Characterization of air/water interface adsorption of a series of partially fluorinated/hydrogenated quaternary ammonium salts

Article abstract of DOI:10.1016/j.jfluchem.2015.07.023

The adsorption at air/water interface of a series of partially fluorinated/hydrogenated quaternary ammonium salts was characterized by the determination of static and dynamic surface tension, critical micelle concentration, surface excess, area per molecule and Krafft temperature. In particular, the variation of these parameters was studied as a function of fluorinated and hydrogenated chain length. Modification of fluorinated and hydrogenated moieties allows to finely tune all the aforementioned physical surface properties: increasing the number of fluorinated carbon atoms boosts both effectiveness and efficiency of surfactant in reducing surface tension, kinetics of migration to interface are favored fastening reaching of equilibrium conditions, critical micelle concentration is reduced and surface excess is increased. Conversely increasing the length of the hydrogenated moiety reduces both effectiveness and efficiency of surfactant, migration to interface is slackened, c.m.c. is increased, and surface excess is depresses. Area per molecule and Krafft temperature appear to be affected mainly by the total number of carbon atoms introduced in the molecules whatever the nature of the substituent (fluorine or hydrogen).

Full text of DOI:10.1016/j.jfluchem.2015.07.023

Journal of Fluorine Chemistry 178 (2015) 241–248
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Characterization of air/water interface adsorption of a series of
partially fluorinated/hydrogenated quaternary ammonium salts
Gennifer Padoan a,b, Thierry Darmanin a, Alessandro Zaggia b, Sonia Amigoni a,
b
a,
*
´ ´
Lino Conte , Frederic Guittard
a University Nice Sophia Antipolis, CNRS, LPMC, UMR 7336, 06100 Nice, France
b
`
Dipartimento di Ingegneria Industriale, Universita degli Studi di Padova, Via Marzolo, 9-35131 Padua, Italy
A R T I C L E I N F O
A B S T R A C T
Article history:
The adsorption at air/water interface of a series of partially fluorinated/hydrogenated quaternary
ammonium salts was characterized by the determination of static and dynamic surface tension, critical
micelle concentration, surface excess, area per molecule and Krafft temperature. In particular, the
variation of these parameters was studied as a function of fluorinated and hydrogenated chain length.
Modification of fluorinated and hydrogenated moieties allows to finely tune all the aforementioned
physical surface properties: increasing the number of fluorinated carbon atoms boosts both effectiveness
and efficiency of surfactant in reducing surface tension, kinetics of migration to interface are favored
fastening reaching of equilibrium conditions, critical micelle concentration is reduced and surface excess
is increased. Conversely increasing the length of the hydrogenated moiety reduces both effectiveness
and efficiency of surfactant, migration to interface is slackened, c.m.c. is increased, and surface excess is
depresses. Area per molecule and Krafft temperature appear to be affected mainly by the total number of
carbon atoms introduced in the molecules whatever the nature of the substituent (fluorine or hydrogen).
ß 2015 Elsevier B.V. All rights reserved.
Received 27 April 2015
Received in revised form 4 July 2015
Accepted 21 July 2015
Available online 26 July 2015
Keywords:
Surfactant
Fluorinated
Ammonium
Interface
1. Introduction
(obtained by lengthening hydrocarbon moieties) plays a favorable
role in antibacterial applications [7,8], a stronger hydrophobic/
Surfactants are among the most versatile products of the
chemical industry, appearing in several industrial applications
such as motor oils [1], pharmaceutics [2], detergents [3], petroleum
recovery [4], electronic printing, magnetic recording or biotech-
nology [5]. Cationic surfactants dissociate in water, forming
surface-active positively charged ions and negatively charged
counter-ions. The introduction of fluorinated chains in cationic
surfactants is very promising because of their strong surface
activity, high hydrophobicity and molecular stiffness which cause
the formation of aggregates with little curvature [6]. One special
type of fluorinated cationic surfactants are mixed quaternary
ammonium compounds which have a fluorinated hydrophobic/
lipophobic moiety and a hydrocarbon hydrophobic/lipophilic
moiety bonded to a hydrophilic quaternary ammonium group.
By varying the length of different segments the hydrophobic–
lipophobic–lipophilic character of surfactants can be modified
allowing to finely tune physico/chemical properties such as surface
and interface tension. While an increased hydrophobic character
lipophobic character (obtained by lengthening the fluorocarbon
chain) causes in the formation of an insulating thin aqueous film on
hydrocarbon fuels during fire-fighting foam flow [9].
In a previous paper [10], we showed that surfactants with long
fluorinated chains and relatively short hydrocarbon chain can
form long and highly flexible aggregates leading to highly viscous
solutions and the formation of an entangled network made of
flexible worm-like micelles. These particular micellar aggregates
are due to weak non-covalent interactions which facilitate an
easy and fast change in their structure in response to external
actions.
