Scaleable two-component gelator from phthalic acid derivatives and primary alkyl amines: Acid-base interaction in the cooperative assembly

Article abstract of DOI:10.1039/c7sm00797c

A series of phthalic acid derivatives (P) with a carbon-chain tail was designed and synthesized as single-component gelators. A combination of the single-component gelator P and a non-gelling additive n-alkylamine A through acid-base interaction brought about a series of novel phase-selective two-component gelators PA. The gelation capabilities of P and PA, and the structural, morphological, thermo-dynamic and rheological properties of the corresponding gels were investigated. A molecular dynamics simulation showed that the H-bonding network in PA formed between the NH of A and the carbonyl oxygen of P altered the assembly process of gelator P. Crude PA could be synthesized through a one-step process without any purification and could selectively gel the oil phase without a typical heating-cooling process. Moreover, such a crude PA and its gelation process could be amplified to the kilogram scale with high efficiency, which offers a practical economically viable solution to marine oil-spill recovery.

Full text of DOI:10.1039/c7sm00797c

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Jure Dobnikar et al.
Rational design of molecularly imprinted polymers
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Scaleable two-component gelator from phthalic acid derivatives
and primary alkyl amines: Acid-base interaction in the
cooperative assembly †
Received 00th January 20xx,
Accepted 00th January 20xx
Ting Su,a Kwon Ho Hong,b Wannian Zhang,a Fei Li,a Qiang Li,a Fang Yu,a Genxiang Luo,a Honghe
Gaoa and Yu-Peng He*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
A series of phthalic acid derivatives (P) with a carbon-chain tail was designed and synthesized as single-component gelator.
Combination of the single-component gelator P and non-gelling additive n-alkylamine A through acid-base interaction
brought out a series of novel phase-selective two-component gelator PA. Gelation capability of P and PA, structural,
morphological, thermos-dynamic and rheological properties of the corresponding gels were investigated. The molecular
dynamics simulation showed that the H-bonding network in PA formed between NH of A and carbonyl oxgen of P altered
the assembling process of gelator P. Crude PA could be synthesized through one-step without any purification and
selectively gel the oil phase without typical heating-cooling process. Moreover, such crude PA and the gelation process of
it could be amplified into kilogram scale with high efficiency, which offers a practically economic viable solution to marine
oil-spill recovery.
There were three main reasons for this: 1) these gelators
couldn’t be obtained from easily available and cheap starting
materials, 2) tedious synthetic routes, 3) poor gelation
Introduction
Phase-selective gelators (PSGs)[1] have drawn considerable
concerns due to their potential applications in dealing with oil
spill,[2] which had damaged the ecosystem and the
environment irrecoverably. Since Bhattacharya and co-workers
published their pioneering findings in this research area in
capability in large scale process. Such performance limited the
application of these gelators. Thus, there is a great need to
develop novel PSGs that can be efficiently synthesized by only
one-step procedure and maintain a high gelation capability in
the scaled-up process.
2001,[3] quite
a
number of PSGs were intensively
Among the reported variety structures for gelation, including
investigated.[4,5,1f] To meet the overwhelming demand of
practical applications, novel PSGs with great gelation capability
were indispensable. Recently, two-component PSGs[6,7] where
two individual species interact via covalent or noncovalent
forces have shown great advantages.[8] Among them, two
species combined through acid-base interaction brought out a
complex which then assembled further to form the fully
gelated network have been widely studied. For example,
Smith‘s lab developed several new and efficient dendritic two-
component systems.[8a] These systems figure high efficiency,
adjustment of gel performance and responsive to chemical
stimuli[8b-g]. However few research on gelation capability of
PSGs or two-component PSGs in kilogram scale was presented.
