SUBJECT AREAS:
NANOPARTICLES
NANOBIOTECHNOLOGY
BIOMATERIALS
POLYMERS AND SOFT MATERIALS
Received
14 June 2011
Ternary phase behaviour and vesicle
formation of a sodium
N-lauroylsarcosinate hydrate/
1-decanol/water system
Nasima Akter1, Shahidan Radiman1, Faizal Mohamed1, Irman Abdul Rahman1
& Mohammad Imam Hasan Reza2
1
Accepted
2 August 2011
Published
23 August 2011
Correspondence and
requests for materials
should be addressed to
N.A. (nasima.
physics@yahoo.com)
School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor,
Malaysia, 2Molecular Biology Lab, Department of Botany, Faculty of Biological Sciences, University of Chittagong, Chittagong
4331, Bangladesh.
The phase behaviour of a system composed of amino acid-based surfactant (sodium N-lauroylsarcosinate
hydrate), 1-decanol and deionised water was investigated for vesicle formation. Changing the molar ratio of
the amphiphiles, two important aggregate structures were observed in the aqueous corner of the phase
diagram. Two different sizes of microemulsions were found at two amphiphile-water boundaries. A stable
single vesicle lobe was found for 152 molar ratios in 92 wt% water with vesicles approximately 100 nm in
size and with high zeta potential value. Structural variation arises due to the reduction of electrostatic
repulsions among the ionic headgroups of the surfactants and the hydration forces due to adsorbed water
onto monolayer’s. The balance of these two forces determines the aggregate structures. Analysis was
followed by the molecular geometrical structure. These findings may have implications for the development
of drug delivery systems for cancer treatments, as well as cosmetic and food formulations.
S
tudies of vesicle formation and morphology for potential applications are rapidly growing areas of
research1. The research acquires immense importance owing to the ability of vesicles to mimic cell properties. A vesicle acts as a nanocarrier with its capacity to encapsulate water-soluble drugs in its aqueous core
and water-insoluble drugs in its membrane2,3. Beyond phospholipids, a number of synthetic surfactants are
known to self-assemble into vesicle structures4–8. These surfactants exhibit a wide variety of self-assembled
structures, all of which have potential applications in drug delivery and, cosmetic and food formulations.
However, the toxic effects of many synthetic surfactants have limited their use in these fields. This adverse
consequence can be avoided by selecting a suitable biocompatible system for vesicle preparation.
In recent years, there has been an increasing interest in using biosurfactants because of their numerous
advantages including biocompatibility, biodegradability, and easy production from renewable natural
sources8–13. Despite their potential advantages, vesicle formation from amino acid-based biosurfactants is limited.
In this study, we used one single chain amino acid-based surfactant, sodium N-lauroylsarcosinate hydrate
(SNLS), which possesses all of these potential advantages. Due to a bulky ionic polar head and strong electrostatic
repulsion, the single chain ionic surfactant always forms micelles in pure water14. Furthermore, like other fatty
acid vesicles, it forms bilayers or vesicles in the presence of other neutral amphiphiles, which doubles the
hydrocarbon volume15–17. An ion pair formed by the association of two headgroups of ionic and neutral surfactants induces a bilayer structure.
Many have reported that the addition of alcohol (particularly long chain alcohols) favours vesicle formation18–23. Andega et al.24 demonstrated in their study that the permeation-enhancing property through porcine
and human skin increases with the alcohol chain length up to 1-decanol and then decreases again with longer
chains. Several other investigations regarding the permeation-enhancing property of alcohols in the vesicles25,26
and bilayers27 have been reported. Any primary alcohol with a C10 to C20 chain is a good and biodegradable
surfactant28. Based on their toxicological studies, Nelson et al.29 reported that 1-decanol is fully nontoxic even for
the foetal rats. Considering these facts, we used 1-decanol as a cosurfactant for vesicle formation.
SCIENTIFIC REPORTS | 1 : 71 | DOI: 10.1038/srep00071
1
www.nature.com/scientificreports
Generally, a mixture of water-soluble and water-insoluble surfactants results in vesicle formation after immersion in water30. With
SNLS and 1-decanol, vesicles are formed when the mixture of the two
amphiphiles (at a particular molar ratio) is immersed into water. In
fact, the displacement of the adsorbed nonpolar surfactant and their
insertion into the hydrophobic area of the monolayer are the driving
forces of this process. Packing of the acyl chains of 1-decanol with
that of the surfactants increases the hydrophobic area. At the same
time, the presence of an OH group between two amino groups forcefully reduced the head group area. The duel effects are responsible
for vesicle formation.