The aim of this study is to examine how the chemical structure
of surfactant, that is the length of fluorinated and hydrocarbon
chains, influences interfacial properties.
The characterization of adsorption phenomena at air/water
interface of partially fluorinated/hydrogenated ammonium qua-
ternary surfactants was achieved determining key parameters
such as parameters such as critical micelle concentration,
superficial tension, surface excess, area per molecule, Krafft’s
temperature and dynamic surface tension allowed the subsequent
characterization of adsorption phenomena of fluorinated quater-
nary surfactants at air/water interface.
*
Corresponding author. Tel.: +33 492076159; fax: +33 492076156.
E-mail address: guittard@unice.fr (F. Guittard).
http://dx.doi.org/10.1016/j.jfluchem.2015.07.023
0022-1139/ß 2015 Elsevier B.V. All rights reserved.

242
G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
2. Experimental
2.1. Materials and methods
twelve times the c.m.c. using a capillary terminating with an open
end below the free surface of a liquid. The test gas is then let flow
into the pipe, while its pressure is constantly monitored. First, a
curved gas/liquid interface forms inside the tube, which is then
driven down the capillary by the gas flow. The pressure rises until a
hemisphere is formed at the tip of the capillary. The value of
pressure measured in this moment (maximum pressure) is directly
proportional to the surface tension at the time when the
hemisphere is formed. If p0 is the hydrostatic pressure at the tip
of the capillary, R is the maximum bubble radius and pmax is the
maximum value of the pressure, the DST at the time when pmax is
reached is derived via Laplace’s relation:
All dialkyl ammine [alkyl = methyl, ethyl, propyl, butyl, hexyl,
octyl] and solvents were purchased from Aldrich and used without
further purification. 3-Perfluorobutyl-1,2-epoxypropane, 3-per-
fluorohexyl-1,2-epoxypropane, and 3-perfluorooctyl-1,2-epoxy-
propanewere synthesized according to the previously reported
procedure [10].
2.2. Surface tension(
g), surface excess (G), area per molecule at
critical micelle concentration (Ac.m.c.
)
pmax ꢀ p
st max
¼
0 R
(3)
2
Surface tension of aqueous solutions of partially fluorinated
surfactants were measured using a Kruss K100 tensiometer by the
Wilhelmy plate technique which allowed to plot surface tension as
a function of time (in order to follow adsorption kinetics) till
equilibrium. Partially fluorinated quaternary ammonium com-
pounds which were sparingly soluble in water were dissolved in a
10% methanol aqueous solution [11] and measurements were
performed at 25 8C.
Once reached the maximum value, the pressure starts to drop as
the bubble size keeps increasing, until the bubble will eventually
drop off the tube and migrate to the surface. At that point, another
bubble will start to form and the process will repeat. By tuning the
frequency of bubbles the DST at different times can be monitored.
2.4. Krafft temperature
Determination of critical micelle concentration (c.m.c.) was
carried out by adding a concentrated surfactant solution to water
and measuring surface tension at each addition. Surface excess
Aqueous solutions were prepared at concentration double than
the c.m.c. and kept at 5 8C for 24 h, where precipitation of
surfactant hydrated crystals occurred. The temperature of the
precipitated system was then raised [13] and conductivity
variation measured.
concentration (
curves as a function of concentration. Surface excess concentration
at surface saturation m is a useful measure of the effectiveness of
G) was determined by the slope of surface tension
G
adsorption of the surfactant at the liquid/air or liquid/liquid
interface, since it is the maximum value that adsorption can attain.
The adsorption effectiveness is a key factor in determining
surfactant properties such as foaming, wetting and emulsification.
Tightly packed, coherent interfacial films display very different
interfacial properties compared to loosely packed, non coherent
films. Hydrophobic chains of surfactants adsorbed at the water–air
or water-hydrocarbon interfaces do not display a close-packed
arrangement normal to the interface at saturation adsorption.
2.5. Synthesis general procedures
Partially
ammines having n fluorinated carbon atoms and m hydrogenated
carbon atoms (Anm and partially fluorinated/hydrogenated
fluorinated/hydrogenated
tertiary
symmetric
)
quaternary surfactants (FnHm) were prepared according to the
procedure previously reported [14]. The schematic structure of
synthesized surfactants is summarized in Scheme 1.
The adsorbed amount of a surfactant (
according to the Gibbs adsorption [12]:
G) can be calculated
2.6. Characterization
ꢀ
ꢁ
1
dg
Intermediates tertiary amines (Anm) and desired surfactants
(FnHm) were characterized by nuclear magnetic resonance (NMR)
(Bruker W-200 MHz instrument) and mass spectrometry (MS)
(Thermo TRACE GC instrument from Thermo Fischer 81 Corp. fitted
with an Automass III Multi spectrometer (electron ionization at
70 eV).
