Hydrophobic and oleophobic surface modification using gelling agents derived from amino acids

Article abstract of DOI:10.1016/j.jfluchem.2011.10.015

A series of fluorinated and non-fluorinated organogelators containing urea and amide functionalities was synthesized from readily available amino acid building blocks. These derivatives showed excellent gelation behavior in a variety of organic solvents at low concentrations ranging from 0.5-4 wt%. Gelation in the presence of a fibrous substrate led to a gel-coated surface, which upon drying provided a composite with a porous microstructure morphology impregnated on the surface. The composites obtained via the impregnation of gelators provided surfaces with excellent hydrophobic properties. The superior hydrophobic behaviors observed in these composites were ascribed to a combination of increased surface roughness created by the xerogel and the presence of hydrophobic functionalities present in the gelator backbone. The composites obtained via the impregnation of gelators bearing long-chain perfluoroalkyl group on non-woven substrates also showed excellent oleophobic behavior.

Full text of DOI:10.1016/j.jfluchem.2011.10.015

Journal of Fluorine Chemistry 135 (2012) 187–194
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Hydrophobic and oleophobic surface modification using gelling agents derived
from amino acids
*
Anilkumar Raghavanpillai , Vincent A. Franco, Walter E. Meredith
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 and non-fluorinated organogelators containing urea and amide functionalities was
synthesized from readily available amino acid building blocks. These derivatives showed excellent
gelation behavior in a variety of organic solvents at low concentrations ranging from 0.5–4 wt%. Gelation
in the presence of a fibrous substrate led to a gel-coated surface, which upon drying provided a composite
with a porous microstructure morphology impregnated on the surface. The composites obtained via the
impregnation of gelators provided surfaces with excellent hydrophobic properties. The superior
hydrophobic behaviors observed in these composites were ascribed to a combination of increased surface
roughness created by the xerogel and the presence of hydrophobic functionalities present in the gelator
backbone. The composites obtained via the impregnation of gelators bearing long-chain perfluoroalkyl
group on non-woven substrates also showed excellent oleophobic behavior.
Received 6 September 2011
Received in revised form 14 October 2011
Accepted 28 October 2011
Available online 15 November 2011
Keywords:
Organogelator
Gelation
Fluorinated urea
Fluorinated amide
Amino acid
ß 2011 Elsevier B.V. All rights reserved.
Xerogel
Nonwoven
Hydropbobicity
Oleophobicity
1. Introduction
several types of physical interaction with a neighboring molecule.
The intermolecular hydrogen bonds or
p–p interactions usually
Organogelation is a much-studied but still poorly understood
subject, which involves the interplay of inter- and intramolecular
forces between small molecules in solution that ultimately change
the macroscopic properties of the system. Low molecular-weight
organogelators have attracted considerable interest and have
potential applications towards the design of new soft materials [1–
6]. The process of self-assembly of small organic molecules into
supramolecular structures is complex and varies based on the
functionalities present in the molecule as well as external factors
such as solvent, temperature, pH, etc. Various non-covalent
facilitate the growth of linear, elongated aggregates in gels, leading
to microscale morphologies consisting of fibers or web-like
structures [3,7]. Evaporation of the solvent leads to a dried gel
(xerogel) with
a microstructure morphology. Thus surface
morphology of a surface could be altered via a gel-impregnation
and drying process and the method could be employed for
designing the low surface energies desired for fabricating surfaces
that behave superhydrophobic in nature [8–11]. Surfaces on which
the contact angle of water exceeds 1508, and show low contact
angle hysteresis, are described as superhydrophobic or ultrahy-
drophobic [12–14]. 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 [15–17].
The self-cleaning ability of these surfaces is essentially due to the
two-tier micro and nano roughness present on the surface. The
microscale morphologies created by organogelator impregnation
could be further controlled by suitable gelling solvents, as well as
concentration and temperature effects. In addition, incorporation
of low surface energy functionalities like fluorinated groups in the
gelator frame work could further lower the surface energy and
bring oleophobic properties to the treated surfaces.
interactions such as hydrogen bonding,
p–p stacking, hydropho-
bic interactions, and metal coordination (or a combination 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 solute molecules [3]. In general, the non-covalent
forces are weak compared to covalent bonds, which makes them
reversible, and it requires several of them to be combined to form a
strong association. Each molecule of an organogelator can establish
Recently, we demonstrated the above concept by fabricating
extremely low surface energy surfaces via the surface modification
* 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 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2011.10.015

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A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
of the nonwoven substrates using simple fluorinated bis urea and
bis amide gelators [11]. 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 resulting composite showed high water and
hexadecane contact angles indicative of excellent hydrophobic
and oleophobic properties. The superior hydrophobic and
oleophobic behaviors observed in these composites are attribut-
ed to a combination of increased surface roughness and the
presence of perfluoroalkyl functionality in the gelator backbone.
Herein, we discuss the design and synthesis of novel fluorinated
and non-fluorinated organogelators derived from amino acids, a
detailed investigation of their gelling behavior, and the effect of
structural changes on repellency behavior on treated non-woven
substrates.
