Mesomorphous structure and macroscopic patterns formed by polymer and surfactant from organic solutions

Article abstract of DOI:10.1021/ma051042g

Ordered mesomorphous structures were obtained from the ternary system of organic solvent, polymer, and surfactant, and this microscopic ordering could lead to unique water-wave-like macroscopic patterns in solid polymer-surfactant film. The mesomorphous s

Full text of DOI:10.1021/ma051042g

9266
Macromolecules 2005, 38, 9266-9274
Mesomorphous Structure and Macroscopic Patterns Formed by Polymer
and Surfactant from Organic Solutions
Shuizhu Wu,* Fang Zeng,* Hongping Zhu, Shaojin Luo, Biye Ren, and Zhen Tong
Department of Polymer Science & Engineering, South China University of Technology,
Guangzhou 510640, China
Received May 22, 2005; Revised Manuscript Received August 1, 2005
ABSTRACT: Ordered mesomorphous structures were obtained from the ternary system of organic solvent,
polymer, and surfactant, and this microscopic ordering could lead to unique water-wave-like macroscopic
patterns in solid polymer-surfactant film. The mesomorphous structures and macroscopic patterns were
obtained by dissolving a nonpolyelectrolyte polymer and cationic surfactant in organic solvents and casting
the solutions on glass substrates. The patterns thus obtained are composed of concentric rings, and these
concentric rings, with their diameters up to centimeters, alternatively consist of macroscopic convex ridges
and concave valleys, with the former being amphormous phase and the latter being ordered mesomorphous
one. This macroscopic patterning in a solid polymer-surfactant system could offer a new way for
fabricating ordered supramolecular structure in macroscopic dimensions.
acryloyl chloride were received from Acros Organics. Methyl
methacrylate and ethyl acrylate were distilled before use. N,N-
Dimethylformamide (DMF), toluene, acetone, and methanol
were analytically pure solvents, and they were distilled before
use. Tetrahydrofuran (THF) was dried over sodium/benzophen-
one and distilled just before use.
Introduction
Supramolecular structures generated through self-
assembly have attracted great attention due to their
enhanced materials properties.1-4 The solid-state su-
pramolecular structures formed by polyelectrolyte and
surfactants through self-assembly also exhibit unique
mechanical, optical, electrical, and biological proper-
ties.1,2,5-8 A number of studies indicate that the strong
interactions between the polyelectolytes and surfactants
often result in highly ordered mesomorphous structures,
e.g., nanoscale or micrometer-scale lamella and cylindri-
cal structures, the less ordered bicontinuous sponge
structure, and perforated layer structures.1,5,9-14 How-
ever, for polymer-surfactant systems with no strong
interaction involved, there is no report on the formation
of highly ordered structure, and no macroscopic pattern
has ever been constructed in solid-state polymer-
surfactant systems.
In this paper, we report the formation of water-wave-
like macroscopic patterns composed of concentric rings
in solid polymer-surfactant film, which were obtained
by dissolving a thiophene-containing polymer and cat-
ionic surfactant in organic solvents and casting the
solutions on glass substrates. The concentric rings, with
their diameters up to centimeters, consist of convex
ridges and concave valleys, with the former being
amphormous phase and the latter being ordered me-
sophase one. The factors that affect the macroscopic
pattern formation were studied experimentally, and
possible mechanisms for the formation of the mesomor-
phous structure as well as the macroscopic pattern were
proposed.
Synthesis of Thiophene Compound. Thiophene-3-acetic
acid and 3-hydroxy-4-methoxybenzaldehyde in molar ratio 1:1
were dissolved in piperidine and refluxed overnight. After
evaporating the solvent, the crude product was dissolved in
methanol and filtered. Then methanol was removed under
vacuum, the product was recrystallized in chlorobenzene and
toluene (1:1 in volume), and a dark yellow crystalline solid
was obtained.
Synthesis of Thiophene-Containing Monomer. To a
solution of thiophene compound (0.02 mol) in 100 mL of
anhydrous tetrahydrofuran at room temperature was added
triethylamine (0.022 mol), and the solution was stirred for 15
min. The reaction mixture was cooled at 0 °C, and freshly
distilled methacryloyl chloride (0.022 mol) in 10 mL of
anhydrous tetrahydrofuran was added. The resulting mixture
was allowed to warm to room temperature and stirred over-
night. The reaction mixture was filtered. The product, obtained
after evaporating the solvent, was washed with large amounts
of hexane and methanol (4:1 in volume). Finally, a dark yellow
1
solid was obtained. H NMR (500 MHz, CDCl3, 25 °C, TMS):
δ (ppm), 6.9-7.5 (aromatic H), 5.7-6.2 (CHdCH), 5.0-5.1
(CH2)), 3.6-3.8 (OCH3), 1.8-2.0 (CH3). FT-IR (KBr): 3100
cm-1 (νCH arom), 2980 and 2950 cm-1 (νCH aliph), 1715 cm-1
(νCdO), 1610 cm-1 (νCdC, aliph), 1510 cm-1 (νCdC, phenyl), 1440
cm-1 (δCH, aliph), 1380 cm-1 (νCdC, thiophenyl), 1250-1000
cm-1 (νC-O), 650-900 cm-1 (δCH, arom).
