Mass density measurement as a tool to distinguish between micelle size shape in nematic and chiral nematic phases

Article abstract of DOI:10.1039/b304693a

The effect of the solute structure on micelle size and micelle shape were studied on two sets of specific solutes. The mass density of the first set, consisting of achiral solutes phenol, benzene, cyclohexanol, and cyclohexane, was measured in the same host phase. The mass density changed in the order: phenol > cyclohexanol > benzene > cyclohexane. The effect of the solutes on mass density of the host phase was due to the capability of the hydrophilic group and the hydrophobic part of the solutes to interact with the corresponding region of the host micelle. The second set contained racemic amphiphilic mixtures and their enantiomers, decyl- and dodecyl-esters of serine and alanine. The mass density increased in the serine phases but decreased in the alanine phases as the DL-racemic amphiphiles of the nematic phases were replaced by their L-isomers. These results were due to a definite arrangement of the head groups in the racemic nematic and intrinsic chiral nematic phases. A distinction between the induced chiral nematic phases and the intrinsic chiral ones is possible on the basis of the mass density difference between the achiral/induced chiral nematics and the racemic/intrinsic chiral nematics.

Full text of DOI:10.1039/b304693a

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Mass density measurements as a tool to distinguish between micelle
size and shape in nematic and chiral nematic phases
M. Acımı s¸ * and E. Akpınar
˙
Abant Izzet Baysal University, Faculty of Arts and Sciences, Department of Chemistry,
4280, Bolu, Turkey. E-mail: mahmut@ibu.edu.tr
1
Received 29th April 2003, Accepted 18th July 2003
First published as an Advance Article on the web 3rd September 2003
The relative alteration in micelle size and micelle shape brought about by two sets of specific solutes have been
investigated by mass density measurements at constant composition and temperature. The mass density of the
first set of solutes, phenol, benzene, cyclohexanol and cyclohexane, was measured in the same host phase and
found to change in the order: phenol > cyclohexanol > benzene > cyclohexane. The contribution of the
solutes to the mass density of the host phase was interpreted to arise from the capability of the hydrophilic
group and the hydrophobic part of the solutes to interact with the corresponding region of the host micelle. The
second set consisted of racemic amphiphilic mixtures and their enantiomers, decyl- and dodecyl-esters of serine
and alanine. It was found that the mass density increases in the serine phases but decreases in the alanine ones as
the DL-racemic amphiphiles of the nematic phases were replaced by their L-isomers. These phenomena were
shown to arise from a definite arrangement of the head groups in the racemic nematic and intrinsic chiral
nematic phases. Furthermore, on the basis of the mass density difference between the achiral/induced chiral
nematics and the racemic/intrinsic chiral nematics, a distinction between the induced chiral nematic phases and
the intrinsic chiral ones is possible.
Micelle size and shape in both nematic and chiral nematic
phases have been of fundamental interest and investigated by
Introduction
3
–5
Amphiphilic molecules, on dissolution in water, self-assemble
to form micelles and liquid crystals as their concentration is
increased. Among the various liquid crystalline structures, we
concentrate on nematic and chiral nematic liquid crystal-
line phases. The nematic phase region exists between the bor-
derlines of the totally ordered lamellar or hexagonal phase
and the totally disordered isotropic micellar solution and in
general can be achieved either from lamellar or hexagonal
some research groups. In the frame of this paper we confine
ourselves to discotic (disc-like) micelles and in order to have an
estimate, we depict some literature values of SDS and DACl
nematic phases: the discs of a particular SDS nematic phase
˚
were found to possess a diameter of ꢀ57 A and a thickness
˚
3
of ꢀ20 A, but for the DACl nematic phase a diameter of
˚
˚
6
ꢀ90 A and a thickness of ꢀ40 A were given.
