Hydrophobic and oleophobic surface modification using fluorinated bis-urea and bis-amide gelators

Article abstract of DOI:10.1016/j.jfluchem.2009.01.006

A series of fluorinated bis-urea and bis-amide derivatives were synthesized from fluorinated amines and explored as surface modifiers for nonwoven substrates. A majority of these derivatives showed excellent gelation properties both in organic solvents as

Full text of DOI:10.1016/j.jfluchem.2009.01.006

Journal of Fluorine Chemistry 130 (2009) 410–417
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Hydrophobic and oleophobic surface modification using fluorinated bis-urea and
bis-amide gelators
*
Anilkumar Raghavanpillai , Stefan Reinartz, Keith W. Hutchenson
DuPont Central Research & Development, Experimental Station, Wilmington, DE 19880, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of fluorinated bis-urea and bis-amide derivatives were synthesized from fluorinated amines and
explored as surface modifiers for nonwoven substrates. A majority of these derivatives showed excellent
gelation properties both in organic solvents as well as in supercritical carbon dioxide (scCO2) at
concentrations ranging from 0.3 to 3 wt%. Gelation in the presence of a nonwoven substrate led to a gel-
impregnated surface, which upon drying produced a composite with porous microstructure morphology
on the surface. The composites thus produced showed high water and hexadecane contact angles,
indicative of excellent hydrophobic and lyophobic properties. The superior hydrophobic and oleophobic
behaviors observed in these composites are attributed to a combination of increased surface roughness
and the presence of fluoroalkyl functionalities in the gelator backbone.
Received 15 December 2008
Received in revised form 20 January 2009
Accepted 21 January 2009
Available online 31 January 2009
Keywords:
Fluorinated amine
Fluorinated bis-urea
Fluorinated bis-amide
Organogelator
Xerogel
ß 2009 Elsevier B.V. All rights reserved.
Nonwoven
Supercritical CO2
Superhydrophobic
Oleophobic
1. Introduction
turation, bidentate metal coordination sites, and favorable packing
geometries.
Organogelation is a much-explored subject in the field of
supramolecular chemistry, which involves the interplay of inter-
and intramolecular forces between small molecules in solution
that ultimately change the macroscopic properties of the system.
The self-assembly of small functional moieties into supramole-
cular structures could be a powerful approach towards the design
of new materials and nanoscale devices [1–6]. Various non-
In general, each molecule of an organogelator can establish
several types of physical interaction with a neighboring molecule.
The intermolecular hydrogen bonds or
p–p interactions usually
facilitate the growth of linear, elongated aggregates in gels, leading
to microscale morphologies consisting of fibers or web-like
structures [3]. The microstructure morphology of the dried gel
(xerogel) could be of interest in altering surface morphology and
hence the low surface energies desired for fabricating surfaces that
show superhydrophobic behavior [7–8]. Surfaces on which the
contact angle of water exceeds 1508, and show low contact angle
hysteresis, are described as superhydrophobic or ultrahydrophobic
[9–11]. Such surfaces repel water like a lotus leaf and are also
considered ‘self-cleaning’ since any surface contamination is
removed by water as the droplets roll across the surface [12–14].
The self-cleaning ability of these surfaces is essentially attributed to
the two-tier micro and nano roughness present on the surface.
Recent independent reports by Zhou et al. [15] and Yamanaka
et al. [16] explored the ability of organogelators to form porous
xerogels that show superhydrophobic behavior. The morphology is
further controlled by suitable gelling solvents as well as
concentration and temperature effects. Incorporation of low
surface energy functionalities such as fluorinated groups in the
gelator framework could further lower the surface energy and
covalent interactions such as hydrogen bonding,
p–p stacking,
hydrophobic interactions, and metal coordination (or a combina-
tion thereof) are involved in the formation and stabilization of
gelator self-assemblies. Gelation occurs by the encapsulation of
solvents in the three dimensional network structures formed from
the self-assembly of molecules [3]. In general, the non-covalent
forces are reversible and weak compared to covalent bonds. For
this reason, a greater number of such interactions are required to
form strong associations. The establishment of these interactions
may often be promoted by the architecture of the molecule, such as
one or more heteroatom-hydrogen bonds, aromatic rings, unsa-
* Corresponding author. Tel.: +1 302 695 6846; fax: +1 302 695 2112.
E-mail address: anilkumar.raghavanpillai@usa.dupont.com (A. Raghavanpillai).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.01.006

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
411
Scheme 1. Preparation of fluorinated bis-urea gelators.
provide oleophobic properties. Herein, we discuss the design and
2.2. Gelation in organic solvents
synthesis of novel fluorinated gelators for organic solvents and
supercritical carbon dioxide (scCO2). Furthermore, we describe
their potential use in fabricating low surface energy surfaces that
show superior hydrophophobic and lyophobic properties.
We then examined fluorinated bis-urea and bis-amide deriva-
tives for their gelation behavior in various organic solvents and
determined the minimum gelation concentration for a given
solvent. A methodology was developed for matching a solvent
system with specific gelators to allow efficient gel formation. In
general, a gelator that is too soluble will dissolve without forming a
gel, even at high concentrations. If the gelator is not soluble
enough, it may dissolve at high temperature, but precipitate again
as the temperature is lowered. Ideally, the organogelators should
dissolve in a solvent at a temperature close to its boiling point and
assemble into a network upon cooling.