Polymerization of Thiophene-Containing Polyacryl-
ate (TPA). 2 g (0.0067 mol) of the above thiophene-containing
monomer was dissolved in dry dimethylformamide; 3 g (0.03
mol) of methyl methacrylate and 5 g (0.05 mol) of ethyl acrylate
were added to the solution. The polymerization was carried
out in the presence of azobis(isobutyronitrile) (AIBN, 1 wt %)
as an initiator. The polymerization medium was outgassed
twice before heating and stirring at 70 °C for 240 h under
nitrogen. Then the polymerization mixture was poured into
cold methanol. The isolated copolymer was redissolved in THF
and precipitated in cold methanol, filtered, washed with
deionized water, and finally dried under vacuum at 60 °C for
72 h. 1H NMR (500 MHz, CDCl3, 25 °C, TMS): δ (ppm), 7.0-
7.4 (aromatic H), 6.6-6.8 (CHdCH), 4-4.2 (C(O)OCH2), 3.5-
3.73 (OCH3, C(O)OCH3), 0.9-2.2 (CH3, backbone CH2 and CH).
Experimental Section
Materials. Thiophene-3-acetic acid, 3-hydroxy-4-methoxy-
benzaldehyde, methyl methacrylate, ethyl acrylate, tetraoc-
tylammonium bromide (TOAB), tetrabutylammonium bromide
(TBAB), tetradodecylammonium bromide (TDAB), dioctylso-
dium sulfosuccinate, and polyoxethylene sorbitan tristearate
were purchased from Aldrich Chemicals. Piperidine and meth-
* To whom correspondence should be addressed: e-mail
shzhwu@scut.edu.cn; Ph +86-20-83683721; Fax +86-20-87114649.
10.1021/ma051042g CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/07/2005

Macromolecules, Vol. 38, No. 22, 2005
Mesomorphous Structure and Macroscopic Patterns 9267
Figure 1. Molecular structure of the polymer and the
surfactant TOAB.
FT-IR (KBr): 2980 and 2950 cm 1 (νCH aliph), 1735 cm-1 (νCd
-
O), 1640 cm-1 (νCdC, aliph), 1530 cm-1 (νCdC, phenyl), 1440 cm-1
(δCH, aliph), 1380 cm-1 (νCdC, thiophenyl), 1250-1000 cm-1
(νC-O), 650-900 cm-1 (δCH, arom).
Film Preparation. The polymer-surfactant films were
prepared as follows: the surfactant and the polymer TPA at
a certain ratio were dissolved in an organic solvent (toluene,
benzene, xylene, or acetone) to form a solution with the
concentration of 6 wt %, a clear solution resulted, and then
the solution was filtered through a 0.50 µm Teflon filter and
cast on 2.5 cm × 4 cm glass substrates. Then a culture dish
was covered over the glass substrate. Afterward, the films were
allowed to dry in a thermostat at a constant temperature.
Characterization. FT-IR spectra were measured by using
Nicolet Magna 760 FT-IR spectrometer. 1H NMR spectra were
recorded on a Varian Unity Inova 500 MHz NMR spectrom-
eter. Molecular weight and molecular weight distribution were
determined by a Waters gel permeation chromatograph with
the 2410 RI detector. Polarizing micrographs were taken on a
Zeiss Axiolab polarizing microscope. Small-angle X-ray scat-
tering (SAXS) measurements were performed on Philips X’Pert
PRO X-ray diffractometer (Cu KR) (scattering vector q ) (4π/
λ) sin θ, where 2θ is the angle between the incident light and
the scattered light). Differential scanning calorimetry (DSC)
experiments were performed with 3-5 mg of samples in a 6
mm aluminum pan on a Netzsch DSC 204 under a nitrogen
atmosphere at a heating/cooling rate of 5 °C/min. In the DSC
measurements, for the polymer-TOAB system with the
polymer content of 55 wt %, the solid film on the concave
regions was carefully scraped off with a knife for the measure-
ment, and all the samples were dried under vacuum at 60 °C
for 72 h before DSC measurement. Elemental analysis was
performed on a Vario EL elemental analyzer. For each
elemental analysis, about 5 mg material was carefully taken
from a convex region or a concave region of a film, so as to
determine the nitrogen content of the materials.
Results and Discussion
Figure 2. Photographs of the macroscopic patterns formed
on 4.0 cm × 2.5 cm glass plates by polymer and surfactant
with the polymer content of 55 wt % in the film; the solvent
was toluene, and the amount of the polymer/TOAB solution
cast on the glass was the same: (A) cast at 20 °C; (B) 25 °C,
scale bar 1 cm; (C) 45 °C.
