Mesophase structure of low-wetting liquid crystalline polyacrylates with new perfluoroalkyl benzoate side groups

Article abstract of DOI:10.1002/pola.24207

The synthesis, thermal behavior, bulk microstructure, and wettability of new polyacrylates carrying spaced 4-perfluorohexylpropyl benzoate and 4-perfluorooctylpropyl benzoate units in the side groups were Investigated. X-ray diffraction analysis proved the formation of different smectic mesophases (SmI₂, SmF₂, and SmC₂) and the evolution of their structures and lattice parameters with temperature. The mesophase polymorphic behavior depended on the length of the perfluorinated chain segment in the repeat unit. The electron density profiles along the smectic layer normal were drawn and provided a deeper insight into the packing of the side chains in a tilted, double layer structure. Thin polymer films were cast from solution, and their low wettability was established by measurements of contact angles with different probing liquids. We suggest that the hydrophobicity and lipophobicity of the films are enhanced by the mesophase surface structure which is mediated by the high-order, mesophase bulk structure.

Full text of DOI:10.1002/pola.24207

Mesophase Structure of Low-Wetting Liquid Crystalline Polyacrylates
with New Perfluoroalkyl Benzoate Side Groups
ELISA MARTINELLI,1 FRANCESCA PAOLI,1 BERNARD GALLOT,2 GIANCARLO GALLI1
1Dipartimento di Chimica e Chimica Industriale, UdR Pisa INSTM, Universita` di Pisa, via Risorgimento 35, Pisa 56126, Italy
2Laboratoire des Mate´riaux Organiques a` Proprie´tes Spe´cifiques, CNRS, Vernaison 69390, France
Received 30 April 2010; accepted 28 June 2010
DOI: 10.1002/pola.24207
Published online in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The synthesis, thermal behavior, bulk microstruc-
ture, and wettability of new polyacrylates carrying spaced
4-perfluorohexylpropyl benzoate and 4-perfluorooctylpropyl
benzoate units in the side groups were investigated. X-ray dif-
fraction analysis proved the formation of different smectic
mesophases (SmI2, SmF2, and SmC2) and the evolution of their
structures and lattice parameters with temperature. The meso-
phase polymorphic behavior depended on the length of the
perfluorinated chain segment in the repeat unit. The electron
density profiles along the smectic layer normal were drawn
and provided a deeper insight into the packing of the side
chains in a tilted, double layer structure. Thin polymer films
were cast from solution, and their low wettability was estab-
lished by measurements of contact angles with different prob-
ing liquids. We suggest that the hydrophobicity and
lipophobicity of the films are enhanced by the mesophase sur-
face structure which is mediated by the high-order, mesophase
C
V
bulk structure.
2010 Wiley Periodicals, Inc. J Polym Sci Part
A: Polym Chem 48: 4128–4139, 2010
KEYWORDS: fluoropolymers; liquid-crystalline polymers; meso-
phase structure; surface energy; thin films; wettability
INTRODUCTION Fluorinated liquid crystalline polymers are a
relatively new class of fluoropolymers; see illustrations of
different structural classes of polymers.1–9 Initial studies on
fluorinated liquid crystals focused on partly fluorinated alka-
nes, namely diblock hydrocarbon-fluorocarbon molecules
such as H(CH2)x(CF2)yF (x, y > ꢀ6).10–14 The ability of these
compounds was shown to form thermotropic mesophases
because of the strong intramolecular phase segregation15
and the rigid, rod-like nature of the fluorocarbon chains.16,17
Moreover, the tendency to aggregation of amphiphilic, fluori-
nated molecules in solutions also manifested in the forma-
tion of different lyotropic mesophases.18,19 Later synthetic
efforts resulted in the development of a diversity of liquid
crystalline materials, including low molar mass com-
pounds,20 polymers,1,5,21–25 and supramolecular struc-
tures26–28 in which the length of the fluorinated mesogen
A(CH2)x(CF2)yF was varied in a range of numbers x and y,
most common examples having x ¼ 2, y > 6. More conven-
tional mesogenic units, for example, biphenyls and bisben-
zoates, have also been used in combination with partly fluo-
rinated tails in low molar mass29–33 and polymeric liquid
crystals.6,25
by several mechanisms, including liquid crystallinity and sur-
face segregation.34 Under some circumstances, these mecha-
nisms may be used together to form an ordered surface struc-
ture. For instance, block copolymers phase separate to
preferred microstructures, but when low-surface energy
blocks are incorporated, surface and interface segregation will
also take place to create further organization in the region of
the low energy surface.4,5,35,36 In particular, liquid crystallinity
may provide a useful means for preparing low-surface energy
polymeric materials for nonstick coating application.9,23,37 The
attachment of a fluorinated mesogen pendent to a polymer
backbone can further improve and stabilize the surface struc-
ture and order, for example, upon exposure to different polar
environments, as a consequence of the induced mesomorphic
behavior in the bulk of the material.
In this study, we designed and prepared new polyacrylates,
p(1–6) and p(1–8), carrying a perfluoroalkylpropyl benzoate
side group that was spaced from the polymer backbone and
had a varied length of the perfluorocarbon chain segment
(6 and 8 CF2 groups, respectively). The new molecular archi-
tecture was preferred to those of the largely used perfluoroal-
kylethyl mesogens because it was expected to enhance the
mesogenic tendency of the polymers and to promote forma-
tion of a mesophase organized over different scales from the
molecular level upwards. This was connected with a pro-
nounced hydrophobic and lipophobic behavior of the polymer
Such fluorinated polymers have lately been considered as can-
didate materials for the macromolecular engineering of low-
surface energy films through self-organization. In fact, sponta-
neous assembling over different length scales may be driven
Correspondence to: G. Galli (E-mail: gallig@dcci.unipi.it)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 4128–4139 (2010) 2010 Wiley Periodicals, Inc.
4128
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
films, with the longer perfluorocarbon chain determining a
lower wettability. An interplay between bulk structure and
surface properties is discussed.
FTIR (film) (cmꢂ1) ¼ 3330 (m OAH), 2958ꢂ2888 (m CAH al-
iphatic), 1146 (m CAF), 654 (x CF2).
3-(Perfluorohexyl)-1-propyl 4-(2-propenyl-1-oxy)
benzoate (5)
EXPERIMENTAL
1.70 g (9.5 mmol) of (4), 3.60 g (9.5 mmol) of (2–6) and 0.15 g
(0.9 mmol) of PPy were dissolved in 60 mL of anhydrous
dichloromethane under nitrogen atmosphere. A solution of
1.97 g (9.5 mmol) of DCC in 30 mL of the same solvent was
slowly dropped at 0 ꢁC. The reaction was carried out under stir-
ring at room temperature for 3 days. The solid precipitated was
filtered off, and the organic phase was washed with 5% HCl,
5% NaHCO3 and water to neutrality. The organic phase was
dried over anhydrous Na2SO4, and the solvent was then evapo-
rated under vacuum. The crude product was purified by column
chromatography (silica gel, eluent n-hexane/ethyl acetate 3:2
v/v) to give pure (5) in 51% yield as a pale yellow liquid.
Starting Materials
The solvents were dried and distilled by conventional meth-
ods and then handled under anhydrous nitrogen atmosphere.
a,a0-Azo-bis(isobutyronitrile) (AIBN) was recrystallized from
methanol. Acrylic acid was distilled under reduced nitrogen
pressure. Acryloyl chloride was distilled under nitrogen.
4-Hydroxybenzoic acid (3), ethyl 4-hydroxybenzoate (7),
4-pyrrolidinopyridine (PPy), N,N0-dicyclohexylcarbodiimide
(DCC), allyl bromide, allyl alcohol, perfluorohexyl iodide, per-
fluorooctyl iodide, and 9-borabicyclononane (9-BBN) (0.5 M
solution in tetrahydrofuran) were purchased from Aldrich
and used without further purification.