Another important property of the liquid crystals is their
preferred alignment, i.e. the alignment of the director (optical
axis) of the phase with respect to a given direction, e.g.
magnetic field direction. This quantity can be assessed by
diamagnetic succeptibility anisotropy (Dw) or optical aniso-
tropy (Dn). Particularly, it is easy to determine the sign of Dn
by using a polarizing light microscope to obtain cono-
1
,2
phases by increasing the temperature or as usual at con-
stant temperature and certain concentrations of the host
amphiphile, water and other additives. The geometry of the
building units, i.e. the shape of the micelles in the nematic
region was revealed to be discotic (D), cylindrical (C) or biax-
ial (B) and designated N , NC or N , respectively, where N
D
B
stands for nematic. Although macroscopically there is no
apparent difference between nematic phases (achiral nematic
phases) obtained from the host amphiphiles e.g. decylammo-
nium chloride (DACl), or sodium decylsulfate (SDS) and the
racemic nematic phases derived for instance from DL-serine
hydrochloride decylester (DL-SDE), or DL-alanine hydrochlo-
ride dodecylester (DL-ADDE), we wish to introduce both terms
for later discussion.
Chiral nematic phases can primarily be obtained either by
adding a suitable chiral solute to an achiral nematic phase or
by using an amphiphilic enantiomer e.g. L-serine hydrochloride
decylester (L-SDE), with water and a salt. As a result, an
induced chiral nematic phase and an intrinsic chiral nematic
phase can be produced, respectively, where we emphasize the
difference between them as we will show in this paper. As
nematic phases, the chiral nematic phases are also designated
scopic measurements for N
director perpendicular to the magnetic field direction,
Fig. 1a. Such N phases possess a positive Dn, but a negative
D
phases which align with their
7
D
Dw, then Dn and Dw are opposite in sign for amphiphilic liquid
crystals.
7
The shape of the micelle of the induced chiral phase was also
of fundamental interest, and small angle X-ray diffraction stu-
dies could not differentiate between the shapes of chiralized
4
,8
micelles and achiral micelles,
however, we have inferred
from our investigations on chiral induction and the results
9
1
0
in the literature that a chiral micelle would possess a screw-
like shape, Fig. 1c and d. The nematic and chiral nematic
phases can easily be recognized by a polarizing light micro-
scope from their schlieren (threaded) textures and the finger
1
1
print texture, respectively. The nematic state can then be
visualized as a dispersion of anisometric micelles of finite size
in water with long range orientational order but with no posi-
tional order. The chiral nematic state, however, can, in a first
approximation, be considered as a nematic state in which the
D C B
Ch , Ch or Ch , where Ch stands for cholesteric, and the
subscript letters indicate the shape of the micelles, being
discotic, cylindrical or biaxial.
DOI: 10.1039/b304693a
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between induced chiral nematics and intrinsic chiral nematics
is possible.
Experimental
Chiral amphiphilic molecules and their racemates were
obtained by esterification of the amino acids, serine and
alanine, with n-decanol and n-dodecanol according to the
procedure given in reference 11. It was found that the yield
of serine esters was better when the mole ratio of serine to
alcohol 1 : 7 was chosen. In this way, L- and DL-serine hydro-
chloride decylesters (L-SDE and DL-SDE), L- and DL-serine
hydrochloride dodecylesters (L-SDDE and DL-SDDE), and
the corresponding esters of alanine, L- and DL-alanine hydro-
chloride decylesters (L-ADE and DL-ADE) as well as L- and
DL-alanine hydrochloride dodecylesters (L-ADDE and DL-
ADDE) were synthesized. Because n-dodecanol in the reaction
mixtures solidifies at room temperature, it was removed from
the crude esters by extraction using diethyl ether. The esters
were obtained in purest form by recrystallizing them four
times from ethylacetate which was distilled over a fractinating
column prior use. Decylammonium chloride (DACl) was
prepared by neutralizing n-decylamine with dilute hydro-
chloric acid in ethanol. After removing the solvent, the crude
material was recrystallized four times from a mixture of petro-
ꢁ
leum ether (bp 40–60 C) and chloroform (4 : 1). All other
materials, cyclohexane, benzene, cyclohexanol, phenol, man-
delic acid (MA) and hexahydromandelic acid (HHMA) were
purchased at high purity ( > 99.5%) and used without further
purification.