The purpose of this study was to develop a non-toxic and low cost
drug delivery system. The detailed phase behaviour was studied in
the water-rich corner. Rich morphology was observed from the surfactant- rich area to the 1-decanol rich area. The 152 molar ratio of
surfactant/1-decanol at 92 wt% water is the most stable point based
on macroscopic observation for six months. Prepared vesicles are
stable at comparatively higher amphiphile concentrations. The long
term stability of this vesicle-forming system will make it promising
for drug delivery.
Results
Before examining the use of 1-decanol for vesicle formation, we
attempted vesicle formation with ethanol, 1-heptanol, 1-hexanol
and 1-octanol as cosurfactants. The ethanol solution was clear and
non-birefringent between cross polarisers, which is indicative of the
formation of mixed micelles. However, only lamella was formed after
treatment with 1-heptanol, 1-hexanol and 1-octanol. The formation
of lamella was confirmed with the observation of their rainbow texture through cross polarisers. In contrast, we obtained vesicles for a
wide range of molar ratios with 1-decanol. Between cross polarisers,
floating birefringent was observed. In addition, transmission electron microscopy (TEM) and dynamic light scattering (DLS) also
indicated the presence of vesicles in solution. These results imply
that the chain lengths of the cosurfactant influence vesicle formation.
Phase behaviour. We have examined the phase behaviour of the
water-rich region of the system. Based on our investigations, we have
drawn a phase diagram of the water-rich corner (see Fig. 1 (a)). With
0.04 wt% 1-decanol, the surfactant formed a slightly bluish turbid
phase consisting of a small viscous cloudy upper phase (2–5%).
Furthermore, this upper phase increased with the increasing
concentration of both amphiphiles. The samples remained in two
phases up to 96 wt% water. Two isotropic single phases were found
at each amphiphile-water border. The first isotropic phase was situated
in the border of the surfactant-water region (SNLS/1-decanol $ 855,
denoted as ‘‘I’’). This phase was clear but scattered some light, while the
other phase was isotropic and milky white and appeared at the
1-decanol-water border (SNLS/1-decanol $ 158.5 termed as ‘‘V’’). A
single vesicle lobe was found in the intermediate region (between the
molar ratios of 556.5 and 154 in 95–90 wt% water) of the phase
diagram. This region is termed as ‘III’ in the phase diagram. A
greater portion of the phase diagram was two phase. For molar
ratios of 855–556.5 (termed as II) and 154–158.5 (region IV) of
SNLS/1-decanol, the solution remained two phase. The macroscopic
appearance of the lower phase changed from clear to milky white with
increasing concentrations of 1-decanol. In both isotropic phases,
microemulsion was the dominant structure, differing in the size
range of the particles. In the surfactant-rich side, the size of the
particles was approximately 35 nm, whereas in the decanol-rich side,
their size was found approximately 300 nm.
Morphology of the self-assembled structure. The observed
microstructures were characterised by TEM (see Fig. 1). In region
‘III’ of the phase diagram, the most bluish phase was found at a molar
ratio of 152 in 92 wt% water. The TEM image of the obtained vesicles
in this region is shown in Figure 1(e). The size of these particles was
found approximately 100 nm, which is also comparable with the
result obtained from the DLS analysis (Fig. 2). The TEM image
clearly shows the internal cavity surrounded by a brighter border.
Figures 1(b) and 1(c) represent one vesicle and microemulsion phase
at 97 wt% water at a molar ratio of 151 SNLS/1-decanol. The bottom
Figure 1 | The phase diagram of sodium N-lauroylsarcosinate hydrate/1-decanol/water systems at 256C. The shaded area represents a two phase
region. The samples’ macroscopic appearance is shown with their corresponding TEM images (followed by a negative staining technique), with, (a) a
phase diagram of the system; (b) and (c) the TEM image of the upper and lower phase of the sample at 97 wt% water in equimolar ratio of SNLS and
1-decanol; (d) TEM image of the microemulsion for the molar ratio of 159.3 in 94 wt% water; and (e) TEM image of vesicles for the molar ratio of 152 in
92 wt% water.