In a typical screening experiment, 1–4 wt% slurries of the
organogelators in various solvents were prepared and heated with
stirring at a temperature close to the boiling point of the solvent to
induce dissolution. Gelation occurred upon cooling, as was evident
by the formation of a translucent-to-opaque appearance without
the formation of solid crystals and/or a significant increase in
viscosity. We found that most of the new fluorinated bis-ureas and
2. Results and discussion
2.1. Fluorinated bis-ureas and bis-amides
Bis-urea derivatives are exceptionally well suited candidates
for the design of low molecular weight gelators owing to their
rigidity, strength and ability to form highly directional hydrogen
bonds [17]. Zhou and co-workers demonstrated that a xerogel
prepared from a novel tripodal gelator functionalized by three urea
and three azobenzene moieties grafted with three long alkyl chains
showed hydrophobic properties owing to the ‘cabbage-like’
surface morphology [15]. To create extremely low surface energy
surfaces, we explored the surface modification of nonwoven
substrates using low molecular weight and structurally simple
fluorinated bis-urea gelators. Fluorinated bis-urea derivatives
were synthesized by the reaction of various commercially available
diisocyanates and fluorinated amines (compounds 1–8, Scheme 1).
The resulting bis-ureas were white crystalline solids and showed
gelation properties in methylene chloride during their isolation.
We also considered investigating the corresponding fluorinated
bis-amide derivatives, which were expected to show gelation
behavior in organic solvents via directional hydrogen bonds. Four
fluorinated bis-amides were synthesized as white crystalline solids
by the reaction of suberoyl chloride with fluorinated amines
(compounds 9–12, Scheme 2).
bis-amides gelled
a wide spectrum of organic solvents in
remarkably low concentrations ranging from 0.5 to 3 wt%.
Compounds 1, 7 and 8 gelled a variety of the organic solvents
(polar, non-polar, protic, and aprotic) and are aptly termed ‘universal
organogelators’. They produced stable gels at RT with typical gelator
concentrationsof1–2 wt%.However,thesegelatorsandtheotherbis-
ureas and bis-amides were insoluble in aliphatic hydrocarbons even
at concentrations <0.5 wt%. Theresultsofgelation of compounds1, 7
and 8 are summarized in Table 1. Ureas 2–6 and amides 9–12 gelled
rather more selectively in a few organic solvents. The results of
gelation of these compounds are summarized in Table 2.
Scheme 2. Preparation of fluorinated bis-amide derivatives.

412
A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
Table 1
Gelation characteristics for bis-ureas gelators 1, 7 and 8.
Solvent
Gelator (wt%)
1
7
8
Toluene
Hazy (1)
Hazy (2)
Hazy (2)
Xylene
Hazy (1)
Hazy (1.5)
Hazy (2)
Chloroform
THF
Hazy (3)
Precipitate (2)
Hazy (2)
Partial (2)
Transparent (1)
Transparent (1)
Hazy (1)
Opaque (2.5)
Opaque (3)
Opaque (2)
Hazy (3)
Acetone
Opaque (2)
Acetonitrile
Ethyl acetate
DMF
Opaque (2)
Transparent (1)
Transparent (1)
Opaque (1)
Transparent (2)
Hazy (1)
Partial (2)
Transparent (1)
Transparent (1)
Transparent (1)
Partial (1.5)
Partial (1.5)
Transparent (1.5)
Transparent (1.5)
Opaque (1.5)
Hazy (1.5)
Transparent (2)
Transparent (2)
Partial (2)
DMSO
Dimethyl acetamide
N-methylpyrolidone
Pyridine
Clear Solution (2)
Hazy (2)
Hazy (1)
n-Butanol
Isopropanol
Methanol
Ethanol
Transparent (1)
Transparent (1)
Hazy (1)
Hazy (2)
Hazy (2)
Transparent (4)
Hazy (3)
Transparent (2)
yNumber in parenthesis indicates minimum gel concentration (wt%). Hazy: solid gel
partially transparent; transparent: solid gel completely transparent; opaque: solid
gel, not transparent; partial: solid or semi-moving gel that has some free flowing
liquid in it; precipitate: more like a precipitate than a gel.
Fig. 1. Melting temperature (Tgel) of bis-urea gelator 1 in gelling solvents.
The gels obtained by gelation of bis-ureas and bis-amides were
stable at room temperature for many days. We determined the
melting temperature (Tgel) of gels obtained from bis-urea gelator 1
in different solvents (entries in the Table 1) by a method similar to
the dropping ball method described in the literature [18–19]. Fig. 1
plots the melting temperature of the gels vs. the corresponding
gelling solvents. All gels of 1 showed excellent thermal stability up
to 40 8C. The majority of gels of 1 were stable up to the 55–60 8C
range. The gel of 1 from NMP showed the highest observed thermal
stability (71 8C), whereas the corresponding gel from DMA was the
least thermally stable (42 8C).
chemical processes because it is readily abundant, environmen-
tally benign, nontoxic, nonflammable, inexpensive, and it is
suitable for use as a supercritical fluid solvent at relatively
moderate temperatures [20]. Carbon dioxide is considered a green
alternative to common organic solvents in a variety of industrial
chemical processes such as extractions [21], polymerizations [22–
25], and organic reactions and catalysis [20]. A particular
advantage of CO2 gelation is that the solvent can be readily
removed after gel formation by slowly venting the carbon dioxide
[23,26]. In addition, scCO2 is an attractive medium for preparing
composites from organogelators because the solvent and trans-
port properties of the supercritical fluid solution (e.g., the solution
density) can be varied appreciably and continuously with
relatively minor changes in temperature or pressure. Thus, the
solvent environment can be optimized for a specific gelation
application by tuning the various density-dependent fluid
properties.