The liquid crystalline samples were prepared by weighing
appropriate amounts of the ingredients into test tubes which
were flame-sealed immediately in order to avoid water loss.
Homogeneous liquid crystalline samples were obtained by
Fig. 1 (a) A schematic representation of the nematic disc-like phase,
, and the alignment of its optical axis with respect to magnetic field
N
D
(B). When a discotic micelle (b) is chiralized, it takes a screw-like shape
c), indicated by two arrows that give a resultant vector, R, with
ꢁ
(
leaving the sealed test tubes in a water bath at 50 C and cen-
respect to the magnetic field, B. For simplicity, R is drawn on the
surface of the skewed micelle (d). (e) A schematic representation of
the fingerprint texture, arising from stacked micelles with different
rotation to complete the 2p distance.
trifuging occasionally. Each liquid crystalline sample was left
for 24 hours at room temperature prior to each density mea-
surement. Approximately 3 grams of liquid crystalline sample
was needed for the density and microscopic measurements.
The water used was distilled 3 times over a 40-cm fractionating
column. The compositions of the components, the phase type
as well as the nematic–isotropic phase transition temperatures
chiralized micelles are arranged in a helicoidal structure, Fig.
1e. The 2p distance corresponds then to the pitch (P) of the
chiral phase, Fig. 1e.
(
TNI) are presented in Table 1.
Great care must be taken when adding the liquid crystalline
From the preceeding picture of nematic and chiral nematic
phases it is easy to conceive that micelle structure may be
extremely sensitive to the addition of solute molecules. Some
solutes may increase the volume of the micelle but some
decrease it, which is reflected in the flow properties of the
phase and changing the nematic–isotropic phase transi-
samples to the U-tube of the densitometer in order to avoid
incuding air bubbles. For this purpose, the densitometer as
well as the liquid crystalline samples were warmed to about
ꢁ
ꢁ
3
5 C and then cooled to 20 C. The mass density measure-
ments were carried out on an Anton Paar DMA 5000 density
meter which measures the density from the oscillation period
of a U-tube. The density meter was calibrated with water at
1
0,12,13
tion.
Particularly of interest is the modification observed
if the DL-amphiphile mixture of a racemic nematic phase is
replaced by its L-enantiomer. Therefore, it is important to cap-
ture such changes by an easily applicable method, mass density
measurements, which give us insight into the phenomena
taking place in the micelle on addition of any solute.
ꢁ
2
were measured. Each liquid crystalline sample was equilibrated
0 C, the temperature at which the liquid crystalline samples
ꢁ
at 20 C for at least 2 hours before each measurement.
Each point of density was measured at least 3 times. The
ꢃ5
standard deviation of a point varied between 1.1 ꢂ 10 and
In a recent communication we have shown for the first time,
by a few examples, that mass density measurements may be
used to detect relative changes in micelle size and micelle shape
in a racemic nematic/L-isomer mixture and we have delivered
some qualitative results on the effect of solutes on the host
ꢃ5
ꢃ3
5
.0 ꢂ 10 g cm . In general, the deviations arise mainly from
Table 1 Compositions of the individual racemic nematic phases
obtained from serine and alanine esters (hosts), salt and water in mole
percent and their nematic–isotropic phase transition temperatures, TNI
1
4
phases. The present investigation is designed to show (i)
quantitatively the effect of specifically chosen achiral solutes
on the micelle dimension of the host phase, (ii) to extend the
studies of racemic nematic/L-isomer mixtures to newly devel-
oped racemic nematic phases and their enantiomers and dis-
cuss why intrinsically chiral micelles can have smaller or
larger densities than their racemic micelles. Furthermore, we
will show, in contrary to common belief, that a distinction
ꢁ
NaCl
DACl
H
2
O
T
NI/ C
DL-SDE, 5.553
DL-ADE, 4.415
DL-SDDE, 3.242
DL-ADDE, 4.072
3.589
3.712
1.804
1.936
–
2.211
90.858
89.662
94.954
93.992
ꢀ34
ꢀ34
ꢀ34
ꢀ31
–
–
4
198
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random errors taking place at the weighing and filling stages
for the samples. The accuracy of the density meter was given
purposes, their mass densities were measured in the same host
phase with the same composition and at constant temperature
(20 C), Table 2.