1H-NMR (CDCl3) d (ppm) ¼ 8.0 (2H, aromatic), 7.0 (2H aro-
matic), 6.1 (1H, CH2¼¼CH), 5.4 (2H, CH2¼¼CH), 4.6 (2H,
COOCH2), 4.4 (2H, CH2OPh), 2.3–2.1 (4H, CH2CH2CF2).
Synthesis of Monomers
4-(2-Propenyl-1-oxy)benzoic acid (4)
29.88 g (0.22 mol) of (3), 26.55 (0.47 mol) of KOH, and 2.96
g (0.018 mol) of KI were dissolved in 750 mL of 80% etha-
nol. 26.56 g (0.21 mol) of allyl bromide was slowly added to
the solution, and the resulting mixture was refluxed for 3
days. The solvent was evaporated under vacuum, and the
solid residue was dissolved in water. The mixture was acidi-
fied to pH ꢀ 1, and the solid precipitated was filtered off
and thoroughly washed with water. The crude product was
purified by crystallization from methanol, giving pure (4)
FTIR (KBr film) (cmꢂ1) ¼ 3100ꢂ3050 (m CAH vinyl and aro-
matic), 1716 (m C¼¼O), 1144 (m CAF), 654 (x CF2).
3-(Perfluorohexyl)-1-propyl 4-(3-hydroxypropyl-1-oxy)
benzoate (6)
2.00 g (3.7 mmol) of (5) in 2 mL of tetrahydrofuran was added
dropwise to 7.4 mL (3.7 mmol) of a 0.5-M solution of 9-BBN in
tetrahydrofuran under nitrogen at reflux. The reaction was car-
ried out at reflux for 4 h. The crude intermediate organoborane
was oxidized by adding simultaneously 1.5 mL (49.0 mmol) of
30% H2O2 and 0.8 mL (4.8 mmol) of a 6-M solution of sodium
acetate at 0 ꢁC. The reaction mixture was kept under stirring at
room temperature overnight. The aqueous phase was saturated
with NaCl and K2CO3 and then extracted with tetrahydrofuran.
The organic phase was washed with water and then dried over
Na2SO4. The solvent was evaporated under vacuum, and the
crude product was purified by column chromatography (silica
gel, eluent n-hexane/ethyl acetate 1:1 v/v). The white solid was
further purified by crystallization from n-hexane to give pure
(6) in 69% yield (m.p. 48–50 ꢁC).
ꢁ
(m.p. 164–165 C) in 58% yield.
1H-NMR (DMSO-d6) d (ppm) ¼ 12.6 (1H, COOH), 7.9 (2H, ar-
omatic), 7.0 (2H, aromatic), 6.0 (1H, CH2¼¼CH), 5.3 (2H,
CH2¼¼CH), 4.6 (2H, CH2OPh).
FTIR (KBr pellet) (cmꢂ1) ¼ 3300ꢂ2500 (m OAH), 1685
(m C¼¼O), 1560 (m C¼¼C aromatic), 1429 and 1320 (d CAH
vinyl), 999 and 949 (c CAH vinyl).
3-(Perfluorohexyl)-1-propanol (2–6)
0.13 g (0.8 mmol) of AIBN was added incrementally over a
period of 45 min to a solution of 24.44 g (54.0 mmol) of
perfluorohexyl iodide and 4.77 g (82.0 mmol) of allyl alcohol
at 80 ꢁC under nitrogen atmosphere. The reaction was then
1H-NMR (CDCl3) d (ppm) ¼ 7.9 (2H, aromatic), 6.9 (2H, aro-
matic), 4.4 (2H, COOCH2), 4.2 (2H, CH2OPh), 3.8 (2H, CH2OH),
2.4ꢂ2.0 (6H, CH2CH2CF2, CH2CH2OH), 1.8 (1H, CH2OH).
ꢁ
carried out at 80 C for another 5 h. The volatile compounds
were removed under vacuum, and the resulting 2-iodo-3-
(perfluorohexyl)-1-propanol was dissolved in 125 mL of an-
hydrous diethyl ether. The solution was added dropwise to
50 mL (50.0 mmol) of 1 M solution of LiAlH4 in diethyl
ether under nitrogen atmosphere. The reaction mixture was
kept at room temperature overnight and then hydrolyzed
with 9 mL of water, 11 mL of 10% NaOH, and finally 9 mL
of water. After filtration of the precipitate, the solvent was
evaporated under vacuum. The crude product was purified
by column chromatography (silica gel, eluent n-hexane/ethyl
acetate 3:2 v/v), giving (2–6) as a pale yellow liquid in 49%
yield.
FTIR (KBr pellet) (cmꢂ1
)
¼
3500ꢂ3300 (m OAH),
3100ꢂ3000 (m CAH aromatic), 1714 (m C¼¼O), 1144 (m CAF),
654 (x CF2).
3-(Perfluorohexyl)-1-propyl 4-(3-acryloyloxypropyl-1-oxy)
benzoate (1–6)
A solution of 0.45 g (2.0 mmol) of DCC in 5 mL of anhydrous
dichloromethane was slowly dropped to a solution of 1.11 g
(2.0 mmol) of (6), 0.14 mL (2.0 mmol) of acrylic acid and
0.03 g (0.2 mmol) of PPy in 10 mL of CH2Cl2 under nitrogen
at 0 ꢁC. The reaction was carried out at room temperature
for 4 days. The solid precipitated was filtered off, and the or-
ganic phase was washed with 5% HCl, 5% NaHCO3 and
water and dried over anhydrous Na2SO4. The solvent was
1H-NMR (CDCl3) d (ppm) ¼ 3.8 (2H, CH2OH), 2.3 (2H,
CH2CF2), 1.9 (2H, CH2CH2OH), 1.7 (1H, CH2OH).
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4129

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
then evaporated under vacuum, and the crude product was
purified by column chromatography (silica gel, eluent n-hex-
ane/ethyl acetate 2:1 v/v) to give pure (1–6) as a pale yel-
under nitrogen atmosphere aꢁt 80 ꢁC. The reaction mixture
was kept under stirring at 80 C for another 5 h. The volatile
compounds were removed under vacuum, and the resulting
2-iodo-3-(perfluorooctyl)-1-propanol was dissolved in 125
mL of anhydrous diethyl ether. The solution was added drop-
wise to a 50 mL (50.0 mmol) of 1 M solution of LiAlH4 in
the same solvent under nitrogen atmosphere. The reaction
mixture was kept at room temperature overnight and then
hydrolyzed with 4 mL of water, 5 mL of 10% NaOH, and
finally 4 mL of water. The precipitate was filtered off, and
the solvent was evaporated under vacuum. The crude prod-
uct was purified by sublimation under high vacuum giving
ꢁ
low solid (m.p. 34ꢂ36 C) in 35% yield.
1H-NMR (CDCl3) d (ppm) ¼ 8.0 (2H, aromatic), 6.9 (2H, aro-
matic), 6.5 (1H, CH¼¼), 6.2 (1H, CH¼¼), 5.8 (1H, CH¼¼), 4.4
(4H, PhCOOCH2, CH2OPh), 4.2 (2H, CH2¼¼CHCOOCH2), 2.2
(6H, CH2CH2CF2, CH2CH2OPh).
FTIR (KBr pellet) (cmꢂ1) ¼ 3100ꢂ3050 (m CAH vinyl and
aromatic), 1718 and 1706 (m C¼¼O), 1142ꢂ1122 (m CAF),
656 (x CF2).
ꢁ
19F-NMR (CDCl3/CF3COOH) d (ppm) ¼ ꢂ5 (3F, CF3), ꢂ38
pure (2–8) as a white solid (m.p. 43ꢂ45 C) in 45% yield.
