3,4-Ethylenedioxypyrrole (EDOP) Monomers with Aromatic Substituents for Parahydrophobic Surfaces by Electropolymerization

Article abstract of DOI:10.1021/acs.macromol.5b01054

In nature, superhydrophobic (low adhesion) and parahydrophobic (high adhesion) properties exist in lotus leaves and red roses, for example. The control in the water adhesion is extremely important for applications in water harvesting, for example. Here, w

Full text of DOI:10.1021/acs.macromol.5b01054

Article
pubs.acs.org/Macromolecules
3,4-Ethylenedioxypyrrole (EDOP) Monomers with Aromatic
Substituents for Parahydrophobic Surfaces by Electropolymerization
Claudio Mortier, Thierry Darmanin, and Frederic Guittard*
́
́
CNRS, LPMC, UMR 7336, Univ. Nice Sophia Antipolis, 06100 Nice, France
S
* Supporting Information
ABSTRACT: In nature, superhydrophobic (low adhesion) and
parahydrophobic (high adhesion) properties exist in lotus leaves and
red roses, for example. The control in the water adhesion is
extremely important for applications in water harvesting, for
example. Here, we report the obtaining of parahydrophobic
properties through the electropolymerization of 3,4-ethylenediox-
ypyrrole (EDOP) derivatives. We report for the first time an
electrochemical study of EDOP derivatives bearing aromatic cycles
(phenyl, naphthalene, biphenyl, and pyrene). Eight novel EDOP
monomers are studied with and without the presence of an ethyl
acetate spacer in order to give more mobility to the aromatic
substituents. Surprinsgly, higher steric hindrance are observed
during electropolymerization with spacer. However, the polymers are more insoluble with spacer, which is an important
point for electropolymerization. The highest parahydrophobic properties are obtained with biphenyl groups and with the spacer,
which are due to the presence of both micro- and nanostructures.
In comparison to other materials, the use of conducting
polymers18 allows to have unique possibilities properties to
control the surface hydrophobicity. On the one hand,
conducting polymers can lead to various nanostructured
materials not only in solution by self-assembling but also
directly on substrates by electropolymerization, for exam-
ple.19−21 Using the electropolymerization technique, the
growth and the shape of nanostructured polymers can be
controlled by electrochemical parameters such as the electro-
deposition method, the electrolyte, or solvent nature.22 On the
other hand, the θYw of the polymer can be reversibly controlled
by introducing/removing dopant agents23 or irreversibly
controlled by grafting hydrophobic chains in the polymer
structure.24
Among the monomers usable for the electropolymerization,
that of the 3,4-ethylenedioxypyrrole (EDOP) family offers
exceptional polymerization capacity and lead to conducting
polymers with unique optoelectronic properties.25−27 However,
due to the extreme difficulty to synthesize these monomers,
usually obtained in about 10 steps, the study of these
derivatives remains a challenge.28−30 Previously, superoleopho-
bic properties and superhydrophobic properties were obtained
using fluorinated31,32 and hydrocarbon33 chains, respectively.
These exceptional properties were in part due to the presence
of nanoporosity, which induces a high increase in the contact
angles. Interestingly, it was shown that the presence of the
INTRODUCTION
■
The control of the surface wettability is necessary for various
potential applications such as in self-cleaning windows, collage,
antifogging surfaces, biofouling coatings, microfluidic devices,
drag reduction, and separation membranes.1−5 The surface
hydrophobicity is extremely dependent on both the material
surface energy (γSV) given by the Young angle θY (cos θY = (γSV
− γSL)/γLV)6 and the presence of surface roughness.6−8 In
nature, superhydrophobic properties characterized by water
apparent contact angle (θw) > 150° with ultralow adhesion or
hysteresis exist.9 This is the case for example of many plants
and animals such as the famous lotus leaves.10 However, other
natural substrates such as the gecko feet or rose petals are
characterized by extremely high θw but with also extremely high
adhesion.11−13 In order to better define these substrates,
Marmur proposed to use the term of parahydrophobic.14 Both
superhydrophobic and parahydrophobic properties can be
predicted by the Cassie−Baxter equation,8 which gives θw for
rough and porous substrates. Following this equation, it is
necessary to have surface roughness able to trap air when a
water droplet is put in contact to the substrate. Moreover, the
water adhesion can be decreased by increasing the air fraction
or θYw. Many strategies can be used to control the water
adhesion.5,15−17 For example, the research group of Jiang
showed the possibility to tune the surface adhesion from highly
adhesive to low adhesive by changing the geometry of surface
structures from nanopillars with flat and concave shape to
nanotubes.15 Athanassiou also showed to possibility of
changing the adhesion forces by playing on the roughness of
micropatterned substrates.17
Received: May 16, 2015
Revised: July 9, 2015
© XXXX American Chemical Society
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Scheme 1. Original EDOP Derivatives Monomers Studied in This Article
Scheme 2. Synthesis Way to the Monomers
nanoporosity is highly sensitive to the polymer planarity.31 For
EXPERIMENTAL SECTION
■
example, the presence of nanoporosity is highly affected by
steric hindrance induced during the polymerization. In order to
increase the water adhesion and obtain parahydrophobic
properties, it is necessary to reduce the hydrophobic chain
length to decrease θYw and/or to use very bulky substituents to
suppress the presence of nanoporosity.