G
¼ ꢀ
T
(1)
4:606 RT d log10C
For surfactants with a single hydrophilic group, either ionic or
nonionic, the area occupied by a molecule at the surface is
determined by the hydrated hydrophilic group rather than by the
hydrophobic group. The area occupied by a surfactant molecule
(Ac.m.c.) at the air/water interface (expressed in square angstroms)
is derived from the value of adsorbed amount of surfactant at the
2.6.1. Characterization of partially fluorinated/hydrogenated tertiary
amines (Anm
1-Dimethylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 hepta-
decafluoro undecan-2-ol (A81
MS m/z (rel. ab. %): 521 ([M]+ꢁ, 5%); 506 ([M ꢀ CH3]+, 20%), 88
([M ꢀ CF3(CF2)7, –CH2]+, 10%), 58 ([M ꢀ CF3(CF2)8CHOHCH2]+,
100%);
)
c.m.c. (
G
c.m.c.) by using the following expression:
1
Gc:m:c:
)
Ac:m:c:
¼
(2)
N
where N is Avogadro’s number. A decrease in the area occupied
by a surfactant molecule indicates a greater effectiveness of
adsorption.
Specific interfacial area per molecule at c.m.c. (Ac.m.c.) provides
information on the degree of packing and orientation of the
adsorbed surfactant molecule and these data are in agreement
with molecule dimensions obtained by molecular models.
1H NMR (CD3OD):
2.49 (d, CH2(c), 2H); 2.29 (t, CH3(d), 6H); 4.2 (d, OH(e), 1H).
19FNMR (CD3OD):
d = 2.39 (m, CH2(a), 2H); 2.6 (m, CH(b), 1H);
d
= ꢀ80.9(t, CF3(a), 3F);ꢀ111.7(m, CF2CH2(b),
2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F); ꢀ122.8 (m,
CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h), 4F).
1-Diethylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptade-
2.3. Dynamic surface tension
cafluoro undecan-2-ol (A82)
MS m/z (rel. ab. %): 549 ([M]+ꢁ, 3%), 116 ([M ꢀ CF3(CF2)7,
Dynamic surface tension (DST) data have been obtained by the
maximum bubble pressure method using a SITA pro line t15
instrument. DST measurements were performed with effective
surface ages ranging from 10 ms to 20 sand at a concentration
–CH2]+, 30%), 86 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%, 69 [CF3]+ 15%;
1H NMR (CD3OD):
d = 2.18(m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2 (c,d,), 6H); 1.04 (t, CH3(e), 6H);
4.1 (d-d,OH(f), 1H).

G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
243
Scheme 1. Synthetic way to surfactants FnHm
.
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2 (g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9(m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1-Dipropylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 hepta-
1-Dimetylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-
decafluoro undecan-2-ol (A83
)
2-ol (A61)
MS m/z (rel. ab. %): 577 ([M]+ꢁ, 2%); 534 ([M ꢀ CH2CH2CH3]+,
MS m/z (rel. ab. %): 421 ([M]+ꢁ, 5%); 406 ([M ꢀ CH3]+, 20%), 88
([M ꢀ CF3(CF2)7, –CH2]+, 100%), 58 ([M ꢀ CF3(CF2)8CHOHCH2]+,
100%);
2%),
144
([M ꢀ CF3(CF2)7,
–CH2]+,
8%),
114
([M ꢀ CF3(CF2)8CHOHCH2]+, 100%), 69 [CF3]+ 15%;
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
1H NMR (CD3OD):
2.49 (d, CH2(c), 2H); 2.29 (t, CH3(d), 6H); 4.2 (d, OH(e), 1H).
19F NMR (CD3OD):
d = 2.39 (m, CH2(a), 2H); 2.6 (m, CH(b), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e), 4H);
1.04 (d-d, CH3(f), 6H); 4.1 (d-d, OH(g), 1H).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Dietylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-2-
ol (A62
)
1-Dibutylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptade-
MS m/z (rel. ab. %): 449 ([M]+ꢁ, 5%); 116 ([M ꢀ CF3(CF2)7, –
cafluoro undecan-2-ol (A84
)
CH2]+, 30%), 86 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
MS m/z (rel. ab. %): 605 ([M]+ꢁ, 5%); 172 ([M ꢀ CF3(CF2)7, –
1H NMR (CD3OD):
d = 2.18 (m, CH2 (a), 1H); 2.49 (m, CH2 (a),
CH2]+,
8%),
142
([M ꢀ CF3(CF2)8CHOHCH2]+,
100%),
1H); 4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.04 (t, CH3(e),
6H); 4.1 (d-d, OH(f), 1H).