1H-NMR (CDCl3) d (ppm) ¼ 3.8 (2H, CH2OH), 2.3 (2H,
CH2CF2), 1.9 (2H, CH2CH2OH), 1.5 (1H, CH2OH).
(2F, CH2CF2), ꢂ46 to ꢂ48 (6F, CF2), ꢂ51 (2F, CF2CF3).
4-(3-Hydroxypropyl-1-oxy)benzoic Acid (9)
FTIR (film) (cmꢂ1) ¼ 3244 (m OAH), 1150 (m CAF), 658
(x CF2).
In a first step, 8.7 g (52.0 mmol) of (7) and 8.2 g (78.0
mmol) K2CO3 were dissolved in 100 mL of anhydrous 2-
butanone and a solution of 8.0 g (57.0 mmol) of 1-bromo-3-
propanol in 8.0 mL of anhydrous 2-butanone was slowly
added at reflux. The reaction mixture was kept at reflux for
48 h and then cooled down to room temperature and fil-
tered. The solvent was removed under vacuum, and the
crude product was crystallized from methanol to give pure
ethyl 4-(3-hydroxypropyl-1-oxy)benzoate (8) in 98% yield.
3-(Perfluorooctyl)-1-propyl 4-(3-acryloyloxypropyl-1-oxy)-
benzoate (1–8)
A solution of 0.61 g (3.0 mmol) of DCC in 15 mL of anhy-
drous CH2Cl2 was added dropwise to a solution of 1.42 g
(3.0 mmol) of (2–8), 0.75 g (3.0 mmol) of (10), 0.04 g (0.3
mmol) of PPy in ꢁ25 mL of anhydrousꢁCH2Cl2 under nitrogen
atmosphere at 0 C. the solution at 0 C under vigorous stir-
ring. The reaction was carried out at room temperature for 3
days. The precipitate formed was filtered off, and the organic
phase was washed with 5% HCl, 5% NaHCO3 and water, and
dried over Na2SO4. The solvent was then evaporated under
vacuum, and the crude product was purified by column chro-
matography (silica gel, eluent n-hexane/ethyl acetatꢁe 3:1
v/v) to give pure (1–8) as a white solid (m. p. 42ꢂ45 C) in
45% yield.
In a second step, 11.5 g (51.0 mmol) of (8) was added to a
solution of 4.25 g (75.0 mmol) KOH in 175 mL of ethanol
and 125 mL of water. The reaction was carried out at reflux
for 6 h. The mixture was acidified with 37% HCl to pH ꢀ 2
and extracted with CH2Cl2. The organic phase was dried over
Na2SO4, and the solvent was evaporated under vacuum. The
crude product was purified by crystallization from methanol
to give pure (9) as a white solid in 97% yield.
1H-NMR (CDCl3) d (ppm) ¼ 7.9 (2H, aromatic), 7.0 (2H, aro-
matic), 4.1 (2H, CH2OPh), 3.5 (2H, CH2OH), 1.8 (2H, CH2CH2OH).
1H-NMR (CDCl3) d (ppm) ¼ 8.0 (2H, aromatic), 6.9 (2H, aro-
matic), 6.5 (1H, CH¼¼), 6.1 (1H, CH¼¼), 5.8 (1H, CH¼¼), 4.4
(4H, PhCOOCH2, CH2OPh), 4.1 (2H, CH2¼¼CHOOCH2), 2.2 (6H,
CH2CH2CF2, CH2CH2OPh).
4-(3-Acryloyloxypropyl-1-oxy)benzoic Acid (10)
5.50 g (28.0 mmol) of (9), 5.68 g (56.0 mmol) of triethyl-
amine and 5 mg of 2,6-dit.butyl-4-cresol were dissolved in
150 mL of anhydrous tetrahydrofuran. 3.30 g (37.0 mmol) ꢁof
acryloyl chloride was added dropwise to the solution at 0 C
under vigorous stirring. The reactionꢁ mixture was kept at
room temperature for 16 h and at 45 C for 3 h. The solvent
was removed under vacuum, and the solid residue was dis-
solved in CHCl3 and washed with 5% HCl and water. The or-
ganic phase was dried over Na2SO4 overnight. The solvent
was removed under vacuum and the crude product was
purified by column chromatography (silica gel, eluent n-hex-
ane/ethyl acetatꢁe 1:1 v/v) to give pure (10) as a white solid
(m.p. 122ꢂ124 C) in 30% yield.
FTIR (KBr pellet) (cmꢂ1) ¼ 3076 (m CAH vinyl and aro-
matic), 1712 and 1711 (m C¼¼O), 1172 (m CAF), 652 (x CF2).
19F-NMR (CDCl3/CF3COOH) d (ppm) ¼ ꢂ6 (3F, CF3), ꢂ38
(2F, CH2CF2), ꢂ46 to ꢂ49 (10F, CF2), ꢂ51 (2F, CF2CF3).
Synthesis of Polymers
p(1–6)
0.29 g (0.48 mmol) of monomer (1–6), 3 mg of AIBN and 3
mL of anhydrous benzene were introduced into a Pyrex vial
and degassed by several freeze-thaw pump cycles. The poly-
merization was carried out at 60 ꢁC for 48 h. The polymer
was purified by several precipitations into methanol from
chloroform/1,1,2-trichlorotrifluoroethane solutions giving a
powdery white polymer in 70% yield.
1H-NMR (CDCl3) d (ppm) ¼ 8.0 (2H, aromatic), 6.9 (2H, aro-
matic), 6.4 (1H, CH¼¼), 6.1 (1H, CH¼¼), 5.8 (1H, CH¼¼), 4.4
(2H, COOCH2), 4.1 (2H, CH2OPh), 2.2 (2H, CH2CH2OPh).
3-(Perfluorooctyl)-1-propanol (2–8)
0.06 g (0.4 mmol) of AIBN was added incrementally over a
period of 45 min to a solution of 13.64 g (25.0 mmol) of
perfluorooctyl iodide and 2.17 g (37.5 mmol) of allyl alcohol
1H-NMR (CDCl3) d (ppm) ¼ 7.9 (2H, aromatic), 6.8 (2H, aro-
matic), 4.3 (4H, COOCH2), 4.0 (2H, CH2OPh), 2.2 (6H,
CH2CH2CF2, CH2CH2OPh), 1.7ꢂ1.2 (3H, CH2CH).
4130
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
19F-NMR (CDCl3/CCl2FCClF2/CF3COOH) d (ppm) ¼ ꢂ14 (3F,
CF3), ꢂ47 (2F, CF2CH2), ꢂ54 to ꢂ56 (6F, CF2), ꢂ59 (2F,
CF2CF3).
camera. The Ni-filtered CuKa radiation was used (k ¼
1.54 Å). Polymer powder samples were studied from room
temperature up to the temperature of disappearance of the
low-angle first-order diffraction signal. The length l1 of the
mesogenic side chain group and the thickness l2 of the poly-
mer main chain were calculated from the known bond angles
and lengths, assuming the repeat unit to be in its fully
extended conformation with the fluorocarbon segment in a
twisted zigzag conformation of span p ¼ 2.59 Å.38 The length
L ¼ 2l1 þ l2 for the repeat unit with two side chain groups
pointing to opposite directions of the polymer chain was used
to evaluate a maximum tilt angle / in the smectic mesophases
with an experimental interlayer spacing d (d ¼ Lcos/).
FTIR (KBr pellet) (cmꢂ1) ¼ 3100ꢂ3050 (m CAH aromatic),
2962ꢂ2850 (m CAH aliphatic), 1714 and 1712 (m C¼¼O),
1144 (m CAF), 652 (x CF2).
p(1–8)
0.50 g (0.7 mmol) of monomer (1–8), 6 mg of AIBN and
3 mL of anhydrous benzene were introduced into a Pyrex
vial and degassed by several freeze-thaw pump cycles. The
polymerization was carried out at 60 ꢁC for 48 h. The poly-
mer was purified by several precipitations into methanol
from chloroform/1,1,2-trichlorotrifluoroethane solutions giv-
ing a powdery white polymer in 85% yield.
