ujconline.netujconline.net/wp-content/uploads/2014/12/cntctfrm_fca... · web viewseveral other...
TRANSCRIPT
Preparation of Different Cationic Gemini Surfactants and their Applications as Corrosion Inhibitors and Oil Dispersants
Review Article
By
Maher Ibrahim Nessim
Associate Professor
Analysis and Evaluation Department,
Egyptian Petroleum Research Institute
Associate Professor
E-mail:[email protected]
1
Contents
Item PageCover 1Contents 2I. Introduction 3II. Chemical Structures of Gemini Surfactants 5III. State Of Gemini Surfactants in the Premicellar Range of Concentration 10IV. Behavior at Interfaces 11V. Efficiency of gemini surfactants as corrosion inhibitors for carbon steel in acid media 17VI. Micelle Formation And Solubilization 19 a. Aqueous Dimeric Surfactant Solutions At Concentrations Below The Critical Micellization Concentration
21
b. dimeric Surfactants At Interfaces 24 b.1. Air–Solution Interface 24 b.2. Solid-Solution Interface 27 c. Solubility In Water, CMC, And Thermodynamics Of Micellization Of Dimeric and Oligomeric Surfactants
28
d. Critical Micellization Concentration 29 e. Thermodynamics of Micellization 30VII. Correlation between the Efficiency of the Cationic Gemini Surfactants as Corrosion Inhibitors and their Quantum Chemical Calculation Studies
33
1- Introduction 332- Quantum chemical parameters 332.1. Atomic charges 34
2.2. Molecular orbital energies 34 2.3. Dipole moment 35 2.4. Energy 35 3. Quantum Chemical Calculation Methods 35
3.1. Ab-initio and MP2 methods 363.2. Semiempirical methods 36
3.2.1.MNDO Method (modified neglect of differential overlap) 36 3.2.2.AM1 Method 36Optimized structure of some cationic gemini surfactants of the type N2,N3-dialkyl-N2,N2,N3,N3-tetramethylbutane diamminium bromide:
37
The frontier molecule orbital density distributions of an example of the prepared cationic gemini surfactants
37
VIII: Different examples of Prepared Cationic Gemini Surfactants in Our work 38References 39
2
I. Introduction
Gemini or dimeric surfactants (Fig. 1) are new types of amphiphilic molecules that
have attracted attention from various industrial and academic research groups. These
surfactants are made up of two amphiphilic moieties connected at the level of the head
groups, or very close to the head groups, by a spacer group, which can be hydrophobic or
hydrophilic, flexible or rigid [1–3]. The gemini surfactants behave mainly as normal
surfactants, with similar sequences of phases and aggregates structures, but they also show
some interesting differences. They exhibit some unusual physicochemical properties that
might prove useful for technical applications in the future. The current interest in such
surfactants arises from three essential properties: (1) gemini surfactants are characterized by
critical micelle concentrations CMC that are one to two orders of magnitude lower than for
the corresponding conventional (monomeric) surfactants [1,4]; (2) gemini surfactants are
much more efficient than the corresponding conventional (monomeric) surfactants at
decreasing the surface tension of water [5–8]; (3) aqueous solutions of some gemini
surfactants with short spacers can have remarkable rheological properties (viscoelasticity,
gelification and shear thickening) at relatively low surfactant concentration whereas the
solution of the corresponding monomer remains low viscous [9]. In addition to those
properties, gemini surfactants appear to have better solubilizing, wetting, foaming, and lime
soap dispersing properties than conventional surfactants [10–13].
Owing to these unique properties, gemini surfactants have been widely used in
industrial detergency, gelation of organic solvents, template synthesis of various materials,
etc. Besides, the Krafft temperatures of gemini surfactants with hydrophilic spacers are
generally very low [10–12,14,15], giving these surfactants the capacity to be used in cold
water. These properties are commonly used to evaluate surfactant performance and are
important for applications such as cleaning and stabilization of dispersed systems. The first
reports on gemini surfactants concerned bis quaternary ammonium halide surfactants.
3
FIG. 1 Schematic representation of a gemini surfactant.
The biological activity of gemini surfactants, in aqueous solution, was studied [13, 16,
17], and micellar solutions of these surfactants were used to catalyze chemical reactions [18].
Most studies, however, reported on the surface tension of the aqueous solutions of gemini
surfactants for CMC determinations and an assessment of their capacity in reducing the
surface tension of water [3, 5–8]. These studies did not raise much interest among surfactant
scientists in spite of the much lower CMC and stronger biological activity found for gemini
surfactants compared with the corresponding monomeric conventional surfactants. It was
only in the early 1990s, following the synthesis of gemini surfactants in a great variety of
chemical structures, that more systematic studies revealed that such surfactants possess
properties that make them superior to conventional surfactants [14]. Thus, their values of C 20,
the surfactant concentration where the surface tension is decreased by 20 mN/m, are much
lower for equal or lower values of CMC (surface tension at the CMC) [14]. The idea
underlying the study of gemini surfactants is that linking surfactants two by two may provide
a new way to control the shape of their assemblies and thus some of their properties [19].
The vast majority of work on gemini surfactants has been made with symmetrical
gemini surfactants, i.e., containing identical polar head groups and identical hydrophobic
tails. These are true gemini surfactants and they can also be regarded as a kind of dimeric
surfactants. Several reviews on gemini surfactants have recently been published [14, 20–25].
It is well known from research on structure–property relationships that surfactants with an
asymmetrical geometry may give interesting characteristics in terms of self-assembly into
aggregates and packing at interfaces. For instance, fine tuning of the internal curvature of
micro emulsions in order to obtain systems with very large solubilization capacity can be
made by designing surfactants with different lengths of the two hydrophobic tails or with
4
asymmetrical branching of one tail [26–29]. Diglycerides and phospholipids are typical
examples [30]. Studies on asymmetrical gemini surfactants are still scarce. Recent studies
have been made on gemini surfactants in which the polar head groups are chemically
different.
Gemini surfactants with non-identical ‘‘halves’’ have been referred to as hetero-
gemini [31,32]. By using a surfactant with such a chemical structure, one may expect to get
the best out of two attractive concepts: (1) gemini surfactants and (2) a 1:1 molar
combination of two different surfactants built into the same molecule. This novel geometry in
the molecule may allow a new way to control the adsorption and shape of surfactant
assemblies and may provide properties that are often obtained by mixed surfactants at
equimolar ratio. The alkanediyl-N-bis(alkyl dimethyl ammonium bromide) or bisquaternary
ammonium bromides have been by far the most investigated gemini surfactants because their
synthesis and purification are relatively easy. These surfactants are designated by the
abbreviation m-s-m, 2Br-, s and m being the carbon numbers of the alkanediyl group (spacer)
and of the alkyl chain of the amphiphilic moieties. These surfactants are formally the dimers
of the quaternary dimethyl ammonium bromide surfactants with two unequal alkyl chains of
carbon numbers m and s/2. The symbolism used above for symmetrical dimeric surfactants
can be easily extended to asymmetrical dimeric surfactants (m-s-mV, 2Br-) and to surfactant
oligomers (m-s-m-s-m, 3Br- for a trimeric surfactant, for instance).
This review refers to dimeric gemini surfactants. Throughout the review,
‘‘conventional surfactants’’ and ‘‘monomeric surfactants’’ are given the same meaning. The
next section discusses chemical structures, of gemini surfactants. Section III reviews the
behavior of gemini surfactants in solutions below the CMC. Section IV deals with their
behavior at interfaces whereas section V emphasizes on their efficiency as corrosion
inhibitors for mild steel. The sixth section reviews micelle formation and solubilization. The
last section predicts the correlation between the efficiency of the cationic gemini surfactants
as corrosion inhibitors and their quantum chemical calculation studies.
II. Chemical Structures of Gemini Surfactants
Gemini surfactants with a great variety of chemical structures have been obtained by
acting on the nature of the head group and spacer group, as illustrated in Fig. 1. The head
group can be anionic, cationic, nonionic, or zwitterionic while the spacer group is hydrophilic
or hydrophobic, rigid or flexible [1–3, 5–13,15–18,33–53]. Gemini surfactants with non-
5
identical head groups have been recently synthesized [31,54–60]. The hydrophobic moieties
are generally normal alkyl chains, CmH2m+1. However, gemini surfactants with mixed
fluorinated-hydrogenated alkyl chains, C8F17C4H8 for instance, have been synthesized [61].
Examples of chemical structures for gemini surfactants are given in Fig. 2. Surfactants [A]–
[D] are cationic, [E]–[I] and [L] are anionic, [J] can be made zwitter ionic, [K] is a nonionic
sugar-based gemini surfactant, and [N] is a surfactant with one positive head group and one
negative head group. [A], [B], [D], [G–J] and [L] have a flexible spacer, whereas [C], [E] and
[F] have a rigid spacer, Fig.2.
G Form [45] H Form [46] I Form [47]
6
J Form [48] K Form [51] L Form [52]
M Form [53] N Form [54] O Form [61]
P Form [59] Q Form [31]FIG. 2 Examples of gemini surfactants
In [A]–[C], [E], [F], [L]–[O] the spacer is hydrophobic whereas it is hydrophilic in
[D] and [G]–[J] where Y=O or O(CH2CH2O)x. [M] and [N] are functional gemini surfactants:
the electrical charge of [M] can be acted upon electrochemically and [N] is cleavable. [O] is a
gemini surfactant with mixed hydrocarbon/fluorocarbon chains. [P] is a gemini surfactant
with one anionic and one cationic head group separated by two methylene groups, the two
alkyl chains may be symmetrical or asymmetrical. These surfactants will be denoted m, mV,
where m and mV being the carbon numbers of the chains bound to the phosphate and
trimethylammonium head groups, respectively.[Q] is a nonionic gemini surfactant when X =
OH and an anionic gemini when X=SO4Na.
Due to lack of space, only three examples of synthesis of gemini surfactants are given.
Surfactant [A] and its homologs (R=C12H25 and Y=(CH2)s-) were obtained via the single-step
reaction of dodecyldimethylamine with the corresponding -dibromoalkane (molar ratio
7
2.1/1) in dry ethanol under reflux for 48 h [1]. Other solvents can be used, such as ethyl
acetate, acetone, methyl cyanide, etc., depending on the surfactant synthesized [1–3,5–
8,13,16– 18,33–35,37–42].
The phosphate-quaternary ammonium hetero-gemini surfactant [P] of Fig. 2 was
synthesized by a surprisingly simple two-step, one-pot reaction, shown in Scheme 1 [58]. A
fatty alcohol was reacted with the cyclic ethylene chlorophosphate to yield the intermediate 1,
which was subsequently ring opened by an alkyldimethylamine to form the desired gemini
surfactant 2.
Scheme 1 Synthesis of surfactants [P] [59].
A large series of surfactants of this type has been prepared with hydrocarbon chains
containing 8–18 carbon atoms. The synthesis is attractive and versatile in that the two main
building blocks, the fatty alcohol and the alkyldimethylamine, are readily available. The
method therefore allows easy access to all types of surfactants with identical or different
hydrocarbon tails. The cyclic ethylene chlorophosphate is somewhat expensive, but the use of
this starting material may be circumvented by preparing the intermediate 1 by reaction the
fatty alcohol with phosphoryl chloride followed by addition of ethylene glycol and a tertiary
amine, as is also shown in Scheme 1.
Contrary to the gemini surfactant [A] of Fig. 2, compound [P] is counter ion free, i.e.,
the zwitterionic surfactant is in the form of an inner salt. Compound [Q] of Fig. 2 is a gemini
surfactant with different polar head groups, one hydroxyl group or sulfate and one methyl-
capped poly (ethylene glycol). The published synthesis is outlined in Scheme 2 [31]. A fatty
nitrile derived from oleic acid was used as starting material. Epoxidation with hydrogen
peroxide over a tungstic acid catalyst yielded the epoxide 1, which was ring-opened by
8
methyl-capped poly (ethylene glycol) to yield the nonionic gemini surfactant 2. Compound
[Q] with the corresponding sulfate 3, was obtained by treatment of 2 with chlorosulfonic acid
[60]. The synthesis strategy lends itself to production in large scale (in which case
chlorosulfonic acid would probably be replaced by SO3). Analogous products with other
anionic groups than sulfate can probably be synthesized from the intermediate 2 by
employing the synthesis routes discussed above.