3,4-Ethylenedioxypyrrole (EDOP) and 2-(2,3-dihydro-[1,4]dioxino-
[2,3-c]pyrrol-6-yl)ethanol (EDOP-OH) were synthesized in eight and
ten steps,28,31 respectively, from iminodiacetic acid as shown in
Scheme 2.
Then, the monomers were obtained either by nucleophilic
substitution from EDOP or by esterification from EDOP-OH. The
monomer mass spectra as well as the H and 13C spectra are available
1
Here, we combine both the decrease θYw and the use of very
bulky substituents by introducing aromatic cycles of different
size (phenyl, naphthalene, biphenyl, and pyrene). Indeed,
aromatic cycles are known to have lower hydrophobicity than
linear alkyl chains. We report for the first time the properties
obtained from EDOP derivatives bearing aromatic cycles in
order to obtain parahydrophobic properties (high adhesion).
Eight novel EDOP monomers bearing were synthesized, as
shown in Scheme 1. In order to study the influence of steric
hindrance, the aromatic cycles are directly grafted on the
nitrogen of EDOP or separated by an ethyl acetate spacer.
in the Supporting Information. The numbers of carbons in the spectra
do not always corresponds to the total number of carbons because
some carbon peaks overlap.
Nucleophilic Substitution of EDOP. To 20 mL of anhydrous
DMF were added 0.5 g of EDOP (4 mM, 1 equiv) and 0.45 g of KOH
(8 mM, 2 equiv). The solution was, then, stirred for 30 min, and 10
mL of anhydrous DMF containing 1.5 equiv of the corresponding
bromide was added. After stirring for 24 h at 50 °C, 100 mL of water
was added, and the product was extracted with ethyl acetate. The
product was then purified by column chromatography using diethyl
ether/cyclohexane (25:75) as eluent and silica gel as stationary phase.
B
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Figure 1. Cyclic voltammogram recorded in 0.1 M Bu4NClO4/anhydrous acetonitrile of the different EDOP derivatives without spacer. Scan rate: 20
mV s−1.
6-Benzyl-3,6-dihydro-2H-[1,4]dioxino[2,3-c]pyrrole (EDOP-Ph).
Yield 54%; crystalline solid; mp 54.9 °C. δH (200 MHz, CDCl3):
7.20 (5 H, m), 6.11 (2 H, s), 4.84 (2 H, s), 4.19 (4 H, s). δC (200
MHz, CDCl3): 138.13, 132.28, 128.61, 127.59, 126.98, 101.74, 65.79,
53.90. FTIR (KBr): νmax/cm−1 2974, 2931, 2862, 1550, 1456, 1424,
1387, 1361, 1056, 1039 cm−1. MS (70 eV): m/z 215 (M+, 100), 91
(C7H7•+, 95).