2. Results and discussion
2.1. Organogelators: design and synthesis
Urea and amide 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. We designed a series of fluorinated organoge-
lators by careful manipulation of hydrogen bonding (urea and
amide) and hydrophobic functionalities (fluorocarbon and hydro-
carbon) in the same molecule from readily available amino acids.
Boc-protected amino acids, N-Boc-
acid were chosen as the building blocks. Thus N-Boc-
transformed to the corresponding N-Boc-protected fluorinated
amides (1a and 1b) by reacting with fluorinated amines (Scheme
b
-alanine and N-Boc-aspartic
-alanine was
b
Scheme 1. Preparation of fluorinated urea and amide gelators from N-Boc-b-alanine.
Scheme 2. Preparation of perfluoroalkyl urea–amide gelators from N-Boc-L-aspartic acid.

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
189
1). The resulting amides were deprotected to obtain the
corresponding free amines (2a and 2b) which upon reaction with
commercially available isocyanates provided the fluorinated urea–
amide derivatives suitable as gelling agents (3a and 3b). All the
urea–amide derivatives were white crystalline solids and showed
gelation properties in methylene chloride during their isolation.
In order to investigate the effect of structural changes on
gelation behavior and repellency, we designed similar urea–
amide-based gelator system which incorporates a bis-fluoroalkyl
chain. Thus fluorinated bis-amide–urea derivatives (6a–6c) were
synthesized by the reaction of N-Boc-L-aspartic acid with 2 equiv.
of fluorinated amine followed by deprotection and reaction with n-
octyl isocyanate as shown in Scheme 2.
In order to compare the effect of structural changes (fluorocar-
bon vs hydrocarbon) on gelation behavior and repellency, we also
synthesized the corresponding non-fluorinated urea amide deri-
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, 0.5–4 wt% slurries of the
organogelators in various organic solvents were prepared and
heated with stirring at a temperature 3–5 8C below the boiling
point of the solvent to induce dissolution. Gelation occurred
upon cooling, as was evident by significant increase in viscosity
and/or the formation of a translucent-to-opaque appearance
without the formation of crystals or precipitate. We found that
the fluorinated and non-fluorinated urea–amide derivatives
underwent gelation in many organic solvents at remarkably low
concentrations ranging from 0.5 to 4 wt%. The gels formed were
stable for several weeks at room temperature. Some of the
gelation attempts and best conditions where stable gels were
vatives 9 and 12 via the reaction of N-Boc-
b
-alanine or N-Boc-
L-
obtained at a minimum concentration of the gelator are
aspartic acid with n-octylamine followed by deprotection and
reaction with n-octyl isocyanate (Scheme 3).
summarized in Table 1.
The fluorinated urea–amide derivatives 3a and 3b formed
stable gels in acetone at 1–2 wt% concentration. 3a also provided a
hazy gel in n-butanol at 2 wt% concentration. Compounds 6a and
6b formed very stable gels in n-butanol at 3.5 and 4 wt%
respectively. Attempted gelation of 6c in n-butanol led to a clear
solution at 1–4 wt% concentration, but provided a stable gel in
toluene at 2 wt% concentration. The fluorinated urea amide
compounds described above could be useful as gelators for
supercritical CO2 [8,11]. The non-fluorinated urea–amide deriva-
tives 9 and 12 provided stable gels in a variety of solvents at 0.5–
2 wt% concentration.
2.2. Gelation in organic solvents
We examined the gelation behavior of fluorinated and non-
fluorinated urea–amide derivatives in various organic solvents and
determined the minimum gelation concentration for each 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
Scheme 3. Preparation of alkyl urea–amide gelators from N-Boc-b-alanine and N-Boc-L-aspartic acid.

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A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
Table 1
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.
Gelation characteristics for compounds 3a, 3b, 6a–6c and 9 and 12.
Compound
Gelation conditions
Appearanceb
Wt% gelator
Solvent
3a
1
Hexane
Insoluble
The preparation of thermally reversible organogelators 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 of the gelator,
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 such as a hand operated Thin
Layer Chromatography (TLC) plate coater to a uniform thickness.
Drying (i.e. removal of the solvent) the treated substrate leaves
behind a microstructured xerogel on the solid or fibrous support.
For fibrous and smaller sized substrates the gel impregnation in
presence of solvent was the preferred method.