simple
amphiphiles,[4d,4e,4f]
alkanes,[4a]
modified
sugars,[1c,4g]
amino
oligopeptides,[4g]
acids,[4b,4c]
bola-
peptide
amphiphiles,[4g,4h,4i] dendrimers,[4c,4g] C3-symmetric molecules,[4c,4g]
nucleobases[4j] etc, to our best knowledge, few easily available
phthalic acid derived PSGs have been reported.[9] In this study, we
designed a series of structurally unique two-component
phthalic acid derived gelators formed by
amine A.[6d] Research result showed that acid-base
interactions between gelators and n-alkylamine brought
P and liner aliphatic
P
A
out a new series of two-component gelator PA, while A alone
are not capable of gelating these solvents. FESEM morphologies
study and X-ray diffraction data showed that the addition of
had changed the assembly manner. Two-component gelator
PA has distinct advantages over single-component gelator as
simply changing mole ratio of and could tailor the
properties of the gel. The optimized mole ratio of and was
A
P
P
A
P
A
depending on the solvent properties. We also tested the
gelation capability of PA (nP = nA = 16) formed by only one-step
procedure without any purification, the minimum gelation
concentration (MGC) of such crude PA had no significant
differences with PA formed by stepwise operation. What’s
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more important is that this highly efficient gelation systems
can phase-selectively gel the oil phase without normal heating-
cooling circle and show superior scale-up gelation ability for
the first time.
Results and discussion
Fig.1 Gels formed by the gelators P in different solvents (nP = 16): (a)
benzene (b) toluene (c) soybean oil (d) diesel (e) paraffin oil (f) cyclohexane
(g) lubricant.
Design and synthesis of gelators P and PA
We started our work by the synthesis of a series of compound P
(Scheme1) through a simple procedure using phthalic anhydride
and n-alkylamines (carbon-chain length from 8 to 18) as starting
materials.[10] Then the gelation ability of compound P was tested in
several organic solvents and oils (Table 1). The data showed that
gelator P did not form gel with any protic or polar solvents, but
congealed the non-polar solvents selectively. The MGC of P ranged
from 0.5 to 12.2 (wt%). Particularly, gelation of soybean oil,
cyclohexane, paraffin oil and n-hexadecane occurred in a relatively
low MGC (1.1, 1.9, 0.5 and 1.4 wt% respectively), while gelation
performance of P were worse in the aromatic solvents.
For diesel and paraffin oil, gelation performance of PA were
extremely regular. The optimized mole ratio of
P and A were
focused on 1:0.4 in diesel and 1:0.2 in paraffin oil while the
hydrophobic-chain length was changed. Under this condition,
MGC of PA (nP = nA
which was 4 times lower than the corresponding
of PA (nP = nA 16, = 1:0.2) in paraffin oil was 0.17 wt
which was 11 times lower than the corresponding (Table 2).
=
16,
P
:A
= 1:0.4) in diesel was 0.83 wt%,
P, and MGC
=
P
:A
%,
P
Moreover, MGC of PA in Table 2 were generally lower than 1
wt%, thus the two-component gelators PA showed remarkable
Fig. 1 showed the gel formed in different solvents when the
carbon-chain length was 16 (nP = 16). It was noteworthy that all of
the formed gels were stable for at least two months in our study.
gelatinizing
performance of PA were relatively random in the case of
benzene and toluene as the optimized mole ratio of and
were changed with both the hydrophobic-chain length and the
solvent (Table 3), the gelation ability of PA (most MGC> 1 wt
was still better than in both benzene and toluene.
property.[1k,2a,11]
Although
the
gelation
Notably, we discovered that the combination of gelators
P
P
A
and n-alkylamine A (nP = nA, n is the carbon number of the
hydrophobic-chain) in different mole ratios formed a new
series of two-component gelators PA. For the study of
molecular co-assembly, we gradually changed the mole ratio
%
)
P
of
P and A from 1:0.2 to 1:1.2, and tested their gelation
Table
2 Minimum gelation concentrations (wt%) of gelators PA with
different mole ratio in diesel and paraffin oil.a
capability in diesel, paraffin oil, benzene and toluene.
