−
ð10Þ
ad
ω
dγ ¼ −RT½ΓAdlnCA + ΓBdlnCBꢂ
ð5Þ
The critical packing parameter of surfactants, CPP,
whose value corresponds to the morphology of the aggre-
gate, is defined as:
suppose that at the interface, the condition of the electro-
neutrality ΓB = фΓA is satisfied. Where ф is the charge
ꢂ ꢂ
ꢂZA
ꢂ
ratio ꢂ ꢂ
ZB
VH
CPP ¼
a0 × lC
ð11Þ
dγ ¼ −ð1 + фÞRTΓAdlnCA
ð6Þ
the factor (1 + ф) is generally noted in the literature by n,
thus the surface excess concentration at the air/water inter-
where VH is the effective volume of the hydrophobic
chains, where a is the surface of the polar head and l is
0
C
face Γ can be written:
the length of the alkyl chain. At saturation, a can be
0
m
ꢃ
ꢄ
replaced by Amin
.
dγ
dlogCA
−
The volume, V , of a hydrophobic chain depends on the
H
Γ ¼
m
ð7Þ
number of carbon atoms, n, inserted in the hydrophobic
2;303nRT
ꢃ
ꢄ
core (Myers, 1999; Tanford, 1980):
dγ
dlogCA
below the CMC.
where
is the slope of the surface-tension plots just
3
VH ¼ 27:4 + 26:9 × ðn−1Þ Å
ð12Þ
The curve of the surface tension (γ) as a function of the
concentration of surfactants is also used to determine the
other physicochemical parameters such as minimum area
the length of the hydrophobic chain I
mated according to n:
C
can also be esti-
lC ≤ 1:5 + 1:265 × ðn−1Þ Å:
For the aggregation number, N, although it was hard and
ð13Þ
per molecule, Amin, surface pressure, ПCMC, free energy of
0
ad
adsorption, ΔG , and efficiency, pC .
20
1
The area occupied by molecules at the interface provides
information on the degree of stacking and the orientation of
the adsorbed surfactant molecule. This parameter, Amin, is
calculated by the following relation:
complex to use conventional methods such as H NMR
measurement and fluorescence quenching to obtain the
value of N, Mandal and coworkers and others have deter-
mined the value of N using the above and other various
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Table 2 Surface properties of surfactants at 298,15 K: Critical micellar concentration (CMC), surface tension of the CMC (γ CMC), surface
excess concentration Γ
m
, minimum area per molecule (Amin), efficiency pC20, the surface pressure П, critical packing parameter CPP, free energy
0
of adsorption ΔG , and the aggregation number N
ad
Surface properties
C
12PrOH
C
12EtOH
C
12iPrOH
C
14PrOH
C
14EtOH
C
14iPrOH
−
1
CMC (mmol L
)
25
15
11.7
35.2
37.8
3.5
2.13
33.5
39.6
3.9
1.77
33.1
40
1.47
35.1
37.9
4.6
−
1
γ
CMC (mN m
1
)
33.9
39.1
2.7
33.9
39.2
3.3
П(mN m−
)
pC20
4.3
2
1.42 × 10−10
1.07 × 10−10
9.87 × 10−11
1.40 × 10−10
1.00 × 10−10
8.83 × 10−11
Γ
m
(mol cm−
)
2
1
16.54
155.07
168.19
118.51
164.92
188.05
A (Å Þ
CPP
0.18
0.13
−67.75
19
0.12
−70.85
17
0.17
−70.33
34
0.12
−82.82
24
0.11
−87.59
21
ΔG (kJ mol−1)
0
ad
−55.92
Aggregation number N
25
techniques (Bossev et al., 1999; James et al., 2005; James
and Mandal, 2011a, 2011b; Krishnan et al., 2003, 2004;
Szajdzinska-Pietek and Wolszczak, 2000).