2.3. Gelation in scCO2
The success of these fluorinated bis-ureas to gel a large number
of organic solvents prompted us to attempt their gelation ability
in scCO2. Carbon dioxide is a potentially attractive solvent for
Compounds that form self-assembled structures could be
useful for surface modifications as described previously for
gelators in organic solvents [15–16] and fluorinated dendrons in
CO2 [27]. In addition, such compounds could be useful as viscosity
modifiers for CO2. For example, CO2 is used extensively as a
flooding agent for enhanced oil recovery from underground
formations [28,29]. Various additives have been used to increase
the viscosity of CO2 in an attempt to improve oil recovery efficiency
and production rates by more closely aligning the mobilities of the
CO2 and oil in the reservoir [30]. There are many reports on new
gelators for CO2, and one primary criterion for their design is
incorporation of CO2-philic functional moieties such as long chain
fluoroalkyl groups in the molecular design [31–32]. The fluorinated
bis-urea and bis-amide compounds described above could be
advantageous as CO2 gelators since they comprise shorter chain
fluoroalkyl functionalities and are relatively easy to synthesize.
We examined the gelation of compounds 1, 5, 7, 8, 9, and 10 in
scCO2 with a gelator concentration of 0.3–0.7 wt% at moderate
temperatures (70–100 8C) and elevated pressures (260–350 bar).
The best gelation conditions of these various bis-urea and bis-
amide gelators in CO2 are summarized in Table 3.
Table 2
Gelation characteristics for bis-urea and bis-amide gelators.
Compound
Gelation conditions
Appearancey
wt% gelator
Solvent
2
2–3
1–2
Methanol, n-butanol
Toluene, THF, acetone,
DMF, DMSO
Partial/precipitate
Clear solution
3
4
2
DMSO
Partial
2.5
Acetonitrile
Partial
1–2
Ethanol, acetone, DMF,
DMSO, THF, ethyl acetate
Clear solution
5
6
2
2
Acetonitrile
Toluene
Transparent
Hazy
2
2
DMSO
Partial
Toluene, ethanol, acetone,
acetonitrile, THF, ethyl acetate
Cloudy solution
9
1–2
2
DMF
Transparent
Opaque
DMSO
10
11
2
CH2Cl2
Opaque
1
2
DMSO
DMF
Opaque
Hazy
2.4. Surface modification of nonwoven supports in organic solvents
12
3
CH2Cl2
Partial
We next explored whether the gelators described above could
be used for creating particular surface effects on porous or solid
y
Same meaning as described for Table 1.

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
413
Table 3
Table 4
Gelation conditions for bis-ureas and bis-amides in scCO2.
Water and hexadecane contact angles of treated nonwoven composites prepared
via gelation in organic solvents.
Compound
Gelation conditions in scCO2
Example
Contact anglea
Water
wt% gelatory
Temperature (8C)
Pressure, bar (MPa)
Hexadecane
Adv CA
1
5
0.44
0.48
0.73
0.49
0.37
0.32
69
68
346 (34.6)
274 (27.4)
307 (30.7)
351 (35.1)
257 (25.7)
259 (25.9)
Adv CA
Rec CA
Rec CA
7
103
100
68
Untreated Tyvek1
Untreated Kolon1
1 on Tyvek1
108 ꢁ 1
115 ꢁ 4
152 ꢁ 5
155 ꢁ 2
136 ꢁ 4
149 ꢁ 4
127 ꢁ 3
130 ꢁ 4
78 ꢁ 1
85 ꢁ 4
abs
abs
8
abs
abs
9
122 ꢁ 5
132 ꢁ 3
100 ꢁ 5
106 ꢁ 3
84 ꢁ 3
89 ꢁ 4
103 ꢁ 4
99 ꢁ 3
110 ꢁ 4
76 ꢁ 4
48 ꢁ 3
50 ꢁ 5
54 ꢁ 4
53 ꢁ 3
58 ꢁ 3
42 ꢁ 3
16 ꢁ 2
10
68
1 on Kolon1
7 on Tyvek1
y
Overall gelator concentration in CO2 in the view cell. The actual gelator
solubility in CO2 was generally less than this concentration at the indicated
conditions.
7 on Kolon1
8 on Tyvek1
8 on Kolon1
110 ꢁ 4
a
substrates. The gelators self-assemble into fiber-like morphologies
in solution, which grow sufficiently long and become entangled
with one another to form a gel with their solvent medium. In the
presence of a solid or fibrous substrate, the gelation occurs on the
surface of the substrate, creating a composite with an altered
surface topology. Removal of the solvent from the gel composite
leaves behind a network of assembled gelator fibers on the
substrate, thus producing a composite surface with high surface
area and roughness which are desired for superior hydrophobic/
oleophobic behavior.