1:0.2
1:0.4
1:0.6
1:0.8
1:1
1:1.2
O
n
8
Di Pa
Di Pa
Di Pa
Di Pa
Di Pa
Di Pa
O
2.71
S
1.75
S
1.89
S
6.44
S
12.7
S
13.5
S
acetone
NHR
OH
O
+
H2NR
10 1.74 0.18 1.01 0.31 1.12 0.44 1.38 0.46 2.49 1.05
S
0.75
rt, 6h
12 0.97 0.45 0.87 0.79 1.16 0.97 1.43 1.00 1.75 0.89 2.05 1.01
14 1.65 0.25 0.92 0.84 1.00 1.21 2.16 0.68 2.80 0.77 2.96 0.88
16 1.84 0.17 0.83 0.39 2.93 0.61 1.38 0.62 0.92 10.5 1.76 11.3
18 1.97 0.23 1.96 0.43 3.53 0.62 5.60 1.87 3.58 1.04 4.43 1.21
O
P
O
A
67-76%
phthalic anhydride
R = CnH2n+1 (n = 8, 10, 12, 14, 16, 18)
Scheme 1 Synthesis of a series of single-component gelators P.
aDi = diesel; Pa = paraffin oil; In this table, carbon-chain length of the
complementary guest A was as same as that of the gelators P (n = nP = nA);
Table 1 Minimum gelation concentration (wt%) of gelators
P with different
S = soluble
.
The gelation time[12] of PA (nP = nA, P:A ≥ 1:1) in the diesel was
hydrophobic-chain lengths in various organic solvents and oils.a
longer than one day (2 hours on the mole ratio of P:A = 1:0.4), and
crystallization of PA in the gel phase could be observed after the gel was
placed longer than two days.[13]
Liquid or oil
benzene
toluene
nP=8
P
P
nP=10
P
P
nP=12
4.3
4.8
1.4
6.3
6.5
0.5
6.9
5.0
S
nP=14
9.2
12.2
3.1
3.6
3.3
1.9
11.6
5.9
S
nP=16
nP=18
10.3
6.3
5.6
5.6
3.3
4.4
11.9
11.6
P
6.4
8.5
4.2
3.5
1.9
1.2
9.8
2.6
S
soybean oil
diesel
paraffin oil
cyclohexane
lubricant
n-hexadecane
tetrahydrofuran
dichloromethane
ethyl acetate
chloroform
acetone
5.0
8.0
P
1.1
4.6
3.8
1.9
P
1.4
S
S
Table
3 Minimum gelation concentrations (wt%) of gelators PA with
different mole ratio in benzene and toluene.a
3.1
P
10.8
S
S
P
1:0.2
1:0.4
1:0.6
1:0.8
1:1
1:1.2
n
8
Be To
Be To
Be To
Be To
Be To
Be To
7.67 4.81 5.14 1.69 5.51 3.18
S
S
S
S
S
S
S
S
S
S
S
S
S
10 6.70 3.52 2.81 2.47 4.97 9.16
12 2.24 2.28 3.55 2.29 5.71 1.97 4.47 2.49 10.52
S
S
P
S
P
P
P
7.03
P
P
P
14 1.98 3.56 2.63 2.78 3.32 2.78 7.77 6.40 10.82 2.40 7.26 2.76
16 1.93 1.92 1.64 2.17 0.71 3.08 2.09 3.35 6.89 4.00 7.38 6.31
18 7.90 8.00 2.79 3.13 5.93 6.01 4.14 3.09 3.62 5.97 4.31 6.41
S
S
S
S
S
P
S
P
S
S
P
P
methanol
S
S
S
S
S
P
ethanol
S
S
S
S
S
S
aBe = benzene; To = toluene; In this table, carbon-chain length of the
1,4-dioxane
S
S
S
P
P
P
complementary guest A was as same as that of the gelators
S = soluble
P (n = nP = nA);
.
aP = precipitation; S = soluble.
bnP is the carbon number of the hydrophobic-chain of the gelators P.
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Table 4 Minimum gelation concentrations (wt%) of gelators PA with
different carbon-chain length of n-alkylamine in paraffin oil.[a]
Obviously, a key issue in the enhancements of either the gelation
capability or thermal stability of PA is the presence of A. In order to
reveal the effect of A on the gelators P, FT-IR study, FESEM study, X-
ray diffraction experiments, molecular dynamics simulation and
rheological analysis were carried out.
n
nA=8
0.43
0.17
nA=10
0.33
nA=12
0.45
nA=14
0.47
nA=16
0.41
nA=18
0.48
nP = 12
nP = 16
0.14
0.16
0.17
0.17
0.20
FT-IR spectroscopy
a The mole ratio is P:A = 1:0.2 (optimized mole ratio in the paraffin oil).