The value of N can be calculated according to the follow-
ing equation (Wadekar et al., 2012):
the case of C PrOH. The results obtained for the other sur-
14
factants for this band are summarized in Table 3. The
377 nm band has been observed for many surfactant and
cationic polymer systems, and its origin has been a subject
of debates (Buwalda and Engberts, 2001).
Figure 4 shows the normalized absorbance spectra
obtained for OM alone (50 μmol L ) and the solutions of
4
× π × l2
Amin
−1
C
N ¼
ð14Þ
surfactant concentration higher than the CMC (8 mmol
−1
All the results of surface tension properties and aggrega-
tion number are summarized in Table 2.
L ) for C14PrOH, C14EtOH, and C14iPrOH. We observe
an offset of the spectra of OM as a function of the OH loca-
tion, between 423 nm and 429 nm for the C14 series and
from 429 to 433 nm for the C12 series. The value of Δλmax
increases while CMC and α values decrease.
UV–Visible Spectroscopy Measurements
As can be seen from Tables 1 and 2, the CMC and the other
physicochemical parameters of surfactants studied depend
on the position of the OH group with respect to quaternary
ammonium N , and the linear alkyl chain, for both C12 and
C14 series.
Discussion
+
If the effect of hydrocarbon length on the variation of the
CMC is well known (Klevens, 1953; Rosen et al., 1999), it
To explain these effects, we have used the sensitivity of
OM dye when it is complexed with a cationic surfactant
(Akba s¸ and Kartal, 2007; Mishra and Haram, 2004). This
study leads to understand the relation between the degree of
ionization, α, the value of CMC, and the degree of hydration
of micelles, this relation can be followed by the displace-
ment of the maximum absorption wavelength, λmax, of the
OM solutions at different concentrations of the surfactant.
Figure 3 shows a typical form of the variation of absor-
bance of OM in the absence and in the presence of surfac-
tant below and above the CMC. The concentration of OM
−
1
retained to conduct this work is 50 μmol L that gives the
suitable absorbance value (Alehyen et al., 2010). The band
at 465 nm corresponds to the solution of OM in the
absence of surfactants according to Rinuy et al. (2000), this
band is attributed to the π π* transition of the hydrated
form of OM. On the other hand, Giri et al. (2012) assign
the same band to a n ! π* transition. The band 431 nm
corresponds to the detection of the surfactant micelles in
Fig. 3 UV–Vis absorption spectrum of Methyl orange OM at differ-
ent concentrations of the C14PrOH (0.45 and 8 mmol) surfactant at
298.15 K and neutral pH
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Table 3 Variation of the maximum wavelength λmax of surfactants at 298.15 K, neutral pH, and surfactant concentration C > CMC
Surfactants
C
12PrOH
C
12EtOH
C
12iPrOH
C
14PrOH
C
14EtOH
C
14iPrOH
wavelength λmax
432.77 nm
430.07 nm
429.05 nm
428.67 nm
426.80 nm
423.20 nm
We must note that the CMC values reported in Tables 1
and 2 are very different: those obtained from conductivity
measurements are more precise (linear scale, instead of log-
arithmic for surface tension). From the measurement of the
surface tension, we note that the maximum surface excess
Γm decreases slightly as the hydrophobicity of the surfac-
tant molecules increases. Indeed, according to Table 2
when the hydrophobic chain length is incremented by two
methylenes (CH2)2 , Γ decreases slightly, therefore the
m
value of the occupied area at the interface, Amin, increases,
this means a rapid saturation of the interface. This result
can also confirm the value of CMC, which decreases from
C12 to C14 for the three types of molecules studied. These
results are in agreement with those of Venable and Nauman
(1964), who found that for quaternary ammonium surfac-
tants, the increase in the length of the alkyl chain leads to
an increase of Amin and a decrease of Γm.
From geometrical considerations, (Eq. 14) the number of
aggregation, N, of the micelles should increase with an
Fig. 4 UV–Vis absorption spectrum of methyl orange (OM) at the
highest concentration of CMC (8 mmol) for the surfactants of
C
14PrOH, C14EtOH, and C14iPrOH at 298.15 K and neutral pH
is not the same for the variations of the physicochemical
parameters accompanying the micellization. Also the effect
of the polar head is often not very well studied and the
results of the literature in this area remain scattered
increase of the hydrophobic part l of the surfactant mole-
cule, and decrease with the increase of the occupied area of
C
the molecule at the interface, Amin
.