ꢃ6
ꢃ3
ꢁ
as 5 ꢂ 10 g cm
.
In Table 2, the densities of the pure solutes, the densities of
the phases, the nematic–isotropic phase transition tempera-
tures (TNI), the phase type and compositions of individual
components are presented. As seen from Table 2, the host
Results and discussion
The effect of solute structure on micelle size
ꢁ
phase is optically isotropic at 20 C, and adding a certain
amount of phenol transforms the host phase into the lamellar
phase (L ) with a density of 1.048733 g cm which is smaller
The micelles, microscopically, are heterogeneous, consisting of
an ionic and/or polar cover at the surface and a hydrophobic
core in the interior, arising from the head groups and the long
hydrocarbon chains, respectively. Inclusion of any solute,
depending on its nature to interact with the ionic surface and
the hydrophobic core of the micelle, may have a dramatic effect
on the size and shape of the host micelle, which modifies the
physical properties of the host phase. In general, the micelle
size changes on addition of any solute, but here we consider
strictly the relative changes in micelle size or shape brought
about by a pair of molecules having the same head group
but different hydrophobic parts (or vice versa) e.g. phenol/
cyclohexanol and an amphiphilic racemic mixture and its
enantiomer.
ꢃ3
a
ꢃ3
than the density of the isotropic host phase (1.048937 g cm ).
On the other hand, the solute, cyclohexanol, added in the same
amount as phenol does not transform the isotropic host phase
into a liquid crystalline phase, but still exhibits a density of
1.046327 g cm , smaller than the L
ꢃ3
produced by phenol
a
and the isotropic host phase, Table 2. It is remarkable to
compare the densities of the phenol/cyclohexanol pair with
those of the benzene/cyclohexane pair. The latter pair is
expected to reside completely in the hydrophobic region of the
micelle. Phenol and benzene produce lamellar phases of com-
parable TNI but of different densities, whereas the lamellar
phase containing phenol is more dense than that containing
benzene with a striking density difference of 0.003444 g
The different effect of the structure of some solute molecules
was discussed in terms of the pitch induced in some host
ꢃ3
cm , Table 2. Nevertheless the solutes, cyclohexanol and
1
2,13
14
phases
case, the mass density of two chiral dopants, mandelic acid
MA) and hexahydromandelic acid (HHMA), were measured
and by measuring the mass density. In the latter
cyclohexane produce an isotropic phase and a nematic phase,
respectively. The isotropic phase containing cyclohexanol
is more dense than that containing cyclohexane with a
(
ꢃ3
in two different host phases and it is found that the chiral
phases containing MA were more dense than those containing
remarkable density difference of 0.003579 g cm
.
These results obtained from the DL-SDE system allow us to
infer two different points, which can be attributed to the inter-
actions of the solutes with the constituents of the host micelle.
(i) The density of the isotropic host phase is higher than the
phases containing the solutes, which means that the isotropic
micelles of the host phase are packed more efficiently in the
given volume than those containing solute molecules. (ii) The
solute, phenol, produces a lamellar phase, but cyclohexanol
an isotropic phase. We can think here of a concerted effect
of the hydrophobic and hydrophilic parts of the solute mole-
cules. Then, we can conceive that the hydrophobic rings of
phenol and cyclohexanol are embeded in the hydrophobic
region and the hydroxy groups are anchored at the hydropho-
bic–hydrophilic interface of the micelle. Therefore, the phenyl
ring can be well accomodated in the micelle, so that the hydro-
phobic and hydrogen bonding interactions of phenol are fully
utilized to form denser phases whereas the spacious cyclohexyl
ring creates a disturbance (probably a hole) in the hydrophobic
region of the micelle which may weaken the hydrophobic and
the hydrogen bonding interactions, Fig. 2.