1,2,3
Toluene
Solution/precipitate
Soluble/precipitate
Transparent gel
Hazy gel
0.5,1,2
0.5,1a,2
2a,3
Tetrahydrofuran
Acetone
n-Butanol
3b
6a
6b
6c
9
1,2,3
1,2,3
1,2a,3
1,2,3
Toluene
Solution/precipitate
Solution/precipitate
Thick gel
Tetrahydrofuran
Acetone
n-Butanol
Partial gel/precipitate
1,2,3
1,2,3,4
1,2,3,4
3,3.5a,4
Toluene
Insoluble
Acetonitrile
Tetrahydrofuran
n-Butanol
Partial gel/precipitate
Solution/precipitate
Opaque gel
1,2,3
1,2
Hexane
Partial gel
Soluble
Toluene
1,2,3,4
4a
Acetonitrile
n-Butanol
Soluble
The urea–amide gelators were gel-impregnated on commer-
cially available nonwoven supports (Tyvek1 polyethylene nonwo-
ven fabric and Kolon1 polyester fabric) in a suitable organic
solvent. These samples were dried in a vacuum oven at room
temperature to produce a composite of xerogel coated on the
substrate. The amount of dried gel coated per unit area of the
support was estimated to be 0.0005–0.0035 g/cm2 and was
dependent on gelation conditions and the support used for surface
modification. The surfaces of the composites were characterized by
scanning electron microscopy (SEM) and showed a porous xerogel
comprised of fibrous structures ranging from 50 nm to about
500 nm in effective average fiber diameter. The average fiber
diameter observed was different from the fiber diameter observed
Transparent gel
2
2a
Hexane
Partial gel
Hazy gel
Solution
Solution
Toluene
Acetone
n-Butanol
2,3
1,2,3,4
1a,2
1a,2
2
Toluene
Transparent gel
Hazy gel
Cyclohexane
Acetone
Opaque gel
Transperent gel
Partial gel
2
Methylene chloride
n-Butanol
1,2
12
0.5a,1
Cyclohexane
Toluene
Transparent gel
Transparent gel
Transparent gel
Hazy gel
1
2
2a,3
n-Butanol
Acetonitrile
for untreated Tyvek1 polyethylene (5–20
m
M) or Kolon1 polyester
a
Minimum gel concentration for stable gel formation.
fabric (15–30 M). This indicates that the self-assembly of
m
b
Hazy, solid gel partially transparent; transparent, solid gel completely
molecular entities can be transferred from the liquid–gel phase
to surfaces, giving a changed surface morphology. The surface
modified composites were stable to mild physical stress such as
bending and rubbing, however not stable for more rigorous
abrasive treatment. Urea–amide gelator 3a was impregnated on
Tyvek1 and Kolon1 fabric in acetone, and dried composites were
analyzed by SEM. Fig. 1 shows SEMs at 10,000Â magnification of
the composite network structures of the Tyvek1 and Kolon1 fabric
surfaces with an average fiber diameter of 140 nm treated with
gelator 3a. The rest of the fluorinated urea–amide gelators (3b, 6a,
6b and 6c) were similarly impregnated on nonwovens from a
solution of acetone (3b), n-butanol (6a and 6b) or toluene (6c) and
dried to obtain the treated composites similar to 3a. Fig. 2 shows
transparent; opaque, solid gel not transparent; partial, solid gel with partial
movement in the liquid.
2.3. Surface modification of nonwoven supports in organic solvents
We next explored whether the gelators described above could
be used for creating particular surface effects on fibrous or solid
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
Fig. 1. SEMs of composite prepared by impregnation of gelator 3a on Tyvek1 (left) and Kolon1 (right) fabric at 10,000Â magnification.

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
191
Fig. 2. SEMs of composite prepared by impregnation of gelator 6a on Tyvek1 (left) and Kolon1 (right) fabric at 10,000Â magnification.
SEMs at 10,000Â magnification of the composite network
structures of the Tyvek1 and Kolon1 fabric surfaces with an
average fiber diameter of 130 nm treated with fluorinated urea–
amide gelator 6a
fluorocarbon or hydrocarbon tails present in the gelator backbone,
essentially leads to the increased water repellency of the treated
composite. Insets in Figs. 1 and 2 show water droplets sitting on the
nonwoven surfaces treated with gelator 3a and 6a with advancing
contact angles above 1508. The effect of surface structure created
by gel-impregnation is particularly important as clear solutions
(no gel with solvents chosen) of fluorinated (3a and 6a) or non-
fluorinated (9 and 12) gelators dip-coated on nonwoven substrates
showed relatively inferior performance (water Adv. CA < 1158).
The treated composites derived from gelators 3a and 6a also
showed a high advancing contact angle for hexadecane, whereas
the corresponding composites 3b and 6b showed slightly reduced
advancing contact angles for hexadecane. This observation was not
surprising, as compounds 3b and 6b are comprised of short
fluoroalkyl groups (Rf = C4) and are expected to show reduced oil
The composites produced by the gel-impregnation of fluorinat-
ed organogelators were evaluated for water/oil repellency by
measuring the dynamic contact angles for water and hexadecane.
Table 2 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 fluorinated gelators 3a, 3b, 6a,
6b and 6c exhibit significantly higher water advancing contact
angles than the untreated controls. Interestingly, the urea–amides
with shorter fluoroalkyl chains (3b, 6b and 6c) also showed high
water advancing angles similar to 3a or 6a indicating that high
water repellency is independent of the length and number of
fluoroalkyl moieties in the molecule.
The water advancing and receding contact angles observed for
all the gelator treated surfaces were higher than the untreated
controls. The advancing contact angle observed for these
composites were much higher than highest possible water contact
angle achievable for a perfectly smooth surface with a hexagonally
packed array of CF3 groups [18]. This reiterates the fact that the
surface created has a higher surface area resulting from the
increased surface roughness due to gelator incorporation. A
combination of surface roughness along with hydrophobic
repellency compared to
a longer chain (Rf = C6 or higher)
perfluoroalkyl containing gelator [19]. Although 6b was composed
of twin fluoroalkyl chains (Rf = C4) in the same molecule, it also still
lacked enough oil repellency underscoring the importance of
longer chain fluoroalkyl group for oil repellency. We then looked at
the oil repellency behavior of composite created by the gel-
impregnation compound 6c, which comprises of a two carbon
fluoroalkyl chain (Rf = C2) and showed no oil repellency. Hex-
adecane sank into the composite that was gel-impregnated with
compound 6c. This further confirms that longer fluoroalkyl chains
(Rf = C6 or higher) need to be incorporated in the gelator backbone
Table 2
Water and hexadecane contact angles of treated nonwoven composites prepared via gelation in organic solvents.