The synthesis strategy shown in Scheme 2 can in principle be used on all unsaturated
lipophilic starting materials. In practice there may not be many alternatives to oleic acid
derivatives for large-scale preparation. An analog to the nonionic surfactant 2 has recently
been synthesized from methyl oleate [62]. The real difficulty when dealing with gemini
surfactants lies in the purification of the raw surfactants. The purification of the crude gemini
surfactants is essential, particularly in studies of adsorption and behavior at interfaces. The
purification procedures are somewhat easier for the quaternary ammonium gemini
surfactants.
Sophisticated procedures must often be used. Indeed, one or more reaction steps that
lead to gemini surfactants usually involves the two ends of some intermediate compound.This
reaction rarely reaches full completion. It results in the formation of a mixture of mono- and
di-functionalized compounds. Their separation is usually achieved through chromatography.
Scheme 2, Synthesis of Surfactants Q [31]
III. State Of Gemini Surfactants in the Premicellar Range of Concentration
9
Many papers discussed the state of ionic gemini surfactants at concentration below the
CMC. Several situations were considered. First, the gemini may be dissociated, and give rise
to one gemini ion and two counter ions, or not completely dissociated, with partial binding of
one counter ion to the gemini ion. The binding equilibrium obeys the mass action law and the
binding is expected to increase with the surfactant concentration. Second, depending on the
conformation of the spacer group of the surfactant gemini, its two alkyl chains may or may
not interact. Third, premicellar aggregation may take place, giving rise to small aggregates of
gemini ions of low aggregation number. Some surface tension data have been interpreted on
the basis that in the premicellar range, one bromide ion of gemini surfactants [A] binds to the
surfactant ion [7,8,13,43], thereby reducing its charge. This effect would be similar to what
has been assumed for the closely related bolaform surfactants or bolaamphiphiles
(amphiphilic molecules that have hydrophilic groups at both ends of a sufficiently long chain
hydrophobic hydrocarbon chain), alkanediyl-,-bis(trimethylammonium bromide) [63,64].
Compared to single-headed amphiphiles, the introduction of a second head group generally
induces a higher solubility in water, an increase in the critical micelle concentration CMC,
and a decrease in aggregation number. The aggregate morphologies of bolaamphiphiles
include spheres, cylinders, disks, and vesicles. Bolaamphiphiles are also known to form
helical structures that can form micro tubular self-assemblies [67].
However, potentiometric studies using surfactant-specific electrodes for 12-s-12
surfactants [A] did not reveal any ion pairing [1]. Indeed, for these surfactants the linear
variation of the electromotive force with lnC (C = surfactant concentration) below CMC
yielded an e.m.f. change close to 30 mV for a concentration change by a factor 10, a value
close to that expected for divalent-univalent (2:1) electrolytes. However, conductivity
measurements suggested that ion pairing takes place in submicellar solutions of 8-s-8, 2Br-
and 10-s-10, 2Br- surfactants which are characterized by high CMC values which favor ion
pairing [35,65].
Another issue concerns a possible premicellar association of gemini surfactants into
dimers and larger oligomers for surfactants [A] with CH2CHOHCH2 or (CH2CHOH)2 spacers
[37,38] and surfactants [C], [E], and [F] with a hydrophobic rigid spacer [3], at m z 14. The
decrease of the surface tension lowering effect of these surfactants and the increase of their
CMC with increasing m, where m ≥ 14–16, were explained on this basis[2, 3, 37, 38]. Besides
some surfactants [A] with R = CmH2m+1 [66] or CmH2m+1OC(O)CH2 [7, 42] and with a
10
polymethylene or other spacer groups did not show this abnormal behavior up to m = 16.
Thus, premicellization appears to depend on the gemini surfactant nature. It is also favored by
long polyethylene spacer as shown in a recent study [65].
IV. Behavior at Interfaces
Extensive surface tension measurements have been performed on aqueous solutions of
gemini surfactants with the purpose of investigating their behavior at the air–solution
interface (measurement of surface area a occupied by one surfactant molecule at the
interface) and determining CMCs. The surface areas (a) were obtained from the slope of the
variation of the surface tension with lnC (C = surfactant concentration) using the Gibbs
expression of the surface excess concentration :
(1)
Where, R is the gas constant and T the absolute temperature. The constant n takes the values
2 for univalent-univalent monomeric ionic surfactants and 3 for divalent-univalent ionic
gemini surfactant, in the absence of a swamping electrolyte. The surface area occupied by
one surfactant at the interface, (a) is then obtained as (NA)-1, NA being Avogadro’s number.
The value n = 2 was used for ionic gemini surfactants in several studies [6–8, 43], on the
assumption that one of the two charged head groups is neutralized by a bound counter ion.
Several other studies used the values n = 3 [3, 68–72]. At any rate, the value used for n does
not affect the qualitative conclusions inferred from the (a) values for a series of homologous
surfactants.
The effectiveness of gemini surfactants in lowering the surface tension of water is
close to that of the corresponding monomeric surfactant. Indeed, the values of the surface
tension at the CMC, CMC, are close for monomeric gemini surfactants, as illustrated by the
results shown in Fig. 3 for 12-3-12, 2Br- [4] and its corresponding monomeric surfactant,
dodecyltrimethylammonium bromide (DTAB) [73].
11
FIG.3 Surface tension vs. concentration of the gemini surfactant 12-3-12, 2Br- (●) and of dodecyltrimethylammonium bromide (■) (Adapted from data in Refs.4 and 73).
However, the former are always more efficient surface-active agents than the latter
because their CMCs are much lower. Thus, the values of the surfactant concentration C20 for
which is lowered by 20 mN/m are much lower for gemini than for monomeric surfactants.
This result is very important for the utilization of gemini surfactants. The behavior of gemini
surfactants at the air-solution interface has been extensively investigated and some important
results are summarized as follows:
1. Surface activity is favored by flexible spacers such as polymethylene or polyoxy-
ethylene chains. Bulky and/or rigid aromatic spacers result in larger values of CMC [3,
37]. Bulky and/or rigid aromatic groups in the hydrocarbon tails near the spacer also
have an unfavorable effect on surface tension lowering [74]. An effect of the aging of
the solution on the measured surface tension has been reported for surfactants with
rigid spacers [2, 3]. This effect is probably in relation with the high Krafft temperature
of these surfactants [75].
2. The alkyl chain carbon number m of the gemini surfactant has generally a small effect
on (a) as long as, say, m < 12–14 [6, 8, 76]. However, for some cationic gemini
surfactants an effect sets in at higher values of m and results in larger values of CMC
and a [2,3,7,37,38,77]. Premicellar association, self-coiling of the alkyl chains, and a
peculiar configuration of the surfactant with its two alkyl chains lying more or less
flat on the interface have been proposed to explain this behavior [2,3,37,38].
Premicellar association appears to be at the origin of the observed behavior [65].
12
3. For flexible spacers, of the -(CH2)iY(CH2)i- type, the value of (a) depends on the
nature of the chemical group Y. Thus, the value of a (in nm2, in parentheses) increases
in the order: -S- (0.84)< -N(CH3)- (1.08)< -CH2- (1.14)< -O- (1.28), for the gemini
surfactants [C12H25(CH3)2N+, Br-]2[(CH2)2Y(CH2)2] [7, 8].
4. Figure 4 shows the variation of (a) with the spacer carbon number s for the
[C12H25(CH3)2N+, Br-]2(CH2)s series (hydrophobic polymethylene spacer [4]) and with
the total number nT of oxygen and carbon atoms separating the two head groups in
anionic gemini which have a hydrophilic polyoxyethylene spacer (Y is O (nT = 9),
OCH2CH2O- (nT = 12), -O(CH2CH2O)2 (nT = 15), and -O(CH2CH2O)3 (nT = 18)) [45].
Focusing only on the qualitative features, (a) is observed to go through a maximum at
s = 10–12 for the hydrophobic spacer series but not for the hydrophilic spacer series.
A similar maximum in a at about the same value of s appears to occur for the
bolaform surfactants [(CH3)3N+, Br- ]2(CH2)s [78]. For the bolaform and the 12-s-12
surfactants this maximum was explained in terms of a change of location of the
polymethylene chain as s increased. At s < 10, the chain has little flexibility and lies
flat with a fairly linear conformation in the air–solution interface. This is supported by
X-ray scattering studies of the lamellar and hexagonal phases in the water/12-s-12,
2Br- surfactant mixtures [79] and by the rapid initial increase of a with s in Fig. 4. At
s > 10 the chain is too hydrophobic to remain in contact with water and moves to the
air side of the interface, adopting a wicket-like or looped conformation in doing so
[4,64,78], which results in an overall decrease of a. This effect may be enhanced by a
change of orientation of the alkyl chains with respect to the interface as s increases, at
large s values. The absence of a maximum for gemini surfactants having a hydrophilic
spacer supports this explanation. The maximum observed for gemini surfactants with
a hydrophobic spacer has been accounted for theoretically [80, 81]. The spacer
conformational entropy and the attractive and repulsive interactions between
surfactant molecules appear to be the dominant factors in determining the variation of
a with s.
13
FIG. 4 Variation of the surface area per gemini surfactant at the air–water interface for the 12-s-12 series(●, from Ref.4) and for[C10H21OCH2CH(OCH2CO2
-, Na+)(CH2)]2O(CH2CH2O) x series (o, from Ref. 45) vs. the spacer carbon number s or the total number of atoms nT
between charged groups at 25oC.
5- The values of the surface area a per surfactant [Q] with X = OH and a number x of
ethylene oxide units equal to 7, 12, and 16, have been found to be 43, 50, and 55 Å 2,
respectively, from surface tension data [31]. Note that for these surfactants n = 1 in
Eq. (1). These values are lower than for a nonionic surfactant with a single
hydrophobic chain and a polyoxyethylene head group even though surfactants [Q]
contain two hydrophobic chains[81].For instance, the values of(a) for C12E8 and C10E8
are 63 Å2 and 70 Å2, respectively. This suggests that the monolayer formed by gemini
surfactants [Q] is relatively closely packed. For surfactants [Q] with X = SO4Na, the
surface tension at the CMC (CMC) increases with the polyoxyethylene chain length, a
phenomenon that is also observed with CmEx surfactants [83]. The value of (a)
calculated from the surface tension data with n = 2 increases with the number of
oxyethylene units, as expected. The surfactant with x = 7 appears to be the most
effective one, with the lowest values of the CMC and CMC. The variation of CMC with
the number of oxyethylene units x is often attributed to steric crowding of the
nonionic head groups, which naturally increases with x.
6- The Gibbs equation was used with n = 1 for the analysis of the surface tension data for
surfactants [P]. Indeed, these surfactants are counter ion free and therefore considered
as neutral molecules. The surface areas per molecule have been obtained to be around
30 Å2 [59]. These values are much lower than one would expect for a surface
monolayer. They are also significantly lower than the values of a measured for
14
equimolecular mixtures of two oppositely charged surfactants. The unrealistically low
values of a obtained for gemini surfactants [P] may be due to some kind of surface
aggregation [59], which remains to be clarified. Dynamic surface tension (DST)
studies of the cationic surfactants [A] with Y = CHOH showed that their adsorption at
the air–solution interface is controlled by diffusion [84]. On the contrary, for gemini
surfactants [Q] (Fig. 5), the results suggest that at the beginning (short times) the
adsorption is essentially diffusion controlled. However, close to equilibrium (long
times) the DST decays are not consistent with a diffusion-controlled adsorption
mechanism [31,60].