Average of 3 runs at different positions on each sample; abs = completely
absorbed into the fabric.
surface treated with gelator 1 at 2000ꢀ and 10,000ꢀ magnifica-
tions with an average fiber diameter of 140 nm. The larger fibers in
Fig. 2 are the nonwoven support, and the smaller fibers are
representative of the xerogel network. Gelators 7 and 8 were
similarly impregnated on nonwovens from a solution of methanol
or n-butanol and dried to obtain the treated composites. Fig. 3
shows SEMs of the composite network structures of the Kolon1
fabric surface treated with gelator 7 at 2000ꢀ and 5000ꢀ
magnifications with an average fiber diameter of 120 nm.
The treated surfaces were evaluated for water/oil repellency by
measuring dynamic contact angles for water and hexadecane.
Table 4 summarizes the results of contact angle measurements for
the composites and that for untreated controls (Tyvek1 and
Kolon1 fabrics). The results indicate that the composite materials
produced by the gel-impregnation of gelators 1, 7 and 8 exhibit
significantly higher advancing contact angles for water than the
untreated controls. Insets in Figs. 2 and 3 show water droplets
sitting on the nonwoven surfaces treated with gelators 1 and 7
showing advancing contact angles above 1508. The treated
composites also showed a high advancing contact angle for
hexadecane; whereas the untreated controls rapidly absorb
hexadecane upon contact. The high water and oil repellency
exhibited by composite surfaces are attributed to a combination of
fluoroalkyl functionalities present in the gelator and the increased
surface roughness created by the fibrous xerogel network. The
effect of surface structure created by gel-impregnation is
particularly important as clear solutions (no gel with solvents
chosen) of fluorinated bis-ureas dip-coated on nonwoven sub-
strates showed relatively inferior performance (water Adv.
CA < 1188).
The preparation of a thermally reversible organogelator on solid
supports (nonwovens) was accomplished by different methods. In
one of the methods (gel-impregnation in the presence of
substrate), the gelator in a preferred solvent was pre-heated in
the presence of a porous support to provide a homogeneous
solution, which was then cooled to room temperature. In another
method (treatment of pre-formed gel on a substrate), a gel
obtained by cooling a gelator solution in a preferred solvent was
spread on a substrate by a mechanical device. Drying (i.e.,
removing the solvent) the treated substrate leaves behind a
microstructured xerogel on the solid or fibrous support.
Bis-urea gelators that showed excellent gelation properties (1, 7
and 8) were chosen and gel-impregnated on commercially
available nonwoven supports (Tyvek1 polyethylene nonwoven
fabric and Kolon1 polyester fabric) in organic solvents. These
samples were dried in a vacuum oven at room temperature to
produce a composite of xerogel on the substrate. The surfaces of
the composites were characterized by scanning electron micro-
scopy and showed a porous xerogel comprised of fibrous structures
ranging from 50 nm to about 500 nm in effective average fiber
diameters as determined with electron microscopy. Bis-urea
gelator 1 was impregnated on Tyvek1 and Kolon1 fabric in
acetone, and dried composites were analyzed by SEM. Fig. 2 shows
SEMs of the composite network structures of the Tyvek1 fabric
Fig. 2. SEMs of composite prepared by impregnation of gelator 1 on Tyvek1 fabric at 2000ꢀ and 10000ꢀ magnifications.

414
A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
Fig. 3. SEMs of composite prepared by impregnation of gelator 7 on Kolon1 fabric at 2000ꢀ and 5000ꢀ magnifications.
Fig. 4. SEMs of composite prepared by impregnation of gelator 9 on Kolon1 fabric at 2000ꢀ and 5000ꢀ magnifications.
2.5. Surface modification of nonwoven supports in scCO2
materials produced by the gel-impregnation of gelators 8, 9, 11 and
12 in scCO2 exhibit significantly higher advancing contact angle
with water than the untreated controls. They also showed high
advancing contact angle with hexadecane; whereas the untreated
controls rapidly absorb hexadecane. In many cases, we observed
water contact angles of >1508 with low contact angle hysteresis
indicative of superhydrophobic behavior. The inset in Fig. 4 shows
a water droplet sitting on the nonwoven surface treated with
gelator 9 from scCO2. The high water and oil repellency exhibited
Gelators 8, 9, 11 and 12 were also gel-impregnated on
commercially available nonwoven supports (Tyvek1 fabric,
Kolon1 fabric) in scCO2 using a high-pressure variable volume
view cell. After the gelation process, the CO2 was slowly vented
from the view cell, and the resulting composite materials were
removed and imaged by scanning electron microscopy. Fig. 4
shows SEMs of the composite network structures of the Kolon1
fabric surface treated with gelator 9 at 2000ꢀ and 10,000ꢀ
magnifications showing long fibrillar structures with an average
fiber diameter of 340 nm. The treated surfaces were evaluated for
water/oil repellency, and Table 5 summarizes the results of these
contact angle measurements for the composites and that for
untreated controls. These results indicate that the composite
by the gelator-impregnated surfaces were attributed to
a
combination of xerogel microstructures and the fluoroalkyl
functionalities present in the gelator.