Composite
Amount of gel impregnated per unit area (g/cm2)
Contact anglea
Water
Hexadecane
Adv CA
Adv CA
Rec CA
Rec CA
3a on Tyvek1
3a on Kolon1
3b on Tyvek1
3b on Kolon1
6a on Tyvek1
6a on Kolon1
6b on Tyvek1
6b on Kolon1
6c on Tyvek1
6c on Kolon1
9 on Tyvek1
0.0009
0.0022
0.0009
0.0021
0.0011
0.0026
0.0010
0.0026
0.0007
0.0024
–
149 Æ 1
159 Æ 2
144 Æ 4
150 Æ 3
154 Æ 2
152 Æ 4
149 Æ 2
152 Æ 1
128 Æ 4
138 Æ 3
132 Æ 4
147 Æ 2
133 Æ 4
151 Æ 4
108 Æ 1
115 Æ 4
141 Æ 3
148 Æ 3
134 Æ 2
136 Æ 1
153 Æ 6
135 Æ 2
135 Æ 5
132 Æ 4
105 Æ 4
114 Æ 2
115 Æ 3
130 Æ 3
109 Æ 4
136 Æ 2
78 Æ 1
104 Æ 2
127 Æ 1
71 Æ 3
71 Æ 4
89 Æ 3
41 Æ 1
39 Æ 3
133 Æ 0
84 Æ 2
61 Æ 3
56 Æ 5
12 Æ 3
57 Æ 2
155 Æ 2
126 Æ 2
92 Æ 1
84 Æ 3
28 Æ 3
Absorbed in 40 s
Absorbed upon contact
Absorbed upon contact
Absorbed upon contact
Absorbed upon contact
Absorbed upon contact
Absorbed upon contact
9 on Kolon1
0.0030
0.0012
0.0028
–
12 on Tyvek1
12 on Kolon1
Untreated Tyvek1
Untreated Kolon1
–
85 Æ 4
a
Average of 3 runs at different positions on each sample.

192
A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
Fig. 3. SEMs at 10,000Â magnification of composites prepared by impregnation of non-fluorinated gelator 9 (left) and 12 (right) on Tyvek1 fabric.
180
160
140
120
100
80
in addition to the roughness (created by the xerogel) to obtain good
oil repellency on the treated composites.
In order to understand whether changes to the surface topology
in the absence of fluorine could result in water/oil repellency, we
water adv
attempted the gel-impregnation of non-fluorinated (R = C8H17
)
water rec
organogelators 9 and 12 on Tyvek1 and Kolon1 fabrics in toluene
and obtained the corresponding treated composites. Fig. 3 shows
SEMs at 10,000Â magnifications of the composite network
structures of the Tyvek1 and Kolon1 fabric surfaces with an
average fiber diameter of 120 nm treated with fluorinated urea–
amide gelator 9.
hexadec adv
hexadec rec
60
40
(R
),
4
20
f
0
6a
6b
6c
12
Surprisingly, the non-fluorinated gelators
9 and 12 also
Urea
provided high advancing contact angles for water similar to 3a
or 6a, indicating that high water repellency could be achieved just
by using urea–amide derivatives containing hydrocarbon tails.
Fluorocarbon functionalities are not essential in achieving high
water repellency on these composites. The combination of
microporous structure created by the gelator and hydrocarbon
functionalities in the gelator backbone helps to provide very good
hydrophobic behavior. However, composites derived from non-
fluorinated gelators 9 and 12 did not show any hexadecane
repellency, and hexadecane was absorbed completely into the
substrate upon contact with the surface. The results of the contact
angle measurements of organogelators 3a and 3b, 6a–6c, 9 and 12
are summarized in Table 2.
A comparison of water/hexadecane contact angles of urea–
amides with bis fluoroalkyl chains, 6a (Rf = C6), 6b (Rf = C4), 6c
(Rf = C2) and corresponding non fluorinated (hydrocarbon) urea–
amide 12, gel-impregnated on Tyvek1 and Kolon1 fabrics is shown
in Figs. 4 and 5 respectively. The contact angles indicate a clear
trend in the reduction of hexadecane advancing and receding
Fig. 5. Water/oil repellency of 6a (Rf = C6), 6b (Rf = C4), 6c (Rf = C2) and
corresponding non fluorinated urea–amides (12) impregnated on Kolon1 fabric.
contact angles as the perfluoroalkyl chain length of the treated
gelator is altered from Rf = C6 (6a) to non-fluorinated (12) in both
Tyvek1 and Kolon1 fabrics [19].