1
4
HHMA. The density changes can be thought to arise from
the contribution of the two parts of the solutes, the hydrophilic
and the hydrophobic parts, phenyl and cyclohexyl, respec-
tively. For instance, the solutes, MA and HHMA, to some
extent, will become ionised in the micelle which can alter the
counter-ion composition and hence the micelle size. Similarly,
the hydrophobic parts, phenyl- and cyclohexyl-rings, of the
solutes, are to be expected to reside in the hydrophobic region
of the micelle and because they possess different shapes, they
can affect the micelle size differently. The questions to be raised
here are, how the two parts of the solute contribute to the
density and whether they can be assessed. Indeed, in the pre-
vious communication some solutes were chosen and their mass
1
4
densities were measured. However, the density measurements
were not complete and not discussed in detail and particularly
the questions raised above were not answered. In order to have
a clear picture of the effect of the structure of the solute mole-
cules on the micelle size, it is important to study simple
molecules from which the outcome may easily be perceived.
The solute pairs, phenol/cyclohexanol and benzene/cyclohex-
ane, were thought to be convenient and for comparison
In summary, phenol and benzene transform the isotropic
host phase into a lamellar phase, respectively, where the
4
Table 2 The composition of the host phase derived from DL-SDE, NH Cl and water without and with dopants, the phase types, nematic (N),
a
lamellar (L ) and isotropic (I) and the phase transition temperatures TNI , and the corresponding mass densities. For comparison purposes the
densities of the pure solutes also are given
ꢁ
ꢃ3
X
DL-SDE
X
NH Cl
4
X
phenol
X
cyclohexanol
X
H O
2
Phase type
I
T
NI/ C
d20/g cm
1
2
3
4.736
4.703
4.703
4.480
4.449
4.449
–
–
–
90.784
90.151
90.151
–
1.048937
1.048733
1.046327
0.697
–
L
I
a
ꢀ51
0.697
–
ꢁ
ꢃ3
X
DL-SDE
X
NH Cl
4
X
benzene
X
cyclohexane
X
H O
2
Phase type
I
T
NI/ C
d20/g cm
1
2
3
4.736
4.703
4.703
4.480
4.449
4.449
–
–
90.784
90.151
90.151
–
1.048937
1.045289
1.042748
0.697
–
–
0.697
L
a
ꢀ49
ꢀ34
N
Phenol
1.0576
Cyclohexanol
0.9624
Benzene
0.8765
Cyclohexane
0.7785
ꢃ3
20/g cm
d
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disc-like structure N
D
, and consequently, the intrinsic chiral
7
nematic phases,N *, possessed a negative Dn.
D
We have measured the changes in the density as the racemic
amphiphilic molecules were replaced by their L-enantiomers at
constant composition and temperature conditions. For the pur-
pose of comparison we have represented the changes in density
of serine andalanine decylesters in Fig. 3aand b, and the changes
in density of serine and alanine dodecylesters in Fig. 4a and b.
As seen from Figs. 3 and 4, the densities of the serine systems
increase as the racemic amphiphiles are substituted by their
L-enantiomers but those of the alanine systems decrease linearly.
The change in density, as one goes from a racemic nematic phase
to its intrinsic chiral one, may be attributed to a change in micelle
size and structure, i.e. the symmetry of the disc-like micelle in
the racemic phase (D ) is expected to change to C or D
1
h
2
1
in the chiral phase, Fig. 1c and d.