3. Conclusions
In conclusion, a series of fluorinated bis-urea and bis-amide
derivatives were explored as surface modifiers for nonwoven
substrates. The majority of the new derivatives showed excellent
gelation behavior in both organic solvents and scCO2. Gelation in
the presence of a nonwoven substrate led to a gel-impregnated
surface which upon drying, created a composite with a micro-
structure morphology on the surface. The composites thus
produced showed excellent hydrophobic and oleophobic behavior
as evidenced by the high water and hexadecane contact angles. The
high water and oil repellency exhibited by the gelator-impreg-
nated surfaces were attributed to the increased surface roughness
created by the xerogel microstructures and the presence of
fluoroalkyl functionalities in the gelator backbone. The composite
materials can be used to produce superior water/oil repellent
surfaces suitable for various applications. We are currently
exploring polymerizable fluorinated organogelators to impart
robustness to the treated surfaces.
Table 5
Water and hexadecane contact angles of treated nonwoven composites prepared
via gelation in scCO2.
Example
Contact anglea
Water
Hexadecane
Adv CA
Adv CA
Rec CA
Rec CA
Untreated Tyvek1
Untreated Kolon1
8 on Tyvek1
108 ꢁ 1
115 ꢁ 4
143 ꢁ 4
160 ꢁ 2
147 ꢁ 4
157 ꢁ 4
159 ꢁ 2
154 ꢁ 3
78 ꢁ 1
85 ꢁ 4
abs
abs
abs
abs
122 ꢁ 3
141 ꢁ 3
131 ꢁ 3
149 ꢁ 2
146 ꢁ 2
129 ꢁ 3
70 ꢁ 1
30 ꢁ 5
66 ꢁ 5
94 ꢁ 4
81 ꢁ 3
68 ꢁ 4
28 ꢁ 3
abs
8 on Kolon1
9 on Tyvek1
24 ꢁ 4
39 ꢁ 4
34 ꢁ 3
29 ꢁ 3
9 on Kolon1
11 on Kolon1
12 on Kolon1
a
Average of 3 runs at different positions on each sample; abs = slowly absorbed
into the fabric.

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
415
4. Experimental
4.4. Synthesis of gelator 3
4.1. General
All solvents and reagents, unless otherwise indicated, were
purchased from commercial sources and used directly as
supplied. 1H,1H,2H,2H-perfluorohexylamine and 1H,1H,2H,2H-
perfluorooctylamine were synthesized from corresponding
commercially-available iodides via the azide followed by
reduction using Raney Ni/N2H4.H2O as described in the
To a solution of 1,8-diisocyanatooctane (1.4 g, 6.9 mmol) in dry
chloroform (25 mL), cooled to ꢂ5 8C, was added and 1H,1H,2H,2H-
perfluorohexylamine (3.6 g, 13.8 mmol) dropwise under nitrogen
atmosphere, maintaining temperature below 0 8C. The reaction
was slowly warmed to RT and stirred overnight. The resulting
precipitate was isolated by filtration, rinsed with diethyl ether and
dried to provide compound 3 as a white solid (5.0 g). 1H NMR (TFA-
literature
procedure
[33].
2-(1H,1H,2H,2H-perfluoroalk-
ylthio)ethylamine was prepared by the reaction of
1H,1H,2H,2H-perfluoralkyl iodides with 2-aminoethanethiol as
disclosed in the literature procedure [34]. Tyvek1 polyethylene
nonwoven fabric was obtained from E.I. du Pont de Nemours,
Wilmington DE, and Kolon1 gsm70 spun bound polyester fabric
was obtained from Korea Vilene Inc. 1H, {1H} 13C and 19F NMR
spectra were recorded on a Brucker DRX 400 or 500 Spectro-
meter. Chemical shifts have been reported in ppm relative to an
internal reference (CDCl3, CFCl3 or TMS). All melting points
reported were uncorrected. Contact angle (CA) measurements
for both water and hexadecane on a surface were performed
according to procedures in the manufacturer’s manual using a
d):
d 3.81 (4H), 3.30 (br, 4H), 2.52 (br, 4H), 1.70 (br, 4H), 1.40 (br,
8H); 19F NMR (TFA-d):
d
ꢂ89.4 (6F), ꢂ122.1 (4F), ꢂ132.3 (4F),
ꢂ133.7 (4F).
4.5. Synthesis of gelator 4
´
Rame-Hart Standard Automated Goniometer Model 200
To a solution of 2,4-tolylene diisocyanate (0.435 g) in dry
methylene chloride (15 mL) was added and 1H,1H,2H,2H-
perfluorohexylamine (2.0 g) dropwise under nitrogen atmo-
sphere at RT. The mixture stirred for 10 h at RT, and the solid
formed was filtered, washed with cold DCM and dried to obtain
employing DROP image standard software and equipped with
an automated dispensing system with a 250
illuminated specimen stage assembly.