The synthesized thiophene-containing polyacrylate
(TPA) is a random acrylate copolymer with long pendant
groups [2-methoxy-5-(2-thiophen-2-yl-vinyl)phenyl ester
groups] (Figure 1). The molecular weight of the polymer,
as characterized by gel permeation chromotography
with polystyrene as the standard, is 3.1 × 104 with the
polydispersity index of 2.9, and the glass transition
temperature as determined by DSC for the polymer is
52 °C. The polymer and the surfactant were dissolved
in toluene with an appropriate TPA to TOAB ratio, a
transparent and dark-yellow solution was obtained, and
then the solution was cast on glass substrate and was
allowed to dry in a thermostat at varied temperatures;
finally, a water-wave-like pattern composed of mil-
limeter-to-centimeter scale concentric rings appeared
(Figure 2) during the solvent evaporation under ap-
propriate conditions. We found that the removal of the
thiophene-containing pendant groups results in the
disappearance of macroscopic patterns.
Factors That Affect Formation of Macroscopic
Pattern. The formation of the pattern was found to be
dependent on several factors. Table 1 shows the effects
of polymer content, the surfactant type, and the solvent
type on the formation of the macroscopic pattern. First,
the polymer content in the cast film was found to be

9268 Wu et al.
Macromolecules, Vol. 38, No. 22, 2005
Table 1. Effects of Polymer Content in Solid Film, Solvent Type, and Surfactant Type on the Formation of a
Macroscopic Patterna
solventb
surfactantc
polymer content (wt %)
acetone
benzene
toluene
xylene
TBAB
TOAB
TDAB
10
25
55
65
75
80
90
O
O
.
.
.
O
O
O
O
.
.
.
O
O
O
.
b
b
.
O
O
O
.
b
b
.
O
O
O
O
O
O
O
O
O
O
.
b
b
.
O
O
O
O
O
O
O
O
O
a The films were cast at 25 °C; O, no pattern formed; ., poorly formed macroscopic pattern; b, well-formed macroscopic pattern. b For
solvent effects investigation, TOAB was used as the surfactant. c For surfactant effects investigation, toluene was used as the solvent.
TOAB: tetraoctylammonium bromide; TBAB: tetrabutylammonium bromide; TDAB: tetradodecylammonium bromide.
critical to the pattern formation. For the TPA-tetraoc-
tylammonium bromide (TOAB) system, no matter what
solvent was used, as the weight percentage of the
polymer was low (10 wt %), no macroscopic pattern
appeared in the solid polymer-surfactant film as the
solvent evaporates. As the weight percentage of polymer
reached 25% in the solid film, poorly formed patterns
could be observed, and the large and well-formed
pattern could be observed as the polymer content was
increased to around 55 wt % in the solid film when
toluene or xylene was used as the solvent, as shown in
Figure 2; when the amount of polymer in the solid film
was too high (80 wt % or higher), no macroscopic pattern
could be observed as well.
As for the surfactant, we used three cationic surfac-
tants with symmetrical structure. They were tetrabu-
tylammonium bromide (TBAB), tetraoctylammonium
bromide (TOAB), and tetradodecylammonium bromide
(TDAB). These surfactants all have four identical alkyl
tails; only the number of carbons in the alkyl tails for
these surfactants is different. However, we could only
obtain macroscopic patterns by using TOAB which has
eight carbon atoms in each tail. No macroscopic patterns
could be observed for the TPA-TBAB systems or the
TPA-TDAB systems, no matter what solvent was used.
Hence, the length of the alkyl tails of the surfactant has
great effects on the structure formation of the polymer-
surfactant systems. We also tried other oil-soluble
surfactants with asymmetrical structure, such as an-
ionic surfactant dioctylsodium sulfosuccinate (aerosol
OT) and nonionic surfactant polyoxethylene sorbitan
tristearate (Tween), and no pattern was observed on the
polymer-surfactant films.
In addition, several solvents with different boiling
temperatures were also employed to prepare the TPA-
TOAB solid films. As for the low-boiling-point solvents
(e.g., acetone and benzene), when the polymer content
is between 55 and 75 wt %, only poorly formed macro-
scopic patterns could be generated. While for the high-
boiling-point solvents (toluene and xylene), when the
polymer content is at 55 or 65 wt %, well-formed
macroscopic patterns could appear as the solvent evapo-
rated, as indicated in Table 1.
The final circular pattern in the solid films was also
affected by the film-forming temperature. When the
solid films were obtained by drying at 45 or 20 °C
instead of room temperature (25 °C), obvious changes
in the circular patterns were observed (see Figure 2).
Photographs of the resultant circular patterning (Figure
2) in the solid polymer-surfactant films show that, as
the film-forming temperature increases, the ring dimen-
sion of the patterns becomes smaller and both the ring
thickness and the inter-ring spacing become lower. We
suppose the pattern formation needs the cooperative
motion (or migration) of both polymer chains and
surfactant molecules during the solvent evaporation,
and at higher film-forming temperature fast solvent
evaporation speed makes the solvent leave more quickly;
hence, the motion of polymer chain segments could be
frozen more quickly, and the concentric rings could not
“grow” to thicker ones. We also found that, as the film-
forming temperature was further increased to 50 °C or
reduced to 15 °C, we could only obtain transparent films
with no patterns on them. So the rough temperature
range for the pattern formation is 20-45 °C.