Now, we have to give a possible answer as to why the den-
sity, on passing from a racemic nematic phase to its intrinsic
chiral one, increases in serine esters but decreases in alanine
esters. Before answering this question, we have to state that
it is not clear whether the average aggregation number changes
as the racemic nematic system is converted into the intrinsic
chiral nematic one. Any change in the average aggregation
number, as the racemic amphiphile in the racemic nematic
phase is substituted by its L-enantiomer may be investigated
Fig. 2 A schematic representation of the locations of phenol and
cyclohexanol in the micelle. For clarity the sketches are exaggerated.
lamellar phase of phenol is more dense than the one of ben-
zene. This result implies that the micelle containing phenol at
the ionic front and the hydrophobic region is shrunk, whereas
the phase with benzene is compact at the hydrophobic region,
but is loose at the ionic surface. The situation for cyclohexanol
and cyclohexane, though the cyclohexyl and cyclohexane rings
5
16,17
by X-ray or neutron
diffraction studies.
In order to understand the striking change in density, we
have constructed framework molecular models (FWM) of ser-
ine and alanine esters, then the density change clearly arises
from the definite packing of the head groups in the racemic
nematic and intrinsic chiral nematic phases, Figs. 5 and 6. In
Fig. 5a, the racemic amphiphile, DL-SDE and in Fig. 5b, the
intrinsic chiral amphiphile, L-SDE, are drawn according to
the FWMs. As seen from Fig. 5a, if the D- and L-amphiphiles
are placed as mirror images, the head groups are in a position
to repulse each other because the equally charged groups, e.g.
the ammonium group in the L-enantiomer experiences the
charge of the ammonium group in the mirror image amphi-
phile. The same situation is valid for the carbonyl group. Other
1
5
swell the micelle, appears to parallel the case of phenol and
benzene. The densities of the solutions change in the same
order as the densities of the pure solutes, phenol > cyclohexa-
nol > benzene > cyclohexane, which arises from the structure
and interactions of individual solute with the corresponding
parts of the host phase. Except for phenol, the densities of
the pure solutes are much less than the densities in the liquid
crystals, Table 2. In all cases the aggregate size increases upon
addition of the solute molecules which is reflected in the
density and TNI changes.
It is important to mention that our density measurements
have been performed only with one host phase and at one con-
centration. Although host phases with a C10 chain length such
as DL-SDE give similar results with the solutes studied, it is
interesting to make density measurements with different
achiral and chiral host phases of different concentrations
and chain lengths using the same and other organic solutes.
Such measurements would allow us to make more accurate
generalizations, and are the subject of our present research.
The origin of the change of mass density in racemic nematic
and intrinsic chiral nematic phases
In a recent communication it was shown for one example that
the mass density has increased as the racemic amphiphile
(
DL-SDE) in the racemic nematic phase was replaced by its
1
4
L-enantiomer (L-SDE). It is of fundamental interest to show
whether this result can be generalized. Having been moti-
vated by this aspect, and because there is very small choice
on racemic/enantiomer amphiphiles we have synthesized
amphiphilic molecules as decylesters and dodecylesters of the
amino acids, alanine and serine. As a result, we have
obtained two racemic amphiphilic molecules of alanine, DL-
ADE and DL-ADDE, and their L-enantiomers, L-ADE and
L-ADDE, and also two racemic amphiphilic molecules of ser-
ine, DL-SDE and DL-SDDE and their L-enantiomers, L-SDE
and L-SDDE. It is of note that the racemic and intrinsic
chiral nematic phases of DL-ADE and L-ADE were stabilized
by adding a small amount of decylammonium chloride,
DACl, as a co-surfactant. All the racemic nematic phases
exhibited a positive optical anisotropy, Dn, indicating a
Fig. 3 The variation of mass density versus mole fraction when (a)
DL-SDE and (b) DL-ADE in the racemic nematic phases were replaced
by their enantiomers L-SDE and L-ADE, respectively.
