Synthesis and structure–activity relationships of nonionic surfactants with short fluorocarbon chains

Article abstract of DOI:10.1016/j.molliq.2020.114486

The biodegradability of fluorinated surfactants can be improved by reducing the length of the fluorocarbon chain. In this study, ten new nonionic fluorinated surfactants with various hydrophilic and hydrophobic chain lengths were synthesized by means of s

Full text of DOI:10.1016/j.molliq.2020.114486

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Synthesis and structure–activity relationships of nonionic
surfactants with short fluorocarbon chains
Ruiguo Wang, Lingyun Song, Yuanqiang Guo, Junjie Kou,
Hongjian Song, Yuxiu Liu, Jingjing Zhang, Qingmin Wang
PII:
S0167-7322(20)35468-4
DOI:
https://doi.org/10.1016/j.molliq.2020.114486
MOLLIQ 114486
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
20 August 2020
28 September 2020
30 September 2020
Please cite this article as: R. Wang, L. Song, Y. Guo, et al., Synthesis and structure–activity
relationships of nonionic surfactants with short fluorocarbon chains, Journal of Molecular
Liquids (2018), https://doi.org/10.1016/j.molliq.2020.114486
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Synthesis and Structure–Activity Relationships of Nonionic Sur-
factants with Short Fluorocarbon Chains
Ruiguo Wanga, Lingyun Songa, Yuanqiang Guoa, Junjie Koua,*, Hongjian Songa,
Yuxiu Liua, Jingjing Zhanga,b,*, Qingmin Wanga,*
a State Key Laboratory of Elemento-Organic Chemistry, Research Institute of
Elemento-Organic Chemistry, College of Chemistry, Collaborative Innovation Center
of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071,
China;
b College of Basic Science, Tianjin Agricultural University, Tianjin 300384, China.
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ABSTRACT
The biodegradability of fluorinated surfactants can be improved by reducing the
length of the fluorocarbon chain. In this study, ten new nonionic fluorinated
surfactants with various hydrophilic and hydrophobic chain lengths were synthesized
by means of substitution and ring-opening reactions using methoxypolyethylene
glycols (mPEGs) or 2-methoxyethanol, epibromohydrin, and perfluoroalkyl alcohols
as raw materials. We measured the static and dynamic surface tension of the
synthesized surfactants and used the resulting data to develop structure–activity
relationships. We found that mPEG molecular weight was the main determinant of
minimum surface tension, and the number of fluorocarbon atoms was the main
determinant of critical micelle concentration. Diffusivity decreased with increasing
number of fluorocarbon atoms but increased with increasing mPEG molecular weight.
Surfactant 5i showed the best performance, lowering the surface tension of water to
17.89 mN/m.
KEYWORDS
Nonionic fluorinated surfactant, Static surface tension, Dynamic surface tension,
Diffusivity coefficient, Structure-activity relationships
1. INTRODUCTION
Compared with traditional hydrocarbon surfactants, fluorinated surfactants have
outstanding physico-chemical properties determined by the very special properties of
fluorine. Fluorinated surfactants have high heat stability and chemical stability
because the C-F bond is very strong and chemically stable. Fluorine has a larger size
than hydrogen and is more electronegative, but its polarizability is smaller. Due to the
low polarizability, the interaction between the fluorinated chains is weak, resulting in
low cohesive energy of fluorocarbons and consequently low surface tension and low
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critical micelle concentration (CMC) [1]. Fluorinated surfactants can be divided into
two categories, ionic and nonionic, depending on the polarity of their hydrophilic
groups. Many syntheses of ionic fluorinated surfactants have been reported [2–6].
Nonionic fluorinated surfactants, which have different properties than ionic
fluorinated surfactants. They can act as antifogging agents for glass, metal, and plastic
surfaces [7]. When used in hard-surface-cleaning formulations, they impart better
wetting, emulsifying, dispersing, and solubilizing properties [8], and they are also
used to lower the surface tension of stimulating fluids for petroleum recovery [9].
Nonionic fluorinated surfactants are divided into two main types on the basis of
their hydrophilic polar groups: polyol types and polyethylene glycol types. Polyol
surfactants are generally obtained by reactions of organic compounds containing
multiple hydroxyl groups (e.g., glycerin, glycerol pentaerythritol, sorbitan, and
sucrose) with fluorinated compounds [10–16]. Polyethylene glycol, a nontoxic and
harmless hydrophilic compound, has been widely used for the synthesis of
nonfluorinated surfactants [17–20]. Modified polyethylene glycols are also used for
the synthesis of nonionic fluorinated surfactants [21–25] by means of reactions with
fluoroalkyl alcohols, which are readily available hydrophobic raw materials [26]. The
Zaggia group [27] investigated the effect of polyethylene glycol molecular weight (up
to approximately 1000 g/mol) on the critical micelle concentration and surface tension
of aqueous solutions of surfactants synthesized by reactions of the polyethylene
glycols with 2-(perfluorooctylmethyl)oxirane, which has eight fluorocarbon atoms.