Several exposures were taken so as to measure the strongest
and the weakest reflections. Experimental amplitudes, am, of
diffraction for the different orders of reflection from the smec-
tic layers were corrected for the Lorentz-polarization factor.
1H-NMR (CDCl3) d (ppm) ¼ 7.9 (2H, aromatic), 6.8 (2H, aro-
matic), 4.3 (4H, COOCH2), 3.9 (2H, CH2OPh), 2.1 (6H,
CH2CH2CF2, CH2CH2OPh), 1.6ꢂ1.2 (3H, CH2CH).
Taking into account the centrosymmetry of the mesophase
19F-NMR (CDCl3/CCl2FCClF2/CF3COOH) d (ppm) ¼ ꢂ14 (3F,
CF3), ꢂ47 (2F, CF2CH2), ꢂ54 to ꢂ56 (10F, CF2), ꢂ59 (2F,
CF2CF3).
structure, the electron density profile q(z) along the layer
normal was given by eq 139
:
X
FTIR (KBr pellet) (cmꢂ1) ¼ 3080ꢂ3050 (m CAH aromatic),
2962ꢂ2860 (m C(H aliphatic), 1714 and 1712 (m C¼¼O), 1150
(m CA F), 658 (x CF2).
qðzÞ ¼
½am cosðm2pz=dÞꢃ
(1)
m¼1
where am is the amplitude of mth reflection. Being not possi-
ble to measure the absolute intensity and amplitude of the dif-
ferent reflection orders, am were obtained by normalizing the
intensity of each order to the respective first order reflection.
The signs of the coefficients am were also unknown; it was
therefore possible to combine them in 2m permutations lead-
ing to 2m different electron density profiles.40
Polymer Films
The polymer films were prepared by casting a 5 wt % solu-
tion of the polymer in trifluorotoluene or 1,1,2-trichlorotri-
fluoroethane on glass cover-slips and letting the solvent to
evaporate slowly at room temperature. The films were
annealed at 10 ꢁC below the isotropization temperature of
the polymer for 48 h and then slowly cooled to room tem-
perature before the measurements (thickness 100ꢂ150 lm).
Tapping-mode atomic force microscopy (TM-AFM) meas-
urements were performed by imaging samples with a
Digital Instruments Nanoscope IIIa with
a Multimode
Characterization
Head. Topographic and phase contrast imaging experi-
ments were performed on 1 ꢄ 1 lm2 regions. Nanoprobe
cantilevers (225 lm, Digital Instrument) were utilized.
Phase contrast AFM was carried out at set-point ampli-
tude to cantilever free-oscillation amplitude (Asp/A0)
ratios higher than 0.8, which is generally regarded as low
tapping force. The root-mean-square roughness (RMS)
was calculated by the software as (Ri Zi2/N)0.5, where Zi
is the height value and N the number of points measured
on the surface analyzed.
1H and 13C spectra were recorded on Varian Gemini VRX
200. 19F spectra were recorded on Varian Gemini VRX 300.
Light scattering measurements were performed with
a
HeꢂNe laser source (k ¼ 633 nm) using a Sofica 4200 pho-
togoniometer. The refractive index increments were also
measured with a KMX 16 laser differential refractometer at
the same wavelength.
Differential scanning calorimetry (DSC) measurements were
ꢁ
performed with a Mettler DSC-30 instrument (10 C/min scan-
Contact angles h were measured with a Rame`-Hart 230 goni-
ometer using 4 lL drops of water and n-alkanes (heptane,
octane, decane, dodecane, and hexadecane) as interrogating
liquids (purity > 99%). The values of h were used to evalu-
ate the solid surface tension cS of the polymer films follow-
ing two different methods.
ning rate). The clearing or isotropization transition temperature
(Ti) was taken at the maximum temperature in the DSC
enthalpic peak of the second heating cycle. The glass transition
temperature (Tg) was set at the half-devitrification temperature.
Polarizing optical microscopy observations were performed
on polymer powder sandwiched between glass slides. A
Reichert-Jung Polyvar microscope equipped with a program-
mable Mettler FP52 heating stage was used. The birefringent
melts were analyzed on heating up to and on cooling from Ti
In the additive component method of Owens and Wendt41
and Kaelble42 the solid surface tension
ꢁ
cS ¼ cdS þ cpS
(2)
at a scanning rate of 3–10 C/min.
Wide-angle X-ray diffraction (WAXD) patterns were recorded
with a home-made diffractometer equipped with a flat film
combined with the Young’s equation yields
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4131

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Routes for the synthesis
of the acrylic monomers and the
respective polymers.
h
i
cLð1 þ cos hÞ ¼ 2 ðcdcdÞ þ ðcSpcLpÞ
(3)
1=2
1=2
propyl segment, 6 and 8 CF2 groups, respectively. The syn-
thesis of the two monomers was carried out following two
different routes from easily available, commercial products
(Scheme 1).
S
L
where cd and cp are the dispersion and the polar compo-
nents, respectively, of the solid, cS, and liquid, cL, surface ten-
sions; vapor adsorption is assumed to be negligible. By
measuring the contact angles of at least two liquids, one po-
lar and one nonpolar, on the same surface two equations can
be obtained from which the two unknowns (cdS and cSp) of
the solid can be calculated. The total surface energy of the
polymer is computed as the sum of the cdS and cSp terms.
Monomer (1–6) was prepared in four steps. In a first step,
4-hydroxybenzoic acid (3) was reacted with allyl bromide.
The resulting 4-substituted benzoic acid (4) was reacted
with 3-(perfluorohexyl)-1-propanol (2–6) to yield the respec-
tive benzoate ester (5) using dicyclohexylcarbodiimide (DCC)
as a condensing agent and 4-pyrrolidinopyridine (PPy) as a
nucleophilic activator. Then (5) was reacted with 9-borabicy-
clononane (9-BBN) and the intermediate organoborane was
oxidized with alkaline hydrogen peroxide to give the corre-
sponding alcohol (6). In a fourth step, (6) was converted to
the desired 3-(perfluorohexyl)-1-propyl 4-(3-acryloyloxy-
propyl-1-oxy)benzoate (1–6) monomer by esterification reac-
tion with acrylic acid in the presence of DCC and PPy.
The equation-of-state method of Li and Neumann43 involves:
2
cos h ¼ ꢂ1 þ 2ðcS=cLV
Þ
1=2 exp½ꢂbðcLV ꢂ cSÞ ꢃ
(4)
by which, for a given set of liquid surface tensions cLV and h
measured on one and the same solid surface, the constant b
and solid surface tension cS values can be determined by a
least-square analysis technique.
Monomer (1–8) was prepared in three steps. In a first step,
ethyl 4-hydroxybenzoate (7) was etherified with 3-bromo-
propan-1-ol under Williamson reaction conditions, and the
4-substituted benzoate intermediate was hydrolyzed to give
the corresponding benzoic acid (9). Then, reaction of (9)
with acryloyl chloride gave the acrylate (10). In a third step,
RESULTS AND DISCUSSION
Synthesis
The novel acrylic monomers (1–6) and (1–8) differed for the
length of the fluorocarbon chain in the 3-(perfluoroalkyl)-
4132
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
that cleared upon further heating to the isotropization tem-
perature Ti. However, no specific optical textures were noted
that could help identify the nature of the mesophases. The
viscosity of the high molar mass polymers prevented the de-
velopment of the textures associated with the various
mesophases.