In fact, Table 2 shows N increases from 12 to 14 carbon
(Chevalier et al., 1991; Dahanayake and Rosen, 1984; Hajji
atoms (l increases), which is in agreement with the results
C
et al., 1990; Omar and Abdel-Khalek, 1998; Venable and
Nauman, 1964).
obtained by Lianos and Zana (1981) for the cationic surfac-
tants: decyl-, dodecyl-, tetradecyl-, and hexadecyl trimethyl
ammonium bromides (DTAB, DDTAB, TTAB, and
HDTAB, respectively): they find that N increases with the
increase of the alkyl chain from 10 to 16 carbon atoms
(from DTAB to HDTAB).
The examination of the polar head of our studied prod-
ucts suggests the presence of two polar parts, the ammo-
nium group and the hydroxyl group. The discussion of this
article will be devoted to these two factors: the increase of
the linear hydrophobic carbon chain and the location of the
alcohol function with respect to the quaternary ammonium.
For the other physicochemical parameters calculated,
such as ПCMC, pC , and ΔG0 , it is clearly observed that
20
M,ad
ПCMC and pC20 increase as a function of the hydrophobic-
ity of the molecule. The adsorption efficiency pC20 is corre-
lated with the hydrophobicity of the most surfactants
Effect of Hydrocarbon Chain
As can be seen from Tables 1 and 2, the CMC values of the
surfactants obtained using both conductometric and surface
tension measurements decrease as a function of the increase
of the linear alkyl chain. The increase of the hydrophobic
chain by two methylene-groups, (CH2)2 , leads to a
decrease in the CMC following the Klevens equation
(Romsted, 2014).
The values of the free energies of adsorption at the air/-
0
water interface, ΔG , and micellization in aqueous media,
ad
0
M
ΔG , are negative and confirm that the spontaneous pro-
cesses of adsorption and micellization are made easier with
hydrophobic chain lengthening.
(Klevens, 1953; Rosen et al., 1999).
logðCMCÞ ¼ A−Bm
ð15Þ
Effect of Polar Head
Parameters A and B are known as Klevens constants, and
are available in the literature for many surfactants (Rosen
and Kunjappu, 2012) and m is the number of carbon atoms
in the hydrophobic chains.
The results reported in this work clearly show that the posi-
tion of the OH group in the polar head with respect to qua-
ternary ammonium, N , affects the physicochemical
+
J Surfact Deterg (2018)

J Surfact Deterg
parameters accompanying micellization and adsorption.
anionic dye to the presence of a cationic surfactant allows
us to use the variation of its maximum absorption wave-
length, λmax, when it is complexed with surfactant
(Karukstis et al., 1998). This study leads to give an idea
about the relationship between the degree of hydration of
micelles and their degree of ionization, α.
For the two-examined series, C12 and C , the CMC
14
obtained by conductometric and surface tension measure-
ments decrease in the following order C PrOH >
n
C EtOH > C iPrOH.
n
n
The maximum surface excess Γ and minimum area per
m
molecule Amin are well affected by the position of OH. It
was found that the surface area occupied by the molecule at
As can be seen from Table 3, Δλmax varies in the follow-
ing order C PrOH > C EtOH > C iPrOH in the same order
n
n
n
the interface has the largest value for C iPrOH, followed
of CMC. This result is also consistent with those obtained
for the degree of ionization α that increases in the same
order, the same behavior is also observed for surfactants
2-(decyldimethylammonio) alkanol bromides, such that the
passage from 2-decyldimethylammoniobutannol bromides
to 2-decyldimethylammonoethanol bromide shows that the
two magnitudes CMC and α vary in the same order (Hajji
et al., 1990). The degree of ionization expresses in fact the
degree of hydration of the micelles, according to Soldi
et al. (2000).