They found that the CMC depended on the number of EO groups. The increase in the
value of n (the number of ethylene oxide units) from 1 to 20 induces an increase of
CMC from 9.3×10-5 mol/L to 188×10-5 mol/L. The Hedhli group [28] prepared
surfactants by means of reactions between polyethylene glycols with molecular
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weights up to 500 g/mol and fluorinated mercaptans with six or eight fluorocarbon
atoms. They found that the CMC was more sensitive to the number of ethylene oxide
units than the numbers of fluorocarbon atoms.
Although there have been important advances in design of polyethylene glycol
nonionic fluorinated surfactants, most of them are concentrated in long fluorocarbon
chains (>6). However, such surfactants are particularly difficult to degrade; not only
are they persistent and bioaccumulative but they also can be transported over long
distances in the environment [27, 29]. Therefore, the need for new, environmentally
friendly fluorinated surfactants is urgent. One way to facilitate biodegradation is to
shorten the fluorocarbon chain [22, 26], and this strategy has potential utility for the
development of biodegradable fluorine-containing surfactants.
In this study, we used environmentally friendly methoxypolyethylene glycols
(mPEGs) or 2-methoxyethanol, epibromohydrin, and short-fluorocarbon-chain (≤6)
perfluoroalkyl alcohols as raw materials for the synthesis of surfactants with various
hydrophilic and hydrophobic chain lengths by means of sequential substitution and
ring-opening reactions. We then measured the static and dynamic surface tension of
aqueous solutions of the surfactants and used the resulting data to develop structure–
activity relationships.
2. MATERIALS AND METHODS
2.1. Chemicals and Instruments
mPEG-1000 (m = 22) were purchased from Innochem Co., Ltd. (Beijing, China);
mPEG-500 (m = 11) was purchased from Macklin Co., Ltd. (Shanghai, China) and
mPEG-200 (m = 4) and 2-methoxyethanol were purchased from 3A Co., Ltd.
(Shanghai, China). 1H,1H-perfluoro-1-heptanol (n = 5) was purchased from J&K Co.,
Ltd. (Beijing, China); 1H,1H-perfluoro-1-hexanol (n = 4) and 1H,1H-perfluoro-1-
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pentanol (n = 3) were purchased from 3A Co., Ltd. (Shanghai, China). All reagents
1
were used as received. All the reactions were performed under Ar atmosphere. H
NMR and 19F NMR spectra were recorded on a Bruker AV 400 spectrometer.
Surfactant molar masses and their distributions were determined by gel permeation
chromatography (GPC) on a Waters 1525 instrument with THF as the mobile phase.
2.2. Surface Tension Measurements
Static surface tension values for aqueous solutions were measured by means of a
platinum ring test at 25 ± 1 °C on an automatic processor tensiometer (JK99M).
Reported values were averages of three measurements. Dynamic surface tension
values were measured by means of the maximum bubble pressure method at 25 ± 1
°C on a Kruss BP100 tensiometer. Both instruments were calibrated with pure water
prior to sample measurements.
3. RESULTS AND DISCUSSION
3.1. Synthesis of Surfactants and Determination of Their Structures
Scheme 1. Synthesis of surfactants 5
Nonionic fluorinated surfactants 5a–5j were obtained by reactions of
epibromohydrin 2 with mPEGs or 2-methoxyethanol 1 at room temperature and
subsequent ring-opening reactions of the resulting mono-epoxide-functionalized
mPEGs or 2-methoxyethanol 3 with perfluoroalkyl alcohols 4 (Scheme 1). Because
the surfactant products have a hydroxyl group, they can also undergo ring-opening
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reactions with 3. To minimize these side reactions, we screened various reaction
1
temperatures and 3:4 feed ratios and monitored the results by means of GPC and H
NMR spectroscopy. In Table 1, the optimal conditions for the synthesis of each
surfactant were listed. In the GPC spectra of 5g (m = 22, n = 5, Figure 1) obtained
under the optimized condition, the product peak appeared at retention times between
25 and 27.5 min, and there were no peaks with shorter retention times, which indicate
that the side reactions were essentially prevented. The purities of surfactants 5a, 5d,
5h were also determined by GPC spectra (see Figure S23).
entry
feed ratio (3:4) temperature (°C) surfactants (5)
3
4
4a, 4b, 4c
4a, 4b, 4c
4a, 4b, 4c
4c
1:3
1:3
1:4
1:5
80
50
70
90
5c, 5f, 5j
5b, 5e, 5i
5a, 5d, 5h
5g
1
2
3
4
3a
3b
3c
3d
a t-BuOK(1 equiv.) was used, the reaction time was 24 h.
Table 1. Ring opening conditions of intermediates 3a
Figure 1. GPC spectra of 5g
1
The structures of products with m = 4 or 1 could easily be determined by H
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NMR spectroscopy. For example, in the spectrum of 5b (m = 4, n = 3; Figure 2), H3
appeared as a triplet at δ 4.20 with an integration value of 2, and the integration values
for H1 and H2 were 2.96 and 0.90, respectively; these values are consistent with the
expected H3/H1/H2 ratio (2:3:1). The purities of surfactants 5 were determined by 1H
NMR and 19F NMR (see Figure S3 - S22).