6-(Naphthalen-2-ylmethyl)-3,6-dihydro-2H-[1,4]dioxino[2,3-c]-
pyrrole (EDOP-Na). Yield 32%; crystalline solid; mp 83.5 °C. δH (200
MHz, CDCl3): 7.60 (4 H, m), 7.30 (3 H, m), 6.08 (2 H, s), 4.92 (2 H,
s), 4.12 (4 H, s). δC (200 MHz, CDCl3): 135.48, 133.26, 132.83,
128.47, 127.82, 127.66, 126.26, 125.98, 125.80, 125.05, 101.83, 65.80,
54.10. FTIR (KBr): νmax/cm−1 2983, 2918, 2866, 1546, 1444, 1421,
1389, 1364, 1054, 1035 cm−1. MS (70 eV): m/z 265 (M+, 48), 141
(C11H9•+, 100).
6-([1,1′-Biphenyl]-4-ylmethyl)-3,6-dihydro-2H-[1,4]dioxino[2,3-c]-
pyrrole (EDOP-BiPh). Yield 22%; crystalline solid; mp 73.0 °C. δH
(200 MHz, CDCl3): 7.41 (9 H, m), 6.07 (2 H, s), 4.81 (2 H, s), 4.12
(4 H, s). δC (200 MHz, CDCl3): 140.67, 137.16, 132.35, 128.76,
127.42, 127.38, 127.33, 127.06, 101.76, 65.80, 53.64. FTIR (KBr):
νmax/cm−1 2987, 2918, 2866, 1551, 1450, 1424, 1389, 1357, 1058,
1039 cm−1. MS (70 eV): m/z 291 (M+, 46), 167 (C13H11•+, 100).
6-(Pyren-1-ylmethyl)-3,6-dihydro-2H-[1,4]dioxino[2,3-c]pyrrole
(EDOP-Py). Yield 10%; crystalline solid; mp 186.4 °C. δH (200 MHz,
CDCl3): 8.15 (9 H, m), 6.19 (2 H, s), 5.58 (2 H, s), 4.19 (4 H, s). δC
(200 MHz, CDCl3): 132.41, 131.26, 131.18, 130.67, 130.57, 128.54,
128.22, 127.49, 127.36, 126.24, 126.04, 125.46, 125.31, 124.91, 122.13,
101.93, 65.81, 51.85. FTIR (KBr): νmax/cm−1 2970, 2925, 2862, 1546,
1464, 1424, 1383, 1361, 1054, 1035 cm−1. MS (70 eV): m/z 339 (M+,
20), 215 (C17H11•+, 100).
Esterification of EDOP-OH. 1.5 equiv of the corresponding acid
was added to 10 mL of dichloromethane containing 30 mg of DMAP
and 0.3 g of N-(3-(dimethylamino)propyl)-N′-ethylcarbodiimide
hydrochloride (EDC) (1.5 equiv). After stirring for 30 min at room
temperature, EDOP-OH (0.17 g, 1 equiv) was added. After a day at 50
°C, the solvent was removed, and the crude was purified by column
chromatography (silica gel; eluent: dichloromethane) to yield the
product.
2-(2H-[1,4]Dioxino[2,3-c]pyrrol-6(3H)-yl)ethyl 2-Phenylacetate
(EDOP-OCO-Ph). Yield 73%; colorless liquid. δH (200 MHz,
CDCl3): 7.28 (5 H, m), 6.00 (2 H, s), 4.25 (2 H, J 5.4, t), 4.18 (4
H, s), 3.87 (2 H, J 5.4, t), 3.63 (2 H, s). δC (200 MHz, CDCl3):
171.18, 133.58, 132.31, 129.28, 128.61, 127.20, 101.74, 65.76, 64.41,
48.76, 41.22. FTIR (KBr): νmax/cm−1 2971, 2924, 2870, 1736, 1552,
1455, 1426, 1395, 1361, 1251, 1157, 1057, 1040 cm−1. MS (70 eV):
+
m/z 287 (M+, 35), 151 (C8H9NO2 , 100), 91 (C7H7•+, 30).