FIG. 5 Dynamic surface tension t vs. time for gemini [Q] with X = SO4Na and x = 12 (from Ref. 60). From top to bottom: 0.032, 0.064, 0.12, 0.207, 0.252, and 0.393 wt. %.
The adsorption of gemini cationic surfactants [A], 12-s-12, 2Br- on solid surfaces has
been investigated. The surfactant 12-2-12, 2Br- was less adsorbed than its corresponding
monomer, DTAB, on silica [85] and titanium dioxide [86], when the adsorption was
expressed in moles of adsorbed dodecyl chain per gram of solid. A similar conclusion was
reached for the adsorption of DTAB and 12-2-12, 2Br- on laponite clay [87]. No explanation
was provided for these results. The maximum amount of 12-s-12, 2Br- gemini surfactant
adsorbed on silica was shown to decrease very much as the spacer carbon number was
increased from 2 to 10 [88].
Adsorption of surfactants [Q] with X = OH and various values of x at silica surfaces
have been investigated by optical reflectometry [31] (Fig. 6). The adsorbed amount of each
surfactant on hydrophilic silica was about twice that on hydrophobic silica. The adsorbed
15
amount depends little on x in the case of hydrophobic silica but decreases upon increasing x
for hydrophilic silica, showing the effect of steric hindrance from the relatively larger head
group. It was concluded that surfactants [Q] are better packed at solid–liquid interfaces than
conventional surfactants. Surfactants [Q] with X = SO4Na show a significant decrease of the
adsorbed amount on hydrophilic silica with increasing number of oxyethylene units [60] (Fig.
6). On both hydrophilic and hydrophobic silica, a increases with the polyoxyethylene chain
length. This result indicates that packing at the solid–liquid interface is improved when the
poly (oxyethylene) molecular weight decreases.
FIG. 6 Amount of adsorbed gemini surfactant [Q], on the hydrophilic silica surface (from Refs. 31 and 60). From top to bottom surfactant (X=OH, x=12), (X=OH, x = 16), (X = SO4Na, x = 8), (X = SO4Na, x = 12), (X = SO4Na, x = 16), respectively.
This is a well-known phenomenon for monodisperse poly(ethylene glycol) monoalkyl
ethers such as CmEx. Thus, the anionic character of the surfactants, introduced via the sulfate
group, is of minor importance for adsorption. It should be pointed out that surfactants [Q]
seem to pack better with X=OH than with X = SO4-Na+ at the air–water and solid–water
interfaces. The sulfate group seems to decrease the ability of the surfactant to align tightly in
a monolayer. The adsorbed amount of surfactants [P] is higher at the surface of hydrophilic
silica than on hydrophobic silica. The adsorbed amount for the pair 10,12 and 12,10 is higher
than for 14,8 and 8,14 on both hydrophilic and hydrophobic silica. This might be due to the
effect of the relatively larger difference between the lengths of the two alkyl chains of the
latter surfactant pair. This asymmetry may be unfavorable for efficient packing at planar
surfaces [59].
16
V. Efficiency of gemini surfactants as corrosion inhibitors for carbon steel in acid media
Low carbon steel is being used extensively under different conditions in industries
because of its low cost and excellent mechanical properties. However, some corrosion
problems take place due to the effect of acid solutions in cooling systems, storage reservoirs,
and water transport pipelines for injection systems [89]. So the study of corrosion of steel in
acid solutions is industrially important field of research [90-92]. The use of inhibitors is one
of the most practical methods for protection against corrosion especially in acidic media [93-
95]. In order to reduce the corrosion of metals, several techniques have been applied; where
among that utilization of organic compounds are gaining high space as corrosion inhibitors.
Among efficient corrosion inhibitors, there are heterocyclic organic compounds consisting of
-system and/ or O, N, P, or S heteroatoms [96].
It is well known that the presence of hydrophilic and hydrophobic groups in the
inhibitor favors the adsorption process at the electriferous surface [97]. Thus, the application
of conventional surfactants made up of one hydrophilic head group and one hydrophobic
chain as corrosion inhibitors has been widely studied. It was found that these amphiphilic
compounds could adsorb on metal surface to form a protective layer and have a marked
inhibiting efficiency near their critical micellar concentrations [98-105].
As a new generation of surfactants, gemini surfactants have attracted great interest in
recent years. This new generation of surfactants has been investigated as corrosion inhibitors
for acid solutions [106]. However, there are few reports on the use of gemini surfactants as
inhibitors of metal corrosion [107, 108].
It has been demonstrated that gemini surfactants are more efficient to form micelles
than conventional surfactants containing one hydrophilic group and one hydrophobic group,
and show lower critical micelle concentration (CMC), better solubilization and greater
efficiency in lowering the surface tension of water. Given that, gemini surfactants show many
unique properties in comparison with single chain conventional surfactants, it is reasonable to
study their effects on corrosion inhibition of metals [109, 110]. It describes corrosion
inhibition of carbon steel in 1M HCl by cationic gemini surfactants of formula Cm-x-Cm. In
general, cationic surfactants and particularly gemini surfactant possessing effective inhibitory
effect. They accumulate in special order at the interfaces and modify the interfaces and thus,
control, reduce, or prevent reactions between a substrate and its surroundings when added to
the medium in small quantities [111]. In order to evaluate compounds as corrosion inhibitors
17
and to design novel inhibitors, much more research works were concentrated on the studies of
the relationship between structural characteristics of the organic compounds and their
inhibiting effects [112].
Gemini surfactants control corrosion, acting over the anodic or the cathodic surface or
both. We and some other researchers have demonstrated that quaternary ammonium gemini
surfactants are excellent candidates for iron and steel in acidic medium [113-119]. The
adsorption behavior of these gemini surfactants on metal surface in acidic medium was found
to be affected remarkably not only by length of hydrophobic chains [120], but also by the
spacer length of the gemini surfactants [121-124]. It was found that adsorption mechanism of gemini surfactants on metal surface is different from that of conventional single-chained surfactants, and the spacer length of the gemini surfactants was found to determine the adsorption mechanism of these gemini surfactants onto metal surface. Also the efficiency of the used gemini
surfactants on the corrosion inhibition is affected by the spacer length between the two heads
[125]. Moreover, the adsorption mechanism of gemini surfactants on metal surface in acid
medium has been rarely investigated till now.
We noticed that many gemini surfactants have been synthesized. The structure of the
gemini surfactants can be tailored either by introducing different types of spacers such as
polymethylene, polyoxyethylene, and aromatic rings in the molecule [129, 131]. Some
research works revealed that the inhibition efficiency of Schiff bases is much greater than that
of corresponding amines and aldehydes due to the presence of a –CH=N- group in the
molecules [132]. The polar unit is regarded as the reaction center for the adsorption process.
Thus, polar organic compounds are adsorbed on the metal surface, forming a charge transfer
complex bond between their polar atoms and the metal. The size, orientation, shape and
electric charge on the molecule determine the degree of adsorption and hence the
effectiveness of the inhibitor [123-132]. Studies have been carried out on the effect of
variation of the spacer polarity and chain length on the physicochemical properties of gemini
surfactants [128–130, 132]. However, the effect of variation in the head group polarity on the
properties of cationic gemini surfactants, which can offer interesting physicochemical
properties, has not been studied earlier. Hence an attempt has been made by researchers,
synthesize and study the physicochemical properties of the cationic gemini surfactants with
variation in their head group polarity.
18
VI. Micelle Formation And Solubilization
Introduction:
It has been known for many years that amphiphilic molecules, which consist of a
hydrophilic head and a hydrophobic tail, can form a wide variety of aggregates including
spherical micelles, worm-like micelles, bilayers, and reverse micelles with properties
different from those of the unassembled molecules. The current interest in such surfactants arises from three essential properties.
1. Dimeric surfactants are characterized by CMC that are one to two orders of magnitude lower than those for the corresponding conventional (monomeric) surfactants [133, 134]. For example, the CMC of the dimeric surfactant 12-2-12 (dimethylene-1,2-bis(dodecyldimethylammonium bromide)) is about 0.055 wt. %, whereas that of the corresponding monomeric surfactant DTAB (dodecyltrimethylammonium bromide) is 0.50 wt. %.
2. Dimeric surfactants are much more efficient than the corresponding monomeric surfactants at decreasing the surface tension of water. For instance, the concentration required for lowering the surface tension of water by 0.02 N/m is 0.21 wt. % for DTAB only 0.0083 wt. % for 12-2-12 [133, 134].
3. Aqueous solutions of dimeric surfactants with short spacers can have very high
viscosities at relatively low concentrations whereas solutions of the corresponding
monomeric surfactants have low viscosities. For instance the viscosity of aqueous
solutions of DTAB is only marginally larger than that of pure water up to a surfactant
concentration of at least 10 wt. % whereas a 5 wt. % solution of 12-2-12 has a
viscosity of several hundred Pa/s and is viscoelastic [133, 134]. Solutions of 12-2-12
can also display shear thickening at fairly low concentrations [135]. These properties
reflect the ability of dimeric surfactants with a short spacer, such as 12-2-12, to give
rise to worm-like micelles at fairly low surfactant concentrations, even in the absence
of added salt [136].
The fact that the properties of dimeric surfactants can differ greatly from those of
conventional surfactants has been related to the distribution of distances between head groups
19
in micelles formed by these two types of surfactants [137]. For conventional surfactants, this
distribution goes through a maximum at a thermodynamic equilibrium distance dT ≈ 0.7–0.9
nm. For dimeric surfactants the distribution is bimodal, with a first maximum at the
thermodynamic distance dT and another more narrow maximum at a distance ds that
corresponds to the length of the spacer. This length is determined by the bond lengths and
bond angles between the atoms making up the spacer group. The bimodal distribution of head
group distances and the effect of the chemical link between head groups on the packing of
surfactant alkyl chains in the micelle core are expected to strongly affect the curvature of
surfactant layers and thus the micelle shape and the properties of the solution. The distance ds
can be adjusted to be smaller than, equal to, or larger than dT by modifying the structure of the spacer. Those different situations are expected to give rise to a rich variety of behaviors.Dimeric surfactants have been also reported to have better solubilizing, wetting, foaming, and lime-soap-dispersing properties than conventional surfactants [14]. These properties are commonly used to evaluate surfactant performances. Besides, the Krafft temperatures of dimeric surfactants with hydrophilic spacers (see below) are generally very low [14], giving these surfactants the capacity to be used in cold water. Finally, cationic dimeric surfactants have been shown to possess a strong biological activity [138]. The interesting properties displayed by dimeric surfactants has led to the synthesis of longer homologs that are subsequently referred to as oligomeric surfactants [139]. The schematic representation of a trimeric surfactant is given in Fig. 1B. Results for oligomeric surfactants are reviewed below whenever appropriate. At the outset it is pointed out that most of the gain in properties is achieved by going from a monomeric to a dimeric surfactant.
Several reviews on dimeric surfactants have been recently published [133, 134, 14, 25, 140, 141]. The present review specifically focuses on the effect of the spacer group. It does not attempt to be thorough. Only the most significant results that refer to the effect of the nature and length of the spacer group on solution properties of dimeric surfactants are presented. Indeed, and this will become clearer below, the
20
nature and length of the spacer group are the most important parameters in determining the properties of dimeric surfactants.
Most of the reviewed results concern cationic dimeric surfactants of the bisquaternary
ammonium type. Table 1 shows some of these surfactants [1,142–151]. The abbreviations
used to refer to the surfactants in Table 1 are retained throughout this review. The surfactants
m-s-m (A1) and m-EOz -m (A3) are the ones that are referred to the most.