Polarizing Optical Micrographs. We selected some
patterns with small rings to observe their morphologies
on the polarizing optical microscope. Parts A and B of
Figure 3 show the morphology for a same area of a
pattern under parallel-polarized light and perpendicular-
polarized light, respectively, in which the stripes rep-
resent a part of rings. Figure 3C shows morphology for
a part of a larger concentric ring under perpendicular-
polarized light, while Figure 3D shows the central part
of a concentric ring under perpendicular-polarized light.
By comparing parts A and B of Figure 3, we can find
that each brighter stripe in Figure 3A corresponds to
one bright stripe in Figure 3B. Since under the parallel-
polarized light (similar to unpolarized light) the thinner
regions of a film absorb less light, the brighter stripes
in Figure 3A represent the concave valleys, while in
Figure 3B, bright stripes represent anisotropic struc-
ture. So, it can be found that only the concave valleys
of the film can transmit the perpendicular-polarized
light, while the ridges cannot; this indicates that the
convex ridges mostly contain the isotropic (amorphous)
structure, while the concave valleys mainly comprise the
ordered anisotropic structure. For the same reason, the
three bright arc stripes in Figure 3C correspond to three
valleys (ordered structure) in a larger pattern, and the
center point of the rings consists of the ordered struc-
ture, as shown in Figure 3D. Thus, it can be concluded
that the concentric rings in the film are organized
alternatively by macroscopic circular amorphous regions
and ordered regions. In addition, a few crystalline
domains of residual surfactant can be seen in Figure
3A,B; it is obvious that the pure surfactant crystalline
domains are different compared with the ordered struc-
ture in the concave regions. On the other hand, we could
not observe any bright stripe for the films with no
macroscopic pattern.
To further confirm that the concave regions mainly
consist of the ordered anisotropic structure and the
convex regions mainly consist of amorphous structure,
a part of the concentric ring was observed on the
polarizing optical microscope as the polarizers were

Macromolecules, Vol. 38, No. 22, 2005
Mesomorphous Structure and Macroscopic Patterns 9269
Figure 3. Photographs for patterns observed on polarizing optical microscope. (A) A part of a pattern under parallel-polarized
light, the arrow points to a brighter stripe. (B) The same part of the pattern as that in (A) under perpendicular-polarized light;
the arrow points to a bright stripe which is an anisotropic area and corresponds to that in (A). (C) A part of another pattern with
larger size under perpendicular-polarized light. (D) The center of a concentric ring under perpendicular-polarized light. Scale bar
0.5 mm. A crystalline domain of residual surfactant is marked with a circle in (A) and (B).
rotated (Figure 4). As the polarizers were rotated (the
angle between the two polarizers was varied from 0° to
90°), the concave regions in a pattern always correspond
to the bright stripes, and the convex regions correspond
to the dark stripes. This indicates that the dark stripes
under perpendicular-polarized light are not the result
of extinction due to orientation effects; instead, they
represent the amorphous structure, while the bright
stripes represent the ordered anisotropic structure.
Small-Angle X-ray Scattering Profiles. The in-
vestigations on ordered structures with small-angle
X-ray scattering (SAXS) measurement are illustrated
in Figure 5, in which the scattering intensities are given
as a function of the scattering vector q (nm-1). The
SAXS measurements for Figure 5C (for concave valley)
and Figure 5D (for convex ridge) were conducted with
the sample with the largest macroscopic pattern (see
Figure 2A macroscopic pattern formed at 20 °C), so the
size of the focal spot of the X-ray beam (about 1 mm2 in
this study) can be comparable with or slightly less than
that of the convex regions or concave regions. It is well-
known that different microphase structures will exhibit
different peak position ratios in the SAXS profile.1,4-7
For examples, the body-centered-cubic (bcc) structure
and the simple cubic structure have the same relative
peak position ratios of 1:(2)1/2:(3)1/2:(4)1/2:(5)1/2:(6)1/2, the
hexagonally packed cylindrical structure has the peak
position ratios of 1:(3)1/2:(4)1/2:(7)1/2, and the lamellar
structure has the peak position ratios of 1:2:3:4. A poly-
mer-surfactant system can also exhibit multiple SAXS
peaks due to its periodic microscopic structure having
a long-range order. Information on the morphology can
be obtained from the relative positions of these peaks.
They can exhibit specific spatial relationships depending
on the shape of the microdomain structure.2,5,15-18 It can
be seen from Figure 5A that for the pure surfactant
there are three sharp peaks in the SAXS profile; the
positions of these peaks are 3.31, 6.55, and 9.92 nm-1
,
and this relative position of peaks is close to that of
lamella structure. With the addition of a small amount
of polymer (10 wt %) into the surfactant (Figure 5B),
there were still three peaks in the SAXS profile with
the peak positions similar to those of the pure surfac-
tant, the relative intensity of the latter two peaks
substantially decreased, and no new peak emerged,
proving that small amount of polymer cannot form any
new structure with the surfactant. As the amount of
polymer was increased to 55 wt %, for the material in a
concave region (Figure 5C), there were six peaks in the
SAXS profile with their peak positions of 3.01, 3.32,
6.00, 6.66, 9.00, and 10.01 nm-1, indicating that new
structure was formed, and the scattering is generated
by a superposition of two different lamellar systems:
one with period around 2π/3.32 nm and one with period
around 2π/3.00 nm (newly formed structure). While for
the convex region (Figure 5D) in this sample, no peaks

9270 Wu et al.
Macromolecules, Vol. 38, No. 22, 2005
Figure 4. Photographs of a part of the pattern on polarizing optical microscope as the polarizers are rotated: (A) 0°, scale bar
0.5 mm; (B) 30°; (C) 45°; (D) 60°; (E) 75°; (F) 90°.