57 [CH2CH2CH2CH3]+ 10%;
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m, CF2CH2
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f), 8H);
1.04 (d-d, CH3(g), 6H); 4.1 (d-d, OH(h), 1H).
(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2 (d), 2F); ꢀ122.8 (m,
CF2 (e), 2F); ꢀ121.8 (m, CF2 (f), 2F).
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2 (g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1-Dipropylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-
2-ol (A63)
MS m/z (rel. ab. %): 477 ([M]+ꢁ, 5%); 448 ([M ꢀ CH2CH3]+, 20%),
144
([M ꢀ CF3(CF2)7,
–CH2]+,
20%),
114
1-Dihexylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptade-
([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
cafluoro undecan-2-ol (A86
)
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
MS m/z (rel. ab.
%):
661
([M]+ꢁ
,
5%);
576
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e), 4H);
1.04 (d-d, CH3(f), 6H); 4.1 (d-d, OH(g), 1H).
([M ꢀ CH2CH2CH2CH2CH2CH3]+, 5%), 228 ([M ꢀ CF3(CF2)7,
–
CH2]+, 20%), 198 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,g,h),
16H); 1.04 (d-d, CH3(i), 6H); 4.1 (d-d, OH(l), 1H).
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Dibutylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-2-
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2 (g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
ol (A64)
MS
m/z
(rel.
ab.
%):
505
([M]+ꢁ
,
5%);
448
([M ꢀ CH2CH2CH2CH3]+, 5%), 172 ([M ꢀ CF3(CF2)7, –CH2]+, 20%),
142 ([M ꢀ CF3(CF2)8CH2OHCH2]+, 100%);
1-Dioctylamino-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptade-
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
cafluoro undecan-2-ol (A88
)
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f), 8H);
1.04 (d-d, CH3(g), 6H); 4.1 (d-d, OH(h), 1H).
MS m/z (rel. ab.
%):
717
([M]+ꢁ
,
5%);
604
([M ꢀ CH2CH2CH2CH2CH2CH2CH2CH3]+, 5%), 284 ([M ꢀ CF3(CF2)7,
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
–CH2]+, 10%), 254 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,g,h,i,l),
24H); 1.04 (d-d, CH3(m), 6H); 4.1 (d-d, OH(n), 1H).
1-Dihexylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-2-
ol (A66
)

244
G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
MS
m/z
(rel.
ab.
%):
561
([M]+ꢁ
,
5%);
476
–
MS
m/z
(rel.
ab.
%):
517
([M]+ꢁ
,
5%);
418
([M ꢀ CH2CH2CH2CH2CH2CH3]+, 10%), 228 ([M ꢀ CF3(CF2)7,
([M ꢀ CH2CH2CH2CH2CH2CH2CH3]+, 10%), 284 ([M ꢀ CF3(CF2)7, –
CH2]+, 20%), 198 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
CH2]+, 15%), 254 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,g,h),
16H); 1.04 (d-d, CH3(i), 6H); 4.1 (d-d, OH(l), 1H).
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,g,h,i,l),
24H); 1.04 (d-d, CH3(m), 6H); 4.1 (d-d, OH(n), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dioctylamino-4,4,5,5,6,6,7,7,8,8,9,9,9 tridecafluoro nonan-2-
2.6.2. Characterization of partially fluorinated/hydrogenated
quaternary ammonium salts (FnHm)
1-Trimethylammonium-4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11
heptadecafluoro undecan-2-ol, iodide (F8H1)
ol (A68
)
MS
m/z
(rel.
ab.
%):
617
([M]+ꢁ
,
5%);
504
([M ꢀ CH2CH2CH2CH2CH2CH2CH2CH3]+, 5%), 284 ([M ꢀ CF3(CF2)7,
–CH2]+, 10%), 254 ([M ꢀ CF3(CF2)8CHOHCH2]+, 100%);
1H NMR (CD3OD):
d
= 2.24 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.51 (t, CH2(c), 2H); 3.26 (m, CH3(d), 9H); 4.7 (m, OH(e), 1H).
19F NMR (CD3OD)
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,-
g,h,i,l), 24H); 1.04 (d-d, CH3(m), 6H); 4.1 (d-d, OH(n), 1H).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1-Diethylmethylammonium-
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptadecafluoro undecan-2-
ol, iodide (F8H2)
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Dimethylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
(A41
)
3.52 (m, CH2(c,d), 6H); 3.14 (s, CH3(e), 3H); 4.7 (m, CH(f), 1H); 1.37
(t, CH3(g), 6H).
MS m/z (rel. ab. %): 321 ([M]+ꢁ, 5%); 306 ([M ꢀ CH3]+, 20%), 88
([M ꢀ CF3(CF2)7, –CH2]+, 100%), 58 ([M ꢀ CF3(CF2)8CHOHCH2]+,
100%);
19F NMR (CD3OD):
d
ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m, CF2CH2(b),
2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F); ꢀ122.8 (m,
CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h), 4F).