TABLE 1
Examples of Bisquaternary Ammonium Bromide Dimeric Surfactants
_________________________________________________________________________A1: R1 = R2 = Cm H2m+1; Y = CH2 ; x + y + 1 = s; m-s-m surfactants [1].A2: R1 = R2 = Cm H2m+1 ; Y = CH2 , O, S, N(CH3 ), x = y = 2 [142, 143].A2l : R1 = R2 = Cm H2m+1 ; Y = CHOH, (CHOH)2 ; x = y = 1 [143].A3: R1 = R2 = Cm H2m+1 ; Y = (OCH2 CH2 )z , x = 2; y = 0; m-EOz -m surfactants [144].A4: R1 = R2 = Cm H2m+1 ; Y = C ≡ C; x = y = 1 [145].A5a : R1 = R2 = Cm H2m+1 ; Y = x = y = 1 [146].A6: R1 = R2 = Cm H2m+1 OC(O)CH2 ; no Y ; x = y = 1; counter ion = chloride [147, 148].A7: R1 = R2 = Cm F2m C4 H8 ; no Y ; x = y = 1 [149].A8: R1 = Cm H2m+1 ; R2 = Cm
/ H2m/+1 ; no Y ; x = y = 1; s; m-2-m/ surfactants [150, 151].
__________________________________________________________________________a represents a phenylene group.
a) Aqueous Dimeric Surfactant Solutions At Concentrations Below The CriticalMicellization Concentration
Many papers discussed the state of ionic dimeric surfactants at concentrations below
the cmc. Several situations were considered. First, the dimer may be completely dissociated,
giving rise to one dimeric ion and two counter ions, or not completely dissociated, with
partial binding of one counter ion to the dimeric ion. Second, depending on the conformation
of the spacer group of the dimeric surfactant, its two alkyl chains may or may not interact.
Third, premicellar aggregation may take place, giving rise to small aggregates of dimeric ions
21
of low aggregation number. The possibility of a partial binding of a counter ion by a dimeric
surfactant ion at concentrations C < CMC arose in the analysis of the plots of the surface
tension γ vs C for dimeric surfactant solutions. These plots permit the determination of the
surface excess and a = 1/NA (NA = Avogadro’s number), surface area occupied by one
surfactant at the air/water interface, on the basis of the Gibbs equation:
= (2)
In Eq. (2) R is the gas constant and T the absolute temperature. The constant n takes
the value 2 for an ionic surfactant where the surfactant ion and the counter ion are univalent
and the value 3 for a dimeric surfactant made up of a divalent surfactant ion and two
univalent counter ions, in the absence of a swamping electrolyte. The reported a values were
calculated on the basis of n = 2 [142, 152–154], on the assumption that one of the two
charged groups is neutralized by a bound counter ion, or n = 3, on the assumption of a full
dissociation of the dimeric surfactants [145, 146, 155–158]. Some studies reported two sets of
values of a based on n = 2 and 3 [144, 4]. The same problem arises for ionic trimeric
surfactants for which the value n = 4 should be used if the surfactant is fully ionized at C <
CMC. The knowledge of the surface area occupied by a surfactant at an interface is very
important in surfactant science.
The problem of the value of n in the case of oligomeric surfactants therefore needed
to be solved. An attempt in this direction was performed by means of neutron reflectivity, a
technique that permits a direct determination of the surface excess [159]. The comparison
of the value of from neutron reflectivity to that of (dγ/d lnC)/RT from surface tension data
made it possible to determine the value of n at any surfactant concentrations. The comparison
yielded n = 2 for the dimeric surfactants 12-2-12, 12-3-12, and 12-12-12 and n = 3 for the
surfactant A5 with m = 12 [159]. For 12-6-12 the value of n was found to decrease from 3 at
low C to 2 at higher C but still below the CMC. The authors concluded that one dimeric
surfactant ion binds one bromide ion (ion pairing) in submicellar solutions of 12-s-12
surfactants. However it has been shown that other effects may explain differences between
neutron reflectivity and surface tension data [160].
Besides, recent electrical conductivity studies did not reveal any ion pairing in
submicellar solutions of 12-s-12 surfactants [161]. However, ion pairing was evidenced in
submicellar solutions of 8-s-8 and 10-s-10 surfactants, owing to the larger CMC values of
these surfactants with respect to 12-s-12 surfactants. Ion pairing is thus a real possibility for
dimeric surfactants with high CMC values, i.e., those with an alkyl chain containing 8 or 10
22
carbon atoms but apparently not those with an alkyl chain containing 12 carbon atoms.
Additional studies are required to explain the different conclusions reached in neutron
reflectivity and electrical conductivity studies of 12-s-12 surfactants. Some consideration
should be given to a possible explanation of the neutron reflectivity results in terms of
premicellar aggregation.
Thermodynamic studies suggested that the two alkyl chains in the surfactant A6 might
be partly associated in the molecularly dispersed state [148]. This suggestion was not
supported by the values of the free energy change associated with the transfer of one alkyl
(dodecyl) chain from the aqueous phase to the micelle, G◦(C12), for two series of oligomeric
surfactants [162]. These values were calculated with the available CMC and ionization data,
using the appropriate equation [163]. Self-coiling of the alkyl chains was mentioned as a
possible explanation for the aging effect observed in measurements of surface tension of
solutions of dimeric surfactants with long alkyl chains, below the CMC [146]. However such
effects are not observed with conventional surfactants having the same long alkyl chains. A 13C and 1H-NMR investigation of the conformation of dimeric surfactant A5 with m = 8
below the CMC did not reveal interactions between octyl chains [36]. Premicellar
aggregation occurs in solutions of conventional surfactants that are sufficiently hydrophobic.
The situation is somewhat similar with dimeric surfactants. Menger and Littau [146]
provided the first evidence for premicellar aggregation in solutions of several series of
dimeric surfactants, in particular for surfactant A5. The variation of the log cmc with the
alkyl chain carbon number m showed a strong upward curvature or a minimum for m ≥ 16,
instead of the usual linear variation. Premicellar aggregation was later reported for other
series of dimeric surfactants [143, 145, 165, 166]. Electrical conductivity measurements are
particularly well suited for obtaining evidence of premicellar aggregation [161, 166]. This is
illustrated in Fig. 7A and 7B. The variations of the electrical conductivity K with the
surfactant concentrations C and of the molar conductivity with C1/2 are represented for the
surfactants 12-8-12 and 16-8-16 [161]. The plots for the 12-8-12 surfactant show a normal
behavior.
For the 16-8-16 surfactant the K vs C plot shows a small upward curvature and the
vs C1/2 plot shows a pronounced maximum in the submicellar concentrations range. The vs
C1/2 plot for the dimers 14-8-14, 16-paraxylylene-16, and 18-8-18 also show a maximum, the
amplitude of which increases rapidly with m [161]. This maximum is the signature of
premicellar association in surfactant solutions. It arises because the equivalent conductivity of
23
a small aggregate of surfactant ions (whether monomeric or dimeric) is larger than the sum of
the equivalent conductivities of the ions constituting it [161, 166]. This effect shows at
different values of m for different dimeric surfactants [143, 145, 165, 38] but always at m ≥
14–16.
However, it is already detected at m = 11 for more complex dimeric surfactants
derived from arginine where the peptide segment separating the two charged groups may help
in stabilizing small premicellar aggregates [166]. For the dimeric surfactants A1 the spacer
carbon number has a strong effect on the occurrence of premicellization. Thus this effect does
not occur for the 12-s-12 dimers up to s = 12 and for 16-3-16 and 16-4-16. However the vs
C1/2 plots for 12-14-12, 12-16-12, 12-20-12, 16-6-16, and 16-8-16 show a maximum [161].
A study of two series of anionic trimeric surfactants suggests that premicellization occurs at a
value of m much lower than that for dimeric surfactants [167, 168].
FIG.7 Variations of the electrical conductivity K with the surfactant concentration and of the molar conductivity with the square root of the surfactant concentration for the dimeric surfactants 12-8-12 (A) and 16-8-16 (B). The arrow in B (top) indicates the CMC as obtained from the K vs C plot in B (bottom). From Ref. (161).
b) dimeric Surfactants At Interfaces
24
1. Air–Solution Interface The studies of the adsorption of dimeric surfactant at the air/solution interface
aimed to assess the efficiency and effectiveness of these surfactants in reducing the
surface tension of water. These measurements also aimed to measure the CMC and
surface area a occupied by one dimeric surfactant at the air/water interface on the
basis of the Gibbs equation (Eq. (2)). The efficiency and effectiveness are
characterized by the value of the surfactant concentration C20 at which the surface
tension of water is reduced by 0.02 N/m and by the value of the surface tension at the
CMC, γCMC, respectively. Figure 8 shows the variation of a with the spacer carbon
number for 12-s-12 surfactants [155, 4] and with the number nT = 3z + 2 of oxygen
and carbon atoms in the spacer group in the case of 12-EOz-12 surfactants [144]. For
the 12-s-12 surfactants (hydrophobic spacer) a is a maximum at a value of s around
10–12. A similar maximum in a at about the same value of s appears to occur for the
bolaform surfactants [N+(CH3)3, Br−]2(CH2)s (42).A maximum in a was observed for
the dimeric surfactants derived from arginine and which also contain a hydrophobic
polymethylene spacer [170]. However only a rather slow increase of a with nT is seen
for the 12-EOz-12 surfactants. A series of anionic surfactants having a poly (ethylene-
oxide) spacer showed the same behavior as the 12-EOz-12 surfactants [171]. Such a
behavior is expected upon increasing the volume and, thus, the surface of the poly
(ethyleneoxide) spacer, which remains located on the water side of the interface.
FIG.8 Surface area a occupied by one dimeric surfactant at the air–water interface. Variation with the spacer carbon number s at 25◦C for 12-s-12 surfactants(●, data from Refs. 155 and 4) and with nT for 12-EOz-12 surfactants (□, from Ref. 144).
25
For the 12-s-12 surfactants the maximum of a was explained in terms of a change in location of the polymethylene spacer upon increasing s. At s < 10, the spacer group is rather rigid and lies flat with a fairly linear conformation at the air–solution interface. This is suggested by the rapid initial increase of a with s in Fig. 8 and is supported by X-ray scattering studies of the lamellar and hexagonal phases in water/12-s-12 surfactant mixtures [172]. At s > 10 the spacer becomes too hydrophobic to remain in contact with water and moves to the air side of the interface, where it adopts a looped (wicket-like) conformation [4, 169]. This results in an overall decrease of a. This effect may be enhanced by a change of orientation of the alkyl chains with respect to the interface as s increases.
The absence of a maximum for dimeric surfactants with a hydrophilic spacer [144, 171] also supports this explanation. The maximum of a observed for the 12-s-12 surfactants was accounted for theoretically by statistical-mechanical calculations [173]. The main factors that determine the variation of a with s were shown to be the spacer conformational entropy and the attractive and repulsive interactions between surfactant molecules. At s > 12 the calculated value of a decreases upon increasing s more slowly than experimentally observed [173]. This discrepancy may be due to premicellar aggregation. Indeed, this effect occurs at s > 12 for 12-s-12 surfactants [161].
It was not taken into account in the calculations [46] and was not considered in the experimental study (30). Other studies do show that premicellar aggregation can cause a significant decrease in the apparent value of a [143, 165]. Monte Carlo simulations were also performed to understand the behavior of dimeric surfactants at the air–solution interface [174]. The results in Fig. 9 are of the utmost importance for explaining the properties of m-s-m surfactants in aqueous solution that are described below as well as the differences in behavior between the two closely related series of
26
dimeric surfactants m-s-m and m-EOz -m. Indeed the large changes of a with s for the 12-s-12 surfactants indicate correspondingly large changes of the surfactant packing parameter that results in changes of micelle shape.
On the contrary the relatively slow change of a with nT = 3z + 2 seen for 12-EOz-12 surfactants suggests that the micelle structure should vary slowly with the number of ethylene oxide groups in the spacer. For cationic oligomeric surfactants the surface area per amphiphilic moiety has been shown to decrease in going from the monomer (DTAB) to the dimer (12-3-12) and the trimer (12-3-12-3-12). It then levels off when going to the tetramer (12-3-12- 4-12-3-12) [162].