Self-assembling processes of gelators were known to be driven by
secondary forces: van der Waals, hydrogen bonding interaction, π-π
stacking, electrostatic, and dipole - dipole.[15] For the study of these
interactions, FT-IR spectra of chloroform solution of P (nP = 16),
diesel xerogel of P (nP = 16), diesel xerogel of PA (nP = nA = 16, P:A =
1:0.4), toluene xerogel of PA (nP = nA = 16, P:A = 1:0.2) and benzene
xerogel of PA (nP = nA = 16, P:A = 1:0.6) were recorded (Fig. 3). The
FT-IR spectrum of no self-assembly P (nP = 16) in chloroform
showed transmission bands at 3439 cm-1 and 1722 cm-1, which were
non-hydrogen-bonded N-H stretching band and C=O stretching
band, respectively (Fig. 3a). The transmission band of P (nP = 16)
diesel xerogel appeared at 3247 cm-1 and 1720 cm-1 respectively
(Fig. 3b). The transmission band of PA appeared at 3245 cm-1 and
1648 cm-1 for diesel xerogel (Fig. 3c), 3308 cm-1 and 1711 cm-1 for
toluene xerogel (Fig. 3d), 3244 cm-1 and 1710 cm-1 for benzene
xerogel (Fig. 3e) respectively. These data all declared that N-H
stretching bands and C=O stretching bands shifted to lower
frequencies. Therefore, intermolecular hydrogen- bonding plays an
important role in this gelation systerm.[16]
The above result was encouraging, since it showed that the
gelation capability of PA could be changed simply by tuning the
mole ratio of the two components.
In addition, we changed carbon-chain length of the non-gelling
additive A in two-component gelators PA (nP ≠ nA) and tested their
MGC in paraffin oil (on the optimized mole ratio of P:A = 1:0.2,
Table 4). It was noteworthy that the gelation property of PA were
scarcely affected by the carbon-chain length of the non-gelling
additive A.
For refine oil like benzene, cyclohexane, toluene, diesel and
petrol, the formed gel could be melted by heating and distilled to
recover the oil.
Thermal stability of gels
Thermal stability of gels formed by gelators
P and PA have
been compared through Tgel (gel-to-sol transition
temperature), which were measured by differential scanning
calorimetry (DSC, Fig. 2).[14] In diesel, Tgel values were 50.98 ˚C
Morphologies from Field-emission scanning electron microscope
(FESEM)
and 67.83 ˚C for
= 16, = 1:0.4, 10.82 wt%) gel (Fig. 2a-b). In paraffin oil, Tgel
values were 44.64 ˚C and 61.92 ˚C for (nP = nA = 16, 5.59
wt%) gel and PA (nP = nA = 16, = 1:0.2, 5.59 wt%) gel (Fig.
2c-d). PA gels demonstrated higher Tgel values then
corresponding gels, which indicated that PA gels were
P (nP = nA = 16, 10.82 wt%) gel and PA (nP = nA
P:A
P
Field-emission scanning electron microscope (FESEM) was
employed to examine the microstructure of organogels (Fig. 4). The
FESEM micrograph of diesel xerogel based on gelator P (nP = 16)
showed lamellar structures of 133 nm thickness and 3.33 μm length
P:A
P
thermally more stable.