can be observed in the SAXS profile, indicating that the
convex ridge in the macroscopic pattern mainly contains
the amorphous region. We also found that further
increase in polymer content to 80 wt % led to disap-
pearance of all scattering peaks. The small-angle X-ray
scattering investigations indicate that the ordered
structure observed on the polarizing optical microscope
is the mesomorphous phase formed by the surfactant
chain packing in the polymer-surfactant system.
DSC Thermograms. The thermal properties of the
polymer-TOAB systems were investigated by using
DSC measurement. In Figure 6, endothermic transitions
have been observed for pure surfactant as well as the
polymer-TOAB systems (except for that with 90 wt %
of polymer) during heating, which is due to melting of
the octyl tail crystal. The pure TOAB shows a melting
range of 95-101 °C with the melting peak at about 98
°C. We found the pure polymer exhibited no melting
peak. At the polymer content of 10 wt %, the polymer-
surfactant system shows a crystalline melting range of
87-101 °C with the melting peak at about 97 °C, which
is close to that of the pure surfactant. At the polymer
content of 55 wt %, the solid substance taken from the
concave region (mesomorphous region) of the pattern
exhibits a melting range of 84-99 °C with the melting
peak at about 93.5 °C, and this melting peak shifts to
lower temperature compared with that of pure TOAB.
This melting peak shift indicates that the addition of

Macromolecules, Vol. 38, No. 22, 2005
Mesomorphous Structure and Macroscopic Patterns 9271
Figure 7. Phase composition curves: TOAB contents of the
convex region and the concave region in the film with the
polymer content of 55 wt % (TOAB content of 45 wt %). The
data for higher temperatures cannot be obtained due to
sampling difficulty. The error bar is presented for each point,
which is the average of five measurement values.
Figure 5. SAXS profiles for (A) pure surfactant TOAB cast
from toluene, (B) the polymer-TOAB system cast from toluene
with the polymer content of 10 wt %, (C) a concave region from
the polymer-TOAB system with the polymer content of 55 wt
%, and (D) a convex region from the polymer-TOAB system
with the polymer content of 55 wt %.
As mentioned before, the pattern can only be obtained
in a limited temperature range (20-45 °C), and the film
cast at 45 °C has very thin patterns from which we
cannot take samples, so we only determined the com-
positions for the films cast at 20, 25, 30, and 35 °C. To
determine the TOAB content more accurately for a film
cast at varied temperatures, we first prepared polymer/
TOAB films under different temperatures; then in each
film we took five samples (about 5 mg in weight each)
from five different concave regions and then took
another five samples from five different convex regions.
Therefore, the TOAB contents as determined by elemen-
tal analysis for the concave region or the convex region
in each film are the average of five measurements. The
averaged values for TOAB contents in concave and
convex regions in these solid films are shown in Figure
7.
From Figure 7, we can see that the convex regions
are comprised of polymer-rich phase, while the concave
regions are comprised of TOAB-rich phase. Therefore,
we can say that the mesomorphous region observed
under the polarizing microscope as shown in Figure 3
was mainly formed by the surfactant-rich materials, and
the amorphous region was formed by the polymer-rich
materials.
In Figure 7, as the film-forming temperature is
increased, the surfactant content in the surfactant-rich
phase (concave region) decreases, while that in the
polymer-rich phase (convex region) increases. It can also
be found from the figure that the change in TOAB
content for convex region as a result of temperature
variation is not as remarkable as that in the TOAB
content for concave region (TOAB-rich phase). The
reason for this is that the thickness contrast between
the convex region and concave region for the film cast
at higher temperature (about 2:1 for the one cast at 35
°C) is less than that of the film cast at lower tempera-
ture (about 3:1 for the one cast at 20 °C).
Figure 6. DSC thermograms of the polymer-surfactant
TOAB systems and pure surfactant TOAB: A (red line), the
polymer-surfactant system with the polymer content of 90 wt
%; B (violet line), the polymer-surfactant system with the
polymer content of 55 wt %; C (blue line), the polymer-
surfactant system with the polymer content of 10 wt %; D
(black line), pure surfactant.
polymer into surfactant affected the crystallization of
the pure surfactant to some extent, and there is few
pure surfactant crystalline phases or domains in the
polymer-TOAB system with the polymer content of 55
wt %. Therefore, the ordered structure we observed in
Figure 3 is the mesomorphous domain (or complex)
formed by polymer and the surfactant, and the patterns
we obtained were not caused by the phase separation
of pure surfactant from the polymer.