2-(2H-[1,4]Dioxino[2,3-c]pyrrol-6(3H)-yl)ethyl 2-(Naphthalen-2-
yl)acetate (EDOP-OCO-Na). Yield 61%; colorless liquid. δH (200
MHz, CDCl3): 7.81 (4 H, m), 7.42 (3 H, m), 6.03 (2 H, s), 4.27 (2 H,
J 5.4, t), 4.16 (4 H, s), 3.88 (2 H, J 5.4, t),3.79 (2 H, s). δC (200 MHz,
CDCl3): 171.17, 133.40, 132.50, 132.32, 131.07, 128.28, 128.04,
127.69, 127.64, 127.33, 126.15, 125.84, 101.41, 65.75, 64.44, 48.75,
41.38, 30.90. FTIR (KBr): νmax/cm−1 2967, 2924, 2870, 1736, 1552,
1449, 1424, 1393, 1364, 1255, 1160, 1057, 1039 cm−1. MS (70 eV):
+
m/z 337 (M+, 30), 151 (C8H9NO2 , 100), 141 (C11H9•+, 45).
2-(2H-[1,4]Dioxino[2,3-c]pyrrol-6(3H)-yl)ethyl 2-([1,1′-Biphenyl]-
4-yl)acetate (EDOP-OCO-BiPh). Yield 78%; colorless liquid. δH (200
MHz, CDCl3): 7.44 (9 H, m), 6.03 (2 H, s), 4.28 (2 H, J 5.4, t), 4.16
(4 H, s), 3.90 (2 H, J 5.4, t), 3.68 (2 H, s). δC (200 MHz, CDCl3):
171.17, 140.76, 140.19, 132.57, 132.33, 129.71, 128.72, 127.37, 127.26,
127.08, 101.43, 65.75, 64.47, 48.76, 40.85. FTIR (KBr): νmax/cm−1
2970, 2922, 2866, 1736, 1553, 1450, 1424, 1394, 1364, 1252, 1157,
1056, 1039 cm−1. MS (70 eV): m/z 363 (M+, 35), 167 (C13H11•+, 40),
+
151 (C8H9NO2 , 100).
2-(2H-[1,4]Dioxino[2,3-c]pyrrol-6(3H)-yl)ethyl 2-(Pyren-1-yl)-
acetate (EDOP-OCO-Py). Yield 40%; colorless liquid. δH (200 MHz,
CDCl3): 8.10 (9 H, m), 5.91 (2 H, s), 4.35 (2 H, s), 4.25 (2 H, J 5.4,
t), 4.08 (4 H, s), 3.81 (2 H, J 5.4, t). δC (200 MHz, CDCl3): 171.18,
132.22, 131.31, 130.90, 130.77, 129.40, 128.40, 128.06, 127.62, 127.41,
127.31, 125.96, 125.26, 125.14 125.02, 124.86, 124.75, 123.13, 101.33,
65.67, 64.55, 48.68, 39.38. FTIR (KBr): νmax/cm−1 2966, 2922, 2866,
1731, 1550, 1445, 1422, 1392, 1362, 1252, 1159, 1054, 1037 cm−1.
Electrochemical Conditions. The depositions were performed
using 0.1 M tetrabutylammonium perchlorate (Bu4NClO4) in
anhydrous acetonitrile as electrolyte. 10 mL of electrolyte were
introduced in an electrochemical cell, and after degassing under argon,
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Figure 2. Cyclic voltammogram recorded in 0.1 M Bu4NClO4/anhydrous acetonitrile of the different EDOP derivatives with spacer. Scan rate: 20
mV s−1.
Figure 3. FT-IR spectra of (a) PEDOP-Py and (b) PEDOP-OCO-Py.
0.01 M monomer was introduced. Three electrodes were used for the
depositions. A platinum tip was used as working electrode for the
cyclic voltammetry experiments and large gold plates for the surface
characterizations. A carbon rod was used as counter electrode and a
saturated calomel electrode (SCE) as reference electrode. The three
electrodes were connected to an Autolab potentiostat (Metrohm).
Surface Characterization. The substrates were characterized by
infrared spectrometry, goniometry, scanning electron microscopy
(SEM), and optical profilometry. The IR spectra were performed by
reflectance using a Spectrum Spotlight 300 FT-IR microscope
(PerkinElmer) and with Image mode. The SEM images were recorded
using a 6700F microscope (JEOL). The mean arithmetic (Ra) and
quadratic (Rq) roughness were determined using a Wyko NT 1100
optical microscope (Bruker) with the working mode High Mag Phase
Shift Interference (PSI), the objective 50×, and the field of view
(FOV) 0.5×. The analyses were performed on 182 × 239 μm2 areas.