According to Muller et al. (1972), the first methylene
groups of the hydrophobic chain adjacent to the hydrophilic
head are often considered in the sphere of hydration. It is,
therefore, useful to divide the interior region of the micelle
into an outer sphere that can be penetrated by water and an
internal one from which water is excluded.
n
by C EtOH and C PrOH.
n
n
It should be noted that the addition of two methylenes
+
(
CH2)2 between two polar groups N and OH causes a
decrease of Amin, from C EtOH to C PrOH. This result is
12
14
in disagreement with Rosen and Kunjappu (2012), which
indicates that if the hydrophobic part of the molecule lies
between two polar groups, it tends to lie flat in the interface
and that the surface occupied by the molecule in the inter-
face is increased, this is proved also by the work of Cheva-
lier et al. (1991).
+
The position of the OH group with respect to N also has
a significant effect on the values of N: according to Table 2,
it is clearly remarkable that the increase of Amin decreases
the value of N for both C12 and C14 series. The same behav-
ior was observed Lianos and Zana (1982), for tetradecyl-
+
−
We can then say that the higher the degree of ionization,
the higher the rate of penetration of water molecules into
the hydration sphere, which also leads to an increase in the
proportion of OM hydrated between the hydrophobic
chains of the surfactant (Akram et al., 2014), which itself
trialkylammonium bromides (C H N (C H ) Br ).
m 2m+1 3
14
29
They found that, in micellar solutions, N decreases with
increasing size of the head group from 1 to 4 carbon atoms.
For the other parameters, pC , П
, and ΔG0
2
0
CMC
M
0
and ΔG , the variation of the position of OH with respect
ad
leads to an increase in the maximum wavelength, λmax
,
+
to N does not have the same behavior as the effect of
according to Fig. 4. According to this agreement, we can
conclude that is a correlation between the three parameters
CMC, α, and λmax as indicated in Fig. 5.
hydrophobicity on ПCMC, such that the latter varies in the
opposite order of the CMC, but the same variation of the
pC20 behavior the effect of hydrophobicity with respect to
CMC was observed for the effect of the location of OH
+
with respect to N according to the following order
C PrOH > C EtOH > C iPrOH.
n
n
n
Conclusion
The micellization and adsorption free energies, ΔG0
M
0
ad
and ΔG , were all negative, confirming the spontaneity of
Cationic surfactants in the series of N-(hydroxyalkyl)-N,N-
dimethyl n-alkylammonium bromides with various alkyl
chain lengths and various hydrophilic groups were synthe-
sized from amino alcohols and alkyl bromides and charac-
formation of micelles and adsorption. As a function of
CMC and Amin, which shows that with each transition from
C PrOH to C EtOH, C PrOH to C iPrOH, and C EtOH to
n
n
n
n
n
1
13
C iPrOH, the CMC and A
n
values indicate spontaneous
min
terized using the usual spectroscopic methods ( H,
C
adsorption and formation of micelles.
According to the theory of the micellar structure devel-
oped by Israelachvili et al. (1977) and Mitchell and Ninham
NMR and IR), their physicochemical properties were calcu-
lated using conductivity, surface tension, and UV spectro-
scopic measurements.
(
0
1981), the values of CPP are all in the range of
The effects of the hydrophobicity of the alkyl chain and
the polar part on the variation of the physicochemical
parameters accompanying the micellization and adsorption
were discussed.
1
≤ CPP ≤ , which corresponds to spherical micelles.
3
From the above discussion, it was found that the position
of the OH group and the alkyl chain length affect all
parameters accompanying the micellization phenomena. To
understand this phenomenon better, we have used the inter-
action of surfactants with the OM dye. The sensitivity of an
+
The effect OH with respect to N on the property of
micellization and adsorption was clearly studied. The inter-
molecular interaction approach between the synthetic
J Surfact Deterg (2018)

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Conflict of Interest The authors declare that they have no conflict
of interest.
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