1-Dipropylmethylammonium-
1H NMR (CD3OD):
2.49 (d, CH2(c), 2H); 2.29 (t, CH3(d), 6H); 4.2 (d, OH(e), 1H).
19F NMR (CD3OD):
d = 2.39 (m, CH2(a), 2H); 2.6 (m, CH(b), 1H);
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptadecafluoro undecan-2-
ol, iodide (F8H3)
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
1-Diethylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol (A42
)
3.52 (m, CH2(c,d,e), 10H); 3.14 (s, CH3(f), 3H); 4.7 (m, CH(g), 1H);
1.37 (t, CH3(h), 6H).
MS m/z (rel. ab. %): 349 ([M]+ꢁ, 10%), 116 ([M ꢀ CF3(CF2)7, –
CH2]+, 30%), 86 ([M ꢀ CF3(CF2)8CH2OHCH2]+, 100%);
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.04 (t, CH3(e), 6H); 4.1
(d-d, OH(f), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1-Dibutylmethylammonium-
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptadecafluoro undecan-2-
ol, iodide (F8H4)
1-Dipropylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol (A43
)
MS m/z (rel. ab. %): 377 ([M]+ꢁ, 5%); 348 ([M ꢀ CH2CH3]+, 30%),
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
144
([M ꢀ CF3(CF2)7,
–CH2]+,
20%),
114
3.52 (m, CH2(c,d,e,f), 14H); 3.14 (s, CH3(g), 3H); 4.7 (m, CH(h), 1H);
1.37 (t, CH3(i), 6H).
([M ꢀ CF3(CF2)8CH2OHCH2]+, 100%);
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e), 4H);
1.04 (d-d, CH3(f), 6H); 4.1 (d-d, OH(g), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dihexylmethylammonium-
1-Dibutylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol (A44
)
4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptadecafluoro undecan-2-
ol, iodide (F8H6)
MS m/z (rel. ab. %): 405 ([M]+ꢁ, 5%); 362 ([M ꢀ CH2CH2CH3]+,
20%),
172
([M ꢀ CF3(CF2)7
,
–CH2]+,
15%),
142
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
([M ꢀ CF3(CF2)8CH2OHCH2]+, 100%);
3.52 (m, CH2(c,d,e,f,g,h), 22H); 3.14 (s, CH3(i), 3H); 4.7 (m, CH(l),
1H); 1.37 (t, CH3(m), 6H).
1H NMR (CD3OD):
d = 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f), 8H);
1.04 (d-d, CH3(g), 6H); 4.1 (d-d, OH(h), 1H).
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dihexylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol (A46
)
1-Dioctylmethylammonium-
MS
m/z
(rel.
ab.
%):
461
([M]+ꢁ
,
5%);
376
4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11 heptadecafluoro undecan-2-
ol, iodide (F8H8)
([M ꢀ CH2CH2CH2CH2CH3]+, 20%), 228 ([M ꢀ CF3(CF2)7, –CH2]+,
10%), 198 ([M ꢀ CF3(CF2)8CH2OHCH2]+, 100%);
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 3.32 (m, CH(b), 1H);
1H NMR (CD3OD):
d
= 2.18 (m, CH2(a), 1H); 2.49 (m, CH2(a), 1H);
3.40 (m, CH2(c,d), 6H); 1.27 (t, CH2(e,f,g,h,i), 20H); 1.70 (m, CH2 (l),
4H); 0.86 (t, CH3(m), 6H); 3.14 (m, CH(n), 3H); 4.7 (t, CH3(o), 1H).
4.2 (d-d, CH(b), 1H); 2.49 (m, CH2(c,d,), 6H); 1.38 (m, CH3(e,f,g,h),
16H); 1.04 (d-d, CH3(i), 6H); 4.1 (d-d, OH(l), 1H).
19F NMR (CD3OD):
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.9 (m, CF2(f), 2F); ꢀ121.6 (m, CF2(g,h),
4F).
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dioctylamino-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-ol (A48
)

G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
245
1-Trimetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9
nonan-2-ol, iodide (F6H1)
tridecafluoro
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dibutylmethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro hep-
tan-2-ol, iodide (F4H4)
1H NMR (CD3OD):
d
= 2.24 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.51 (t, CH2(c), 2H); 3.26 (m, CH3(d), 9H); 4.7 (m, OH(e), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
3.52 (m, CH2(c,d,e,f), 14H); 3.14 (s, CH3(g), 3H); 4.7 (m, CH(h), 1H);
1.37 (t, CH3(i), 6H).