The apparent contact angles (θ) were measured using a DSA30
(α). If the droplet does not move even for α > 90°, the hysteresis is
extremely high and the substrate is called sticky.
RESULTS AND DISCUSSION
■
Cyclic Voltammetry Experiments. The growth of the
conducting polymers were investigated by cyclic voltammetry.
The cyclic voltammogram allows to have extremely important
information on the substitutent effect, for example. First, it was
necessary to determine the monomer oxidation potential
(Eoxm). These potentials were determined by adding 0.01 M
of monomers in anhydrous acetonitrile containing 0.1 M of
tetrabutylammonium perchlorate (Bu4NClO4). Eox was found
m
to be in the range 0.93−1.0 V vs SCE whatever the substituent.
A decrease in Eox was measured using the spacer (0.96 V for
m
EDOP-OCO-Ph, 0.93 V for EDOP-OCO-Na, 0.94 V for
EDOP-OCO-BiPh, and 0.95 V for EDOP-OCO-Py), but the
differences are slight (1.00 V for EDOP-Ph, 0.94 V for EDOP-
Na, 0.95 V for EDOP-BiPh, and 0.98 V for EDOP-Py). The
goniometer (Kruss) by taking the tangent at the triple point contact
̈
line. For the dynamic contact angles, a 6 μL water droplet was put on
the substrate, and the substrate was inclined until the droplet moves.
The advanced and receding contact angles are taken just before the
droplet moving. The maximum inclination angle is called sliding angle
lowest Eox were also obtained with the naphthalene
m
substituent and the highest Eox with the phenyl substituent.
m
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Table 1. Roughness Parameters as a Function of the Polymer
(Qs = 100 mC cm−2)
polymer
θwater [deg]
Ra [nm]
Rq [nm]
PEDOP-BiPh
110.4
85.0
88.0
81.5
102.8
76.5
670
60
1060
120
180
235
505
85
PEDOP-Py
PEDOP-OCO-Ph
PEDOP-OCO-Na
PEDOP-OCO-BiPh
PEDOP-OCO-Py
125
95
200
65
for each monomer are given in Figure 1 and Figure 2. Without
spacer, the polymer oxidation potentials are 0.20 V vs SCE for
PEDOP-Ph, 0.21 V for PEDOP-Na, 0.22 V for PEDOP-BiPh,
and 0.32 V for PEDOP-Py. These data are extremely important
because they gave information on the polymer chain length.
Indeed, usually, the polymer oxidation potential decreases as
the polymer chain length increases. Here, the polymer
oxidation potential is quite the same for PEDOP-Ph,
PEDOP-Na, and PEDOP-BiPh. Hence, the steric hindrance
induced by the presence of a phenyl, naphthalene, and biphenyl
group is quite the same, which is surprising because the size of
these substituents is very different. On the opposite, the
presence of a very big pyrene substituent induces higher steric
hindrance and shortens the polymer chain length. Moreover,
the curves are superposed after each scan, indicating that
polymer chain lengths are the same during the polymer growth.
However, the intensity of the peaks is extremely important for
PEDOP-BiPh and extremely low for PEDOP-Ph and PEDOP-
Na. The solubility of PEDOP-Ph and PEDOP-Na is extremely
important. Usually, the polymer solubility is dependent on the
polymer chain length and the presence of a substituent. Hence,
the presence of biphenyl and pyrene groups highly increases the
polymer insolubility by π-stacking interactions in comparison to
phenyl and naphthalene groups.
Figure 4. SEM images at two magnifications (5000× and 25 000×) of
the different PEDOP polymers without spacer (Qs = 100 mC cm−2).
With spacer, the polymer oxidation potentials are 0.23 V vs
SCE for PEDOP-OCO-Ph, 0.34 V for PEDOP-OCO-Na, 0.36
V for PEDOP-OCO-BiPh, and 0.68 V for PEDOP-OCO-Py.
The polymer oxidation potential are higher with spacer
indicating higher steric hindrance, which is surprising because
a spacer is very often used to move substituent away from the
polymer backbone. Moreover, for PEDOP-OCO-Na, PEDOP-
OCO-BiPh, and PEDOP-OCO-Py, a very high increase in the
polymer oxidation potential is observed after each scan (for
example, for PEDOP-OCO-Na from 0.25 V for 1 scan to 0.37
V for 10 scans), indicating that the mean polymer chain lengths
decrease during the polymer growth. Using the spacer, the
polymer solubility remains important only with a phenyl
substituent.