SCIENTIFIC REPORTS | 1 : 71 | DOI: 10.1038/srep00071
2
www.nature.com/scientificreports
Figure 4 | Zeta potential of the sample at the molar ratio of 152 at 92 wt%
water concentration.
Figure 2 | The size distribution of unilamellar vesicles in the aqueous
SNLS/1-decanol mixture (152 molar ratios) at a water concentration of
92 wt%.
phase contains a microemulsion of approximately 40 nm, and the
top phase contains vesicles approximately 200 nm in diameter. The
trend of increasing vesicle size may be due to the reduction of
electrostatic repulsion between inter-vesicular dispersion. This
result indicates that the proper mole fraction of amphiphiles is
necessary; otherwise, the sample is rendered into two phases.
Figure 1(d) represents one microemulsion phase of approximately
300 nm in diameter. It is clear from the phase map that microemulsion is the dominant structure above the equimolar ratio and
on the 1-decanol rich side of the phase diagram.
From the small angle X-ray scattering investigation of the vesicle
dispersion (SNLS/1-decanol molar ratio 5 152 in 92 wt% water), it
was found that the scattering spectra consists of two peaks, a broad
scattering peak and a small sharp peak (Fig. 3). The broad peak
represents a single bilayer31,32, and the second sharp peak arises from
the interparticle interference33. For the confirmation of the vesicle
morphology in dry conditions, we dried the sample in a desiccator.
The broad scattering peak of the dry vesicles appeared at the same
position in both cases, indicating that the vesicle morphology did not
change even in dry conditions. The second peak changed according
to the concentration of vesicles. The reason behind the observed
stability may be due to the high absolute value of the zeta potential
Figure 3 | Small angle scattering X-ray result for the molar ratio 152
system in 92 wt% water, where, (a) represents the scattering peak of
vesicles in solution and (b) represents the scattering peak of vesicles in dry
samples.
SCIENTIFIC REPORTS | 1 : 71 | DOI: 10.1038/srep00071
(42 mV, see Fig. 4). This strong repulsive force prevents the agglomeration of vesicles. Considering all of the experimental results, we
selected the molar ratio of 152 at 92 wt% water as the most stable
point in the system.
Figure 5 shows the FTIR spectra of the vesicle solution. Maxima
were found at 1656 cm21 (amide region), which is shifted from a split
peak in the surfactant at 1640 and 1648 cm21. The shift is attributed
to the hydrogen bonding between the C5O of the amide group and
the alcoholic hydroxyl group. Tenaciously bound water also contributes to this bonding. Strong hydrogen bonding yields a significant
band broadening in region of 3400 cm21. Both OH stretching vibrations from the alcohol group and adsorbed water contributes this
broadening. However, a hydrogen band at 3304–3229 cm21 is an
evidence of the tertiary ammonium cation (R3N1H)34. In the case
of the micelle solution, a single very broad peak was observed at
3400 cm21, while no peak was observed at 3304–3229 cm21.
Strong hydrogen bonding between water and the amino acid head
group is responsible for such a peak in the micelle solution. In the
vesicle solution, a reduction of hydrogen bonding with water occurs.
The most probable reason for such an occurrence is the tendency
towards a reduction of interfacial hydration due to the addition of 1decanol. The strong asymmetric and symmetric stretch of methyl
group of surfactant and 1-decanol appears as very weak stretching
vibration at the peak value 2956 cm21 and 2856 cm21 in vesicle
solution, because the association of more acyl chains weakens the
peak strength.
Discussion
The phase map shows significant changes of the self-assembled properties. In both surfactant-rich and decanol-rich regions (region I and
V) of the phase map, the presence of excess ionic surfactant accumulates around some free 1-decanol molecules. Consequently, the
hydrophilic surface of each monolayer remains in contact with water,
and the hydrophobic surface remains in contact with excess 1decanol. The interfacial tension is smaller in the region of water
and the hydrophilic surface monolayer than that of the region of
1-decanol and the hydrophobic surface. As a result, the hydrophilic
surface swells, and the hydrophobic surface contracts. Thus, the
convexing of the surfactant monolayer with respect to the water
phase containing the oil phase (1-decanol) in its interior, forms a
micro emulsion. The size of the aggregates depends on the relative
concentration of the hydrophilic and hydrophobic areas. Specifically,
a larger hydrophilic area favours the formation of a microemulsion of
below 40 nm in size in the surfactant-rich corner. However, at the
same water concentration, a comparatively large hydrophobic area
favours the formation of a larger microemulsion. The size of the
particles depends on the availability of
1-decanol molecules. In the intermediate region, i.e., area III in the
phase diagram, the situation is better for a bilayer structure.