4
200
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Fig. 4 The change of mass density with mole fractions as (a) DL-
SDDE and (b) DL-ADDE in the racemic nematic phases were replaced
by their L-enantiomers, L-SDDE and L-ADDE, respectively.
Fig. 6 Representation of the arrangements of alanine hydrochloride
decylester (a) in the racemic nematic phase and (b) in the intrinsic
chiral phase.
possible arrangements did not offer a favourable case where
the groups could attract each other. If we have a pure enantio-
meric amphiphile, however, as in the case of L-SDE, Fig. 5b,
the ammonium groups and the carbonyl groups in adjacent
molecules can attract each other which leads to efficient pack-
ing. From Figs. 5a and b, it is then easy to infer that the mass
density has to increase as the DL-amphiphile of the racemic
nematic phase is replaced by its enantiomer. Alanine ester
phases, however, show exactly the opposite behaviour i.e.
as DL-ADE or DL-ADDE in the racemic nematic phase is
substituted by its L-enantiomer, the mass density decreases,
which means that in the racemic nematic phases attraction
forces, but in the intrinsic chiral nematic ones repulsion forces,
are dominant. This situation is shown in Figs. 6a and b. In Fig.
6
a, from left to right the ammonium group of the D-enantio-
mer is close to the carbonyl group of the L-enantiomer, which
continues in the neighbouring pairs, therefore a close packing
of the head groups is possible. This situation, however, is
reversed if we consider the pure enantiomer, Fig. 6b, where
oppositely charged groups can not approach each other closely
enough due to methyl groups in the adjacent molecules. So,
close packing does not take place, and therefore the mass den-
sity decreases as the DL-amphiphile of alanine in the racemic
nematic phase is substituted by its L-enantiomer.
In summary, the change in mass density, as a DL-amphiphile
of a racemic nematic phase is replaced by its L-enantiomer,
depends on the packing of the head groups of the amphiphilic
molecules in the racemic nematic and intrinsic chiral nematic
ones which is predominantly determined in our case by specific
attraction or repulsion forces of groups attached to the chiral
centre of the amphiphilic molecules. Since the disc-like micelles
in the racemic nematic phase change symmetry from D
D
to
h
1
1 2
or C on replacing the DL-amphiphile by its L-enantiomer,
the shape and size of the micelles are expected to change.
Although mass density measurements give valuable insight
into what takes place in the micelle, for quantitative determi-
nation of micelle size, X-ray or neutron diffraction studies
are required. Such studies are envisaged.
Is a distinction between the induced chiral nematic and
intrinsic chiral nematic phases possible?
As pointed out in the introduction, X-ray diffraction studies
could not differentiate clearly between the achiral nematic
4
phases of sodium decylsulfate (SDS) and potassium laurate
(
cine sulfate doping. So, we have asked ourselves the basic
Phys. Chem. Chem. Phys., 2003, 5, 4197–4203 4201
Fig. 5 Illustration of the arrangements of serine hydrochloride decy-
lester (a) in the racemic nematic phase and (b) in the intrinsic chiral
nematic phase.