(Fig. 4a). Referring to diesel xerogel based on gelator PA (nP
=
a0.15
b 0.3
30.12°C
27.06°C
0.10
0.05
0.2
a
b
c
3439
1722
1720
0.1
0.0
0.00
3427
3245
-0.1
-0.2
-0.3
-0.05
-0.10
-0.15
50.98
°C
67.83
60
°C
d
1648
20
40
60
80
100
20
40
80
100
Temperature (°
C
)
Temperature (°C)
e
3308
0.4
0.4
0.3
c
d
22.33°C
12.43°C
0.3
1711
1710
0.2
0.1
0.2
0.1
3244
0.0
0.0
-0.1
-0.2
-0.3
-0.4
-0.1
-0.2
-0.3
-0.4
44.64
40
°C
61.92
40
°C
20
60
80
100
20
60
Temperature (°
80
100
4000
3500
3000
2500
2000
1500
1000
500
Temperature (°C)
C
)
Wavenumber ( )
cm-1
Fig. 3 a: Gelator P (nP = 16) in choroform solution; b: Diesel xerogel of P (nP =
16); c: Diesel xerogel of PA (nP = nA = 16, P:A = 1:0.4); d: Toluene xerogel of
PA (nP = nA = 16, P:A = 1:0.2); e: Benzene xerogel of PA (nP = nA = 16, P:A =
1:0.6).
Fig. 2 DSC thermograms of diesel gel of a: P (nP = 16), b: PA (nP = nA = 16, P:A
= 1:0.4), and paraffin oil gel of c: P (nP = 16) d: PA (nP = nA = 16, P:A = 1:0.2).
Top four curves are cooling curves and bottom four curves are heating
curves.
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22500
20000
17500
15000
12500
10000
7500
5000
2500
0
7000
6000
5000
4000
3000
2000
1000
0
a
b
c
d
5
10 15 20 25 30 35 40 45
5
10 15 20 25 30 35 40 45
Two -Theta (deg)
Two - Theta (deg)
Fig. 5 XRD spectra of a:
1:0.4) diesel xerogels, c:
P:A = 1:0.6) benzene xerogel.
P
(
P
nP = 16) diesel xerogels, b: PA
(nP = 16) benzene xerogel, d: PA (nP = nA = 16,
(nP = nA= 16, P:A=
in
peaks at 2.49 nm, 1.24 nm (1/2) and 0.82 nm (1/3). This result
indicated that gelator assembled into single set lamellar
organization in -hexadecane. Such difference in lamellar structure
between P (nP = 16) diesel and -hexadecane gel may arise from the
complex additions in diesel.[20] PA (nP = nA = 16, P:A = 1:0.4)
n-hexadecane xerogel of P (nP = 16), which showed diffraction
Fig. 4 FESEM images of a:
P
(
nP = 16) diesel xerogels, b: PA
(nP = 16) benzene xerogel, d: PA (nP = nA
= 16, P:A = 1:0.6) benzene xerogel.
(nP = nA= 16,
P:A= 1:0.4) diesel xerogels, c:
P
P
n
n
nA = 16, P:A = 1:0.4), flower-like structure with a diameter in the
n
-
range of 3.1 3.8 μm was observed (Fig. 4b). It is clear that there
~
hexadecane xerogel also presented less peaks in the small-angle
region, which was coincide with PA (nP = nA =16, P:A = 1:0.4) diesel
xerogel (Fig. S13 in the Supporting Information).
are vast tiny platelets branched from the corner of the ball. Such
flower-like ball network possibly facilitate the entrapment of more
solvent molecules and the branched platelets might bring out
better interpenetration to the adjacent balls, therefore PA-gel
shows higher gelation capability and thermal stability than P-gel. It
is assumed that the adding of A leds to the branching process at the
growing of lamellar structure. This could be understood as the
result of the unsaturated salt formation.[17]
XRD of benzene xerogel of P (nP = 16) showed a group of
diffraction peaks at d1 = 3.91 nm, d2 = 1.97 nm (1/2), d3 = 1.31 nm
(1/3), d4 = 0.98 nm (1/4), d5 = 0.78 nm (1/5), indicating that gelator
P assembled into single set lamellar organization in benzene. And
this periodicity lost in the PA (nP = nA = 16, P:A = 1:0.6) benzene
xerogel (Fig. 5c-d).
Gelator P and PA formed complete different structure in benzene.
From Fig. 4c-d, it is obvious that in benzene gelator P and PA
assemble into fiber stucture. With the combination of A, fibers
inside PA xerogel were much longer (Fig. 4d). This also explain the
better gelation performance of PA in benzene. And it indicated that
solvents had great influence on the assembly way of gelators.