Elemental Analysis and Phase Composition. To
determine the composition for both the ordered and
amorphous regions in the macroscopic pattern, we
carefully took samples from the concave regions (ordered
region) and convex (amorphous) regions respectively and
determined the content of nitrogen element through
elemental analysis; thus, the surfactant (TOAB) con-
tents can be calculated for the two regions.
As for those poorly formed macroscopic patterns on
the films, because of the small inter-ring spacing, the
sampling from the concave or convex region in a film
becomes extremely difficult, so the determination for the
content of surfactant or the polymer is impossible.
However, we can still anticipate that concave regions
in those films were formed by surfactant-rich phase and
the convex regions formed by polymer-rich phase.

9272 Wu et al.
Macromolecules, Vol. 38, No. 22, 2005
Although we can obtain the composition for both the
polymer-rich phase and the surfactant-rich phase of our
prepared polymer/TOAB film, as shown in Figure 7, we
suppose the data may not be able to represent the
equilibrium composition for the polymer/TOAB system,
since the composition of two phases is affected by both
thermodynamic factors and kinetic factors. In general,
the pattern formation is a solvent evaporation induced
phase separation. Thermodynamically, during the evapo-
ration of solvent, the polymer-surfactant interactions
led to the formation of mesomorphous structures, and
then phase separation occurred, which led to the forma-
tion of macroscopic pattern. Several processes can take
place during evaporation of the solvent. One important
thermodynamic factor affecting phase separation is the
changes in the composition of the solution during the
evaporation of solvent. As the solvent evaporates, the
total composition of the mixture changes. At some
specific composition of the mixture, the bionodal region
in the phase diagram is passed and the region of
incompatibility (spinodal region) is reached, and spin-
odal decomposition type phase separation occurs.19
On the other hand, the kinetic trapping of structures
as a result of reduced mobility is also an important
factor affecting the composition of the two phases.20,21
Since the glass transition temperature Tg of the polymer
(52 °C) and the melting point of the surfactant (98 °C)
are all higher than the film-forming temperature (e45
°C), as the solvent evaporated, the polymer chain
segments and the surfactant molecules were gradually
frozen as a result of the viscosity increase of the mixture,
and eventually the phases are solidified and a film is
formed. So for this solution-casting process, the result-
ing phase-separated morphology may be far from ther-
modynamic equilibrium, and relaxation toward equi-
librium may be hindered by kinetic barriers formed by
the nonequilibrium phase morphology.20,21
Formation of Mesophase Structure. For the self-
assembly of microscopic mesomorphous phases in the
best-known polyelectrolyte-surfactant complex in water
or high-polar solvents, the driving force is the electro-
static interaction, sometimes reinforced by hydrophobic
interaction or hydrogen bond.1,2,5 While in this study
we obtained macroscopic mesomorphous phases by
dissolving polymer and a structurally symmetrical
surfactant in the low-polar solvent like toluene, thus the
three interactions mentioned above are much weaker
or even do not exist, since neither the polymer nor
surfactant can ionize in toluene; however, there does
exist polar interaction between polar groups in the
system. The driving force(s) for the formation of meso-
morphous region in this study is not quite clear, but we
suppose they could be the van der Waals interactions
between polymer chain and surfactant, and these
interactions involve polar interactions and nonpolar
interactions. The polar groups on the polymer side
chains might interact with the polar groups of surfac-
tant with the formation of joint associates, the interac-
tion could also exist between the long thiophene-
containing side chains and surfactant tails, and there
also exist the steric (nonpolar) interactions between the
alkyl tails of the surfactant and the polymer back-
bone.1,4,22 These relatively weak interactions could prob-
ably lead to the formation of the mesomorphous struc-
tures of the surfactant-polymer system in the solid
films. Furthermore, the fact that only the symmetrical
surfactant with eight-carbon (C8) tails can form mac-
roscopic patterns implies that both the polar interac-
tions and the nonpolar interactions are all critical to
the formation of the mesomorphous structure. A delicate
balance between these two kinds of interactions is
necessary for this structure formation because the
increase in the polar interaction by using surfactant
TBAB (with four C4 alkyl tails) or the increase in the
nonpolar interaction by using surfactant TDAB (with
four C12 alkyl tails) cannot lead to the formation of this
mesomorphous structure as well as the macroscopic
pattern.
Therefore, because of the effect of solvent evaporation,
the patterns obtained by solution-casting are not in
thermodynamic equilibrium, although they are stable,
kinetically “frozen” structures.
Formation of Macroscopic Pattern. The photo-
graphs showing the formation process of the macro-
scopic patterns are listed in Figure 8. In the homoge-
neous solution of the TPA and TOAB system, as the
solvent evaporated, first several nuclei of the concentric
rings appeared, and then a ring formed around each
nucleus after the formation of the nuclei; afterward, two
rings formed for each concentric ring after the formation
of the first ring; by this way the concentric rings
continued to “grow”; finally, some concentric rings
stopped to grow upon contact with one another. It can
be concluded that the formation of each concentric ring,
which makes up the macroscopic pattern, started from
the center and then “grew” outward ring by ring.