Hence, as expected, steric hindrances are observed by the
presence of these bulky aromatic substituents, which is
important to reduce the presence of surface nanoporosity.31
The steric hindrance seem even to be higher with the presence
of the spacer.
Then, in order to characterize the polymer surfaces, polymer
films were electrodeposited at constant potential and using
different polymer charges (Qs) up to 400 mC cm−2 in order to
investigate the effect of the polymer growth on the surface
properties. Polymer films could be obtained using all
monomers except EDOP-Ph and EDOP-Na, for which the
polymers were too soluble in acetonitrile, confirming the cyclic
voltammetry experiments.
Figure 5. SEM images at two magnifications (5000× and 25 000×) of
the different PEDOP polymers with spacer (Qs = 100 mC cm−2).
Then, the polymerization was studied by cyclic voltammetry:
10 scans at a scan rate of 20 mV s−1 and from −1 V to a
potential slightly lower than Eoxm. The cyclic voltammograms
E
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Figure 6. Apparent contact angle (θ) as a function of the deposition charge (Qs) for all the polymers.
Infrared Spectroscopy. All the polymer films were
characterized by infrared spectrocopy. Figure 3 shows examples
of FT-IR spectra for PEDOP-Py and PEDOP-OCO-Py. The
polymers display peaks in the range 1400−1550 cm−1
attributed to the stretching of CC in the pyrrole ring and
the aromatic substituents while the peaks in the range 1000−
1200 cm−1 are attributed to the stretching of C−O in the
ethylenedioxy bridge. The main difference is the presence of
peak at about 1740 cm−1 attributed to the stretching of CO
of the ester groups in the case of the polymers with spacer.
Surface Morphology and Roughness. The SEM of the
polymers for Qs = 100 mC cm−2 are available in Figures 4 and
5. At this deposition charge, the less structured polymer is
PEDOP-OCO-Ph while the most structured is PEDOP-BiPh.
Indeed, PEDOP-BiPh is composed of nanoparticles forming a
highly porous surface, which highly increases the surface
roughness (Table 1). For the other polymers, the surfaces are
not porous but composed of large cauliflower structures. These
structures are relatively smooth except for PEDOP-OCO-BiPh,
for which the presence of nanostructures is present. However,
no nanoporosity was observed in the polymers contrary to
other polymers report in the literature.31 Indeed, the formation
of surface nanoporosity requires that the polymer is highly
planar, but here the planarity is too affected by the presence of
the bulky aromatic cycles.
Surface Wettability. The water apparent contact angles
(θ) for each polymer and as a function of the deposition charge
(Qs) are displayed in Figure 6. For most of the polymers it is
observed a decrease in θ in the first instances of the polymer
growth and an increase after. The maximal θ is obtained at 100
F
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liquid, and liquid−vapor surface tensions, respectively. Here,
the smooth substrates were obtained by reducing Qs to 1 mC
cm−2 in order to form a thin polymer film but without surface
structures. An example of smooth substrate is shown in Figure
8. The θY as well as the roughness parameters of these smooth
substrates are given in Table 2. The θY is close to the
hydrophilic/hydrophobic limit (θY = 90°) for PEDOP-OCO-
Py. The other polymers are clearly intrinsically hydrophilic with
θY < 90°. The most hydrophilic polymer is PEDOP-OCO-Ph,
which also explains the solubility problems observed by cyclic
voltammetry.