Figure 2. 1HNMR spectrum of 5b
3.2. Static Surface Tension
For each surfactant 5, we plotted surface tension (γ) versus the logarithm of
surfactant concentration (C, millimolar) to determine the CMC and the lowest surface
tension (γmin); representative plots are shown in Figure 3. In addition, we calculated
maximum surface excess concentrations (Гmax) and minimum areas per surfactant
molecule (Amin) by using the Gibbs adsorption isotherm equations [30, 31]. The
formulas for calculating these quantities are as follows:
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(
)
(1)
(2)
Where γ is the surface tension of surfactant solution, C is the bulk concentration of
surfactant, n is a constant (for nonionic surfactants, n = 1), R is the gas constant
(8.314 J/(mol• K)), T is absolute temperature (K), and NA is the Avogadro constant
(6.022 × 1023 mol−1). The value of ∂γ/∂lgC is determined from the slope of the linear
fitting of the surface tension and lg C curve before CMC. The values determined from
the plots and equations are shown in Table 2.
c
d
e
CMCb
(mmol/L)
4.46
γmin
Гmax
Amin
surfactant
n
m
(mN/m)
23.05
(mol/m2)
(nm2)
5a
5b
5c
5d
5e
5f
4.94 × 10-3
3.36 × 10-4
3
3
3
4
4
4
5
5
5
5
11
4
6.07 × 10-3
─
2.74 × 10-4
─
4.27
18.41
34.89a
22.62
18.10
24.42a
34.51
23.21
17.89
1
─
5.47 × 10-3
6.18 × 10-3
─
3.04 × 10-4
2.69 × 10-4
─
1.21
0.95
11
4
1
─
5g
5h
5i
3.36 × 10-3
5.99 × 10-3
6.28 × 10-3
─
4.90×10-4
2.77 × 10-4
2.65 × 10-4
0.77
0.35
0.20
22
11
4
18.26a
1
5j
─
─
b
c
aThe γ of the surfactant at 0.5 mmol/L. The critical micelle concentration. The lowest
d
e
surface tension measured. The maximum excess surface concentration. The minimal area per
surfactant molecule.
Table 2. γmin, CMCs, Гmax, and Amin of surfactants 5
The data provided in Figure 3 show that for a given concentration, surface
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tension decreased with decreasing mPEG molecular weight. In table 2, γmin also
decreased as mPEG molecular was decreasing. For example, when n was 5,
decreasing m from 22 to 4 decreased γmin from 34.51 (5g) to 17.89 (5i) mN/m,
respectively. The reason for this trend may have been that changing the size of the
hydrophilic group changed the adsorption density of the surfactant; that is, decreasing
the size of the mPEG chain may have increased the ability of the surfactant molecules
to replace water molecules at the water–air interface, resulting in tighter gathering of
the surfactant molecules at the interface [27].
Figure 3. Surface tension as a function of logC for aqueous solutions of 5a, 5b, 5d,
5e, 5h and 5i
Plots of surface tension versus surfactant concentration for surfactants with a
given mPEG molecular weight and different numbers of fluorocarbon atoms are
compared in Figure 4. These plots show that for a given concentration, surface tension
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decreased with increasing number of fluorocarbon atoms. As shown in Table 2, γmin
also decreased as the number of fluorocarbon atoms was increased. For example, for
surfactants with m = 4, increasing n from 3 to 5 decreased γmin from 18.41 (5b) to
17.89 (5i) mN/m, respectively.
Further analysis of the data in Figure 4 and Table 2 shows that surfactants with m
= 11 or 4 exhibited the same trend, the γmin values for 5a, 5d, 5h (n = 3–5) were all
approximately 23 mN/m and all the surfactants with m = 4 (5b, 5e, 5i, n = 3–5) had
similar γmin values of approximately 18 mN /m. These results indicate that mPEG
molecular weight was the main determinant of γmin, a result that differs from that for
previously reportedly surfactants prepared by reactions of fluorinated mercaptan and
polyethylene glycol [28], probably because when there are fewer fluorocarbon atoms,
the hydrophobicity is much lower than when there are eight. It was worth noting that
for m = 1 (5c, 5f, 5j), when the concentration was higher than 0.5 mmol/L, the sample
would not dissolve completely, but the surface tension would still decrease slowly.
The surface tension was not balanced before 0.5 mmol/L; therefore, we could not
calculate the CMC and γmin values.
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Figure 4. Surface tension against logC for aqueous solutions of 5a, 5b, 5c, 5d, 5e, 5f,
5h, 5i and 5j
The value of γmin can be an indication of a surfactant’s effectiveness at reducing
surface tension. From Table 2, when n was 3, 4, or 5 and m was 4, γmin dropped below
20 mN/m. Surfactant 5i had the greatest effect on surface tension, reducing γmin to as
low as 17.89 mN/m.