The kinetics of adsorption of dimeric surfactants at the air–water interface strongly depends on the nature of the surfactant. Two reports on anionic [180] and cationic [176] dimeric surfactants, the latter of type A2´ and A5, indicated a diffusion controlled adsorption of the investigated surfactants. On the contrary, a large barrier to adsorption was reported to exist for cationic surfactant dimers derived from disulfur betaine [156]. Dimeric surfactants with a flexible spacer lowered the surface tension of water faster than dimers with a rigid spacer.
FIG.9 Spacer carbon number dependence of the maximum amount of adsorbed 12-s-12 surfactant on raw (●) and HCl-treated(o)silica (from the results in Refs. 178 and 179).
27
b.2 Solid-Solution Interface:The adsorption isotherms of dimeric 12-s-12 [182-184],
trimeric 12-s-12-s-12 [162, 180], and tetrameric 12-3-12-4-12-3-12 cationic surfactants on macro porous amorphous silica showed that the adsorption involves two steps, as for conventional surfactants [162]. The first step occurs at very low concentration and corresponds to a binding of individual dimeric surfactants to charged sites on the silica surface by an ion exchange mechanism. The second step occurs at concentrations slightly below the CMC and corresponds to the formation of surface aggregates. Figure 4 shows that in the case of the adsorption of 12-s-12 surfactants on both raw and HCl-treated silica the maximum amount of adsorbed surfactant, max, decreases as s increases [177-179]. This variation is in relation with the structure of the surface aggregates. An atomic force microscopy study [181] showed that 12-2-12 adsorbs as a flat bilayer, whereas 12-4-12 and 12-6-12 adsorb as parallel cylinders. A surfactant with still lower packing parameters was shown to adsorb under the form of spherical surface aggregates [181]. Obviously the maximum amount of adsorbed surfactant decreases as the structure goes from a flat bilayer to parallel cylinders and to spheres. Since mica and silica surfaces differ mostly by their charge density, it is likely that differences in structure of the surface aggregates similar to those seen on mica occur on silica, thereby explaining the change of max.
c. Solubility In Water, CMC, And Thermodynamics Of Micellization Of Dimeric and Oligomeric Surfactants
Solubility in water, Krafft temperature, and melting temperature of dimeric surfactants:
28
Ionic dimeric surfactants with m ≤ 12 are generally highly soluble in water particularly those with a hydrophilic spacer. The reported Krafft temperatures, TK, of several series of anionic dimeric surfactants with hydrophobic or hydrophilic spacers are below 0oC [134, 14, 25, 171]. Such low values of TK permit the use of dimeric surfactants in cold water. The variation of TK with the spacer carbon number s has been determined for solutions of the cationic dimeric surfactants 12-s-12 and 16-s-16 [24, 183] and compared to the variation of the melting temperature, TM, of the solid surfactants. The results are shown in Fig. 10. There appears to be no correlation between the variations of TK and TM with s. For homologous series of conventional surfactants it is usually observed that the variations of TK and TM are correlated. For instance both TK and TM increase with the surfactant chain length. The maximum of TM at s = 5 for the two series of surfactants in Fig. 6 is noteworthy. The minimum of TM at s = 10–12 for the 12-s-12 surfactants was mentioned in Ref. [172]. Figure 10A also shows the variation of the melting temperature of 12-EOz-12 surfactants with nT = 3z + 2, total number of oxygen and carbon atoms in the spacer [184]. The plot apparently goes through a minimum at nT = 11, a value close to that of s for which TM is a minimum for the 12-s-12 series. The few instances where the Krafft temperatures of a dimeric surfactant and of the corresponding monomeric surfactant could be directly compared revealed no systematic trend. Thus, the values of TK for 16-2-16 and CTAB (cetyltrimethylammonium bromide) are, respectively, 45 and 25o C [182, 24]. Those for 12-2-12 and DTAB are 15◦C and below O◦C, respectively [182, 24]. On the contrary, dimeric surfactants derived from arginine have TK values lower than those of the corresponding monomeric surfactants [185].
d. Critical Micellization Concentration
29
One of the main reasons for the current interest in dimeric surfactants is that their CMC are much lower than those of the corresponding monomeric surfactants, by about one order of magnitude and more. For instance, the CMC of 12-2-12 and DTAB are 0.055 and 0.50 wt%, respectively [1]. The low CMC values of dimeric surfactants with respect to the corresponding conventional surfactants arise mainly because two alkyl chains, rather than one, are transferred at a time from water to the micelle pseudo phase [163, 186]. The results concerning the effects of various parameters on the CMC of dimeric surfactants are briefly summarized.
(i) The CMC of surfactant A2 with the flexible hydrophobic spacer (CH2)2Y(CH2)2 depends little on the chemical nature of Y . Thus, the CMC of surfactant A2 with m =12 were found to be [139, 145] 1.2, 1.1, 1.0 and 0.84 mM for Y≡N(CH3), O, CH2, and s, respectively.
(ii) The CMC of anionic or cationic dimeric surfactants with a poly (ethylene oxide) spacer increase with the number z of ethylene oxide groups [144, 171, 187] whereas the CMC of conventional surfactants decreases upon intercalation of ethylene oxide groups between the alkyl chain and the charged group.
(iii) The CMC of surfactants m-s-m with a hydrophobic polymethylene spacer is a maximum at s = 5–6, irrespective of the value of m (see Fig. 11) [1, 188, 189]. This value of s is also that for which the melting temperature of the m-s-m surfactants is a maximum. A similar maximum of CMC was observed for dimeric surfactants derived from arginine that also includes a hydrophobic spacer [43]. On the contrary, for both anionic and cationic surfactants with a hydrophilic poly(ethylene oxide) spacer the CMC increased progressively with nT = 3z + 2, total number of oxygen and carbon atoms in the spacer, as seen in Fig. 11 for 12-EOz-12 surfactants [144, 171]. The increase of CMC with s observed for s ≤ 6 for m-s-m surfactants is probably due to
30
a conformational change in the surfactant molecule. The two alkyl chains would be in a gauche or trans position at low s values and in a cis position at higher s. Monte Carlo simulations of dimeric surfactant solutions attempted to account for the behavior of the CMC of the surfactant [174]. The calculations correctly predicted the presence of a maximum in the CMC vs s plot for surfactants with a hydrophobic spacer. However, the calculated overall variations of the CMC with s were much larger than experimentally observed. Also, the calculations predicted a decrease of CMC with increasing nT for hydrophilic spacers [174], whereas the experimental results show the opposite behavior.
(iv) The CMC of quaternary ammonium oligomeric surfactants with m = 12 decreased in a somewhat hyperbolic manner in going from the monomer to the dimer, trimer, and tetramer [162]. The largest part of the decrease occurred in going from the monomer to the dimer.
e. Thermodynamics of Micellization Several recent papers have reported on the thermodynamics of
micellization of 12-s-12 surfactants [190-193].Figure 8 shows the variation of the enthalpy of micellization, HoM, of 12-s-12 surfactants with the spacer carbon number, as obtained from direct calorimetric measurements [190-192]. The two sets of data represented show important differences in numerical values that may be due to the calibration of the measuring devices. Nevertheless the trends are similar, with -HoM going through a rather shallow minimum at around s = 5–6, i.e., at about the same s value as some of the properties reviewed above. A very large decrease of -HoM is observed in going from 12-2-12 to 12-4-12; -HoM depends only weakly on s at s > 4. The large decrease of -HoM at low s has been attributed to the conformational change discussed in the preceding section [192]. The value of the free energy of micellization of a dimeric surfactant, GoM, can be
31
obtained from Eq. (3), where α is the micelle degree of ionization [163]:
GoM = 2RT(1.5 − α) ln cmc (3)A recently reported set of α values (see Ref. [191] and below)
has been used together with available cmc data [1] to calculate the values of GoM and of the entropy of micellization SoM of 12-s-12 surfactants. The data show that the free energy of micellization is nearly independent of s and that most of the variation of SoM and GoM with s occurs in going from s = 2 to s = 4. The volume change upon micellization VoM of m-s-m surfactants has been determined [193]. For 12-s-12 surfactants VoM goes through a shallow minimum at s around 5–6 (see Fig. 12). The free energy of micellization per dodecyl chain Go (C12) for DTAB, 12-3-12, 12-3-12-3-12, and 12-3-12-4-12-3-12 was calculated by inserting the available CMC and α values into Eq. 4, valid for oligomeric surfactants [163]:
GoM (C12) = RT(1 + 1/x − α) lnCMC. (4) In Eq. (4), x is the number of dodecyl chains in the oligomeric
surfactant. GoM (C12) was found to be equal to −18.3, −20.8, −21.5, and −22.8 kJ/mol, respectively [162]. This variation is rather small, within the experimental error on α. A similar result was found for the three surfactants 12-3 (monomer), 12-6-12, and 12-6-12-6-12 [162]. Such results do not support the existence of an intramolecular association of the alkyl chains of the oligomeric surfactant below the CMC postulated in Ref. [151].
32
FIG.10 Spacer carbon number dependence of the Krafft temperature TK (o) and of the melting temperature TM (●,□). (A) 12-s-12 (●) and 12-EOz-12 (□) surfactants; (B) 16-s-16 surfactants (from Refs. 56 and 58). The lines are guides to the eye. The data points for the Krafft tempe- rature of surfactants 12- 6-12, 12-8-12, and 12-10-12 have been set at 0o
C, while in fact the TK values for these surfactants could not be measured (TK <0o C).
FIG.11 Dependence of the CMC on the spacer carbon number s for the surfactants 10-s-10 (□, from Ref. 62), 12-s-12 (∇, from Ref. 12), and 16-s-16 (o, from Ref. 12; ●, from Ref. 189) and on nT = 3z + 2 for the 12-EOz-12 surfactants (▲, from Ref. 144).
33
FIG.12 Variation of the enthalpy of micellization _H◦M (●, from Refs. 52 and 66; ■, from Ref. 191) and of the volume change upon micellization ∆VoM (o, from Ref. 193) for the 12-s-12 surfactants at 25◦C.
VII. Correlation between the Efficiency of the Cationic Gemini Surfactants as Corrosion
Inhibitors and their Quantum Chemical Calculation Studies
1. Introduction:
Quantum chemical methods have already proven to be very useful in determining the
molecular structure as well as elucidating the electronic structure and reactivity [194]. Thus,
it has become a common practice to carry out quantum chemical calculations in corrosion
inhibition studies. The concept of assessing the efficiency of a corrosion inhibitor with the
help of computational chemistry is to search for compounds with desired properties using
chemical intuition and experience into a mathematically quantified and computerized form.
Once a correlation between the structure and activity or property is found, any number of
compounds, including those not yet synthesized, can be readily screened employing
34
computational methodology [195] and a set of mathematical equations which are capable of
representing accurately the chemical phenomenon under study [196, 197].
The study of corrosion processes and their inhibition by organic inhibitors is a very
active field of research [198]. Many researchers report that the inhibition effect mainly
depends on some physicochemical and electronic properties of the organic inhibitor which
relate to its functional groups, steric effects, electronic density of donor atoms, and orbital
character of donating electrons, and so on [199, 200]. The inhibiting mechanism is generally
explained by the formation of a physically and/or chemically adsorbed film on the metal
surface [201, 202]. It is well known that organic compounds which act as inhibitors are rich
in heteroatoms, such as sulfur, oxygen, and nitrogen [203, 204]. These compounds and their
derivatives are excellent corrosion inhibitors in a wide range of media and are selected
essentially from empirical knowledge based on their macroscopic physicochemical
properties. Recently, theoretical prediction of the efficiency of corrosion inhibitors has
become very popular in parallel with the progress in computational hardware and the
development of efficient algorithms which assisted the routine development of molecular
quantum mechanical calculations [205]. Due to the enormous complexity of this type of
studies which need to consider the metallic surface, inhibitor and solvent molecules,
theoretical calculations of the corrosion inhibition processes cannot be achieved in a rigorous
way from the viewpoint of quantum chemistry.