1-Diethylmetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9
fluoro nonan-2-ol, iodide (F6H2)
trideca-
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dihexylmethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro hep-
tan-2-ol, iodide (F4H6)
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.52 (m, CH2(c,d), 6H); 3.14 (s, CH3(e), 3H); 4.7 (m, CH(f), 1H); 1.37
(t, CH3(g), 6H).
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 3.34 (m, CH(b), 1H);
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
3.52 (m, CH2(c,d,e,f,g,h), 22H); 3.14 (s, CH3(i), 3H); 4.7 (m, CH(l),
1H); 1.37 (t, CH3(m), 6H).
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
1-Dipropylmetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9 trideca-
fluoro nonan-2-ol, iodide (F6H3)
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dioctylmethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro hep-
tan-2-ol, iodide (F4H8)
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.52 (m, CH2(c,d,e), 10H); 3.14 (s, CH3(f), 3H); 4.7 (m, CH(g), 1H);
1.37 (t, CH3(h), 6H).
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 3.34 (m, CH(b), 1H);
3.40 (m, CH2(c,d), 6H); 1.27 (t, CH2(e,f,g,h,i), 20H); 1.70 (m, CH2 (l),
4H); 0.86 (t, CH3(m), 6H); 3.14 (m, CH(n), 3H); 4.7 (t, CH3(o), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dibutylmetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9
fluoro nonan-2-ol, iodide (F6H4)
trideca-
3. Results and discussion
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.52 (m, CH2(c,d,e,f), 14H); 3.14 (s, CH3(g), 3H); 4.7 (m, CH(h), 1H);
1.37 (t, CH3(i), 6H).
3.1. Static surface tension
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
Fig. 1 shows curves of static surface tension as a function of the
logarithm of concentration of FnHm. Surface tension values at the
critical micelle concentration (gc.m.c.) are summarized in Table 1.
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Dihexylmetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9
fluoro nonan-2-ol, iodide (F6H6)
trideca-
Fig. 2 plots surface tension at critical micelle concentration
(g
c.m.c.) of solutions of FnHm as a function of the number of carbon
1H NMR (CD3OD):
d
= 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
atoms (n) in the fluorinated chain keeping constant the number of
hydrogenated carbon atoms. It is noteworthy that an increase in
the length of the hydrogenated carbon atoms keeping constant the
3.52 (m, CH2(c,d,e,f,g,h), 22H); 3.14 (s, CH3(i), 3H); 4.7 (m, CH(l),
1H); 1.37 (t, CH3(m), 6H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
number of fluorinated carbon atoms produces a noticeable
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
increase in surface tension indicating a negative contribution on
the effectiveness in reducing surface tension of the hydrogenated
moiety [15].
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Dioctylmetylammonium-4,4,5,5,6,6,7,7,8,8,9,9,9
fluoro nonan-2-ol, iodide (F6H8)
trideca-
This effect is attributed to the fluorocarbon chain, which favors
the migration of surfactant molecules at the air/water interface.
Data shown in Table 1 for critical micelle concentration and gc.m.c.
clearly show that decreasing fluorocarbon chain length and/or
increasing that of the hydrocarbon moiety depresses the surface
activity of surfactants and induces an increase in the c.m.c.
It follows that both effectiveness and efficiency in reducing
surface tension of surfactant FnHm are positively affected by
increasing the number of carbon atoms in the fluorinated moiety at
the expense of carbon atoms in the hydrogenated one. Conversely
hydrocarbon chain length enhances the hydrophobicity of surfac-
tant without contributing to the reduction of surface tension.
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 3.33 (m, CH(b),
1H); 3.40 (m, CH2(c,d), 6H); 1.27 (t, CH2(e,f,g,h,i), 20H); 1.70 (m,
CH2 (l), 4H); 0.86 (t, CH3(m), 6H); 3.14 (m, CH(n), 3H); 4.7 (t,
CH3(o), 1H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F);
ꢀ122.8 (m, CF2(e), 2F); ꢀ121.8 (m, CF2(f), 2F).
1-Trimethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro heptan-2-
ol, iodide (F4H1)
1H NMR (CD3OD):
3.51 (t, CH2(c), 2H); 3.26 (m, CH3(d), 9H); 4.7 (m, OH(e), 1H).
19F NMR (CD3OD):
d = 2.24 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
Fig. 1 shows that introduction and lengthening of the
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Diethylmethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro hep-
tan-2-ol, iodide (F4H2)
fluorocarbon-based hydrophobic/lipophobic moiety appears to
give a major contribution in increasing both the efficiency and
effectiveness of the surfactant in reducing surface tension.
Further, Fig. 1 shows that lengthening of the hydrocarbon
moiety induces both a decrease in the efficiency and effectiveness
of the surfactant in decreasing surface tension.