8
KL) and their induced chiral nematic ones obtained by bru-

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Table 3 The compositions of the achiral nematic pases of DACl in mole percent containing DL-ADE/L-ADE, DL-SDE/L-SDE and DL-MA/S-
MA, respectively, the pitch of the induced chiral phases, (P), the TNI and the corresponding mass densities are represented
ꢁ
ꢃ3
d20/g cm
X
DACl
X
NaCl
X
H O
2
X
DL-ADE
X
L
-ADE
P/mm
T
NI/ C
ꢃ5
ꢃ5
6
6
.454
.454
1.258
1.258
91.815
91.815
0.473
–
–
0.473
N
D
ꢀ31
ꢀ31
0.984642 ꢄ 5.56 ꢂ 10
0.984613 ꢄ 1.21 ꢂ 10
29.55
ꢁ
ꢃ3
X
DACl
X
NaCl
X
H O
2
X
DL-SDE
X
L
-SDE
P/mm
T
NI/ C
d20/g cm
ꢃ5
ꢃ5
6
6
.307
.307
1.173
1.173
92.084
92.084
0.436
–
–
0.436
N
D
ꢀ29
ꢀ29
0.986399 ꢄ 3.57 ꢂ 10
0.986483 ꢄ 1.60 ꢂ 10
67.74
ꢁ
ꢃ3
X
DACl
X
NaCl
X
H O
2
X
DL-MA
X
L
-MA
P/mm
T
NI/ C
d20/g cm
ꢃ5
ꢃ5
6
6
.626
.626
1.286
1.286
91.314
91.314
0.774
–
–
0.774
N
D
ꢀ30
ꢀ30
0.992072 ꢄ 1.21 ꢂ 10
0.992055 ꢄ 1.60 ꢂ 10
15.82
question: can density measurements verify these results? If yes,
then it can be concluded that the micelle size would not change
appreciably, but micelle shape has to change due to symmetry
change. In order to have a clear picture on this subject, we
have developed achiral nematic and induced chiral nematic
phases of the DACl host amphiphile using the dopant pairs,
DL-ADE/L-ADE, DL-SDE/L-SDE and DL-MA/S-MA, respec-
tively, and their densities were measured. The results are sum-
marized in Table 3. In Table 3 the composition of the
individual components, the type of achiral nematic phase
of the chiral centres of the pure enantiomers in the intrinsic
chiral nematic phase as in Figs. 5 and 6.
Conclusions
The effect of the solute structure on the micelle size and shape
has been investigated by mass density measurements employ-
ing two specific sets of guest molecules. The first set consisted
of the achiral solutes, phenol, benzene, cyclohexanol and
cyclohexane, whose mass densities were measured in a host
phase of DL-serine hydrochloride decylester. The mass density
measurements indicate clearly that the hydrophobic parts and
the hydrophilic groups are important in changing the mass
density where the effect of the hydrophilic groups outweighs
the one of the hydrophobic parts. In the second set, it was
established that the mass density may decrease (alanine ester
phases) or increase (serine ester phases) when the racemic
amphiphilic molecule in a racemic nematic phase is substituted
by its L-enantiomer. These phenomena were shown to arise
from the specific arrangements of the head groups in the
racemic nematic and intrinsic chiral nematic phases. In addi-
tion, we have inferred from mass density differences between
the achiral nematic and their induced chiral phases, and the
racemic nematics and their intrinsic chiral ones, that the
induced chiral nematics and the intrinsic chiral phases have
to be different in spatial structure.
D
(N ), the induced pitch (P), the TNI and the mass densities
are represented. As can be seen for the three phases the
difference in mass density between the achiral nematic and
induced chiral nematic phases is within the limit of measure-
ment error. These results indicate that the micelle size in the
achiral nematic phase and the induced chiral nematic phase
of the DACl host amphiphile for the three dopant pairs
remains essentially unchanged, but micelle shape changes from
2 1
disc-like micelle (D1h) to screw-like micelle (C or D ), Fig.
1b and c. Nevertheless, the situation of the intrinsic chiral
nematic phase is different. Then, we know that there is a strik-
ing mass density difference e.g. 0.00213 g cm for the ADDE
ꢃ3
phase, between the racemic nematic and its intrinsic chiral one,
Figs. 3 and 4. Consequently, the intrinsic chiral micelle in our
studied systems has two quantities, the shape and the size, dif-
ferent from the racemic micelle. These results allow us to con-
clude that the induced chiral nematics and the intrinsic chiral
nematics are different. Pictorially, the induced chiral nematic
phase can be thought to consist of a hollow screw-like pipe,
whereas the intrinsic chiral nematic phase also exhibits a
screw-like pipe, but it is different in spatial structure, Fig. 7a
and b. The spatial structure arises from the special packing
Acknowledgements
We wish to thank T u¨ bitak (Turkish Scientific and Technical
Research Council) for supporting this project (TBAG-1821).
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