3. Conclusions
A series of fluorinated and non-fluorinated organogelators
bearing urea and amide functionalities were synthesized from
readily available amino acid building blocks. These derivatives
showed excellent gelation properties in a variety of organic
solvents at concentrations ranging from 0.5 to 4 wt%. Gelation in
the presence of a nonwoven substrate led to a gel-coated surface,
which upon drying provided a composite with porous microstruc-
ture morphology impregnated on the surface. The composites
obtained via the impregnation of gelators provided surfaces with
excellent hydrophobic properties. The superior hydrophobic
behavior shown by these composites were attributed to
a
180
160
140
combination of microsurface morphology created by the xerogel
and the presence of hydrophobic functionalities present in the
gelator backbone. The composites obtained via the impregnation
of gelators bearing long chain perfluoroalkyl group on non-woven
substrates also showed excellent oleophobic behavior. Analogous
gelators bearing short fluoroalkyl chains or non-fluorinated
organogelators showed poor or no oleophobicity.
water adv
120
water rec
100
80
60
40
20
0
hexadec adv
hexadec rec
4. Experimental
6a
6b
6c
12
4.1. General
Urea
All solvents and reagents, unless otherwise indicated, were
purchased from commercial sources and used directly as supplied.
Fig. 4. Water/oil repellency of 6a (Rf = C6), 6b (Rf = C4), 6c (Rf = C2) and
corresponding non fluorinated urea–amides (12) impregnated on Tyvek1 fabric.

A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
193
1H,1H,2H,2H-perfluorobutylamine, 1H,1H,2H,2H-perfluorohexy-
lamine and 1H,1H,2H,2H-perfluorooctylamine were synthesized
from corresponding commercially available iodides via the azide
followed by reduction using Raney Ni as described in the literature
[20]. Tyvek1 polyethylene nonwoven fabric was obtained from E.I.
du Pont de Nemours and Company, 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 Spectrometer. 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
45.0 mmol) with N-Boc-
b
-alanine (8.5 g, 45.0 mmol) provided 1b
(16.9 g, 38.9 mmol, 87%) as a crystalline solid. Mp 135–137 8C; 1H
NMR (acetone-d6): d 7.25 (bs, 1H), 5.76 (bs, 1H), 3.41 (q, J = 6.8 Hz,
2H), 3.16 (q, J = 6.4 Hz, 2H), 2.32 (m, 2H), 1.42.24 (t, J = 7.2 Hz, 2H),
1.26 (s, 9H); 19F NMR (acetone-d6):
À125.5 (m, 2F), À127.1 (m, 2F).
d
À82.4 (m, 3F), À115.2 (m, 2F),
Deprotection of 1b (16.9 g, 38.9 mmol) using trifluoroacetic
acid at RT followed by treatment with saturated NaHCO3 provided
compound 2b (11.9 g, 35.6 mmol, 97%) as a crystalline solid. Mp
90–92 8C; 1H NMR (acetone-d6):
d 7.46 (bs, 1H), 3.40 (q, J = 4.8 Hz,
2H), 3.28 (t, J = 6.8 Hz, 1H), 2.34 (m, 2H), 2.25 (t, J = 4.8 Hz, 2H),
1.78–1.65 (bs, 2H); 19F NMR (acetone-d6):
(m, 2F), À125.5 (m, 2F), À127.1 (m, 2F).
d
À82.4 (m, 3F), À115.2
´
manual using a Rame-Hart Standard Automated Goniometer
Reaction of 2b (3.0 g, 8.98 mmol) with n-octyl isocyanate
(1.39 g, 8.98 mmol) provided compound 3b (3.68 g, 7.5 mmol,
Model 200 employing DROP image standard software and
equipped with an automated dispensing system with a 250
syringe and an illuminated specimen stage assembly.
m
l
84%) as a white solid. Mp 135–136.5 8C; 1H NMR (acetone-d6):
d
3.39 (q, J = 7.2 Hz, 2H), 3.22 (q, J = 6.4 Hz, 2H), 2.97 (q, J = 6.8 Hz,
2H), 2.33 (m, 2H), 2.22 (t, J = 6.4 Hz, 2H), 1.32 (m, 2H), 1.19 (m,
10H), 0.77 (t, J = 6.8 Hz, 3H); 19F NMR (acetone-d6):
4.2. Synthesis of gelator 3a
d
À82.4 (m, 3F),
À115.3 (m, 2F), À125.5 (m, 2F), À127.1 (m, 2F). Elemental analysis:
A
mixture of dichloromethane (250 mL), N-Boc-
b
-alanine
C, 44.17; H, 5.77; N, 8.59; found: C, 44.53; H, 5.94; N, 8.66.
(5.67 g, 30.0 mmol), 1-[3-(dimethylamino)propyl]-3-ethylcarbo-
diimide hydrochloride (EDCl) (5.75 g, 30.0 mmol) and 4-(dimethy-
lamino)pyridine (3.66 g, 30.0 mmol) was stirred for 10 min at
room temperature (RT) followed by addition of 1H,1H,2H,2H-
perfluorooctylamine (11.2 g, 31.0 mmol) via an addition funnel.