As shown in Table 2, CMC decreased with increasing fluorocarbon chain length
but increased with increasing mPEG molecular weight. For example, the CMCs of 5b,
5e and 5i (m = 4) were 4.27, 0.95, and 0.20 mmol/L, respectively; and the CMCs of
5g, 5h, and 5i (n = 5) were 0.77, 0.35, and 0.20 mmol/L, respectively. These results
can be explained by the fact that an increase in the length of the hydrophilic chain
enhanced the solubility of the surfactant and therefore hindered micelle formation;
shorter mPEG chains seem to favor micelle formation [28]. In addition, increasing the
fluorocarbon chain length increased the steric bulk of the surfactant, which led to an
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increase in the aggregation number and favored micelle formation [32]. Further
analysis of the data in Table 2 indicates that for a given fluorocarbon chain length (5a,
5b (n = 3); 5d, 5e (n = 4); and 5g, 5h, 5i (n = 5)), there was little variation in CMC.
For example, the CMCs of 5a and 5b were 4.46 and 4.27 mmol/L. However, for a
given mPEG molecular weight, CMC varied considerably; for example, the CMCs of
5a, 5d, and 5h (m = 11) were 4.46, 1.21, and 0.35 mmol/L, respectively. These results
suggest that the number of fluorocarbon atoms was the main determinant of CMC.
For surfactants with a given fluorocarbon chain length, the saturated adsorption
capacity (Гmax) decreased with increasing mPEG molecular weight (Table 2). For
surfactants with a given mPEG molecular weight, Гmax increased as the number of
fluorocarbon atoms increased. Accordingly, Amin decreased with decreasing mPEG
molecular weight and increasing number of fluorocarbon atoms. This result can be
explained by noting that increasing the size of the mPEG increases the head group
size and thus lowers surfactant adsorption and that increasing the fluorocarbon chain
length results in closer packing of the surfactant molecules [32–34].
In short, the structures of both the hydrophobic and the hydrophilic portions of
the surfactants markedly affected their adsorption at the air–water interface. The
molecular weight of mPEG was the main determinant of γmin, and the number of
fluorocarbon atoms was the main determinant of CMC.
3.3. Dynamic Surface Tension
For the three surfactants with the same hydrophobic chain (n = 5, 5i, 5h and 5g)
and the three surfactants with the same hydrophilic chain (m = 4, 5b, 5e, 5i), the
temporal dependences of surface tension at concentrations of 0.1, 0.5, 1, and 2 times
the CMC are plotted in Figures 5 and 6, respectively. The plots indicate that as the
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surfactant concentration increased, both the rate and the magnitude of the reduction in
dynamic surface tension increased.
Figure 5. Dynamic surface tension data for 5i, 5h and 5g at various concentrations
As shown in Figure 5, the trends for surfactants 5h and 5g, which have relatively
large hydrophilic groups (m = 11 and 22, respectively), were similar to each other.
The initial surface tension decreased with increasing concentration; for example, at 10
ms, the surface tension of an aqueous solution of 5g at a concentration of 2 times the
CMC was 50 mN/m, versus 73 mN/m at 0.1 times the CMC. However, when the
hydrophilic group was small (m = 4 for 5i), regardless of the concentration, the
surface tension dropped more slowly. For example, the surface tension of an aqueous
solution of 5i with 2 times the CMC was 65 mN/m at 100 ms.
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Figure 6. Dynamic surface tension data for 5b, 5e and 5i at various concentrations
As shown in Figure 6, when the number of fluorocarbon atoms was small (n = 3
for 5b), surface tension dropped quickly to below the solvent surface tension
regardless of the concentration. For example, when the concentration of 5b was 0.5
times the CMC, the surface tension dropped to about 50 mN/m at 10 ms. When the
concentration of 5e (n = 4) was 0.5 times the CMC, at 10 ms, the surface tension was
close to that of water. For surfactants with n = 5, the surface tension dropped more
slowly, regardless of the concentration. These results indicate that the structure of a
surfactant strongly affected its diffusion rate; surfactants with large mPEGs and short
fluorocarbon chains diffused faster at the air–water interface and were adsorbed more
efficiently than surfactants with small mPEGs and long fluorocarbon chains. The
effects of surfactant structure on diffusion in aqueous solution will be discussed later.
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The curves in Figures 5 and 6 can be divided into four regions: the induction
region, the rapid-fall region, the meso-equilibrium region, and the equilibrium region.
The first three regions can be described by Eq. 3. Take the logarithm of both sides of
[(
Eq. 3 to get Eq. 4. Ploting log t with
)⁄(
)]
, We can obtain n and
t* values from slope and intercept, respectively[35].
( )
(3)
(4)
[(
)⁄(
)]
Where γ0 is the surface tension of water; γt is the surface tension of the solution
at time t; and γm is the surface tension at the meso-equilibrium. The values of
parameters t* and n can be used to understand the characteristics of the surfactant.
These values can be obtained by fitting the surface tension value at different times.