mL syringe and an
4.2. Synthesis of gelator 1
compound 4 as an off-white solid (2.1 g): 1H NMR (Acetone d6)
d
7.79 (s, 2H), 7.67 (dd, J = 6.4, 2.0 Hz, 1H), 7.13 (d, J = 2.0 Hz, 1H),
6.83 (d, J = 8.0 Hz, 1H), 6.1 (bs, 2H), 3.44 (q, J = 6.8 Hz, 4H), 2.39
(m, 4H), 1.99 (s, 3H); 19F NMR (Acetone d6)
2 Hz, 6F), ꢂ114.8 (m, 4F), ꢂ122.6 (m, 4F), ꢂ123.8 (m, 4F), ꢂ124.6
(m, 4F), ꢂ127.1 (m, 4F).
d
ꢂ82.1 (tt, J = 10,
To a mixture of 1H,1H,2H,2H-perfluorooctylamine (1.81 g,
5.0 mmol) and triethylamine (0.02 g, 0.2 mmol) in dry methy-
lene chloride (15 mL), under nitrogen atmosphere and cooled to
0 8C, was added dropwise 1,6-diisocyanatohexane (0.420 g,
2.5 mmol). The mixture was slowly warmed to RT, and stirred
for 3 h. The precipitated urea was filtered and washed
repeatedly with cold methylene chloride. The resulting solid
was dried to provide compound 1 as a white solid (2.0 g): mp
4.6. Synthesis of gelator 5
Using a similar procedure as described in the synthesis of
gelator 3, reaction of lysine diisocyanate (1.1 g) with 1H,1H,2H,2H-
perfluorooctylamine (3.9 g) provided compound 5 as a white solid
(5.05 g): 1H NMR (TFA-d):
156.8–158.5 8C; 1H NMR (methanol-d4):
3.06 (t, J = 6.8 Hz, 4H), 2.34 (m, 4H), 1.46 (m, 4H,), 1.34 (m, 4H);
19F NMR (methanol-d4):
d 3.41 (t, J = 6.8 Hz, 4H)
d
4.58 (m, 1H), 3.90 (s, 3H), 3.76, 3.70,
d
ꢂ81.4 (m, 6F), ꢂ114.2 (m, 4F), ꢂ121.8
3.33 (t, 2H each, J = 6.4 Hz), 2.55–2.37 (m, 4H), 1.83, 1.74 (m, 1H
(s, 4F), ꢂ122.8 (s, 4F), ꢂ123.7 (s, 4F), ꢂ126.3 (m, 4F). Elemental
analysis: C24H24F26N4O2, calc. C 32.23, H 2.70, N 6.26; found C
32.37, H 2.77, N 6.35.
each), 1.71, 1.54 (m, 2H each); 19F NMR (TFA-d):
d
ꢂ89.9 (6F),
ꢂ112.5 (4F) ꢂ129.6 (4F), ꢂ131.0 (4F), ꢂ132.0 (4F), ꢂ134.6 (4F); 13
C
NMR (TFA-d): d 178.1, 162.3, 161.8, 56.5, 55.6 43.7, 36.4, 35.8, 33.7,
32.9 (t), 32.6 (t), 29.7, 24.6.
4.3. Synthesis of gelator 2
4.7. Synthesis of gelator 6
Using a similar procedure as described in the synthesis of
gelator 1, reaction of 1H,1H,2H,2H-perfluorohexylamine (2.10 g)
with of 1,6-diisocyanatohexane (0.672 g) provided compound 2 as
Using a similar procedure as described in the synthesis of
gelator 3, reaction of lysine diisocyanate (1.4 g) with 1H,1H,2H,2H-
perfluorohexylamine (3.6 g) provided compound 6 as a white solid
a white solid (2.18 g): mp 130–131.8 8C; 1H NMR (methanol-d4):
d
3.45 (t, J = 6.8 Hz, 4H) 3.10 (t, J = 6.8 Hz, 4H), 2.35 (m, 4H), 1.48 (m,
4H), 1.35 (m, 4H); 19F NMR (methanol-d4):
ꢂ81.7 (m, 6F), ꢂ114.4
(m, 4F), ꢂ124.7 (m, 4F), ꢂ126.2 (m, 4F). Elemental analysis:
20H24F18N4O2, calc. C 34.59, H 3.48, N 8.07; found C 34.59, H 3.30,
N 7.93.
(5.05 g): 1H NMR (TFA-d):
d
4.57 (br, 1H), 3.91 (s, 3H), 3.77, 3.71,
d
3.34 (m, 2H), 2.46 (br, 4H), 2.00, 1.83 (br, 1H each), 1.72, 1.53 (br,
2H each); 19F NMR (TFA-d):
d
ꢂ89.4 (6F), ꢂ122.0 (4F), ꢂ132.2 (4F),
C
ꢂ133.6 (4F); 13C NMR (TFA-d): 178.1, 162.4, 161.8, 56.5, 55.7, 43.7,
36.4, 35.8, 33.7, 32.8, 32.6, 29.8, 24.6.

416
A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
4.8. Synthesis of gelator 7
solid (3.2 g): mp 114.1–115.2 8C; 1H NMR (methanol-d4):
J = 6.8 Hz, 4H), 2.41 (m, 4H), 2.20 (t, J = 7.6 Hz, 4H), 1.63 (m, 4H),
1.36 (m, 4H); 19F NMR (methanol-d4):
ꢂ83.1 (m, 6F), ꢂ116.0 (m,
4F), ꢂ126.1 (m, 4F), ꢂ127.6 (m, 4F). Elemental analysis:
20H22F18N2O2, calc. C 36.16, H 3.34, N 4.22; found C 36.10, H
d 3.51 (t,
d
C
3.22, N 4.31.