2. Quantum chemical parameters:
Quantum chemical methods and molecular modeling techniques enable the definition
of a large number of molecular quantities characterizing the reactivity, shape, and binding
properties of a complete molecule as well as of molecular fragments and substituents. The
use of theoretical parameters presents two main advantages: firstly, the compounds and their
various fragments and substituents can be directly characterized on the basis of their
molecular structure only; and secondly, the proposed mechanism of action can be directly
accounted for in terms of the chemical reactivity of the compounds under study [206].
Quantum chemically derived parameters are fundamentally different from experimentally
measured quantities, although there is some natural overlap. Unlike experimental measure-
ments there is no statistical error in quantum chemical calculations. There is inherent error
however, associated with the assumptions required to facilitate the calculations. In most cases
the direction but not the magnitude of the error is known [206]. In using quantum chemistry
based parameters with a series of related compounds, the computational error is considered to
35
be approximately constant throughout the series. The prominent quantum chemical
parameters can be subdivided as follows:
2.1. Atomic charges
All chemical interactions are either electrostatic (polar) or orbital (covalent). Electric
charges in the molecule are obviously responsible for electrostatic interactions. The local
electron densities or charges are important in many chemical reactions and for physico-
chemical properties of compounds. Thus, charge-based parameters have been widely
employed as chemical reactivity indices or as measures of weak intermolecular interactions.
Despite its usefulness, the concept of a partial atomic charge is somewhat arbitrary, because it
depends on the method used to delimit between one atom and the next. As a consequence,
there are many methods for estimating the partial charges. Mulliken population analysis [207]
is mostly used for the calculation of the charge distribution in a molecule. These numerical
quantities are easy to obtain and they provide at least a qualitative understanding of the
structure and reactivity of molecules [208]. Furthermore, atomic charges are used for the
description of the molecular polarity of molecules
2.2. Molecular orbital energies
Highest occupied molecular orbital energy (EHOMO) and lowest unoccupied molecular
orbital energy (ELUMO) are very popular quantum chemical parameters. These orbitals, also
called the frontier orbitals, determine the way the molecule interacts with other species. The
HOMO is the orbital that could act as an electron donor, since it is the outermost (highest
energy) orbital containing electrons. The LUMO is the orbital that could act as the electron
acceptor, since it is the innermost (lowest energy) orbital that has room to accept electrons.
According to the frontier molecular orbital theory, the formation of a transition state is due to
an interaction between the frontier orbitals (HOMO and LUMO) of reactants [209]. The
energy of the HOMO is directly related to the ionization potential and the energy of the
LUMO is directly related to the electron affinity. The HOMO–LUMO gap, i.e. the difference
in energy between the HOMO and LUMO, is an important stability index [210]. A large
HOMO–LUMO gap implies high stability for the molecule in chemical reactions [211]. The
concept of ‘‘activation hardness” has been also defined on the basis of the HOMO–LUMO
energy gap. The qualitative definition of hardness is closely related to the polarizability, since
a decrease of the energy gap usually leads to easier polarization of the molecule [212].
36
2.3. Dipole moment
The most widely used quantity to describe the polarity is the dipole moment of the
molecule [213]. Dipole moment is the measure of polarity of a polar covalent bond. It is
defined as the product of charge on the atoms and the distance between the two bonded
atoms. The total dipole moment, however, reflects only the global polarity of a molecule. For
a complete molecule the total molecular dipole moment may be approximated as the vector
sum of individual bond dipole moments.
2.4. Energy
The total energy calculated by quantum chemical methods is also a beneficial parameter.
The total energy of a system is composed of the internal, potential, and kinetic energy.
Hohenberg and Kohn [214] proved that the total energy of a system including that of the
many body effects of electrons (exchange and correlation) in the presence of static external
potential (for example, the atomic nuclei) is a unique functional of the charge density. The
minimum value of the total energy functional is the ground state energy of the system. The
electronic charge density which yields this minimum is then the exact single particle ground
state energy.
3. Quantum Chemical Calculation Methods:
3.1. Ab-initio and MP2 methods
Semiempirical methods serve as efficient computational tools which can yield fast
quantitative estimates for a number of properties. This may be particularly useful for
correlating large sets of experimental and theoretical data, for establishing trends in classes of
related molecules, and for scanning a computational problem before proceeding with higher
level treatments. There remains the need to improve semiempirical methods with regard to
their accuracy and range of applicability, without compromising their computational
efficiency. In addition, there is a need to develop new algorithms in order to exploit modern
computer architectures and extend semiempirical calculations to ever larger molecules.
3.2. Semiempirical methods
3.2.1 MNDO Method (modified neglect of differential overlap)
It is based on the NDDO (neglect of diatomic differential overlap) approximation and in
turn NDDO is an improved version of INDO (intermediate neglect of differential overlap)
method. INDO itself is an improvement over the CNDO (complete neglect of differential
overlap) approximation. There are several such semiempirical LCAO MO methods,
developed for specific purposes.
3.2.2 AM1 Method
37
AM1 is a semiempirical method based on the neglect of differential diatomic overlap
integral approximation. Specifically, it is a generalization of the modified neglect of diatomic
differential overlap approximation. AM1 was developed by Michael Dewar and coworkers
reported in 1985 [215]. AM1 is an attempt to improve the MNDO model by reducing the
repulsion of atoms at close separation distances. The atomic core–atomic core terms in the
MNDO equations were modified through the addition of off-center attractive and repulsive
Gaussian functions. The complexity of the parameterization problem increased in AM1 as the
number of parameters per atom increased from seven in MNDO to 13–16 per atom in AM1.
By using these methods, the experimentally obtained inhibition efficiency was
correlated with energy gap which is theoretically calculated by quantum chemical
calculations. The difference in energy between the EHOMO and ELUMO decreased with
increasing the inhibition efficiency. The energy gap (ΔE) is an important stability index
[210]. A large HOMO–LUMO gap implies high stability for the molecule in chemical
reactions [211]. The values of (ΔE) indicate remarkably that the smaller energy gap results in
a high corrosion inhibition, reflecting the stronger interaction between the inhibitors and
metal surface. The interactions are probably physical adsorption [216-218].
Optimized structure of some cationic gemini surfactants of the type N2,N3-dialkyl-N2,N2,N3,N3-tetramethylbutane diamminium bromide:
38
HOMO LUMO
The frontier molecule orbital density distributions of an example of the prepared cationic gemini surfactants
VIII: Different examples of Prepared Cationic Gemini Surfactants in Our work
Where R = C12H25, C14H29 and C16H33 4,4'-((1E,1'E)-(1,4-phenylenebis(azanylylidene))bis(methanylylidene))bis(N-alkyl-N,N-dimethyl-benzenaminium) bromide
39
Where R = C12H25, C14H29 and C16H33
N,N'-(1,4-phenylenebis(methylene))bis(N,N-dimethylalkan-1-aminium) bromide
Where R = C12H25, C14H29 and C16H33
N2,N3-dialkyl-N2,N2,N3,N3-tetramethylbutane-2,3-diaminium bromide
Where R = C12H25, C14H29 and C16H33
N1,N2-dialkyl-N1,N1,N2,N2-tetramethylethane-1,2-diaminium bromide
Where R = C10H21 and C12H25
N1,N5-dialkyl-N1,N1,N5,N5-tetramethylpentane-1,5-diaminium bromide
REFERENCES
1. Zana, R.; Benrraou, M.; Rueff, R. Langmuir 1991, 7, 1072.2. Menger, F.M.; Littau, C.A. J. Am. Chem. Soc. 1991, 113, 1451.3. Menger, F.M.; Littau, C.A. J. Am. Chem. Soc. 1993, 115, 10083.4. Alami, E.; Beinert, G.; Marie, P.; Zana, R. Langmuir 1993, 9, 1465.5. Parreira, H.C.; Lukenbach, E.R.; Lindemann, M.K. J. Am. Oil Chemists Soc. 1979, 56, 1015.6. Devinsky, F.; Masarova, L.; Lacko, I. J. Colloid Interface Sci. 1985, 105, 235.7. Devinsky, F.; Lacko, I. Tenside Det. 1990, 27, 344.8. Devinsky, F.; Lacko, I.; Bittererova, F.; Tomeckova, L. J. Colloid Interface Sci. 1986, 114, 314,
40
and references therein.9. Kern, F.; Lequeux, F.; Zana, R.; Candau, S. Langmuir 1994, 10, 1714.10. Zhu, Y.P.; Masuyama, A.; Okahara, M. J. Am. Oil Chemists Soc. 1990, 67, 459.11. Zhu, Y.P.; Masuyama, A.; Okahara, M. J. Am. Oil Chemists Soc. 1991, 68, 268.12. Zhu, Y.P.; Masuyama, A.; Kirito, A.; Okahara, M. J. Am. Oil Chemists Soc. 1991, 68, 539.13. Devinsky, F.; Lacko, I.; Mlynarcik, D.; Racansky, V.; Krasnec, L. Tenside Det. 1985, 22, 10.14. Rosen, M. J. Chem. Technol. 1993, 30.15. Zhu, Y.P.; Masuyama, A.; Kirito, A.; Okahara, M.; Rosen, M.J. J. Am. Oil Chemists Soc. 1992, 69, 626.16. Imam, T.; Devinsky, F.; Lacko, I.; Mlynarcik, D.; Krasnec, L. Pharmazie H.5 1983, 38, 308.17. Kralova, K.; Sersen, F. Tenside Surf. Det. 1994, 31, 192.