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.52 (m, CH2(c,d), 6H); 3.14 (s, CH3(e), 3H); 4.7 (m, CH(f), 1H); 1.37
(t, CH3(g), 6H).
19F NMR (CD3OD):
d
= ꢀ80.9 (t, CF3(a), 3F); ꢀ111.7 (m,
Values of surface excess at c.m.c. (Gc.m.c.) and area per molecule
CF2CH2(b), 2F); ꢀ126.2 (m, CF2(c), 2F); ꢀ123.3 (m, CF2(d), 2F).
1-Dipropylmethylammonium-4,4,5,5,6,6,7,7,7 nonafluoro hep-
tan-2-ol, iodide (F4H3)
at c.m.c. (Ac.m.c) for FnHm are listed in Table 1. These data clearly
show that the greater the effectiveness of adsorption the smaller
the area occupied by the surfactant molecules. Ac.m.c. values for
FnHm obtained are three times greater than the molecular area of
monomeric and surfactants (0.41–0.55 nm2 per molecule) [16]. In
addition, the Ac.m.c. values for FnHm are greater than those for the
1H NMR (CD3OD):
d = 2.46 (m, CH2(a), 2H); 4.6 (m, CH(b), 1H);
3.52 (m, CH2(c,d,e), 10H); 3.14 (s, CH3(f), 3H); 4.7 (m, CH(g), 1H);
1.37 (t, CH3(h), 6H).

246
G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
Fig. 1. Static surface tension as a function of the concentration of FnHm for n = 4, 6, 8 and m = 1, 2, 3, 4, 6, 8.
Table 1
Surfactant parameters.
Surfactant
–
gc.m.c.
Gc.m.c.
Ac.m.c.
p
Tk
c.m.c.
[mN mꢀ1
]
[mol mꢀ2
]
10ꢀ21 [nm2]
[mN mꢀ1
]
[8C]
[mol Lꢀ1
]
F8H1
F6H1
F4H1
F8H2
F6H2
F4H2
F8H3
F6H3
F4H3
F8H4
F6H4
F4H4
F8H6
F6H6
F4H6
F8H8
F6H8
F4H8
15.7
16.6
19.0
17.5
20.2
22.9
18.9
20.9
25.0
22.0
24.6
27.7
28.2
30.0
32.7
29.2
31.0
33.8
8.40E ꢀ 04
1.28E ꢀ 03
1.47E ꢀ 03
7.56E ꢀ 04
1.20E ꢀ 03
1.36E ꢀ 03
6.72E ꢀ 04
1.14E ꢀ 03
1.27E ꢀ 03
6.22E ꢀ 04
1.04E ꢀ 03
1.19E ꢀ 03
5.50E ꢀ 04
8.29E ꢀ 04
1.07E ꢀ 03
5.19E ꢀ 04
7.25E ꢀ 04
9.40E ꢀ 04
1.98
1.30
1.12
2.20
1.39
1.21
2.47
1.45
1.31
2.67
1.59
1.40
3.02
2.00
1.54
3.20
2.29
1.77
56.9
56.0
52.7
55.1
52.4
49.7
53.7
51.7
47.6
50.6
48.0
44.8
44.4
42.5
39.95
43.4
41.6
38.8
<5
2.0E ꢀ 04
<5
7.00E ꢀ 04
3.00E ꢀ 03
4.0E ꢀ 04
<5
<5
<5
2.88E ꢀ 03
1.10E ꢀ 02
4.12E ꢀ 04
4.64E ꢀ 03
2.10E ꢀ 02
2.53E ꢀ 04
2.39E ꢀ 03
2.00E ꢀ 02
7.87E ꢀ 06
3.91E ꢀ 04
2.65E ꢀ 03
3.15E ꢀ 06
1.86E ꢀ 05
2.12E ꢀ 04
<5
Insoluble
Insoluble
<5
Insoluble
Insoluble
<5
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble

G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
247
100
100
FH1
FH2
FH3
FH4
FH6
FH8
10
1
10
1
0.1
0.1
0.01
1E-3
0.01
1E-3
2
3
4
5
6
7
8
9
10
number of carbon in fluorinated chain
Fig. 4. Number of carbon atoms in the fluorocarbon chain against the logarithm of
Fig. 2. Surface tension as a function of carbon’s number in fluorinated chain of FnHm
.
the critical micelle concentration.
corresponding completely hydrogenated quaternary ammonium
salts indicating that the adsorption at the air/water interface
depends on the nature of hydrophobic chains.
Fig. 5 shows values of log(c.m.c.) for FnHm as a function of
number of carbon atoms in the alkyl chain.