Molecular Dynamics Simulation
From the FESEM micrograph and XRD experiments, we could see
that three-dimensional network rather than lamellar structures
formed after
n-alkylamine A was added. In order to obtain an
insight of the gelation process of PA with diesel in a molecular level,
a molecular dynamics (MD) simulation of the two components P
Molecular packing arrangements from X-ray diffraction data
and A in n-hexadecane molecules was performed using Desmond
X-ray diffraction (XRD) experiments were carried out to investigate
the molecular packing and orientation of the gelators in the gel
state (Fig. 5). Diesel xerogel of P (nP = 16) showed two groups of
diffraction peaks at d1 = 2.87 nm, d2 = 1.42 nm (1/2), d3 = 0.94 nm
(1/3) and d1’ = 2.51 nm, d2’ = 1.25 nm (1/2), d3’ = 0.83 nm (1/3),
respectly (Fig. 5a). These results indicated the presence of two sets
of lamellar structures in the gel network.[4e] The extended
molecular length of gelator P (nP = 16) was 2.62 nm (Fig. 6a,
calculated by Material Studio 5.5). Moreover, the XRD response
revealed one intense peak in the wide angle region at 2θ = 19.92°,
which may be attributed to the hydrogen bonding distance ~ 0.45
package[21]. A novel inverse micelle type PA-complex was formed
through the H-bonding network among the hydrophilic heads of
five P and two A (Fig. 6f and 6g). Representative frames showed
that the hydrocarbon tails of PA-complex form efficient
hydrophobic interactions (van der Waals interactions) with
n-
hexadecane molecules by aligning themselves parallel to the
hydrocarbons (Figure 7). Thus we could concluded that the addition
of n
-alkylamine A has changed the self-assembling[22] way of P by
forming H-bonding network with P, which leading to a novel ball-
like structure.
nm.[18] In the presence of
n-alkylamine A, diesel xerogel of PA (nP =
nA = 16, P:A = 1:0.4) showed less and low intensity peaks in the Rheological properties
small-angle region (Fig. 5b), which indicating more amorphous
character.[19] This is in good coincidence with the FESEM data.
In order to figure out the exact reason for two groups of
diffraction peaks in diesel xerogel, XRD experiment was conducted
Rheological behaviour of these organogels can be very important
for their practical applications. This is largely depended on the
supramolecular aggregation of gelator molecules. Fig. 8a and 8c
showed the plots of G’ and G’’ against strain at a constant
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106
105
104
103
102
101
100
106
105
104
103
102
7.5%
2.1%
''
G
G
'
G
''
P
P
G
G
'
G ''
P
P
101
100
'
G
''
PA
PA
'
G
PA
PA
b)
102
a)
102
10-2
10-1
100
101
10-1
100
101
γ
%
ω
(rad / s)
105
104
103
102
101
105
104
103
102
101
100
33.3%
9.5%
G
'
G
''
G
G
'
G ''
P
P
P
P
'
G
''
PA
G
'
G
''
PA
PA
PA
d)
c)
102
10-1
100
101
102
10-2
10-1
100
101
γ
%
ω
(rad / s)
Fig. 8 Rheological studies for the diesel gel of P (10.82 wt%, nP = 16) and PA
(10.82 wt%, nP = nA = 16, P: A = 1:0.4) (a) stress sweep, (b) frequency sweep;
and for the paraffin oil gel of P (5.59 wt%, nP = 16) and PA (5.59 wt%, nP = nA
= 16, P: A = 1:0.2) (c) stress sweep, (d) frequency sweep.
sol (G’ < G’’) change beyond the critical strain. Overall, the
mechanical properties of P and PA gels are very robust and similar,
whereas the gels based on single-component gelator
mechanically weaker.
P are
Frequency sweep experiments were taken in the linear
viscoelastic region (γ fixed at 0.05%) decided by the strain sweeps
experiments. It was showed that the storage modulus (G’) was
higher than the loss modulus (G”) at any given frequency (Fig. 8b,
8d). This observation confirmed the formation of soft solid-like
gels.[23] Also, the two-component gels possessed higher G’ values
(one order) compared to the single-component gels on the same
concentration. These results showed A-induced enhancements in
the mechanical property of gels which was in line with our
expectation.