18. Bunton, C.A.; Robinson, L.; Schaak, J.; Stam, M.F. J. Org. Chem. 1971, 36, 2346.19. Danino, D.; Kaplun, A.; Talmon, Y.; Zana, R. In Structure and Flow in Surfactant Solutions. Herb, C.A.; Prud’Homme, R.K., Eds.; ACS Symp. Ser. 578. American Chemical Society: Washington, DC, 1994;105. 20. Zana, R. In Novel Surfactants: Preparation, Applications and Biodegradability; Holmberg, K., Ed., Chapter 8 Marcel Dekker: New York, 1998; Chapter 8, 241. 21. Fisicaro, E.; Compari, C.; Rozycka-Roszak, B.; Viscardi, G.; Quagliotto, P.L. Curr. Top. Colloid Interface Sci. 1997, 2, 53. 22. Zana, R. Curr. Opin. Colloid Interface Sci. 1996, 1, 566. 23. Menger, F.M.; Keiper, J.S. Angew. Chem. Int. Ed. 2000, 39, 1906. 24. Zana, R. Adv. Colloid. Interface Sci. 2002, 97, 205. 25. Rosen, M.J.; Tracy, D.J. J. Surf. Det. 1998, 1, 547. 26. Asgharian, N.; Otken, P.; Sunwoo, C.; Wade, W.H. Langmuir 1991, 7, 2904. 27. Asgharian, N.; Otken, P.; Sunwoo, C.; Wade, W.H. J. Disp. Sci. Technol. 1992, 13, 515. 28. Sunwoo, C.K.; Wade, W.H. J. Disp. Sci Technol. 1992, 13, 491. 29. Shinoda, K.; Shibata, Y. Colloids Surf. 1986, 19, 185. 30. Larsson, K. Lipids—Molecular Organization, Physical Functions and Technical Applications; Oily Press: Dundee, Scotland, 1994. 31. Alami, E.; Holmberg, K. J. Colloid Interface Sci. 2001, 239, 230. 32. Alami, E.; Holmberg, K. Adv. Colloid Interface Sci. available on the web, Dec 2, 2002. 33. Deinega, Y.; Ul’berg, Z.; Marochko, L.; Rudi, V.; Denisenko, V. Kolloidn. Zh. 1974, 36, 64. 34. Ul’berg, Z.; Podol’skaja, V. Kolloidn. Zh. 1978, 40, 292. 35. Frindi, M.; Michels, B.; Levy, H.; Zana, R. Langmuir 1994, 10, 1140. 36. Devinsky, F.; Lacko, I.; Imam, T. J. Colloid Interface Sci. 1991, 143, 336. 37. Song, L.D.; Rosen, M.J. Langmuir 1996, 12, 1149. 38. Rosen, M.J.; Liu, L. J. Am. Oil Chemists Soc. 1996, 73, 885. 39. Kim, T.-S.; Kida, T.; Nakatsuji, Y.; Ikeda, I. Langmuir 1996, 12, 6304. 40. Kim, T.-S.; Hirao, T.; Ikeda, I. J. Am. Oil Chemists Soc. 1996, 73, 67. 41. Kim, T.-S.; Kida, T.; Nakatsuji, Y.; Hirao, T.; Ikeda, I. J. Am. Oil Chemists Soc. 1996, 73, 907. 42. Rozycka-Roszak, B.; Witek, S.; Przestalski, S. J. Colloid Interface Sci. 1989, 131, 181. 43. Pinazo A.; Diz, M.; Solans, C.; Pe´ s, M.A.; Era, P.; Infante, M.R. J. Am. Oil Chemists Soc.1993, 70, 37. 44. Zhu, Y.-P.; Ishahara, K.; Masuyama, A.; Nakatsuji, Y.; Okahara, M. J. Jpn. Oil Chem. Soc. 1993, 42, 161. 45. Zhu, Y.-P.; Masuyama, A.; Kobata, Y.; Nakatsuji, Y.; Okahara, M.; Rosen, M.J. J. Collo Interface Sci. 1993, 158, 40. 46. Zhu, Y.-P.; Masuyama, A.; Nagata, T.; Okahara, M. J. Jpn. Oil Chem. Soc. 1991, 40, 473. 47. Zhu, Y.-P.; Masuyama, A.; Nakatsuji, Y.; Okahara, M. J. Jpn. Oil Chem. Soc. 1993, 42, 86. 48. Masuyama, A.; Hirono, T.; Zhu, Y.-P.; Ishahara, K.; Okahara, M.; Rosen, M.J. J. Jpn. Oil Chem. Soc. 1992, 41, 301. 49. Okahara, M.; Masuyama, A.; Sumida, Y.; Zhu, Y.-P. J. Jpn. Oil Chem. Soc. 1988, 37, 746. 50. Masuyama, A.; Yokota, M.; Zhu, Y.-P.; Kida, T.; Nakatsuji, Y. J. Chem. Soc. Chem. Comm.
41
1994,1435. 51. Eastoe, J.; Rogueda, P.; Harrison, B.J.; Howe, A.M.; Pitt, A.R. Langmuir 1994, 10, 4429. 52. Kim, J.-M.; Thompson, D.H. Langmuir 1992, 8, 637. 53. Gallardo, B.S.; Abbott, N.L. Langmuir 1997, 13, 203. 54. Jaeger, D.A.; Li, B.; Clark, T., Jr. Langmuir 1996, 12, 4314. 55. Oda, R.; Huc, I.; Candau, S.J. Chem. Comm. 1997, 2105. 56. Renouf, P.; Mioskowski, C.; Lebeau, L.; Hebrault, D.; Desmurs, J.-R. Tetrahedron Lett. 1998, 39, 1357. 57. Oda, R.; Huc, I.; Homo, J.-C.; Heinrich, B.; Schmutz, M.; Candau, S.J. Langmuir 1999, 15, 2384. 58. Peresypkin, A.V.; Menger, F.M. Org. Lett. 1999, 1, 1347. 59. Seredyuk, V.; Alami, E.; Nyde´n, M.; Holmberg, K.; Peresypkin, A.V.; Menger, F.M. Langmuir 2001, 17, 5160. 60. Alami, E.; Holmberg, K.; Eastoe, J. J. Colloid Interface Sci. 2002, 247, 447. 61. Huc, I.; Oda, R. Chem. Commun. 1999, 2025. 62. Hedman, B.; Piispanen, P.; Alami E.; Norin, T. J. Surf. Deter. 2003, 6, 47.
63. Fuoss, R.M.; Chu, V.F. J. Am. Chem. Soc. 1951, 73, 949. 64. Abid, S.K.; Hamid, S.M.; Sherrington, D.C. J. Colloid Interface Sci. 1987, 120, 245. 65. Zana, R. J. Colloid Interface Sci. 2002, 246, 182. 66. Zana, R.; Le´vy, H. Colloids Surf. A: Physicochem. Eng. Aspects 1997, 127, 229. 67. Mosae Selvakumar et al, J. Mol. Struct. 919 (2009) 72-78 68. Espert, A.; Klitzing, R.V.; poulin, P.; Colin, A.; Zana, R.; Langevin, D. Langmuir 1998, 14, 4251. 69. Menger, F.M.; Keiper, J.S.; Azov, V. Langmuir 2000, 16, 2062. 70. Pinazo, A.; Infante, M.R.; Chang, E.I. Colloids Surf. A 1994, 87, 117. 71. Takemura, T.; Shiina, M.; Izumi, M. et al. Langmuir 1999, 15, 646. 72. Esumi, K.; Taguma, K.; Koide, Y. Langmuir 1996, 12, 4039. 73. Tanaka, A.; Ikeda, S. Colloids Surf. 1991, 56, 217. 74. Zhu, Y.P.; Ishahara, K.; Masuyama, A.; Nakatsuji, Y.; Okahara, M. J. Jpn. Oil Chem. Soc. 1993, 42, 161. 75. Zana, R. J. Colloid Interface Sci. 2002, 252, 259. 76. Eastoe, J.; Rogueda, P.; Howe, A.M.; Pratt, A.R.; Heenan, R.K. Langmuir 1996, 12, 2701. 77. Okahara, M.; Masuyama, A.; Sumida, Y.; Zhu, Y.-P. J. Jpn. Oil Chem. Soc. 1988, 37, 746. 78. Menger, F.M.; Wrenn, S. J. Phys. Chem. 1974, 78, 1387. 79. Alami, E.; Le´vy, H.; Zana, R.; Skoulios, A. Langmuir 1993, 9, 940. 80. Diamant, H.; Andelman, D. Langmuir 1994, 10, 2910. 81. Diamant, H.; Andelman, D. Langmuir 1995, 11, 3605. 82. Eastoe, J.; Dalton, J.S.; Rogueda, P.G.A.; Crooks, E.R.; Pitt, A.R.; Simister, E.A. J. Colloid Interface Sci. 1997, 188, 423. 83. Rodakiewicz-Nowak, J. J. Colloid Interface Sci. 1981, 84, 532. 84. Rosen, M.; Song, L.D. J. Colloid Interface Sci. 1996, 179, 261. 85. Esumi, K.; Goino, M.; Koide, Y. J. Colloid Interface Sci. 1996, 183, 539. 86. Esumi, K.; Uda, S.; Goino, M.; Ishiduki, K.; Suhara, T.; Fukui, H.; Koide, Y. Langmuir 1997, 13, 2803. 87. Esumi, K.; Takeda, Y.; Goino, M.; Ishiduki, K.; Koide, Y. Langmuir 1997, 13, 2585. 88. Chorro, C.; Chorro, M.; Dolladille, O.; Partyka, S.; Zana, R. J. Colloid Interface Sci. 1998, 199, 169; 1999, 210, 134.
89. Ghareba S. and Omanovic S., Electrochimica., 15: 3890-3898, 2011. 90. Sharma H.K., Quraishi M.A., Indian Journal of Chemistry, 14, 994 (2002). 91. Quraishi M.A., W.Khan M.A., Jamal D., Ajmal M., Muralidharan S. and Iyer S.V.K., J. Appl. Electrochem, 26, 1253 (1996). 92. Osman M.M., Omar A.M.A. and Al-Sabagh A.M.; Mater.Chem.Phys, 50, 271 (1997). 93. Qiu L., Xie A. and Shen Y., Materials Chemistry and Physics, 91, 269 (2005). 94. El-Ashry E.H., El-Nemra A., Essawyb S.A., and Ragab S., Progress in Organic Coatings, 61, 11 (2008).
42
95. Li X. and Mu G.; Corrosion Science, 252, 1254 (2005). 96. Kokalj A.; Electrochimica Acta, 56, 745 (2010). 97. El-Achouri M., Kertit S., Gouttaya H.M., Nciri B., Bensouda Y., Perez L., Infante M.R., and Elkacemi K., Proc. Org. Coat. 43 (2001) 267–273. 98. Zhao T.P. and Mu G.N., Corros. Sci. 41 (1999) 1937–1944. 99. Branzoi V., Branzoi F. and Baibarac M., Mater. Chem. Phys. 65 (2000) 288–297.100. Guo R., Liu T.Q. and Wei X., Colloids Surf. A 209 (2002) 37–45.101. Ma H.Y., Chen S.H., Yin B.S., Zhao S.Y. and Liu X.Q., Corros. Sci. 45 (2003) 867–882.102. Fuchs-Godec R. and Dolecek V., Colloids Surf. A 244 (2004) 73–76.103. Fuchs-Godec R., Colloids Surf. A 280 (2006) 130–139.104. Moura E.F., Neto A.O.W., Dantas T.N.C., Scatena Junior H. and Gurgel A., Colloids Surf. A340 (2009) 199–207.105. Fuchs-Godec R., Ind. Eng. Chem. Res. 14 (2010) 6407–6415.106. El Achouri M., Infante M.R., Izquierdo F., Kertit S., Gouttaya H.M. and Nciri B.; Corrosion Science, 43, 19 (2001).107. El Achouri M., Infante M.R. and Izquierdo, et al. F., Corros. Sci. 43 (2001) 19.108. El Achouri M., Kertit S. and Gouttaya, et al. H.M., Prog. Org. Coat. 43 (2001) 267.109. Shukla D., and Tyagi V.K.; Journal of Oleo Science, 55, 381 (2006).110. Hegazy, M.A. M.Abdallah, and H.Ahmed, Corr. Sci., 52: 2897–2904, (2010).111. Yan Y., Li W., Cai L. and Hou B., Electrochimica Acta, 53, 5953 (2008). 112. Qiu L.-G., Xie A.-J. and Shen Y.-H., Corros. Sci. 47 (2005) 273–278.113. Qiu L.-G., Xie A.-J., and Shen Y.-H., Appl. Surf. Sci. 246 (2005) 1–5.114. Nessim M. I., Hamdy A., Osman M.M. and Shalaby M.I.; Journal of American science, 2011; 7(8). 115. Nessim M.I., Abdelraheem O.H., and Osman M.M.; Materials Science, an Indian Journal, MSAIJ, 9(9), 2013, 336-345.116. Nessim M.I., Abdelraheem O.H., Elshamy O.A.A., and Osman M.M.; Materials Science, an Indian Journal, MSAIJ, 2013(In Press)117. El Achouri M., Kertit S. and Gouttaya H.M., et al., Prog. Org. Coat. 43 (2001) 267–273.118. El Achouri M., Infante M.R., Izquierdo F., et al. Corros. Sci. 43 (2001) 19–35.119. De S., Aswal V.K., Goyal P.S. and Bhattacharya S., J. Phys. Chem. B 102 (1998) 6152.120. Menger F.M. and Littau C.A., J. Am. Chem. Soc. 113 (1991) 1451.121. De S., Aswal V.K., Goyal P.S. and Bhattacharya S., J. Phys. Chem. 100 (1996) 11664.122. Agrawal Y.K., Talati J.D., Shah M.D., Desai M.N. and Shah N.K., Corros. Sci. 46 (2004) 633.123. Emregul K.C., Kurtaran R. and Atakol O., Corros. Sci. 45 (2003) 2803.124. Li S., Chen S., Lei S., Ma H., Yu R. and Liu D., Corros. Sci. 41 (1999) 1273.125. Ehteshamzadeh M., Shahrabi T. and Hosseini M.G., Appl. Surf. Sci. 252 (2006) 2949.126. Emregul K.C. and Atakol O., Mater. Chem. Phys. 82 (2003) 188.127. Arshadi M.R., Hosseini M.G. and Ghorbani M., Br. Corros. J. 37 (2002) 76.128. Ashassi-Sorkhabi H., Shaabani B. and Seifzadeh D., Appl. Surf. Sci. 239 (2005) 154.129. Shokry H., Yuasa M., Sekine I., Issa R.M., El-Baradie H.Y. and Gomma G.K., Corros. Sci. 40 (1998) 2173.130. Hashiomar I., Surf. Coat. Technol. 29 (1998) 141.131. Li S.L., Wang Y.G., Chen S.H., Yu R., Lei S.B., Ma H.Y. and Liu D.X., Corros. Sci. 41 (1999) 1769. 132. Alami E., Abrahmsen-Alami S., and Eastoe J.; Langmuir 19 (2003) 18. 133. Zana, R., (C. Holmberg, Ed.), Chap. 8, p. 241. Dekker, New York, 1998. 134. Zana, R., Adv. Colloid Interface Sci., in press (2002). 135. Schmitt, V., Schosseler, F., and Lequeux, F., Europhys. Lett. 30, 31 (1995). 136. Zana, R., and Talmon, Y., Nature 362, 228 (1993). 137. Danino, D., Kaplun, A., Talmon, Y., and Zana, R., (C. A. Herb and R. K. Prud’homme, Eds.), ACS Symp. Ser. 578, Chap. 6, p. 105. Am. Chem. Soc.,Washington, DC, 1994. 138. Devinsky, F., Lacko, I., Mlynarcik, D., Racansky, V., and Krasnec, L., Tenside Deterg. 22, (1985).