In the polymer-surfactant solution, after the forma-
tion of the mesophase structure between the polymer
and surfactant, as the solvent further evaporated, the
unstable region (spinodal) in the phase diagram was
reached, and phase separation occurred; consequently,
surface undulation formed on the polymer-surfactant
film. The following forces could be responsible for
surface undulation: evaporation-induced convection23,24
and/or the large interfacial tension between the surfac-
tant-polymer mesomorphous phase and the polymer
amorphous phase. Previously, researchers have also
generated surface undulation (concentric rings) on dif-
As for the film-forming temperature, it affects not only
the composition of the two phases but also the evapora-
tion rate of the solvent as well as the size of a single
ring in the patterns. Increasing the temperature results
in a decrease in the film formation time, and the
viscosity of the solution dramatically increases; this
produces a rapid quench of the polymer mixture, which
“freeze” in a nonequilibrium phase separation morphol-
ogy. Therefore, a single ring in a pattern has no time to
grow to large size before its structure being frozen. On
the other hand, at lower temperature, the film-forming
time is longer, and a single ring in the patterns has time
to grow to larger size. So, the size of the rings (domains)
is determined by the complex interplay between the
quench and the continuously decreasing mobility of the
molecules, both caused by solvent evaporation.
As the temperature was further increased above 45
°C, the evaporation may be too fast, and the polymer
chains and surfactant molecules have no time to move;
thus, we cannot observe the pattern. On the other hand,
as the temperature was reduced below 20 °C, we can
only obtain a transparent film with no pattern on it. It
is possible that as the solvent evaporates both the
polymer chains and surfactant molecules can hardly
move before the phase separation can take place.

Macromolecules, Vol. 38, No. 22, 2005
Mesomorphous Structure and Macroscopic Patterns 9273
Figure 8. Photographs showing the formation process of the macroscopic pattern at the temperature of 35 °C (polymer content
in the solid film is 55 wt %): (A) the homogeneous solution of the polymer and surfactant TOAB in toluene at the concentration
of 6 wt % in a glass container; (B) about 60 min later, several nuclei of the concentric rings appeared; (C) a ring formed around
each nucleus about 2 min after the formation of nuclei; (D) two rings formed for each concentric ring 3 min after formation of first
ring; (E) concentric rings continued to “grow”; (F) some concentric rings stopped to grow upon contact with one another, at this
stage more than half of the solvent remained in the system. The diameter of the glass container is about 4 cm.
ferent systems23,24 (e.g., PS and PMMA or block copoly-
mer) through evaporation convection, but no mesophase
structure was involved in those convection patterns, and
usually no surfactants were added to those systems.
Some other researchers have generated spiral patterns
(usually in microscopic scale) in liquid crystal polymers
or biomacromolecules.25,26 Hydrogen bonding is mainly
responsible for appearance of the spiral patterns in
biomacromolecules, while the interaction between dis-
clinations is the main cause of the spiral patterns in

9274 Wu et al.
Macromolecules, Vol. 38, No. 22, 2005
liquid crystal polymers.25,26 Hence, the formation mech-
anism of spiral patterns is different from that of the
concentric macroscopic patterns in our polymer-sur-
factant system. In our case, a large amount of surfactant
was involved in the formation of the macroscopic pat-
tern, and the formation of the mesophase structure
could also be critical to the patterning; the macroscopic
pattern can only be obtained under specific conditions.
For example, macroscopic patterns can only be gener-
ated in those TPA-TOAB systems that form the me-
sophase structure; no patterns can be formed by the
polymer with other surfactants with similar structure
as that of TOAB such as tetrabutylammonium bromide
and tetradodecylammonium bromide, and the removal
of the thiophene-containing pendant groups results in
the disappearance of macroscopic patterns. Our polymer-
TOAB-organic solvent is a new system that can form
macroscopic patterns.
and this unique microscopic ordering can cause macro-
scopic patterns in solid state. A macroscopic pattern is
alternatively organized by circular convex ridges and
concave valleys, with the former being the polymer-rich
amorphous phase and the latter being the surfactant-
rich mesomorphous phase. The formation of the mac-
roscopic patterns involves three processes: (1) formation
of mesoscopic structure, (2) phase separation, and (3)
surface undulation. This macroscopic patterning in the
solid polymer-surfactant system could offer a new way
for fabricating ordered supramolecular structure in
macroscopic dimensions.
Acknowledgment. This work was supported by
NSFC (Project No. 50573023 and 50473035), NSFG (No.
04020043), and NCET.
Supporting Information Available: Monomer synthesis
scheme, FTIR spectra, and 1H NMR spectra. This material is
available free of charge via the Internet at http:// pubs.acs.org.