The phase transition temperatures, with relevant enthalpies, of
the polymers were determined by differential scanning calorim-
etry (DSC) measurements or by wide-angle X-ray diffraction
(WAXD) investigations. Above the glass transition temperature
Tg, both polymers exhibited at least two phase transitions
(Fig. 1), suggesting the occurrence of a polymorphic behavior
(Table 1). In particular, p(1–6) formed a sequence of two meso-
phases between 17 ꢁC (Tg) and 127 ꢁC (Ti);ꢁp(1–8) gave rise to
three successive mesophases between 48 C (Tg) and 166 ꢁC
(Ti). Furthermore, a mesophase occurred at room temperature,
above Tg, in p(1–6), whereas it was frozen in a glassy state,
below Tg, in p(1–8). The increase in Tg in the latter polymer is
consistent with the reduced flexibility of the polyacrylate main
chain imposed by incorporation of the longer, rigid rod-like per-
fluoroalkyl chain in the side group. The higher aspect ratio of
the fluorinated mesogenic unit in the side chain also accounts
for the broader mesophase range with a higher Ti in p(1–8).
The onset of different mesophases with decreasing degree of
order with rising temperature was demonstrated by our inves-
tigations by X-ray diffraction. No mesophase was formed in ei-
ther monomer 1–6 or 1–8. Thus, liquid crystallinity was stabi-
lized in polymers only, where the anisometric side groups were
interconnected along the polymer backbone.
FIGURE 1 DSC traces of polymer p(1ꢂ8) (scan rate 10 ꢁC/min).
esterification of (10) with 3-(perfluorooctyl)-1-propanol (2–
8) in the presence of DCC and PPy led to the desired 3-(per-
fluorooctyl)-1-propyl 4-(3-acryloyloxypropyl-1-oxy)benzoate
(1–8) monomer.
The fluorinated alcohols (2–6) and (2–8) used in the synthe-
sis are not commercially available compounds and were pre-
pared44 via the regioselective, azobis(isobutyronitrile)-
(AIBN)-initiated radical addition of the perfluoroalkyl iodide
of selection to the double bond of allyl alcohol and subse-
quent reduction of the fluorinated iodoalcohol intermediate.
These perfluoroalkylpropyl precursors were designed and
preferred to the most common perfluoroalkylethyl precur-
sors for incorporation into anisometric aromatic units, since
the longer aliphatic segment was expected to enhance intra-
molecular phase segregation of the side chain core of the ac-
rylate monomer, thereby increasing its mesogenic character.
A trimethylene spacer segment was also used to connect the
side chain to the acrylate moiety of the monomer, and even-
tually to the acrylate backbone of the derived polymer, to
introduce sufficient conformational freedom enabling an or-
dered assembly of the side groups in a mesophase structure
at accessible temperatures.
X-Ray Diffraction Studies
To identify the mesophases, X-ray diffraction patterns of
the two polymers were recorded on powder samples as a
function of temperature. The structural parameters for
the encountered mesophases are reported in Table 2. For
p(1–8), the lower temperature diagrams showed one sharp
wide-angle reflection pointing to the presence of a structure
of the hexatic type with a pseudohexagonal lattice of side aH
¼ 5.7 Å and an available average surface (S) per fluorinated
side chain of ꢀ28 Å2 (Fig. 2, left). Three low-angle Bragg
reflections with periodicities in the ratio 1:3:4 indicated
a smectic (Sm) mesophase with an interlayer spacing d ¼
49.8 Å. Comparison of the measured d with the calculated
length L (L ¼ 55 Å) of a structural motif consisting of two
antiparallel side groups pointing to opposite directions above
and below the polyacrylate main chain46,47 suggests the side
groups to be arranged in a double layer structure, either
The polymerization reactions of the acrylate monomers, (1–
6) and (1–8), to the respective polyacrylates, p(1–6) and
p(1–8), were performed with free radical initiation (AIBN,
60 ꢁC) in benzene solution (yields 70–85%). Both polymers
were insoluble in common organic solvents, but soluble in
fluorinated solvents such as trifluorotoluene and 1,1,2-tri-
chlorotrifluoroethane, and their mixtures with chloroform.
Because of this, molar mass and dispersity of the polymers
could not be fully characterized by size exclusion chromatog-
raphy. A weight average molar mass Mw of 70,000 g/mol
was evaluated by light scattering measurements for p(1–6)
only. Similar values of Mw were previously found for other
perfluoroalkyl polyacrylates,45 which confirms that such fluo-
rinated acrylates can be conveniently free-radically polymer-
ized to relatively high polymers.
TABLE 1 Transition Temperatures (in 8C) (Enthalpies in J/g)a
for Polymers p(1–6) and p(1–8)
Polymer
Transition Temperature (Enthalpy)
p(1–6)
p(1–8)
a
g 17 SmF2 (or SmI2) 113 (1.1) SmC2 127 (0.7) iso
g 48 SmI2 74 (8.4) SmF2 95 (nd)b SmC2 166 (0.7) iso
Mesophase Behavior of the Polymers
Polarizing optical microscopy observations revealed the for-
mation of a birefringent melt for both p(1–6) and p(1–8)
By DSC, 10 ꢁC/min heating rate. g: glassy; SmI2, SmF2, and SmC2:
double layer SmI, SmF, and SmC; iso: isotropic liquid.
b
Not detected; recorded by WAXD only.
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4133

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Structural Parameters of the Different Smectic
Mesophases of Polymers p(1–6) and p(1–8)
The diffraction patterns of the two high-order smectic
phases are consistent with the presence of SmI2 and SmF2
mesophases. In both cases, the mesogens are organized over
a pseudohexagonal lattice, but tilted toward the apex and
the side of the hexagon in the SmI and SmF, respectively.
There is a greater in-plane correlation length in the SmI than
in the SmF phase.50 However, the subtle differences in the
tilt direction of the molecules in the two mesophases make
it very difficult to recognize them, unless they are formed
successively in a polymorphic polymer.51 In p(1–8) the
phase transition SmI-SmF was associated with a decreased
in-plane correlation and a shortened layer spacing.
Mesophase
SmI2
Parameter
p(1–6)
p(1–8)
˚
L (61 A)
50
55
˚
d (60.3 A)
49.8
5.7
24
˚
aH (60.1 A)
/ (61ꢁ)
a
˚
SmF2
d (60.3 A)
41.7
5.7
33
48.1
5.7
28
˚
aH (60.1 A)
/ (61ꢁ)
˚
SmC2
d (60.3 A)
38.7
5.1
39
44.2
5.0
36
˚
D (60.1 A)
Another significant modificatiꢁon of the X-ray diffraction pat-
tern was observed above 95 C (Fig. 2 right). The low-angle
reflections, with a periodicity ratio of 1:3, indicated d ¼ 44.2
Å corresponding to / ¼ 36ꢁ. A wide-angle diffuse halo was
due to a mesophase lacking long-range in-plane correlation
between the side chains (average intermolecular distance
D ꢀ 5.0 Å, S ꢀ 25Å2), such as in a SmC2 phase.
/ (61ꢁ)
a
SmF2 or SmI2 for p(1–6).
tilted or interdigitated (Fig. 3). However, the terminal CF3
groups are rather bulky with a van der Waals volume of the
equivalent hemisphere of 42.6 Å3 (compare with 16.8 Å3 for
the CH3 group)48,49 and a large cross-section area of ꢀ23 Å2
as estimated by molecular models. For the given S, there
would be an excessive steric hindrance for two antiparallel
fluorinated tails to overlap within the layer of an interdigi-
tated smectic phase, particularly in densely crowded poly-
mers such as poly(acrylate)s. By contrast, an efficient space
filling can be achieved by tilting the fluorinated side chains
in an end-to-end arrangement of a double layer smectic
structure. A maximum tilt angle / of the mesogen long axis
to the smectic plane normal of 24ꢁ was evaluated (Fig. 3). It
is not known whether the mesogens had a synclinic or anti-
clinic correlation along the normal to the smectic planes.
p(1–6) exhibited temperature-dependent X-ray diagrams
similar to those of the two higher temperature mesophases
of p(1–8). Accordingly,
a SmF2 (or SmI2) mesophase
occurred at temperatures lower than 100 ꢁC and a SmC2
mesophase between 100 ꢁC and the clearing temperature
(Table 2).