The mixture was stirred for 12 h at RT. The mixture was washed
with 2% HCl (2 Â 60 mL), saturated NaHCO3 solution (1 Â 50 mL)
and brine (1 Â 50 mL). The resulting organic layer was dried
(MgSO4) and concentrated to provide compound 1a (15.1 g,
28.4 mmol, 94%) as a white crystalline solid. Mp 107–108 8C; 1H
4.4. Synthesis of gelator 6a
N-Boc-L-aspartic acid (13.9 g, 60.0 mmol) was condensed with
1H,1H,2H,2H-perfluorooctylamine (43.6 g, 120.0 mmol) and pro-
vided compound 4a (50.8 g, 55.0 mmol, 92%) as a white crystalline
solid. Mp 162.5–164 8C; 1H NMR (acetone-d6):
d
7.68 (bs, 2H), 6.30
(bs, 1H), 4.35 (bs, 1H), 3.54 (bm, 4H), 3.03–2.65 (bm, 2H), 2.28 (bm,
4H), 1.37 (s, 9H); 19F NMR (acetone-d6):
d
À81.6 (m, 6F), À114.3 (m,
4F), À122.5 (s, 4F), À123.5 (s, 4F), À124.2 (s, 4F), À126.8 (m, 4F).
Deprotection of 4a (49.0 g, 53.1 mmol) using trifluoroacetic
acid at RT followed by treatment with saturated NaHCO3 provided
compound 5a (36.2 g, 43.9 mmol, 83%) as a white crystalline solid.
NMR (acetone-d6):
2H), 3.42 (q, J = 5.8 Hz, 2H), 2.44 (t, J = 6.8 Hz, 2H), 2.37 (m, 2H),
1.45 (s, 9H); 19F NMR (acetone-d6):
À81.2 (m, 3F), À114.3 (m, 2F),
d 6.25 (bs, 1H), 5.09 (bs, 1H), 3.61 (q, J = 6.8 Hz,
d
À122.2 (s, 2F), À123.2 (s, 2F), À124.0 (s, 2F), À126.5 (m, 2F).
A suspension of compound 1a (14.5 g, 27.1 mmol) in dichlor-
omethane (50 mL) was stirred with trifluoroacetic acid (TFA)
(24.7 g, 217.2 mmol) at RT for 3 h. Chloroform (50 mL) was added
and the bulk of the solvents and TFA were evaporated under
vacuum. The resulting trifluoroacetate salt was stirred with
saturated NaHCO3 solution (200 mL) and the solid formed was
filtered. The residue was washed with cold water and dried under
vacuum to provide compound 2a (9.1 g, 20.9 mmol, 77%) as a white
Mp 108 8C; 1H NMR (acetone-d6):
3.48 (m, 4H), 2.65 (dd, J = 14.4, 4.4 Hz, 1H), 2.55–2.38 (m, 5H); 19
NMR (acetone-d6):
À82.2 (m, 6F), À115.0 (m, 4F), À122.8 (s, 4F),
d 4.37 (q, J = 4.5 Hz, 2H), 3.61–
F
d
À123.8 (s, 4F), À124.6 (s, 4F), À127.2 (m, 4F).
Reaction of 4a (8.23 g, 10.0 mmol) with n-octyl isocyanate
(1.55 g, 10.0 mmol) provided compound 6a (9.4 g, 9.6 mmol, 96%)
as a white crystalline solid. Mp 183–185 8C; 1H NMR (acetone-d6):
d
7.78 (t, J = 5.2 Hz, 1H), 7.68 (bs, 1H), 6.09, (bs, 1H), 5.90 (bs, 1H)],
4.62 (t, J = 5.6 Hz, 1 H), 3.57 (m, 4H), 3.18 (m, 2H), 2.80 (dd, J = 15.6,
6.0 Hz, 1H), 2.66 (dd, J = 15.2, 6.0 Hz, 1H), 2.47 (m, 4H), 1.51 (m,
2H), 1.31 (m, 10H), 0.89 (t, J = 6.1 Hz, 3H); 19F NMR (acetone-d6):
À82.1 (m, 6F), À115.1 (m, 4F), À122.8 (s, 4F), À123.8 (s, 4F), À124.5
(s, 4F), À127.1 (m, 4F). Elemental analysis: C, 35.59; H, 3.30; N,
5.73; found: C, 35.82; H, 3.39; N, 5.75.
crystalline solid. Mp 115–117 8C; 1H NMR (acetone-d6):
1H), 3.57 (q, J = 6.8 Hz, 2H), 3.43 (t, J = 6.0 Hz, 1H), 2.51 (m, 2H),
2.41 (t, J = 6.8 Hz, 2H), 1.95–1.77 (bs, 2H); 19F NMR (acetone-d6):
d 7.62 (bs,
d
d
À81.1 (m, 3F), À114.9 (m, 2F), À122.8 (s, 2F), À123.8 (s, 2F), À124.0
(s, 2F), À126.5 (m, 2F).