Fig. 6 Possible arrangements of gelator P (nP = 16) and PA (nP = nA= 16, P:A =
1:0.4) in diesel. a) The energy-minimized structure of P; b and c) possible
arrangements of P; d) potential ball-like structure of PA; e) selected regions
of the XRD pattern of P (nP = 16) diesel xerogel; f) MD simulation of PA
complex ; g) H-bonding network in the PA-complex.
Applications
It was noteworthy that we also tested the gelation capability of
crude PA (nP = nA = 16) formed by only one-step procedure (phthalic
anhydride and n-alkylamine A were stirred together in a glass bottle
in a ratio of 1:1.2 and 1:1.4, respectively) without any purification
(Scheme 2). To our delight, MGC of such PA (nP = nA= 16) in diesel
and paraffin oil (0.90 and 0.21 wt%, respectively) had no significant
differences with PA (nP = nA= 16) formed by adding an extra n-
alkylamine A to the pure P (0.83 and 0.17 wt%, showed before in
Table 2). Thus, such PA formed by only one-step procedure is a
readily alternative to PA formed by stepwise operation in practical
applications.
Fig. 7 Representative frames of the 5 ns MD simulation (1024 frames) of the
PA-complex in n-hexadecane molecules.
Having established the ability of gelator PA to form strong and
stable gel in biphase mixture (Fig. S16), we further examined the
gelation process without heating-cooling cycle. Since gelator PA (nP
= nA= 10, P:A = 1:0.4) showed a comparative gelation perfomance
and better solubility than PA (nP = nA= 16, P:A = 1:0.4), we used it
for oil-spill recovery. For the recovery of diesel, petroleum ether
(5% ethanol) was used as non-polar gelator carrier (Fig. 9, Video 1).
frequency of 1 Hz. The storage modulus (G’) of these gels decreased
rapidly and fell below the loss modulus (G’’) after the critical strain
region indicated that the oil gels underwent gel (G’ > G’’) to
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To our great satisfaction, the diesel layer was thickened in about 1
minute and could be skimmed off with a sieved scoop. The mass
fraction of gelator used was 6 wt% to produce enough gel solidity.
Rheological properties of the recovered diesel gel were shown in
the supporting information (Fig. S17). Recovery of crude-oil was
also tested and the crude-oil layer was thickened within 5 minute
(Fig. S18, Video 2). The remained liquor phase was extracted and
Experimental
Synthesize of single-component gelator P
All alkylamines, solvents were purchased from well-known
commercial sources and were used without further
purification, as appropriate. 1.07 g (7.2 mmol) of phthalic
anhydride and 65 mL acetone (solvent) were introduced into a
concentrated, the results showed that neither gelator PA nor n-
150-mL round-bottomed flask. Then 6.6 mmol of
n-alkylamine
decanamine was detectived.
A
was added slowly with rapid stirring. After the completion of
In order to examine the scale-up capability of the target gelators,
a kilogram-scale gelation between paraffin oil (1 kilogram, 1.2 L)
and crude PA was attempted (Fig. 10). The gelation capability of
the PA was 10.47 wt% (9.1g L-1) in the beaker. Thus, this gelator
might be practically viable approach for marine oil-spill recovery.
addition, stirring was continued for 6h at room temperature.
The crude product was recrystallized from water/ethanol
mixture to give the mono-alkylamide phthalic acid
from 67% to 76%.
P with yield
Gelation Studies
O
H2
N
O
+
15
The gelation propensity of P/PA was initially investigated in paraffin
oil. For evaluation of MGC, a known amount of P/PA in paraffin oil
was heated to 85-90°C, which resulted in a clear solution. The
resulting clear solution on spontaneous cooling transformed into
gel within 1-2 min. The organo-gelation propensity of P/PA has
been checked systematically by gradually increasing the amount of
the paraffin oil. In that way the minimum concentration of the
gelators that required to immobilize 1 mL of paraffin oil, i.e, MGC
value was determined. The above measurement was carried out
three times and the average MGC value has been reported.
A
O
1.0 equiv.
1.4 equiv.