For both polymers, d decreased, and apparently / increased,
in passing from the high-order smectic mesophase to the
low-order smectic mesophase. Although this particular fea-
ture has already been noted for fluorinated polyacrylates,45
it is actually rather uncommon for liquid crystals, in which
normally either less tilted or orthogonal mesophases are ori-
ginated at higher temperatures above tilted mesophases, the
most frequent and best known of such phase transitions
being the SmC-SmA transition with rising temperature.
Shortening of d was due to a small shrinkage of the smectic
layers probably because of conformational changes in the
perfluorinated chain groups and/or the spacer segments at
the higher temperatures. The layer thickness remained con-
stant all over the range of existence of each smectic
A variation in the diffraction pattern was revealed by heating
the sample up to 95 ꢁC with the appearance of two reflec-
tions in the low-angle region with a periodicity ratio 1:3
(d ¼ 48.1 Å) and a wide angle reflection indicative of a pseu-
dohexagonal lattice (aH ¼ 5.7 Å, S ꢀ 28 Å2). The comparison
of d with L evidenced that the side chains were organized in
a tilted, double layer structure with / ¼ 28ꢁ.
FIGURE 2 X-ray diffraction pat-
terns of p(1ꢂ8) at 65 ꢁC (left) and
at 160 ꢁC (right).
4134
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 3 Schematic of a double
layer, tilted smectic mesophase
with pseudohexagonal packing
of mesogens.
mesophase, a decrease in d being detected at the phase tran-
sition temperatures only. Examples of polymorphism in the
liquid crystalline state of fluorinated polymers are rare in
the literature.35,45,52
three reflection orders of amplitude a1 ¼ 1.00, a3 ¼ 0.32,
and a4 ¼ 0.15 (a2 ¼ 0), which resulted in eight density pro-
files. Only four density profiles (combinations of signs q
,
ꢂþꢂ
q
, q
, and q
) are shown in Figure 4, the four sym-
ꢂþþ ꢂꢂþ
ꢂꢂꢂ
metrical ones being omitted for brevity.
Electron Density Profiles
The q(z) profiles (e)ꢂ(h) (not shown) exhibited a central
minimum for the fluorinated chains (ꢀ0.3 < z/d < ꢀ0.7),
for which by contrast the expected electron density (q0) was
maximum (q0 ¼ 16 e/Å). The profiles (c) and (d) were also
discarded because they showed two minima for the polymer
main chains (z/d ¼ 0 and 1), for which q0 ¼ 9 e/Å was cal-
culated. The last two profiles (a) and (b) appeared to be
It was not possible to draw oriented fibers of the polymers
from their mesophase states, and the nature of the tilted mes-
ophase could not be confirmed on well-aligned specimens.
Further support to the formation of tilted mesophases was
provided by an evaluation of the electron density profiles q(z)
along the layer normal of the smectic mesophases.40
both physically acceptable, but (b) (sign combination q
)
As one example we discuss the electron density profiles
derived from the intensities of the low-angle reflections in
the smectic I mesophase of p(1–8). Analogous considerations
apply to the other mesophases of both polymers. There were
ꢂþþ
was preferred as it showed two minima corresponding to
the methylene spacers (z/d ꢀ 0.1 and 0.9; q0 ¼ 6 e/Å),
besides an absolute maximum for the fluorinated tails and
FIGURE 4 Electron density profiles for the smectic I phase of p(1ꢂ8), at room temperature on cooling from the isotropic melt, for
combinations of signs: (a) q , (b) q , (c) q , and (d) q . The four symmetrical profiles are not shown.
ꢂþꢂ
ꢂþþ
þꢂꢂ
ꢂꢂꢂ
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4135

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 6 cosh versus cLV trends for p(1–6) (l) and p(1–8) (^)
with best fit of the LiꢂNeumann equation of state (b ¼ 3.211 ꢄ
10ꢂ4 (m/mN)2 for p(1–6) and b ¼ 1.450 ꢄ 10ꢂ4 (m/mN)2 for p(1–8)).
FIGURE 5 TM-AFM imaging of a polymer film of p(1–8).
secondary, comparatively weak maxima corresponding to the
hydrocarbon main chains. Furthermore, the central maxi-
mum in q(z) was not sufficiently intense to account for
interdigitation of two, even partly, overlapping fluorinated
chains. Therefore, the side mesogenic groups were arranged
in a double layer, tilted smectic mesophase for which /
could be estimated (Table 2).
cLV of the n-alkanes. One can also note that the contact angle
values depended on the length of the perfluorinated tail
incorporated in the side chain, the values of h being higher
for the perfluorooctyl containing films.
It is common practice in surface science to use contact
angles data for the evaluation of solid surface tension. How-
ever, the correlation between h and cS is still a controversial
question and none of the various methods proposed are
generally accepted.53,54 Therefore, we followed two concep-
tually different approaches to evaluating cS from h, namely
an additive component approach and an equation-of-state
approach.
Wettability Studies
To evaluate the effect of surface structure and ordering on
surface energy, contact angles h of the polymer films were
measured using a range of n-alkanes (C7, C8, C10, C12, and
C16) as apolar liquids and water as polar liquid. Prior to
measurements, the cast and thermally annealed films were
analyzed by tapping-mode atomic force microscopy (TM-
AFM). The film surfaces were relatively smooth (RMS <
ꢀ100 nm) and displayed no regular ordered topographies
(Fig. 5). This made it possible to compare the values of h
found with the different solvents.
The former method was after Owens, Wendt, and Kaelble
(OWK)41,42 that relies on the Fowkes’s model55 assuming the
total surface energy to be the sum of different interaction
components (van der Waals dispersive, dipole, hydrogen
bonding, etc.) at the liquid–solid interface and postulating a
geometric mean relationship for both of the solid–liquid and
liquid–liquid interfacial tensions. cS is computed as the sum
of dispersion and polar components, cdS and cSp, respectively
(eq 2). The latter method followed the equation of state of Li
and Neumann (LN) (eq 4).43 This is essentially based on a
modification of the Berthelot’s combining rule,56 that states
the potential energy parameter of unlike-pair molecular
interactions to be the geometric mean of the potential
energy parameters of like-pair molecular interactions. The
LN approach provides cS by fitting the cosh values found
with a set of probing liquids of varied surface tension cLV
The values of h with water and n-hexadecane are conven-
tionally used to estimate qualitatively hydrophobicity (hw
>
ꢀ90ꢁ) and lipophobicity (hhd > ꢀ60ꢁ), respectively. The fluo-
rinated polyacrylates showed large contact angles with all
the interrogating liquids, exhibiting distinct hydrophobic (hw
ꢅ 105ꢁ) and lipophobic (hhd ꢅ 74ꢁ) properties (Table 3).
This twofold character is typical of fluorinated polymers, as
opposed to most other polymers that are hydrophobic, but
not lipophobic at the same time.
For both p(1–6) and p(1–8) films a continuous increase in
contact angle was detected with increasing surface tension
TABLE 3 Contact Angles ha and Solid-Surface Tension cS for Polymers p(1–6) and p(1–8)
Polymer
hw (ꢁ)
hh (ꢁ)
ho (ꢁ)
hd (ꢁ)
hdd (ꢁ)
hhd (ꢁ)
cpS (mN/m)
b
cOSWK (mN/m)
cLSN (mN/m)
b
cdS (mN/m)
b
c
p(1–6)
p(1–8)
a
105
113
53
58
57
63
59
66
65
67
74
76
12.7
11.5
2.0
0.8
14.7
12.3
13.5
12.0
Measured with water, n-heptane, n-octane, n-decane, n-dodecane, and n-hexadecane.