The t* value depends on how fast the surfactant diffuses from the bulk solution to the
subsurface, a lower t* value indicates a smaller diffusion barrier and faster diffusion
of the surfactant. The n value reflects the difference between the energies of surfactant
adsorption and desorption. The larger the n value, the higher the potential barrier of
surfactant adsorption and the slower the molecular diffusion [32].
As can be seen from the data in Table 3, for solutions of surfactants 5i, 5h, and
5g (n = 5), whose surface tension values reached equilibrium in 200,000 ms, t*
decreased as the molecular weight of mPEG increased, regardless of concentration.
This result shows that the larger the hydrophilic group, the faster the surfactant
diffused at the air–water interface and the more efficiently it was adsorbed. The
reason for this phenomenon may be that increasing the size of the hydrophilic group
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increased the solubility of the surfactant in the aqueous solution, which in turn
accelerated diffusion of the surfactant molecules from the bulk phase to the air–water
interface [36].
surfactant (n = 5) Conc (time of CMC)
n
t* (ms) γm (mN/m)
0.1CMC
1.69
17246
43.06
0.5CMC
1.23
1.15
1.04
1.25
1980
1068
647
28.77
22.24
19.96
43.44
5i, m = 4
1CMC
2CMC
0.1CMC
6194
0.5CMC
0.79
0.71
0.65
0.84
636
237
84
31.64
28.64
26.36
47.07
5h, m = 11
1CMC
2CMC
0.1CMC
601
0.5CMC
0.57
0.55
0.47
43
10
3
41.46
39.41
37.65
5g, m = 22
1CMC
2CMC
Table 3. Dynamic surface tension parameters for aqueous solutions of 5i, 5h, and 5g
at various concentrations
surfactant (m = 4) Conc (time of CMC)
n
t* (ms) γm (mN/m)
0.1CMC
0.70
151
37.36
0.5CMC
0.47
0.30
0.41
1.17
3.75
0.11
0.06
3225
30.32
24.99
21.88
42.98
5b, n = 3
1CMC
2CMC
0.1CMC
0.5CMC
0.94
0.76
0.70
1.69
294
81
30.39
24.49
20.19
43.06
5e, n = 4
1CMC
2CMC
21
0.1CMC
17246
0.5CMC
1.23
1.15
1.04
1980
1068
647
28.77
22.24
19.96
5i, n = 5
1CMC
2CMC
Table 4. Dynamic surface tension parameters for aqueous solutions of 5b, 5e and 5i at
various concentrations
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For surfactants 5b, 5e, and 5i (m = 4), whose surface tension values reached
equilibrium in 200,000 ms, t* increased with increasing fluorocarbon chain length at
all concentrations (Table 4), which shows that the surfactant with a short fluorocarbon
chain diffused faster at the air–water interface and was adsorbed more efficiently than
the surfactant with long fluorocarbon chains. The reason for this may be that the long-
chain surfactant molecules are larger, which would hinder their diffusion from the
bulk solution to the subsurface, making it difficult for them to be adsorbed from the
solution to the air–water interface [37, 38].
3.4. Diffusivity Coefficients
The surfactant adsorption process includes two sequential steps: the surfactant
molecules diffuse from the bulk aqueous phase to the subsurface and then they adsorb
from the subsurface to the air–water interface [39]. The modified Ward–Tordai
equation can be used to describe diffusion-controlled adsorption on a fresh surface.
For the nonionic surfactants, corresponding simplified Eqs. (5) was obtained at the
initial stage of the adsorption [40–42].
( )
√
(5)
where γ0 is the surface tension of pure water; Гeq is the surface excess concentration,
which can be obtained from the equilibrium surface tension measurements; C0 is
surfactant concentration; and D is the diffusion coefficient.
We evaluated the temporal dependence of surface tension for solutions of 5i, 5h,
and 5g, which have the same hydrophobic chain, at a concentration of 0.2 mmol/L
and for solutions of 5b, 5e, and 5i, which have the same hydrophilic chain, at a
concentration of 0.6 mmol/L (Figure 7). These concentrations were chosen to ensure
that the initial surface tension value of the surfactant solution was >65 mN/m and that
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the adsorption layer was a dilute solution; if these conditions are not met, the formula
(5) is no longer applicable [37]. In addition, the concentration must be high enough to
minimize lateral diffusion of the surfactant from the thick surface to the thin surface
of a generated air bubble, known as the Gibbs–Marangoni effect [43], causing the
dominance of the vertical surfactant diffusion from the bulk liquid to the new surface
of a generated air bubble.
Figure 7. Dynamic surface tension data for 5i, 5h, 5g at 0.2 mmol/L and 5b, 5e, 5i at
0.6 mmol/L
According to Eq. (5), γ(t)(t→0) of the solution is linearly related to t1/2, therefore
the D values can be determined from the slopes of the plots in Figure 8 and the values
are listed in Table 5. During the initial stage of adsorption, D increased with
increasing mPEG molecular weight and decreased as fluorocarbon chain length
increased. These results indicate that increasing the size of the hydrophilic group
increased surfactant solubility, enhanced surfactant mobility in the aqueous solution,
and thus resulted in an increase in the diffusion rate. In contrast, increasing the
hydrophobic chain length increased the size of a surfactant molecule and decreased its
solubility, which reduced the its mobility in the aqueous solution, which in turn
resulted in a decrease in the diffusion rate [32]; these results are the same as those
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obtained by comparing the t* values.