For vesicle formation, two major phases must be fulfilled in a
system. One is the requirement of energy; i.e., the energy level of
vesicle phase, should be lower than that in molecular dispersion
3
www.nature.com/scientificreports
Figure 5 | FTIR spectra of (a) sodium N-lauroylsarcosinate hydrate, (b) 1-decanol, (c) micelle solution of 0.08% SNLS in 99.92 wt% water, (d) vesicle in
solution for the molar ratio of 152 system in 92wt% water.
state19. The other requirement is the molecular packing parameter
introduced by Israelachvili35. In fact, the packing of the acyl chain in
the hydrophobic core determines the aggregate structure, and is
defined as the ratio of the volume of the hydrocarbon tail of the
surfactant in the core (vc) and the product of the optimal head group
area (a0) and the critical chain length of the tail (lc).
P~vc =a0 lc
The spherical micelles are formed at 0,P,1/3, and the cylindrical
micelles are formed at 1/3,P,1/2. For 1/2,P,1, vesicles are
formed, at P<1, lamella formed, and for P.1, reverse micelles are
formed.
It is clear that, a certain concentration of 1-decanol must be used
for vesicle formation in this system. Addition of decanol at a molar
ratio of 152 shows the most bluish and turbid phase in this system,
which implies that the insertion of decanol molecules at 92 wt%
water enlarges the hydrophobic area, which is beneficial for vesicle
or bilayer formation. Similar results were also found in other systems.
It was previously shown that a specific molar ratio is beneficial for
vesicle formation15, and the importance of the interfacial properties
of a mixed surfactant system36 were also emphasised.
Generally, in a system consisting of an ionic surfactant and a
cosurfactant, the system balanced at some optimum mixing ratio37.
Regarding this matter, it can be assumed that, the maximum solubilisation of amphiphiles is achieved in the intermediate region (region
III) of the phase diagram. We considered this region to be the solubilisation boundary. In catanionic systems, both cationic-rich38
anionic-rich39 vesicle lobe regions were reported, but precipitates at
equimolar ratios, i.e., excess surfactant, should be present within
these bilayers. Zhai et al.40 also showed that an aqueous anionic
and neutral amphiphile mixture forms vesicles at certain molar
ratios. The excess amphiphiles weaken the repulsive forces between
two ionic head groups. The combination of reduced interfacial
hydration, as well as weak repulsion, makes the polar head group
area smaller than the micelle, and the packing of acyl chain increases
the hydrophobic area. The combination of these effects reduces the
free energy of the system and also favours the formation of a cup-like
structure, which is the basis for vesicle formation.
With the increase in bonding interactions, the two molecules
closer together, were making more space to for new 1-decanol molecules to enter. Due to the strong hydrogen bonding property, the
new OH group also associates with adsorbed water and with other
SCIENTIFIC REPORTS | 1 : 71 | DOI: 10.1038/srep00071
surrounding headgroups. It is notable that not all mixing ratios
yielded vesicle formation, however, a molar ratio of 556.5–154
(SNLS/1-decanol) in 95–90 wt% water is sufficient for vesicle formation. Adequate insertion of 1-decanol leads to the decrease of the
curvature, consequently closing the bilayer, which then contains a
fraction of the aqueous part in its core. Furthermore, the compressed
bilayers and adsorbed water on the monolayer prevents the outer
molecules from entering the inner layer of the vesicle. This effect
limits the diameter of the vesicles to a certain range.
In conclusion, the sodium N-lauroylsarcosinate hydrate/ 1decanol/water system has similar properties of forming bilayer
structures to that of an oppositely-charged amphiphile system.
Furthermore, different aggregate structures can be achieved by changing the mixing ratio of both amphiphiles. Previously, it was reported
that the addition of alcohol is beneficial for vesicle formation in some
mixed surfactant systems. However, 1-decanol enhances not only the
vesicle formation, but also two different sizes of microemulsion
phases in one single chain ionic surfactant. Vesicles were stable
between the temperatures of 20 and 37uC. This result indicates that,
changes in interfacial hydration and the interactions between amphiphiles in different mixing ratios greatly change the phase behaviour.