On the basis of the above investigations and observa-
tions, we propose the following pattern formation pro-
cess. Upon addition of polymer and surfactant into some
organic solvent like toluene, a ternary homogeneous
solution was formed. As the solution was cast on the
glass substrate and with the evaporation of some
organic solvent, the interaction between the solvent and
some solute molecules substantially decreased, and the
surfactant-rich mesomorphous structures were thereby
formed by some surfactant and polymer molecules
driven by van der Waals interactions which include
polar interactions and nonpolar interactions, and then
the system was turned from the one-phase stable region
into the unstable region. Phase separation seems to
occur through spinodal decomposition. At this point
concentration fluctuations become unstable and grow,
rather than decay, giving domains rich in one species;
by this way the mesomorphous domains phase-sepa-
rated from the solution and gradually constituted the
nuclei of the concentric rings (Figures 3D and 8). At this
time, the amorphous domains might form around each
nucleus and constitute a ring because the center had
been occupied. As the evaporation went on, another
mesomorphous ring formed around the former amor-
phous ring, and then this process continued until the
motion of polymer chains were frozen due to the solvent
evaporation. The convection and/or the capillary forces
due to the interfacial tension on both sides of the
amorphous ring might “push” the polymer-rich amor-
phous phase to protrude and eventually form the
circular ridge. In addition, we think the molecular chain
motion of both the polymer and the surfactant is also
important to the pattern formation. As evidenced by our
observation that the solvent evaporation at lower tem-
perature or using higher boiling point solvent can all
result in larger and well-formed pattern, the slow
solvent evaporation makes the solvent leave more
slowly; hence, the molecular chain motion could have
enough time to move and settle to form the ordered
pattern during the phase separation.
References and Notes
(1) Kotz, J.; Kosmella, S.; Beitz, T. Prog. Polym. Sci. 2001, 26,
1199-1232.
(2) Zhou, S. Q.; Chu, B. Adv. Mater. 2000, 12, 545-556.
(3) Muthukumar, M.; Ober, C. K.; Thomas, E. L. Science 1997,
277, 1225-1232.
(4) Thunemann, A. F. Adv. Mater. 1999, 11, 127-130.
(5) Thunemann, A. F. Prog. Polym. Sci. 2002, 27, 1473-1572.
(6) Thunemann, A. F.; Muller, M.; Dautzenberg, H.; Joanny, J.
F.; Lowen, H. Adv. Polym. Sci. 2004, 166, 113-171.
(7) Zhou, S. Q.; Hu, H. B.; Burger, C.; Chu, B. Macromolecules
2001, 34, 1772-1778.
(8) Norenberg, R.; Klingler, J.; Horn, D. Angew. Chem., Int. Ed.
1999, 38, 1626-1629.
(9) Yeh, F. J.; Sokolov, E. L.; Khokhlov, A. R.; Chu, B. J. Am.
Chem. Soc. 1996, 118, 6615-6618.
(10) Zhou, S. Q.; Liang, D. H.; Burger, C.; Yeh, F. J.; Chu, B.
Biomacromolecules 2004, 5, 1256-1261.
(11) Kurth, D. G.; Meister, A.; Thunemann, A. F.; Forster, G.
Langmuir 2003, 19, 4055-4057.
(12) Thunemann, A. F.; Kubowicz, S.; Burger, C.; Watson, M.;
Tchebotareva, N.; Mullen, K. J. Am. Chem. Soc. 2003, 125,
352-356.
(13) Antonietti, M.; Conrad, J.; Thunemann, A. Macromolecules
1994, 27, 6007-6011.
(14) Antonietti, M.; Maskos, M. Macromolecules 1996, 29, 4199-
4205.
(15) Merta, J.; Garamus, V. M.; Willumeit, R.; Stenius, P. Lang-
muir 2002, 18, 7272-7278.
(16) Thunemann, A. F.; General, S. Macromolecules 2001, 34,
6978-6984.
(17) Thunemann, A. F.; Kubowicz, S.; Pietsch, U. Langmuir 2000,
16, 8562-8567.
(18) Chu, B.; Hsiao, B. S. Chem. Rev. 2001, 101, 1727-1761.
(19) Henderson, I. C.; Clarke, N. Macromolecules 2004, 37, 1952-
1959.
(20) Petersson, M.; Loren, N.; Stading, M. Biomacromolecules
2005, 6, 932-941.
(21) Walheim, S.; Bo1tau, M.; Mlynek, J.; Krausch, G.; Steiner,
U. Macromolecules 1997, 30, 4995-5003.
(22) Hsiao, M. S.; Chen, H. L.; Liaw, D. J. Macromolecules 2000,
33, 221-224.
(23) Mitov, Z.; Kumacheva, E. Phys. Rev. Lett. 1998, 81, 3427-
3430.
(24) Sakurai, S.; Tanaka, K.; Nomura, S. Macromolecules 1992,
25, 7066-7068.
(25) Zhang, S.; Eugene, M. T.; Donald, A. M. Macromolecules
2004, 37, 390-396.
Conclusions
(26) Kurihara, S.; Mori, T.; Nonaka, T. Macromolecules 1998, 31,
5940-5942.
The highly ordered mesomorphous structure can also
be obtained from the polymer (nonpolyelectrolyte) and
surfactant system with no strong interaction involved,
MA051042G