1/2
Figure 8. The linear behavior of γ(t)–t
and 5b, 5e, 5i
determined by the short time of 5i, 5h, 5g
surfactant
D (m2/s)
2.49 × 10-9
5.01 × 10-9
Same hydrophobic
5i, m = 4
chain (n = 5)
5h, m = 11
C = 0.2 mmol/L
5g, m = 22
5b, n = 3
5e, n = 4
5i, n = 5
1.97 × 10-8
2.20 × 10-9
2.05 × 10-9
6.91 × 10-10
Same hydrophilic
chain (m = 4)
C = 0.6 mmol/L
Table 5. Diffusion coefficients of 5i, 5h, 5g and 5b, 5e, 5i
4. CONCLUSION
Ten nonionic surfactants with short fluorocarbon chains (≤6) and various mPEG
1
molecular weights or 2-methoxyethanol were synthesized and characterized by H
19
NMR, F NMR, and GPC. Detailed analysis of structure–activity relationships were
conducted, which can provide a theoretical basis for designing nonionic fluorinated
surfactants with practical applications. Measurement of the static and dynamic surface
tension of the surfactants revealed that for a given number of fluorocarbon atoms,
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decreasing the mPEG molecular weight decreased the surface tension, CMC, and
diffusion rate. In contrast, for a given mPEG molecular weight, increasing the number
of fluorocarbon atoms decreased the surface tension, CMC, and diffusion rate. The
molecular weight of mPEG was the main determinant of γmin, and the number of
fluorocarbon atoms was the main determinant of CMC. Surfactant 5i reduced the
surface tension the most, reducing γmin to 17.89 mN/m. On the basis of the results of
this structure–activity relationship study, we are exploring applications of the
surfactants for pesticides.
AUTHOR INFORMATION
Corresponding Authors
*(Jingjing Zhang) E-mail: jingjingzhang216@outlook.com. Phone: 0086-22-
23503792. Fax: 0086-22-23503792.
*(Junjie Kou) E-mail: Kjj@nankai.edu.cn. Phone: 0086-22-23503792. Fax: 0086-22-
23503792.
*(Qingmin Wang) E-mail: wangqm@nankai.edu.cn. Phone: 0086-22-23503952. Fax:
0086-22-23503952.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China
(21977056, 21732002), and the Tianjin Technical Expert Project (19JCTPJC57800).
Supplementary Material
Supporting Information of general synthesis procedure and characterization for 3a–3d
and 5a–5j.
REFERENCES
20

Journal Pre-proof
[1] N.M. Kovalchuk, A. Trybala, V. Starov, O. Matar, N. Ivanova, Fluoro-vs
hydrocarbon surfactants: Why do they differ in wetting performance?, Adv. Colloid
Interface Sci. 210 (2014) 65–71.
[2] H.K. Wu, J.Q. Zhong, H.M. Shen, H.X. Shi, Synthesis of branch fluorinated
cationic surfactant and surface properties, J Chem. (2014) 1–5.
[3] H.K. Wu, J.Q. Zhong, H.M. Shen, H.X. Shi, Synthesis of a novel branch
fluorinated cationic surfactant and its surface activity, J. Fluorine Chem. 156 (2013)
5–8.
[4] L.J. Chen, H.X. Shi, H.K. Wu, J.P. Xiang, Synthesis and combined properties of
novel fluorinated anionic surfactant, Colloids Surf. A Physicochem. Eng. Asp. 384(1–
3) (2001) 331–336.
[5] D. Zhang, M. Sha, R.M. Pan, X.Y. Lin, P. Xing, B. Jiang, CF3CF2CF2C(CF3)2-
based fluorinated surfactants with high surface activity, Chem. Zvesti. 73 (2019)
1499–1508.
[6] M. Nuer, J. Duan, Z.F. Wei, W.H. Wu, J.X. Ma, A.D. Zhang, Fluorocarbon-
hydrocarbon hybrid cationic surfactants: Synthesis, surface-activity properties and
anti-corrosion performance, J. Mol. Liq. 306 (2020) 112897.
[7] R.A. Falk, Method of improving fluorinated surfactants, U.S. Patent 4089804,
1978.
[8] J. Block, Method and composition for removing calcium sulfate scale deposits
from surfaces, U.S. Patent 4144185, 1979.
[9] S.C. Crema, Liquid foaming additives used in the stimulation of oil and gas wells,
U.S. Patent 4609477, 1985.
[10] O. Wagner, J. Thiele, M. Weinhart, L. Mazutis, D.A. Weitz, W.T.S. Huck, R.
Haag, Biocompatible fluorinated polyglycerols for droplet microfluidics as an
21

Journal Pre-proof
alternative to PEG-based copolymer surfactants, Lab Chip 16 (2016) 65–69.