To a mixture of compound 2a (4.34 g, 10.0 mmol), dichlor-
omethane (50 mL) and triethylamine (0.05 g, 0.5 mmol) under a N2
purge was added n-octyl isocyanate (1.55 g, 10.0 mmol) and the
mixture was stirred for 5 h at RT. The solid product was filtered and
washed with cold hexanes (2 Â 5 mL) to provide compound 3a
(5.29 g, 9.0 mmol, 90%) as a white crystalline solid. Mp 149–
4.5. Synthesis of gelator 6b
Using a similar procedure as described for the synthesis of
gelator 6a, reaction of 1H,1H,2H,2H-perfluorohexylamine (14.2 g,
54.0 mmol) with N-Boc-
4b (15.6 g, 21.6 mmol, 86%) as a white crystalline solid. Mp 155–
156 8C; 1H NMR (acetone-d6):
7.57 (bs, 2H), 6.32 (bs, 1H) 4.38 (q,
L-aspartic acid (5.8 g, 25.0 mmol) provided
151 8C; 1H NMR (acetone-d6 @ 50 8C):
d 7.27 (bs, 1H), 5.33 (bs, 2H),
3.40 (q, J = 6.0 Hz, 2H), 3.23 (q, J = 6.4 Hz, 2H), 2.96 (q, J = 6.0 Hz,
2H), 2.36 (m, 2H), 2.20 (t, J = 6.4 Hz, 2H), 1.30 (m, 2H), 1.16 (m,
d
J = 7 Hz, 1 H), 3.55 (m, 4H), 2.69 (dd, J = 16, 6 Hz, 1H), 2.64 (dd,
10H), 0.74 (t, J = 6.8 Hz, 3H); 19F NMR (acetone-d6 @ 50 8C):
(m, 3F), À114.7 (m, 2F), À122.6 (s, 2F), À123.6 (s, 2F), À124.4 (s,
2F), À126.9 (m, 2F). Elemental analysis: calculated C, 40.75; H,
4.79; N, 7.13; found: C, 40.40; H, 4.83; N, 7.55.
d
À82.1
J = 16, 4 Hz, 1H), 2.45 (m, 4H), 1.4 (s, 9H); 19F NMR (acetone-d6):
À82.4 (m, 6F), À115.3 (m, 4F), À125.6 (s, 4F), À127.1 (m, 4F).
d
Deprotection of 4b (14.8 g, 20.4 mmol) using trifluoroacetic
acid at RT, followed by treatment with saturated NaHCO3
provided 5b (12.2 g, 19.58 mmol, 96%) as a white solid. Mp 81–
4.3. Synthesis of gelator 3b
82 8C; 1H NMR (CDCl3):
d 7.73 (bs, 1H), 6.40 (bs, 1H), 3.58 (dd, 6.4,
4.8 Hz, 1H), 3.52 (m, 4H), 2.60–2.50 (m, 2H), 2.33–2.20 (m, 5H);
Using a similar procedure as described for the synthesis of
gelator 3a, reaction of 1H,1H,2H,2H-perfluorohexylamine (11.8 g,
19F NMR (CDCl3):
À126.4 (m, 4F).
d
À81.5 (m, 6F), À114.6 (m, 4F), À125.0 (s, 4F),

194
A. Raghavanpillai et al. / Journal of Fluorine Chemistry 135 (2012) 187–194
Reaction of 5b (6.0 g, 9.6 mmol) with n-octyl isocyanate (1.49 g,
9.6 mmol) provided compound 6b (7.25 g, 9.3 mmol, 97%) as a
white crystalline solid. Mp 172 8C; 1H NMR (acetone-d6):
7.72
(t, distorted, J = 6.8 Hz, 9H). Elemental analysis: C, 68.19; H, 11.44;
N, 10.97; found: C, 68.28; H, 11.62; N, 10.87.
d
(bs, 1H), 7.58 (bs, 1H), 6.08 (d, J = 8.0 Hz, 1H), 5.93 (bs, 1H), 4.58 (q,
J = 5.8 Hz, 1 H), 3.55 (m, 4H), 3.15 (m, 2H), 2.74 (dd, J = 15.2, 6.0 Hz,
1H), 2.55 (dd, J = 15.2, 6.0 Hz, 1H), 2.47 (m, 4H), 1.48 (m, 2H), 1.30
4.9. Gelation in organic solvents
Generally, 1–4 wt % of a gelator in an organic solvent in a closed
vial was heated in a reactor block equipped to heat multiple vials to
5 8C below the boiling point of the solvent until a clear solution was
obtained. The vials were allowed to cool to RT either 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. Stability of the gel was tested by inverting the vial,
and gel samples for which the whole mass remains a single phase
(no phase separation between solid and liquid phase) are
considered stable.
(m, 10H), 0.90 (t, J = 6.1 Hz, 3H); 19F NMR (acetone-d6):
d
À82.4 (m,
6F), À115.3 (m, 4F), À125.5 (t, J = 8.6 Hz, 4F), À127.1 (m, 4F).
Elemental analysis: C, 38.57; H, 4.14; N, 7.20; found: C, 38.51; H,
4.21; N, 7.22.
4.6. Synthesis of gelator 6c
Using a similar procedure as described for the synthesis of
gelator 6a, reaction of 1H,1H,2H,2H-perfluorobutylamine (2.23 g,
12.27 mmol) with N-BOC-
provided 4c (2.06 g, 5.06 mmol, 83%) as a white crystalline solid.