The wettability results can now be explained using the
Wenzel and Cassie−Baxter equations.7,8 These two equations
are very often used to explain the wettability of rough
substrates. In the Wenzel equation, the water droplets put on
a rough substrate is in full contact with it.7 The liquid interface
follows all the surface roughness. The Wenzel equation is cos θ
= r cos θY, r being a roughness parameter. With this equation it
is possible to have θ > θY but only if θY > 90°. Hence, in the
first instance of the polymer growth, the decrease in θ as Qs
increases can be explained by the Wenzel equation. However,
the Wenzel equation cannot explain the high increase in θ at
higher Qs. Indeed, at high Qs the substrates are more
structured. When a water droplet is put on these substrates,
it cannot penetrate in all the surface roughness. As a
consequence, an air fraction is trapped between the water
droplet and the surface and the Cassie−Baxter equation has to
be used.8 The Cassie−Baxter takes into account the presence of
air between a droplet and a substrate. The Cassie−Baxter
equation is cos θ = rff cos θY + f − 1, rf being the roughness
ratio of the substrate wetted by the liquid, f the solid fraction,
and (1 − f) the air fraction.34,35 Hence, the very high increase in
θ observed for micro- and nanostructured PEDOP-OCO-BiPh
films is due to a high rf and also a high air fraction trapped
between the droplet and the substrate. However, the solid
fraction is sufficiently important to induce a high water
adhesion and parahydrophobic properties.14
Figure 7. Water droplet deposited on PEDOP-OCO-BiPh (for Qs =
200 mC cm−2) after a surface inclination of 90°.
Figure 8. Smooth PEDOP-OCO-BiPh obtained at Qs = 1 mC cm−2
(magnification 25 000×).
Table 2. Roughness Parameters for the Smooth Polymer (Qs
= 1 mC cm−2)
polymer
θY
[deg]
Ra [nm]
Rq [nm]
water
PEDOP-BiPh
85.1
8.6
10.1
8.1
10.6
14.6
11.5
11.6
12.4
15.9
PEDOP-Py
85.5
72.3
79.4
82.3
89.7
PEDOP-OCO-Ph
PEDOP-OCO-Na
PEDOP-OCO-BiPh
PEDOP-OCO-Py
8.2
CONCLUSIONS
■
8.9
We have shown the possibility to reach parahydrophobic
properties by electropolymerization of 3,4-ethylenedioxypyrrole
(EDOP) monomers with aromatic cycles (phenyl, naphthalene,
biphenyl, and pyrene), separated or not by an ethyl acetate
spacer. If higher steric hindrance were observed without spacer,
the most insoluble polymers were obtained with spacer. We
also showed the highest parahydrophobic properties could be
obtained with biphenyl groups and with the spacer thanks to
the presence of both micro- and nanostructures. This work is
extremely important in order to reproduce the parahydropho-
bic properties of natural substrates and for application in water
harvesting, for example.
10.7
mC cm−2 for PEDOP-BiPh, 200 mC cm−2 for PEDOP-OCO-
BiPh, and 400 mC cm−2 for the other polymers. Hence, the
presence of nanoparticles on PEDOP-BiPh films induces a high
increase in the surface roughness and as a consequence the
highest θ (θ = 112.3° for Qs = 100 mC cm−2) is obtained more
quickly, but the presence of microstructures allows sometimes
to have higher θ. The presence of both micro and
nanostructures on PEDOP-OCO-BiPh films allows to reach
higher θ (θ = 122.4°) but for Qs = 200 mC cm−2. Moreover,
the water adhesion on these substrates is extremely high,
indicating parahydrophobic properties.14 Experiments using the
tilted-drop process revealed their sticking behavior. Indeed,
water droplets put on these substrates remained stuck on them
even for a tilting angle of 90° (Figure 7).
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR, 13C NMR and mass spectra of the monomers. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.macromol.5b01054.
Discussion. To explain these wetting behaviors, it is first
necessary to evaluate the apparent contact angles of the same
polymer but “smooth” in order to estimate the effect of the
surface structures. The apparent contact angle of smooth
substrates also called Young angles (θY)6 are dependent on
AUTHOR INFORMATION
■
three surface tensions. The Young equation is cos θY = (γSV
γSL)/γLV where γSV, γSL, and γLV are the solid−vapor, solid−
−
Corresponding Author
*E-mail Frederic.Guittard@unice.fr (F.G.).
G
DOI: 10.1021/acs.macromol.5b01054
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Applications of Conducting Polymer Nanotubes and Nanofibers. Prog.
Polym. Sci. 2011, 36, 1415−1442.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We thank Jean-Pierre Laugier of the Centre Commun de
Microscopie Appliquee
for the realization of the SEM images.
́
(CCMA, Univ. Nice Sophia Antipolis)
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