Additionally, a similar chain length (C11 for the surfactant and C10
for the 1-decanol) greatly influences the hydrophilic and hydrophobic portion. Due to these properties, the system is promising
for development into a nanocarrier-forming system.
Methods
Materials and sample preparation. Sodium N-lauroylsarcosinate hydrate (SNLS)
was purchased from TCI (Japan), 1-decanol with 97% purity was purchased from
Fluka-Chemica (Switzerland). Deionised water was used to prepare all of the samples.
To obtain vesicles, the desired amounts of amphiphile were measured in the glass tube
and then the required amount of water was added. The resulting suspension was
sonicated at 20uC for 10 min using a bath-type sonicator. To obtain microemulsion,
the mixture was vortexed for 5 min. The homogenous dispersions were then
centrifuged at 4,000 rpm for 10 min to see the phase separation. Before analysis, all
samples were left undisturbed at equilibration for several days.
Phase diagram determination. After equilibration, inspection between cross
polarisers was performed to identify the birefringent and isotropic phase. We studied
the expected phase sequence over the composition range 0.08–6 wt% of surfactant
and 1-decanol and 90–99.92 wt% water. The composition of each solution was
expressed in molar fraction (as) and defined in equation (1)
as ~½Surfactant=f½Surfactantz½1-decanolg
ð1Þ
where, [surfactant] and [1-decanol] are the molar concentrations of surfactant and
4
www.nature.com/scientificreports
1-decanol.The macroscopic appearance was monitored at regular intervals by both
visual inspection and between cross polarisers after subsequent centrifugation.
It was observed that the samples’ appearance remained unchanged in the temperature range of 20–35uC. The macroscopic appearance of samples is shown in
Figure 1 with their corresponding TEM images. This inspection was conducted over
the course of months to check the phase separation or flocculation above the isotropic
or vesicular region.
Transmission electron microscopy (TEM). Observation of the vesicle formation was
examined using TEM (Philips-CM12). A drop of vesicle dispersion was applied to the
carbon grid and left for partial drying to allow some of the vesicles to adhere to the
carbon grid. The excess sample was removed by filter paper from the opposite
direction. A drop of 3% uranyl acetate solution was added to the grid and left for
10 sec. Again, the excess solution was removed washing the grid thrice. Each time the
liquid was adsorbed with filter paper, and the sample was dried in the air. The sample
was then characterised under an electron microscope at an accelerating voltage of
100 kV.
Measurement of the particles. Vesicle size and zeta potential were determined with a
Zetasizer Nano ZS (Malvern Instruments, Herrenberg, Germany) after equilibration.
Z-average particle sizes were measured at the scattering angle of 90u at 25uC using
DLS combined with Malvern’s DTS software (v.5.02). Zeta potential values were
measured by laser Doppler anemometry at 25uC and calculated using DTS software.
Further investigation of the vesicular phase was performed by small angle scattering X-ray technique at 25uC using a kratky compact small angle system, which is
equipped with a position-sensitive detector containing 1024 channels of 54 mm in
width. The wavelength used was 0.154 nm, and the sample-detector distance was
274 mm. A few milligrams of sample were enclosed in the sample holder on a flat
miler sheet. Data were normalised for an acquisition time for 30 min. The results are
represented in Figure 3 after background subtraction.
The Fourier transform infrared (FTIR) spectra were recorded using a Perkin Elmer
Spectrum BX FTIR system over the region of 4000–400 cm21 of the sample solution.
Prior to the assay, liquid samples were prepared by placing a few drops of the vesicle
solution between two sodium chloride (NaCl) salt plates.
1. Lovell, J. F. et al. Porphysome nanovasicles generated by porphyrin bilayers for use
as multimodal biphotonic contrast agents. Nature Mater. 10, 324–332 (2011).
2. Chu, C. et al. Proliposomes for oral devivery of dehydrosilymarin: preparation and
evaluation in vitro and in vivo. Acta Pharmacol.Sin. 32, 973–980 (2011).
3. Yang, T. et al. Enhanced solubility and stability of PEGylated liposomal paclitaxel:
in vitro and in vivo evaluation. Int. J. Pharm. 338, 317–326 (2007).
4. Fendler, J. H. Membrane Mimetic Chemistry (Willey, New York, 1982).
5. Jones, M. N. The surface properties of phospholipid liposome systems and their
characterization. Adv. Colloid Interface Sci. 54, 93–128 (1995).