[11] Y.L. Chiu, H.F. Chan, K.K.L. Phua, Y. Zhang, S. Juul, B.R. Knudsen, Y.P. Ho,
K.W. Leong, Synthesis of fluorosurfactants for emulsion-based biological
applications, ACS Nano. 8(4) (2014) 3913–3920.
[12] M. Abla, G. Durand, C. Breyton, S. Raynal, C. Ebel, B. Pucci, A diglucosylated
fluorinated surfactant to handle integral membrane proteins in aqueous solution, J.
Fluorine Chem. 134(2) (2012) 63–71.
[13] M. Abla, S. Unger, S. Keller, F. Bonneté, C. Ebel, B. Pucci, C. Breyton, G.
Durand, Micellar and biochemical properties of a propyl-ended fluorinated surfactant
designed for membrane-protein study, J. Colloid Interface Sci. 445 (2015) 127–136.
[14] A. Polidori, S. Raynal, L.-A. Barret, M. Dahani, C. Barrot-Ivolot, C. Jungas, E.
Frotscher, S. Keller, C. Ebel, C. Breyton, F. Bonneté, Sparingly fluorinated maltoside-
based surfactants for membrane-protein stabilization, New J. Chem. 40(6) (2016)
5364–5378.
[15] N. Bongartz, S.R. Patil, C. Stubenrauch, D. Blunk, A new fluorinated inositol-
based surfactant, Colloids Surf. A Physicochem. Eng. Asp. 414 (2012) 320–326.
[16] K. Debbabi, F. Guittard, J. Eastoe, S. Rogers, S. Geribaldi, Reverse water-in-
fluorocarbon microemulsions stabilized by new polyhydroxylated nonionic
fluorinated Surfactant, Langmuir. 25(16) (2009) 8919–8926.
[17] M.A. Twaik, M. Tahan, A. Zilkha, Grafting of poly(ethylene oxide) on
poly(methyl methacrylate) by transesterification, J. Polym. Sci., Part A-1: Polym.
Chem. 7(9) (1969) 2469–2480.
[18] H.C. Chiu, C.S. Chern, C.K. Lee, H.F. Chang, Synthesis and characterization of
amphiphilic poly(ethylene glycol) graft copolymers and their potential application as
drug carriers. Polymer. 39(8–9) (1998) 1609–1616.
22

Journal Pre-proof
[19] L.L. Sun, Z.P. Du, W.X. Wang, Y. Liu, Synthesis and self-assembly behavior of
comb-like surfactant polymethyl methacrylate-g-methoxy polyethylene glycol, J.
Surfact. Deterg. 14 (2011) 161–166.
[20] N.A. Negm, M.A.E. Hashash, M.A. Youssif, E.A. Ismail, Z.I. Abdeen, N.R.A.
Rahman, Novel nonionic polyurethane surfactants and Ag nanohybrids: influence of
nonionic polymeric Chains, J. Surfact. Deterg. 20 (2017) 173–182.
[21] S.P. Liu, L.B. Du, D.Q. Zhuang, Y.X. Zhang, J.Y. Chen, M. Jiang, S.G. Wu, G.
Swift, Synthesis and characterization of surfactant PEG macromonomers with
fluorocarbon end-capped groups and its copolymers, Chin. J. Chem. 19(4) (2001)
386–393.
[22] Y.C Shen, Y. Jin, S.Q. Lai, L.J, Shi, W.N. Du, R. Zhou, Synthesis, surface
properties and cytotoxicity evaluation of nonionic urethane fluorinated surfactants
with double short fluoroalkyl chains, J. Mol. Liq. 296 (2019) 111851.
[23] M.C. Parlato, J. -P. Jee, M. Teshite, S. Mecozzi, Synthesis, characterization, and
applications of hemifluorinated dibranched amphiphiles, J. Org. Chem. 76(16) (2011)
6584–6591.
[24] J. Eastoe, A. Paul, A. Rankin, R. Wat, J. Penfold, J.R.P. Webster, Fluorinated
nonionic surfactants bearing either CF3- or H-CF2- terminal groups: adsorption at the
surface of aqueous solutions, Langmuir. 17(25) (2001) 7873–7878.
[25] Z.R. Xin, S.J. Yan, B.B. Du, S.S. Du, C. Liu, P. Stagnaro, On properties of graft
copolymers of LLDPE and novel fluorine surfactants obtained via reactive extrusion,
Des. Monomers Polym. 17(8) (2014) 746–752.
[26] M. Sha, P. Xing, B. Jiang, Strategies for synthesizing non-bioaccumulable
alternatives to PFOA and PFOS, Chin. Chem. Lett. 26 (2015) 491–498.
23

Journal Pre-proof
[27] A. Zaggia, G. Padoan, L. Conte, Synthesis and surface properties
characterization of perfluoroalkylated oligo(oxyethylene)glycols, J. Surfact. Deterg.
13(4) (2010) 409–415.
[28] N. Jaoued-Grayaa, B. Boughariou-Charrad, A. Hedhli, Synthesis and the
structure to property relationship of monoperfluoroalkyl polyethylene glycol, J.