1H NMR (CDCl3):
7.29 (bs, 1H), 6.26 (bs, 1H), 6.11 (bs, 1H), 4.35 (q,
L-aspartic acid (1.43 g, 6.13 mmol)
4.10. Gel-impregnation on nonwoven supports in organic solvents
d
J = 4.0 Hz, 1H), 3.57 (m, 4H), 2.83 (dd, J = 15.2, 4.4 Hz, 1H), 2.56 (dd,
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 to 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 usually observed in about 0.5–6 h, and the gels
were allowed to age at RT for an additional 6 h. The gelator-
impregnated samples were removed and dried in a vacuum oven
at RT overnight. The dried samples were weighed and used for
contact angle measurements.
J = 15.6, 6.4 Hz, 1H), 2.32 (m, 4H), 1.47 (s, 9H); 19F NMR (CDCl3):
À86.2 (d, J = 26 Hz,6F), À118.4 (dq, J = 18.4, 7.8 Hz, 4F).
d
Deprotection of 4c (1.94 g, 4.77 mmol) using trifluoroacetic acid
at RT, followed by treatment with saturated NaHCO3 provided 5c
(1.5 g, 3.54 mmol, 74%) as a white solid. 1H NMR (CDCl3):
d 7.83 (bs,
2H), 6.33 (bs, 1H), 6.10 (bs, 1H), 4.32 (bs, 1H), 3.57 (m, 4H), 2.64 (m,
2H), 2.30 (m, 4H); 19F NMR (CDCl3):
d
À86.2 (d, J = 26 Hz,6F),
À118.3 (dq, J = 18.4, 7.8 Hz, 4F).
Reaction of 5c (0.5 g, 1.18 mmol) with n-octyl isocyanate
(0.183 g, 1.18 mmol) provided compound 6c (0.56 g, 0.963 mmol,
82%) as a white crystalline solid. 1H NMR (acetone-d6):
d 7.78 (t,
J = 5.2 Hz, 1H), 7.68 (bs, 1H), 7.58 (bs, 1H), 5.92 (bs, 1H), 5.54 (bs,
1H), 4.41 (bs, 1H), 3.53 (m, 4H), 3.13 (t, J = 7.6 Hz, 2H), 2.80 (dd,
J = 15.6, 6.0 Hz, 1H), 2.66 (dd, J = 15.2, 6.0 Hz, 1H), 2.41 (m, 4H),
1.47 (m, 2H), 1.31 (m, 10H), 0.90 (t, distorted, 3H); 19F NMR
Acknowledgements
(CDCl3):
d
À86.2 (d, J = 26 Hz,6F), À118.3 (dq, J = 18.4, 7.8 Hz, 4F).
We gratefully acknowledge Stefan Reinartz of DuPont Perfor-
mance Coatings for helpful insight into this research and Liang
Liang of DuPont Corporate Center for Analytical Sciences (CCAS) for
microscopy.
Elemental analysis: C, 43.60; H, 5.58; N, 9.69; found: C, 44.2; H,
5.87; N, 9.5.
4.7. Synthesis of gelator 9
References
Using a similar procedure as described in the synthesis of
gelator 3a, reaction of n-octylamine (5.71 g, 45.0 mmol) with N-
Boc-b-alanine (8.50 g, 45.0 mmol) provided 7 (11.6 g, 38.6 mmol,
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86%) as a white crystalline solid. Mp 67.5–68.4 8C. Deprotection of
7 (10.5 g, 35.0 mmol) with trifluoroacetic acid at RT provided 8
(6.5 g, 32.5 mmol, 93%) as a white solid. Mp 142–143.5 8C. Reaction
of 8 (1.5 g, 7.5 mmol) with n-octyl isocyanate (1.16 g, 7.5 mmol)
provided compound 9 (2.41 g, 6.78 mmol, 91%) as a white solid. Mp
176.5–177.5 8C; 1H NMR (methanol-d4):
d 3.38 (t, J = 6.4 Hz, 2H),
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4.8. Synthesis of gelator 12
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reaction of N-Boc-L-aspartic acid (10.0 g, 43.1 mmol) with n-
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octylamine (11.1 g, 86.2 mmol) provided N-Boc-
L
-Asp-dioctyla-
mide 10 (18.8 g, 41.3 mmol 92%) as a white solid. Mp 112–113 8C.
Compound 10 (18.6 g, 41.0 mmol) was deprotected using trifluor-
oacetic acid to obtain 11 (13.4 g, 37.7 mmol, 96%) as a white solid.
Mp 120.5–122 8C. Reaction of 10 (1.78 g, 5.0 mmol) with n-octyl
isocyanate (0.776 g, 5.0 mmol) provided compound 12 (2.53 g,
4.96 mmol, 99%) as a white crystalline solid. Mp 169.6–171.4 8C;
1H NMR (DMF-d7):
d 7.38 (bs, 2H), 6.06 (d, J = 8.0 Hz, 1H), 6.01 (t,
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J = 5.2 Hz, 1H), 4.52 (g, J = 6.4 Hz, 1H), 3.13 (m, 6H), 2.59 and 2.55 (2
merged dd, J = 15.0, 6.5 Hz, 2H), 1.48 (m, 6H), 1.31 (bs, 30H), 0.89