6. Makino, K. & Shibata, A. Surface properties of liposomes depending on their
composition. in Advances in Planar Lipid Bilayers and Liposomes (ed. Liu A. L.)
4, 49–53 (Elsevier, 2006).
7. Bandyopadhyay, P. & Neeta, N. S. Evidence of vesicle formation from 151
nonionic surfactant span 60 and fatty alcohol mixtures in aqueous ethanol:
Potential delivery vehicle composition. Colloids Surf. B 58, 305–308 (2007).
8. Rosa, M., Moran, M., Miguel, M. & Lindman, B. The association of DNA and
stable catanionic amino acid-based vesicles. Colloids Surf. A 301, 361–375 (2007).
9. Mulligan, C. N. Recent advances in the environment applications of
biosurfactants. Curr. Opi. Colloid Interface Sci. 14, 372–378 (2009).
10. Ruiz, C. C., Hierrezuelo, J. M. & Molina-Bolı́var, J. A. Effect of glycine on the
surface activity and micellar properties of N-decanoyl-N-methylglucamide.
Colloid Polym. Sci. 286, 1281–1289 (2008).
11. Muthusamy, K., Gopalakrishnan, S., Ravi, T. K. & Sivachidambaram, P.
Biosurfactants: Properties, commercial production, and application.Curr. Sci. 94,
736–747 (2008).
12. Worakitkanchanakul, W. et al. Aqueous phase behavior and vesicle formation of
natural glycolipid biosurfactants, mannosylerythritol lipid-B. Colloids Surf. B 68,
207–212 (2009).
13. Ohta, A., Toda, K., Morimoto, Y., Asakawa, T. & Miyagishi, S. Effect of the side
chain of N-acyl amino acid surfactants on micelle formation: An isothermal
titration calorimetry study. Colloids Surf. A 317, 316–322 (2008).
14. Zemb, T., Dubois, M., Deme, B. & Gulik-Krzywicki, T. Self-Assembly of flat
nanodiscs in salt-free catanionic surfactant solutions. Science 283, 816–819 (1999).
15. Gradzielski, M, Müller, M., Bergmeier, M., Hoffmann, H. & Hoinkis, E. Structural
and macroscopic characterization of a gel phase of densely packed monodisperse,
unilamellar vesicles. J. Phys. Chem. B 103, 1416–1424 (1999).
16. Morigaki, K. & Walde, P. Fatty acid vesicles. Curr. Opi. Colloid Interface Sci. 12,
75–80 (2007).
17. Vlachy, N. et al. Spontaneous formation of bilayers and vesicles in mixtures of
single-chain alkyl carboxylates: effect of pH and aging and cytotoxicity studies.
Langmuir 24, 9983–9988 (2008).
18. Seo, D. et al. Two-dimensional packing patterns of amino acid surfactant and
higher alcohols in an aqueous phase and their associated packing parameters.
J. Colloid Interface Sci. 273, 596–603 (2004).
SCIENTIFIC REPORTS | 1 : 71 | DOI: 10.1038/srep00071
19. Huang, J. B., Zhu, B. Y., Zhao, G. X. & Zhang, Z. Y. Vesicle formation of a 151
catanionic surfactant mixture in ethanol solution. Langmuir 13, 5759–5761
(1997).
20. Huang, J., Zhu, Y., Zhu, B., Li, R. & Fu, H. Spontaneous vesicle formation in
aqueous mixtures of cationic surfactants and partially hydrolyzed
polyacrylamide. J. Colloid Interface Sci. 236, 201–207 (2001).
21. Hoffmann, H., Thunig, C. & Miller, D. Vesicle phases from N-methyl-Nalkanoylglucamin and various co-surfactants. Colloids Surf. A 210, 147–158
(2002).
22. Danino, D. et al. Microstructures in the aqueous solutions of a hybrid anionic
fluorocarbon/hydrocarbon surfactant. J. Colloid Interface Sci. 259, 382–390
(2003).
23. Gradzielski, M., Bergmeier, M., Hoffmann, H., Mueller, M. & Grillo, I. Vesicle gel
formed by a self-organization process. J. Phys. Chem. B 104, 11594–11597 (2000).
24. Andega, S., Kanikkanan, N. & Singh, M. Comparison of the effect of fatty alcohols
on the permeation of melatonin between porcine and human skin. J. Controlled
Release 77, 17–25 (2001).