Using a similar procedure as described in the synthesis of
gelator 1, reaction of 2-(1H,1H,2H,2H-perfluorooctylthio)ethyla-
mine (4.23 g) with 1,6-diisocyanatohexane (0.84 g) provided
compound 7 as a white solid (4.3 g): mp 176.8–177.5 8C; 1H
4.12. Synthesis of gelator 11
NMR (DMF-d7 100 8C):
d 5.84 (bs, 2H), 5.73 (bs, 2H), 3.38 (q,
J = 6.4 Hz, 4H), 3.15 (q, J = 6.8 Hz, 4H), 2.83 (t, J = 6.4 Hz, 4H), 2.73 (t,
J = 6.8 Hz, 4H), 2.57 (m, 4H), 1.56 (m, 4H), 1.35 (m, 4H,); 19F NMR
Using a similar procedure as described in the synthesis of
gelator 9, reaction of 2-(1H,1H,2H,2H-perfluorooctylthio)ethyla-
mine (2.09 g) with suberoyl chloride (0.475 g) provided compound
11 as a white solid (3.2 g): mp 144.8–146.2 8C: 1H NMR (acetone-
(DMF-d7 100 8C):
ꢂ122.7 (m, 4F), ꢂ123.2 (s, 4F), ꢂ126.0 (m, 4F). Elemental analysis:
28H32F26N4SO2, calc. C 33.14, H 3.17, N 5.52; found C 33.18, H
d
ꢂ81.4 (m, 6F), ꢂ113.4 (m, 4F), ꢂ121.7 (m, 4F),
C
d6):
2.75 (t, J = 6.8 Hz, 4H), 2.57 (m, 4H), 2.16 (t, J = 7.2 Hz, 4H), 1.59 (m,
4H), 1.35 (m, 4H); 19F NMR (acetone-d6):
(m, 4F), ꢂ122.8 (m, 4F), ꢂ123.8 (m, 4F), ꢂ124.2 (s, 4F), ꢂ126.2 (m,
4F). Elemental analysis: C28H30F2N2S2O2, calc. C 34.15, H 3.07, N
2.85; found C 34.05, H 3.12, N 2.94.
d 7.22 (bs, 2H), 3.42 (q, J = 6.0 Hz, 4H), 2.86 (t, J = 6.4 Hz, 4H),
3.18, N 5.53.
d
ꢂ82.1 (m, 6F), ꢂ115.0
4.9. Synthesis of gelator 8
4.13. Synthesis of gelator 12
Using a similar procedure as described in the synthesis of
gelator 1, reaction of 2-(1H,1H,2H,2H-perfluorohexylthio)ethyla-
mine (1.94 g) with 1,6-diisocyanatohexane (0.504 g) provided
compound 8 as a white solid (1.97 g): mp 160–162 8C; 1H NMR
(DMF-d7 100 8C):
d 5.85 (bs, 2H), 5.74 (bs, 2H), 3.39 (q, J = 6.4 Hz,
4H), 3.13 (q, J = 6.8 Hz, 4H), 2.84 (t, J = 6.4 Hz, 4H), 2.72 (t, J = 6.8 Hz,
4H), 2.58 (m, 4H), 1.55 (m, 4H), 1.35 (m, 4H); 19F NMR (DMF-d7
Using a similar procedure as described in the synthesis of
gelator 9, reaction of 2-(1H,1H,2H,2H-perfluorohexylthio)ethyla-
mine (1.59 g) with suberoyl chloride (0.475 g) provided compound
12 as a white solid (1.4 g): mp 122–123.5 8C; 1H NMR (acetone-
100 8C):
d
ꢂ81.6 (m, 6F), ꢂ113.5 (m, 4F), ꢂ124.2 (m, 4F), ꢂ125.8
(m, 4F). Elemental analysis: C24H32F18N4SO2, calc. C 35.38, H 3.96,
N 6.88; found C 35.56, H 3.92, N 6.84.
d6):
2.75 (t, J = 6.8 Hz, 4H), 2.55 (m, 4H), 2.15 (t, J = 7.2 Hz, 4H), 1.56 (m,
4H), 1.37 (m, 4H); 19F NMR (acetone-d6):
ꢂ82.4 (m, 6F), ꢂ116.2
(m, 4F), ꢂ126.2 (m, 4F), ꢂ127.7 (m, 4F). Elemental analysis:
24H30F18N2S2O2, calc. C 36.74, H 3.85, N 3.57; found C 36.61, H
d 7.22 (bs, 2H), 3.40 (q, J = 6.0 Hz, 4H), 2.85 (t, J = 6.4 Hz, 4H),
4.10. Synthesis of gelator 9
d
C
3.83, N 3.65.
4.14. Gelation in organic solvents
To
a mixture of 1H,1H,2H,2H-perfluorooctylamine (3.6 g,
9.9 mmol), methylene chloride (30 mL) and triethylamine
(0.999 g, 9.9 mmol) under a N2 purge was added suberoyl chloride
(0.949 g, 4.5 mmol), and the mixture was stirred for 12 h at RT. The
reaction mixture was concentrated to half its volume and filtered.