Calculated with the Owens–Wendt–Kaelble method: cdS dispersion component, cSp polar component.
Calculated with the Li–Neumann method.
b
c
4136
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
(Fig. 6). Values of the constant b narrowly scattered around
the average value of 1.234 ꢄ 10ꢂ4 (m/mN)2 have been
reported in the literature.54
cosane (C20F42) with an hexagonal closed array of CF3 groups
on the surface.62 Liquid-crystalline surface structures are also
considered more stable to surface reconstruction upon ageing
in different conditions than amorphous surface structures.4,9
The introduction of a mesogenic core, such as the perfluor-
oalkyl benzoate core, contributes to the organization and sta-
bilization of the fluorinated chains at the surface of the films
of p(1–6) and p(1–8).
The values of cS calculated by the two independent
approaches agreed quite well with each other, demonstrating
a low surface energy of the polymer films (Table 3). The dis-
persive component overwhelmed the associated polar compo-
nent cpS in determining the total surface tension, as the fluori-
nated surfaces experienced dispersion forces but prevented
polar interactions. Both cdS and cpS were lower for p(1–8) than
for p(1–6). The longer perfluorooctyl chains induce a more
effective surface segregation at the air–polymer interface,
which would account for the lower values of surface energy.
CONCLUSIONS
New polyacrylates carrying a spaced perfluoalkylpropyl ben-
zoate side group of different length (6 and 8 CF2 groups)
were synthesized. Although relatively long perfluoralkyl
chains are per se mesogenic components of liquid crystalline
polymers, their tendency to mesophase formation was
greatly reinforced when linked to the phenyl ring of a benzo-
ate core. The nature and polymorphism of the mesophases
depended on the length of the perfluoroalkyl chain and
changed from high-order to low-order structures with
increasing temperature up to isotropization.
Surface micro- and nanophase segregation is a specially rele-
vant phenomenon in thin films of fluorinated polymers. Pref-
erential migration to the outermost surface in fact occurs to
minimize the surface and interface energies of the system and
gives rise to enrichment of fluorine atoms in the surface phase
with respect to the depleted bulk phase.57 Gradient chemical
structures have been proven by element sensitive depth profil-
ing, for example, by X-ray photoelectron spectroscopy (XPS)
and near-edge X-ray fine absorption structure spectroscopy
(NEXAFS); for very recent investigations see.58,59 Further-
more, the often contrasting tendencies for liquid crystalline
polymers to mesophase ordering and to structure and mor-
phology formation result in assemblies with order and orien-
tation at different length scales from the bulk to the surface of
the films.35,60 Polymers carrying perfluoroalkylethyl side
groups have been shown to self-organize in liquid crystalline
surface structures, where the rodlike perfluorinated chains
were stretched outwards at the polymer-air interface.5,61 The
NEXAFS orientational order parameter increased with length
of the perfluoroalkyl segments (from 4 to 8 CF2 groups). In
general, the surface had a higher degree of order than the
bulk, independent of the bulk phase, and a liquid crystalline
bulk phase caused a higher surface order than an isotropic
bulk phase. More importantly for the sake of our discussion, a
correlation was found between the increasing order parame-
ter and the decreasing surface energy at room temperature.61
The segregation of the CF3 terminal groups of the fluoroalkyl
segment, which is responsible for the low surface energy,62
was enhanced by the orientation of the fluoroalkyl side
chains.63 Thus, the bulk phase appeared to ultimately deter-
mine the achievable surface order and the surface energy
associated with it.61
The existence of a mesophase at room temeprature was
related with the occurrence of both hydrophobic and lipo-
phobic properties. The low wettability of fluorinated polymer
surfaces is generally due to the surface segregation of the
low surface tension fluorinated moieties. However, it may be
further diminished by orientation and order of the fluo-
roalkyl mesogens residing in a smectic mesophase at the
polymer–air interface. We suggest the high molecular order
of the bulk mesophase to be transferred to the surface meso-
phase. A correlation between bulk order and surface order
has been proposed for poly(perfluoroalkyl methacrylate)s,61
but basically nothing is known for fluorinated polymers
where more complex, polymorphic structures exist. Confor-
mational freedom introduced by flexible segments spacing
the mesogenic core from the polymer backbone is another
parameter that can govern mesophase structure and degree
of order of the polymers.
The nonpolar and ordered nature of perfluoroalkyl liquid crys-
talline surfaces makes them potentially useful in a wide range
of technological applications of inert, nonwetting films from
photonics and optoelectronics to medicine and biology. We are
interested in thin films for alignment layers of ferroelectric/
antiferroelectric liquid crystals in electrooptical devices64 and
for nonbiocidal, nontoxic coatings with antibiofouling per-
formance in the marine and freshwater environments.65
The low wetting properties of the films of p(1–6) and p(1–8)
derive from surface segregation of the perfluorinated tails,
that can be enhanced by their anisotropic orientation in a liq-
uid crystalline surface structure. The lower cS evaluated for
p(1–8) is in agreement with the stronger mesogenic character
of the longer perfluorooctyl chain and its better orientation.
We propose that the high order of the bulk mesophase, for
example the close-packed, pseudo-hexagonal SmI2 mesophase
of p(1–8), is sustained at the surface mesophase and favors
lowering of the surface free energy. Note that the lowest value
of cS reported in the literature is possibly that evaluated (cS ¼
6.7 mN/m) for epitaxially grown crystallites of n-perfluoroei-
The work was funded by the EU Framework 6 Integrated Pro-
ject ‘AMBIO’ (Advanced Nanostructured Surfaces for the Con-
trol of Biofouling) and the Italian MiUR (fondi PRIN).
REFERENCES AND NOTES
1 Volkov, V. V.; Plate´, N. A.; Takahara, A.; Kajiyama, T.; Amaya,
M.; Murata, Y. Polymer 1992, 33, 1316.
2 Percec, V.; Lee, M. J. Macromol Sci Pure Appl Chem 1992,
A29, 723.
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4137

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
3 Krupers, M.; Moller, M. Macromol Chem Phys 1997, 198,
29 Nguyen, H. T.; Sigaud, G.; Achard, M. F.; Hardouin, F. T.;
¨
2163.
Twieg, K.; Betterton, R. Liq Cryst 1991, 10, 389.
4 Xiang, M.; Li, X.; Ober, C. K.; Char, K.; Genzer, J.; Sivaniah,
30 Liu, H.; Nohira, H. Liq Cryst 1997, 22, 217.
E.; Kramer, E. J.; Fischer, D. A. Macromolecules 2000, 33, 6106.
31 Chen, B. Q.; Yang, Y. G.; Wen, J. X. Liq Cryst 1998, 24, 539.
5 Li, X.; Andruzzi, L.; Chiellini, E.; Galli, G.; Ober, C. K.;
Hexemer, A.; Kramer, E. J.; Fischer, D. A. Macromolecules
2002, 35, 8078.
32 Taffin de Givenchy, E.; Guittard, F.; Bracon, F.; Cambon, A.
Liq Cryst 1999, 26, 1371.
33 Guittard, F.; Taffin de Givenchy, E; Geribaldi, S; Cambon, A
6 Hartmann, P. C.; Collet, A.; Viguier, M.; Blanc C. J Fluorine
J Fluorine Chem 1999, 100, 85.
Chem 2004, 125, 1909.
34 Muthukumar, M.; Ober, C. K.; Thomas, E. L. Science 1997,
7 Ragnoli, M.; Pucci, E.; Bertolucci, M; Gallot, B; Galli, G. J
277, 1225.
Fluorine Chem 2004, 125, 283.