Critical micelle concentration increases with increasing the
number of carbon atoms in the alkyl chain until it reaches a
maximum. A short chain (<2 carbons) or a long-chain (>6 carbons)
alkyl substituent reduces the efficiency of the surfactant, although
the effect on effectiveness is smaller than that obtained with
variation of the fluorinated chain. Alkyl groups of a length in the
range of 2–4 carbon atoms give almost the same value of critical
micelle concentration. When the hydrophilic group is branched,
carbon atoms in ramification appear to have about one-half the
effect of carbon atoms on a fluorinated straight chain.
Fig. 3 shows the increase of area per molecule as a function of
hydrocarbon chain for F8Hm, F6Hm, F4Hm. The reduction of area
values obtained by decreasing the fluorinated chain length could
be explained by the chain localization changes at the interface as a
result of the reduced steric hindrance for shorter fluorinated
branches which enables a closer packing of molecules.
Values of critical micelle concentration for FnHm were obtained
by break points of the surface tension as a function of concentra-
tion as shown in Fig. 4.
Critical micelle concentration of partially fluorinated surfac-
tants decreases exponentially with increasing the number of
carbon atoms (nc), according to the empirical equation of Klevens
[15]:
3.2. Krafft’s temperature
Krafft temperature and c.m.c. provide information about the
conditions at which a compound acts as surfactant. Surfactants
with a high Krafft’s temperature are very efficient in lowering
surface tension [17]. Krafft’s temperature is defined as the melting
point of a hydrated surfactant. It was observed that at low
temperature, the conductance of pure as well as mixed hydrated
surfactant mixture increases slowly because the solubility of the
ionic surfactants are quite limited.
log10ðc:m:cÞ ¼ A ꢀ B ꢂ nc
(4)
where A and B are constants for the a particular ionic head group at
a given temperature. It is based on the assumption that (nc) value is
equal to the sum of carbons in the hydrophobic chain. In this case,
there are n carbon atoms in the fluorocarbon chain plus 3 carbon
atoms in the 2-hydroxypropyl chain. The values of A and B are
ꢀ0.54 and 0.29 respectively.
Cationic surfactants are generally water soluble when there is
only one long alkyl group. In contrast, cationic with two or more
long alkyl chains and with iodide counter-ion are soluble in
100
10
100
10
F4H
F6H
F8H
1
1
0.1
0.1
0.01
1E-3
1E-4
0.01
1E-3
1E-4
0
1
2
3
4
5
6
7
8
9
10
number of carbon in alkyl chain
Fig. 5. Values of log (c.m.c.) for FnHm as a function of number of carbon in alkyl chain.
Fig. 3. Area per molecule as a function of hydrocarbon chain.

248
G. Padoan et al. / Journal of Fluorine Chemistry 178 (2015) 241–248
surface tensions for F8H6 are significantly greater than equilibrium
values. The time required to attain equilibrium increases with
increasing hydrocarbon chain length, indicating the difficulty of
adsorption at interface from the interior of the solution because of
steric hindrance caused by long chains. This implies that
fluorinated surfactants with shorter hydrocarbon chains diffuse
faster. Moreover, dynamic surface tension for n = 8 and m = 8 is
close to that of water, even for long measurement time.
Furthermore, time required for attaining surface tension equilib-
rium increases with decreasing surfactant concentration; the
equilibration is more rapid above the critical micelle concentration
than below it.
4. Conclusions
A series of partially fluorinated quaternary ammonium salts are
characterized at air/water interface. The lengthening of the
fluorocarbon moiety boosts the surface active properties of the
surfactant increasing both its efficiency and effectiveness. Dou-
bling the number of fluorinated carbon atoms keeping the
hydrogenated moiety constant reduces surface tension by an
order of magnitude. Further kinetic of migration to interface are
extraordinarily speeded up by long fluorinated chains as shown by
dynamic surface tension measurements [20,21]. The lengthening
of the hydrocarbon moiety enhances surfactant’s hydrophobicity
leading to sparingly soluble or insoluble surfactants but without
contributing significantly to efficiency and effectiveness in
reducing surface tension [22]. Further the hydrocarbon chain
induce an increase in time required to attain the equilibrium
surface tension.
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During the temperature transition stage, the conductance
increases sharply with increasing temperature, due to larger
dissolution of the surfactant until Tk is reached. Then, above Tk, the
conductance increases slowly due to the increase in ionic mobility
with increasing temperature.
Solubility of fluorinated surfactants depends on the hydrophilic
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hydrocarbon moieties and iodide counter-ion limits the surfac-
tants solubility and consequently the majority of surfactants
synthesized are insoluble in pure water.
3.3. Dynamic surface tension
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surface tension measurements. The variation of the dynamic
surface tension as a function of bubble life time for FnHm with n = 4,
6, 8 and m = 2 is shown in Fig. 6. Dynamic surface tension values
after 20 s for F8H1 are close to equilibrium values, whereas dynamic
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