The solid product was washed with cold methylene chloride (5 mL)
followed by 1% HCl (2 ꢀ 5 mL), water (2 ꢀ 5 mL) and finally
hexanes (2 ꢀ 5 mL). The resulting solid was recrystallized from
methanol to provide compound 9 as a white solid (4.0 g): mp
Generally 0.5–3 wt% of a gelator in an organic solvent in a
closed vial was heated to 5–10 8C below the boiling point of the
solvent until a clear solution was obtained in a reactor block
equipped to heat multiple vials. The vials were allowed to cool to
RT either by a slow cool by switching off the heat or by transferring
the vials to a constant temperature water bath kept at 25 8C. The
state of the solution was evaluated after 2–12 h. Stable gel
formation was tested by inverting the vial. Compounds 1, 7 and 8
gelled a variety of the organic solvents with various polarities,
whereas compounds 2–6 and 9–12 gelled more selectively.
133.5–134.6 8C; 1H NMR (methanol-d4):
2.39 (m, 4H), 2.18 (t, J = 7.6 Hz, 4H), 1.59 (m, 4H), 1.34 (m, 4H); 19
NMR (methanol-d4):
d 3.48 (t, J = 6.8 Hz, 4H),
F
d
ꢂ84.3 (m, 6F), ꢂ117.1 (m, 4F), ꢂ124.6 (m,
4F), ꢂ125.9 (m, 4F), ꢂ126.6 (m, 4F), ꢂ128.9 (m, 4F). Elemental
analysis: C24H22F26N2O2, calc. C 33.35, H 2.57, N 3.24; found C
33.37, H 2.58, N 3.31.
4.15. Gelation in scCO2
A gelator was charged to a high-pressure variable volume view
cell equipped with a TEFLON1 polymer-coated stir bar and an
electrical heating jacket. The cell was sealed and then charged
volumetrically with liquid CO2 dispensed by an Isco syringe pump
(Isco Model 260D) to give a final overall gelator concentration of
0.3–0.7 wt%. The cell was then heated to about 70–100 8C and
pressurized to about 260–350 bar (26.0–35.0 MPa) with agitation
to solubilize a significant portion of the gelator. Agitation was then
suspended, and the cell was slowly cooled to room temperature
over several hours at constant pressure to allow gel formation
4.11. Synthesis of gelator 10
Using a similar procedure as described in the synthesis of
gelator 9, reaction of 1H,1H,2H,2H-perfluorohexylamine (2.6 g)
with suberoyl chloride (0.949 g) provided compound 10 as a white

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 130 (2009) 410–417
417
within the cell volume. The CO2 was then slowly vented from the
Acknowledgements
view cell, and the gelled sample was removed from the cell and
imaged by scanning electron microscopy, revealing ‘xerogel’
microstructure.
We gratefully acknowledge Walter Meredith, Janice Hytrek and
Gregg Sunshine of DuPont CR&D for their assistance with the
experiments, and Liang Liang of DuPont Corporate Center for
Analytical Sciences (CCAS) for SEMs.
4.16. Tgel of bis-urea gelator 1
References
A procedure similar to that described in the literature [18–19]
was used to measure the melting temperature of the gel. A steel
ball (260 mg, diameter ꢃ4.5 mm) was gently placed on the top of
the gel (4 g) in a glass vial. The closed vial was placed firmly in a
water bath initially at 25 8C which was then heated progressively
at a rate of 2 8C per minute. The sample temperature was
determined by a sensor dipped in a separate vial next to the
heating gel which was filled with the same solvent used for
gelation. The Tgel was defined as the temperature at which the ball
touched the bottom of the vial. The experiment was repeated
multiple times to produce consistent results.
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Nonwoven fabrics: Tyvek1 polyethylene nonwoven fabric and
Kolon1 spun bound polyester fabric (about 3.0 cm ꢀ 3.0 cm) were
immersed in a suspension of a gelator in organic solvent kept in
closed reaction flask equipped with a stir bar and temperature
controller. The mixtures were heated 5 8C below the boiling point
of the solvent for 1–2 h until clear solutions formed. The flasks
were then either rapidly cooled to RT by removing the oil bath or
slowly cooled to RT by switching off the heat. Gel formation was
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for an additional 6 h. The gelator-impregnated samples were
removed and dried in a vacuum oven at RT overnight. The dried
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4.18. Gel-impregnation on nonwoven supports in scCO2
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those of Section 4.17 were mounted in a high-pressure variable
volumeviewcellwhichhad beenchargedwithgelatorand equipped
with a TEFLON1-coated stir bar and an electrical heating jacket. The
cell was sealed and then charged with liquid CO2 to give a final
overall gelator concentration of 0.2–0.5 wt%. The cell was then
heated to about 70 8C and pressurized to about 210 bar (21.0 MPa)
with agitation to solubilize a significant portion of the gelator.
Agitation was then suspended, and the cell was slowly cooled to
room temperature over several hours at constant pressure to allow
gel formation within and upon the nonwoven fabric samples. The
CO2 was then slowly vented from the view cell, and the gelator-
impregnated samples were removed, imaged by scanning electron
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