35 Al-Hussein, M.; Se´ re´ ro, Y.; Konovalov, O.; Mourran,
8 Martinelli, E.; Glisenti, A.; Gallot, B.; Galli, G. Macromol
A.; Moller, M.; de Jeu, W. H. Macromolecules 2005, 38,
¨
Chem Phys 2009, 210, 1746.
9610.
9 Caillier, L.; Taffin de Givenchy, E.; Geribaldi, S.; Guittard, F. J
36 Hikita, M.; Tanaka, K.; Nakamura, T.; Kajiyama, T.; Takahara,
Mater Chem 2008, 18, 5382.
A. Langmuir 2004, 20, 5304.
10 Mahler, W.; Guillon, D.; Skoulios, A. Mol Cryst Liq Cryst
37 Wang, J.; Mao, G.; Ober, C. K.; Kramer, E. J. Macromole-
1985, 2, 111.
cules 1997, 30, 1906.
11 Viney, C.; Twieg, R. J.; Russel, T. P.; Depero, L. E. Liq Cryst
38 Davidson, T.; Griffin, A. C.; Wilson, L. M.; Windle, A. H. Mac-
1989, 5, 1783.
romolecules 1995, 28, 354.
12 Viney, C.; Twieg, R. J.; Gordon, B. R.; Rabolt, J. F. Mol Cryst
39 Gudkov, V. A.; Kristallogr 1984, 29, 529; ibidem 1984, 29,
Liq Cryst 1991, 198, 285.
1122.
13 Wilson, L. M. Macromolecules 1995, 28, 325.
14 Napoli, M. J Fluorine Chem 1996, 79, 59.
40 Davidson, P.; Levelut, A. M.; Achard, M. F.; Hardouin, F. Liq
Cryst 1989, 4, 561.
15 Semenov, A. M.; Vasilenko, S. V. Sov Phys JEPT 1986, 63,
41 Owens, D. K.; Wendt, R. C. J Appl Polym Sci 1969, 13,
70.
1741.
16 Bunn, C. W.; Howells, E. R. Nature 1954, 174, 549.
42 Kaelble, D. H. J Adhesion 1970, 2, 66.
17 Russell, T. P.; Rabolt, J. F.; Twieg, R. J.; Siemens, R. L.;
43 Li, D.; Neumann, A. W. J Colloid Interf Sci 1992, 148,
Farner, B. L. Macromolecules 1986, 19, 1135.
190.
18 Ropers, M. H.; Ste´be´, M. J.; Schmitt, V. J. Phys Chem B
44 Ren, Y.; Lodge, T. P.; Hillmyer, M. A. Macromolecules 2001,
1999, 103, 3468.
34, 4780.
19 Lester, C. L.; Guymon, A. C. Macromolecules 2000, 33, 5448.
45 Andruzzi, L.; D’Apollo, F.; Galli, G.; Gallot, B. Macromole-
cules 2001, 34, 7707.
20 Johansson, G.; Percec, V.; Ungar, G.; Smith, K. Chem Mater
1997, 9, 164.
46 Honda, K.; Morita, M.; Otsuka, H; Takahara, A Macromole-
cules 2005, 38, 5699.
21 Percec, V.; Schlueter, D.; Kwon, Y. K.; Blackwell, J.; Moeller,
M.; Slangen P. J. Macromolecules 1995, 28, 8807.
47 de Crevoisier, G.; Fabre, P.; Leibler, L.; Tence´-Girault, S.;
Corpart, J. M. Macromolecules 2002, 35, 3880.
22 Johansson, G.; Percec, V.; Ungar, G.; Zhou J. P. Macromole-
cules 1996, 29, 646.
48 Seebach, D. Angew Chem Int Ed Engl 1990, 29, 1320.
49 Bondi, A. J Phys Chem 1964, 68, 441.
23 Wang, J.; Ober, C. K. Macromolecules 1997, 30, 7560.
24 Beyou, E.; Babin, P.; Bennetau, B.; Dunogues, J.; Teyssie,
50 Gane, P. A. C.; Leadbetter, A. J.; Benattar, J. J.; Moussa, F.;
D.; Boileau, S. J Polym Sci Part A: Polym Chem 1994, 32, 1673.
Lambert, N. Phys Rev A 1981, 24, 2694.
25 Bracon, F.; Guittard, F.; Taffin de Givenchy, E; Cambon, A. J
51 Gallot, B.; Galli, G.; Ceccanti, A.; Chiellini, E. Polymer 1999,
Polym Sci Part A: Polym Chem 1999, 37, 4487.
40, 2561.
26 Hudson, S. D.; Jung, H. T.; Percec, V.; Cho, W. D.; Johans-
son, G.; Ungar, G.; Balagurusamy, V. S. K. Science 1997, 278,
449.
52 Galli, G.; Martinelli, E.; Chiellini, E.; Ober, C. K.; Glisenti, A.
Mol Cryst Liq Cryst 2005, 441, 211.
53 Della Volpe, C.; Maniglio, D.; Brugnara, M.; Siboni, S.;
27 Percec, V.; Glodde, M.; Bera, T. K.; Miura, Y.; Shiyanov-
skaya, I.; Singer, K. D.; Balagurusamy, V. S. K.; Heiney, P. A.;
Schnell, I.; Rapp, A.; Spiess, H. W.; Hudson, S. D.; Duan, H. Na-
ture 2002, 419, 384.
Morra, M. J Colloid Interf Sci 2004, 271, 434.
54 Kwok, D. Y.; Neumann, A. W. Adv Colloid Interf Sci 1999,
81, 167.
55 Fowkes, F. M. Ind Eng Chem 1964, 56, 40.
56 Berthelot, D.; Compt Rend 1898, 126, 1857.
28 Percec, V.; Imam, M. R.; Bera, T. K.; Balagurusamy, V. S. K.;
Peterca, M.; Heiney, P. A. Angew Chem Int Ed 2005, 44, 4739.
4138
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
57 Thomas, R. R.; Anton, D. R.; Graham, W. F.; Darmon, M. J.;
Sauer B. B.; Stika, K. M.; Swartzfager D. G. Macromolecules
1997, 30, 2883.
62 Nishino, T.; Meguro, M.; Nakamae, K.; Matsushita, M.;
Ueda, Y. Langmuir 1999, 15, 4321.
63 Nishino, T.; Urushihara, Y.; Meguro, M.; Nakamae, K. J Col-
58 Mielczarski, J.; Mielczarski, E.; Galli, G.; Morelli, A.;
loid Interf Sci 2005, 283, 533.
Martinelli, E.; Chiellini, E. Langmuir 2010, 26, 2871.
64 Bennis, N.; Spadlo, A.; Dabrowski, R.; Martinelli, E.; Galli,
G.; Quintana, X.; Oton, J. M.; Geday, M. A. Opto-Electron Rev
2006, 14, 281.
59 Sohn, K. E.; Dimitriou, M. D.; Genzer, J.; Fischer, D. A.;
Hawker, C. J.; Kramer, E. J. Langmuir 2009, 25, 6341.
60 Busch, P.; Krishnan, S.; Paik, M.; Toombes, G. E. S.; Smilgies,
65 Marabotti, I.; Morelli, A.; Orsini, L. M.; Martinelli, E.; Galli,
G.; Chiellini, E.; Lien, E. M.; Pettitt, M. E.; Callow, M. E.; Callow,
J. A.; Conlan, S. L.; Mutton, R. J.; Clare, A. S.; Kocijan, A.;
Donik, C.; Jenko, M. Biofouling 2009, 25, 481.
D.-M.; Gruner, S. M.; Ober, C. K. Macromolecules 2007, 40, 81.
61 Luning, J.; Stohr, J.; Song, K. Y.; Hawker, C. J.; Iodice, P.;
¨
¨
Nguyen C. V.; Yoon, D. Y. Macromolecules 2001, 34, 1128.
MESOPHASE OF LOW-WETTING POLYACRYLATES, MARTINELLI ET AL.
4139