NH
HN
O
HO
O
OH
O
H
O
H
O
N
H
15
HO
O
H
O
O
H
N
N
H
O
H2
N
O
O
NH
N
+
15
H
OH
HO
O
NH
O
P
A
1.0 equiv.
0.4 equiv.
PA
only a simple one-step procedure
without any purification (MGC < 1 wt%)
Scheme 2 Synthesis of two-component gelator PA via one-step procedure
(nP = nA = 16, phthalic anhydride: A = 1:1.4).
Characterization
NMR spectra were recorded on Agilent Technologies 400/54
Premium Shielded instruments and calibrated using residual solvent
peaks as internal reference. Multiplicities are recorded as: s =
singlet, d = doublet, t = triplet, dd = doublet of doublets, dt =
doublet of triplets, m = multiplet. High resolution ESI mass
experiments were operated on a Bruker Daltonics, Inc. APEXIII 7.0
TESLA FTMS instrument. FTIR measurements were carried out in a
Perkin Elmer Spectrum-GX Spectrometer using KBr pellet,
respectively. Gels were carefully mounted on the glass slide and
dried for a few hours under vacuum before imaging. The samples
were then coated with platinum vapor and analyzed on a Hitachi
SU-8010 microscope operated at 1 kV. Gels were analyzed using a
Rigaku D/MAX-RB instrument. The X-ray beam generated with a
rotating Cu anode at the wavelength of Kα beam at 1.5406 Å was
directed toward the film edge and scanning was done up to a 2θ
value of 48°. Differential scanning calorimetry (DSC) was carried out
by using a TA DSC-TGA. A volume of 0.5 ml of P diesel gel (10.3 wt%
as example) was placed into a screw-capped vial. The sample vial
was placed into the DSC apparatus together with an empty sample
vial as reference. Each sample was heated to melting to remove the
anisotropic history. The heating-cooling-heating cycle from 0 ˚C to
Fig.9 a) Petroleum ether (5% ethanol) solution of gelator PA (nP = nA= 10,
P:A = 1:0.4) was spread over a diesel/water mixture (20 mL:400 mL). b)
Gelation of the diesel layer in about 1 min. c) Removal of the diesel gel with
a sieved scoop. d) The removed diesel gel.
100˚C was performed at
a
rate of 5˚C min-1. Rheological
measurements were performed with a hybrid rheometer (TA
instrument DHR-2) equipped with steel coated parallel-plate
geometry (25 mm diameter). The gap distance was fixed at 1mm.
All measurements were done at 25˚C. Firstly, a stress sweep at fixed
frequency (1 Hz) was performed to determine the linear regime of
Fig. 10 Gelation of 1.2L paraffin oil with the crude product.
6 | J. Name., 2012, 00, 1-3
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Conclusions
We have successfully designed and prepared
a novel two-
component gelation system derived from phthalic acid (MGC < 1
wt%). MD simulation showed the additive A changed the self-
assembling way of gelator P by forming H-bonding network in the
acid-base complex, which bring out better gel properties comparing
to the simple-component gelation system. Unlike other previously
reported two-component gelation systems, we can readily modify
the mole ratio of gelator P and additive A to control the gelation
capability of PA. Especially, the obtained two-component gelation
system has a high two phase selectivity between aqueous and
organic solvent, this process could be finished without heating-
cooling operation. Furthermore, the gelation process can be
progressed in a kilogram scale, which is reported for the first time
and thereby showed to be an alternative solution for practical oil
spill recovery.
Acknowledgements
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This research work is supported by National Natural Science
Foundation of China (Grant No: 21402078), the Scientific Research
Foundation of Liaoning Science and Technology Agency (Grant No.
2015020691), General and Young Scholars Project of Liaoning
Education Department (Grant No: L2015308 and LJQ2015060) and
Fushun Science & Technology Program (Grant No: 20141116).
We thank the Minnesota Supercomputing Institute for the
support of the computational simulations.
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Soft Matter
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DOI: 10.1039/C7SM00797C
Acid-base interaction in the cooperative assembly enhanced the gelation capability dramatically,
which lead to an efficient kilogram-scale gelation.

Soft Matter
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DOI: 10.1039/C7SM00797C
416x164mm (300 x 300 DPI)