25. Oliveira, G., Beezer, A. E., Hadgraft, J. & Lane, M. E. Alcohol enhanced
permeation in model membranes. Part I. Thermodynamic and kinetic analyses of
membrane permeation. Int. J. Pharm. 393, 61–67 (2010).
26. Williams, A. C. & Berry, B. W. Penetration enhancers. Adv. Drug Deliv. Rev. 56,
603–618 (2004).
27. Greipernau, B., Leis, S., Schneider, F., Sikor, M., Steppich, D. & Bockmann, R. A.
1-Alkanols and membranes: A story of attraction. Biochim. Biophy. Acta 1768,
2899–2913 (2007).
28. Nelson, R. Dispersing Powders in Liquid. 4, 1–8 (Elsevier 2003).
29. Nelson, B. K., Brightwell, W. S., Khan, A., Krie, E. Fg. & Hoberman, Jr. A. M.
Developmental toxicology assessment of 1-octanol, 1-nonanol, and 1-decanol
administered by inhalation to rats. Int. J. Toxicol. 9, 93–97 (1990).
30. Lasic, D. D., Kidric, J. & Zagorc, S. A simple method for the preparation of small
unilameller vesicles. Biochim. Biophys. Acta 896, 117–122 (1987).
31. Hauser, H. Naturally occurring amphiphiles: aspects of their phase behavior. in
Reverse Micelles (eds. Luisi, P. L. & Straub, B. E.) 37–53 (Plenum Press, New York,
1984).
32. Riske, K. A., Amaral, L. Q., Döbereiner, H. -G. & Lamy, M. T. Mesoscopic
structure in the chain-melting regime of anionic phospholipid vesicles: DMPG.
Biophy. J. 86, 3722–3733 (2004).
33. Feigin, L. A. & Svergun, D. I. Structure Analysis by Small-Angle X-Ray and
Neutron Scattering (ed. Taylor, G. W.) (Plenum Press, New York, 1987).
34. Hummel, D. O., Baum, A., Liu, M., Pastura, A. & Weber, A. Analysis of surfactants:
Atlas of FTIR-spectra with interpretations (Hanser Gardner Publications,
Germany, 1996).
35. Israelachvili, J. N. Intermolecular and Surface Forces (Academic Press, 1992).
36. Patist, A., Devi, S. & Shah, D. O. Importance of 153 Molecular Ratios on the
Interfacial Properties of Mixed Surfactant Systems. Langmuir 15, 7403–7405
(1999).
37. Gillberg, G., Lehtinen, H. & Friberg, S. NMR and IR investigation of the conditions
determining the stability of microemulsions. J. Colloid Interface Sci. 33, 40–53
(1970).
38. Marques, E. F., Regev, O., Khan, A., Graca Miguel, M. & Lindman, B. Vesicle
formation and general phase behaviour in the catanionic mixture SDS-DDABwater. The anionic rich side. J. Phys. Chem. B 102, 6746–6758 (1998).
39. Marques, E. F., Regev, O., Khan, A., Graca Miguel, M. & Lindman, B. Vesicle
formation and general phase behaviour in the catanionic mixture SDS-DDABwater. The cationic rich side. J. Phys. Chem. 103, 8353–8363 (1999).
40. Zhai, L., Li, G. & Sun, Z. Spontaneous vesicle formation in aqueous solution
of zwitterionic and anionic surfactant mixture. Colloids Surf. A 190, 275–283
(2001).
Acknowledgements
The authors would like to thank Universiti Kebangsaan Malaysia for the financial support
of this research work through the grant numbers UKM-GUP-NBT-08-27-106,
UKM-GGPM-NBT-163-2010 and STGTL-007-2010/11.
Author Contributions
N. A. and S. R. designed the research. N. A. drafted the manuscript. N. A., S. R. and F. M.
contributed to the experiments. I. A. R. and M. I. H. R. contributed intellectually. All authors
discussed the results and contributed to the revision of the final manuscript.
Additional information
Competing financial interests: The authors declare no competing financial interests.
License: This work is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this
license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/
How to cite this article: Akter, N., Radiman, S., Mohamed, F., Rahman, I.A. & Reza, M.I.H.
Ternary phase behaviour and vesicle formation of a sodium N-lauroylsarcosinate hydrate/
1-decanol/water system. Sci. Rep. 1, 71; DOI:10.1038/srep00071 (2011).
5