43
139. Zana, R., and In, M., Uzbek. J. Phys. 1, 24 (1999). 140. Menger, F. M., and Keiper, J. S., Angew. Chem. Int. Ed. 39, 1906 (2000). 141. Fisicaro, E., Compari, C., Rozycka-Roszak, B., Viscardi, G., and Quagliotto, P. L., Curr. Top. Colloid Interface Sci. 2, 53 (1997). 142. Devinsky, F., Lacko, I., Bittererova, F., and Tomeckova, L., J. Colloid Interface Sci. 114, 314 (1986), and references therein. 143. Rosen, M. J., Mathias, J. H., and Davenport, L., Langmuir 15, 7340 (1999). 144. Dreja, M., Pyckhout-Hintzen,W.,Mays, H., and Tiecke, B., Langmuir 15, 391 (1999). 145. Menger, F. M., Keiper, J. S., and Azov, V., Langmuir 16, 2062 (2000). 146. Menger, F. M., and Littau, C. A., J. Am. Chem. Soc. 115, 10083 (1993). 147. Rozycka-Roszak, B., Witek, S., and Przestalski, S., J. Colloid InterfaceSci. 131, 181 (1989). 148. Rozycka-Roszak, B., Fisicaro, E., and Ghiozzi, A., J. Colloid Interface Sci. 184, 209 (1996). 149. Huc, I., and Oda, R., Chem. Commun. 2025 (1999). 150. Oda, R., Huc, I., and Candau, S. J., Chem. Commun. 2105 (1997). 151. Oda, R., Huc, I., Homo, J.-C., Heinrich, B., Schmutz, M., and Candau, S. J., Langmuir 15, 2384 (1999). 152. Devinsky, F., and Lacko, I., Tenside Deterg. 27, 344 (1990). 153. Pinazo, A., Diz, M., Solans, C., P´es, M. A., Era, P., and Infante, M. R., J. Am. Oil Chem. Soc. 70, 37 (1993). 154. Devinsky, F., Masarova, L., and Lacko, I., J. Colloid Interface Sci. 105, 235 (1985), 155. Espert, A., v. Klitzing, R., Poulin, P., Colin, A., Zana, R., and Langevin, D., Langmuir 14, 1140 (1998). 156. Pinazo, A., Infante, M. R., Chang, C.-H., and Franses, E. I., Colloids Surf. A 87, 117 (1994). 157. Takemura, T., Shiina, M., Izumi, M., Nakamura, K., Miyazaki, M., Torigoe, K., and Esumi, K., Langmuir 15, 646 (1999). 158. Esumi, K., Taguma, K., and Koide, Y., Langmuir 12, 4039 (1996). 159. Li, Z. X., Dong, C. C., and Thomas, R. K., Langmuir 15, 4392 (1999). 160. Eastoe, J., Nave, S., Downer, A., Paul, A., Rankin, A., Tribe, K., and Penfold, J., Langmuir 16, 4511 (2000). 161. Zana, R., J. Colloid Interface Sci. 246, 182 (2002). 162. In, M., Bec, V., Aguerre-Chariol, O., and Zana, R., Langmuir 16, 141 (2000). 163. Zana, R., Langmuir 12, 1208 (1996). 164. Hattori, N., Yoshino, A., Okabayashi, H., and O’Connor, C. J., J. Phys. Chem. B 102, 8965 (1998). 165. Song, L., and Rosen, M. J., Langmuir 12, 1149 (1996). 166. Pinazo, A., Wen, X., P´erez, L., and Infante, M. R., Langmuir 15, 3134 (1999). 167. Masuyama, A., Yokota, M., Zhu, Y.-P., Kida, T., and Nakatsuji, Y., J. Chem. Soc. Chem. Commun. 1435 (1994). 168. Sumida, Y., Oki, T.,Mayusama, A., Maekawa, H., Nishiura, M., Kida, T., Nakatsuji, Y., Ikeda, I., and Nojima, M., Langmuir 14, 7450 (1998). 169. Menger, F. M., and Wrenn, S., J. Phys. Chem. 78, 1387 (1974). 170. P´erez, L., Pinazzo, A., Rosen, M. J., and Infante, M. R., Langmuir 14, 2307 (1998). 171. Zhu, Y.-P., Masuyama, A., Kobata, Y., Nakatsuji, Y., Okahara, M., and Rosen, M. J., J. Colloid Interface Sci. 158, 40 (1993). 172. Alami, E., L´evy, H., Zana, R., and Skoulios, A., Langmuir 9, 940 (1993). 173. Diamant, H., and Andelman, D., Langmuir 10, 2910 (1994); 11, 3605 (1995).
44
174. Maiti, P. K., and Chowdhury, D., Europhys. Lett. 41, 183 (1998); J. Chem. Phys. 109, 5126 (1998). 175. Gao, T., and Rosen, M. J., J. Am. Oil Chem. Soc. 71, 771 (1994). 176. Rosen, M., and Song, L. D., J. Colloid Interface Sci. 179, 261 (1996). 177. Chorro, C., Chorro, M., Dolladille, O., Partyka, S., and Zana, R., J. Colloid Interface Sci. 199, 169 (1998). 178. Chorro, C., Chorro, M., Dolladille, O., Partyka, S., and Zana, R., J. Colloid Interface Sci. 210, 134 (1999). 179. Grosmaire, L., Doctorat de l’Universit´eMontpellier 2, University of Montpellier 2, Montpellier, France, July 2001, and manuscript in preparation. 180. Esumi, K., Goino, M., and Koide, Y., J. Colloid Interface Sci. 183, 539 (1996). 181. Manne, S., Sch¨affer, T. E., Huo, Q., Hansma, P. K., Morse, D. E., Stucky, G. D., and Aksay, I. A., Langmuir 13, 6382 (1993). 182. Fielden, M. L., Claesson, P. M., and Verrall, R. E., Langmuir 15, 3924 (1999). 183. Zhao, J., Christian, S. D., and Fung, B. M., J. Phys. Chem. B 102, 761 (1998). 184. Dreja, M., Gramberg, S., and Tieke, B., Chem. Commun. 1371 (1998). 185. P´erez, L., Torres, J. L., Manresa, A., Solans, C., and Infante, M. R., Langmuir 12, 5296 (1996). 186. Camesano, T. A., and Nagarajan, R., Colloids Surf. 167, 165 (2000). 187. Zhu, Y.-P., Ishahara, K., Masuyama, A., Nakatsuji, Y., and Okahara, M., J. Jpn. Oil Chem. Soc. 42, 1611 (1993). 188. Devinsky, F., Lacko, I., and Imam, T., Acta Fac. Pharm. 44, 103 (1990). 189. De, S., Aswal, V. K., Goyal, P. S., and Bhattacharya, S., J. Phys. Chem. 100, 11664 (1996). 190. Bai, B., Yan, H., and Thomas, R. K., Langmuir 17, 4501 (2001). 191. Bai, B., Wang, J., Yan, H., Li, Z., and Thomas, R. K., J. Phys. Chem. B 105, 3105 (2001). 192. Grosmaire, L., Chorro, M., Chorro, C., Partyka, S., and Zana, R., J. Colloid Interface Sci., Issue 1, 1 February 2002, Pages 175-181 193. Verrall, R. E., and Wettig, S. D., J. Colloid Interface Sci. 235, 301 (2001). 194. E. Kraka, D. Cremer, J. Am. Chem. Soc. 122 (2000) 8245-8264. 195. M. Karelson, V. Lobanov, Chem. Rev. 96 (1996) 1027–1043. 196. A. Hinchliffe, John Wiley & Sons, New York, 1994. 197. A. Hinchliffe, John Wiley & Sons, New York, 1999. 198. M. Bouayed, H. Rabaa, A. Srhiri, J.Y. Saillard, A. Ben Bachir, Corros. Sci. 41 (1999) 501–517. 199. M.A. Quraishi, R. Sardar, Mater. Chem. Phys. 78 (2002) 425–431. 200. E. Stupnišek-Lisac, S. Podbršcˇek, T. Soric´, J. Appl. Electrochem. 24 (1994) 779–784. 201. F. Touhami, A. Aouniti, Y. Abed, B. Hammouti, S. Kertit, A. Ramdani, K. Elkacemi, Corros. Sci.42 (2000) 929–940. 202. L. Tang, X. Li, L. Li, G. Mu, G. Liu, Surf. Coat. Technol. 201 (2006) 384–388. 203. M. Hosseini, S.F.L. Mertens, M. Ghorbani, M.R. Arshadi, Mater. Chem. Phys. 78 (2003) 800– 808. 204. N.C. Subramanyam, B.S. Sheshardi, S.A. Mayanna, Corros. Sci. 34 (1993) 563–571. 205. A. Domenicano, I. Hargittai, Oxford University Press, New York, 1992. 206. I.N. Levine, Quantum Chemistry, Prentice Hall, New Jersey, 1991. 207. J.N. Murrell, S.F. Kettle, J.M. Tedder, The Chemical Bond, John Wiley & Sons, Chichester,
45
1985. 208. C. Gruber, V. Buss, Chemosphere 19 (1989) 1595–1609. 209. K. Fukui, Springer Verlag, New York, 1975. 210. D.F.V. Lewis, C. Ioannides, D.V. Parke, Xenobiotica 24 (1994) 401–408. 211. Z. Zhou, R.G. Parr, J. Am. Chem. Soc. 112 (1990) 5720–5724. 212. R.G. Pearson, J. Org. Chem. 54 (1989) 1423–1430. 213. O. Kikuchi, Quant. Struct.-Act. Relat. 6 (1987) 179–184. 214. P. Hohenberg and W. Kohn, Phys. Rev. 136 (1964) B864–871. 215. M.J.S. Dewar, E.G. Zoebisch, E.F. Healy, J.J.P. Stewart, J. Am. Chem. Soc. 107(1985) 3902- 3909 216. I. Lukovits, K. Palfi, E. Kalman, Corrosion 53, 915 (1997) . 217. M. O¨ zcan, ˙I. Dehri, Prog. Org. Coat. 51, 181 (2004) . 218. Y. Yana,,W. Li , L. Caia, B. Hou, Electrochimica Acta, 53, 5953 (2008).
46