Surfact. Deterg. 17(4) (2014) 767–772.
[29] A. Zaggia, B. Ameduri, Recent advances on synthesis of potentially non-
bioaccumulable fluorinated surfactants, Curr. Opin. Colloid Interface Sci. 17(4)
(2012) 188–195.
[30] Y.J. Jiang, T. Geng, Q.X. Li, G.J. Li, H.B. Ju, Equilibrium and dynamic surface
tension properties of salt-free catanionic surfactants with different hydrocarbon chain
lengths, J. Mol. Liq. 204 (2015) 126–131.
[31] M. Nuer, J. Duan, Z.F, Wei, W.H. Wu, J.X. Ma, A.D. Zhang, Fluorocarbon-
hydrocarbon hybrid cationic surfactants: Synthesis, surface-activity properties and
anti-corrosion performance, J. Mol. Liq. 306 (2020) 112897.
[32] P. Kanokkarn, T. Shiina, M. Santikunaporn, S. Chavadej, Equilibrium and
dynamic surface tension in relation to diffusivity and foaming properties: Effects of
surfactant type and structure, Colloids Surf. A Physicochem. Eng. Asp. 524 (2017)
135–142.
[33] I. Varga, R. Mészáros, C. Stubenrauch, T. Gilányi, Adsorption of sugar
surfactants at the air/water interface, J. Colloid Interface Sci. 379 (2012) 78–83.
[34] A. Casandra, S. Ismadji, B.A. Noskov, L. Liggieri, S.-Y. Lin, A study on the
method of short-time approximation-Criteria for applicability, Int. J. Heat Mass
Transf. 90 (2015) 752–760.
24

Journal Pre-proof
[35] J. Eastoe, J.S. Dalton, Dynamic surface tension and adsorption mechanisms of
surfactants at the air-water interface, Adv. Colloid Interface Sci. 85 (2000) 103–144.
[36] X.C. Liu, Y.X. Zhao, Q.X. Li, T.L. Jiao, J.P. Niu, Surface and interfacial tension
of nonylphenol polyethylene oxides sulfonate, J. Mol. Liq. 216 (2016) 185–191.
[37] H.H. Chang, Y. Wang, Y. Cui, G.J. Li, B. Zhang, X.X. Zhao, W.L. Wei,
Equilibrium and dynamic surface tension properties of Gemini quaternary ammonium
salt surfactants with hydroxyl, Colloids Surf. A Physicochem. Eng. Asp. 500 (2016)
230–238.
[38] H.B Ju, Y.J Jiang, T. Geng, Y.K. Wang, C.Q. Zhang, Equilibrium and dynamic
surface tension of quaternary ammonium salts with different hydrocarbon chain
length of counterions, J. Mol. Liq. 225 (2017) 606–612.
[39] J.J. Liu, Y. Xu, H.X Sun, Diffusion-controlled adsorption kinetics of surfactant at
air/solution interface, Chin. J. Chem. Eng. 21 (9) (2013) 953–958.
[40] R.S. Hansen, The theory of diffusion-controlled absorption kinetics with
accompanying evaporation, J. Phys. Chem. 64 (1960) 637–641.
[41] E. Rillaerts, P. Joos, Rate of demicellization from the dynamic surface tensions
of micellar solutions, J. Phys. Chem. 86 (1982) 3471–3478.
[42] J.L. Chai, X.C. Cui, X.Y. Zhang, M.M. Song, J. Wang, J.J. Lu, Adsorption
equilibrium and dynamic surface tension of alkyl polyglucosides and their mixed
surfactant systems with CTAB and SDS in the surface of aqueous solutions, J. Mol.
Liq. 264 (2018) 442–450.
[43] C.M. Phan, T.N. Le, S.-i. Yusa, A new and consistent model for dynamic adsorp-
tion of CTAB at air/water interface, Colloids Surf. A Physicochem. Eng. Asp. 406
(2012) 24–30.
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Journal Pre-proof
Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which
may be considered as potential competing interests:
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CREDIT AUTHOR STATEMENT
Ruiguo Wang, Data collection, writing papers.
Lingyun Song, Data curation, Formal analysis, Investigation.
Yuanqiang Guo, Data curation, Formal analysis, Investigation.
Junjie Kou, Data curation, Formal analysis, Investigation.
Hongjian Song, Work concept or design/Funding acquisition, Project administration,
Supervision.
Yuxiu Liu, Writing - review & editing.
Jingjing Zhang, Work concept or design/Funding acquisition, Project administration,
Supervision.
Qingmin Wang, Work concept or design/Funding acquisition, Project administration,
Supervision.
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GRAPHICAL ABSTRACT
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Highlights
1. Ten new nonionic fluorinated surfactants were designed and synthesized.
2. The synthesized surfactants exhibited a novel structure-activity relationship.
3. Methoxypolyethylene glycol molecular weight determines minimum surface
tension.
4. The number of fluorocarbon atoms determines critical micelle concentration.
29