Langmuir
ARTICLE
13C NMR (100 MHz, CDCl3): δ 13.89, 22.45, 22.86, 26.1, 29.13,
29.33, 29.36, 29.43, 29.45, 31.68, 50.78, 56.57, 65.76.
2.1.3. N,N0-Didodecyl-N,N,N0,N0-tetramethyl-N,N0-butanediyl-dia-
mmonium Dibromide [12-4-12]. N,N,N-Dodecyldimethylamine (9.39 g,
44 mmol, 10% excess) was dissolved in acetone (30 mL) in a round-
bottomed flask. 1,4-Dibromobutane dissolved in 20 mL of acetone
(4.32 g, 20 mmol) was added dropwise under stirring. The mixture was
refluxed for 24 h and cooled to room temperature, and then a white solid
was collected by filtration and washed with acetone. The product was
recrystallized from a 1:9 mixture of ethanol and diethyl ether. Yield: 81%
1H NMR (400 MHz, CDCl3): δ 0.86 (t, 6H), 1.19ꢀ1.30 (m, 32H),
1.34 (m, 4H), 1.75 (m, 4H), 2.14 (m, 4H), 3.27 (s, 12H), 3.41 (t, 4H),
3.94 (t, 4H).
Figure 1. From left to right, dodecyltrimethylammonium bromide
(DTAB), the general structure of the gemini surfactants, the spacers
used in the study, and the names given to the surfactants.
13C NMR (100 MHz, CDCl3): δ 13.90, 19.72, 22.47, 22.72, 26.2,
29.06, 29.12, 29.28, 29.31, 29.41, 31.69, 50.77, 63.33, 64.99.
2.1.4. N,N0-Didodecyl-N,N,N0,N0-tetramethyl-N,N0-hexanediyl-dia-
mmonium Dibromide [12-6-12]. N,N,N-Dodecyldimethylamine (9.39 g,
44 mmol, 10% excess) was dissolved in acetone (30 mL) in a round-
bottomed flask. 1,6-Dibromohexane dissolved in 20 mL of acetone (4.88 g,
20 mmol) was added dropwise under stirring. The mixture was refluxed
for 24 h and cooled to room temperature, and then a white solid was
collected by filtration and washed with acetone. The product was
recrystallized from a 1:9 mixture of ethanol and diethyl ether. Yield: 78%
1H NMR (400 MHz, CDCl3): δ 0.85 (t, 6H), 1.19ꢀ1.30 (m, 32H),
1.33 (m, 4H), 1.55(m, 4H), 1.69 (m, 4H), 1.98 (m, 4H), 3.35 (s, 12H),
3.42 (t, 4H), 3.68 (t, 4H).
minerals, and spin-coated polymers have been used as a sub-
strate. In this work, SPR was used on gold and QCM-D was
employed on four widely different surfaces: gold, silica, gold
made hydrophobic by the self-assembly of an alkane thiol, and
gold made hydrophilic by the self-assembly of a hydroxyl-
terminated alkane thiol.
The surfactants studied are cationic geminis with bromide as
the counterion prepared by reacting a bis-dimethylamino spacer
with 2 equiv of dodecyl bromide or a dibromoalkane spacer with
2 equiv of docecyldimethylamine. Two types of spacer units have
been used: a linear alkane with 2, 4, or 6 methylene groups
(named 12-n-12 with n = 2, 4, and 6) and a meta- or para-
phenylene group (denoted 12-m-Φ-12 and 12-p-Φ-12, re-
spectively). The structures are given in Figure 1.
The alkane spacer is flexible, and the phenylene unit is rigid.
The main aim of this work is to evaluate to what extent the
rigidity of the spacer affects the adsorption characteristics. The
results are also compared with the adsorption of the correspond-
ing monomeric surfactant, dodecyltrimethylammonium bromide
(DTAB).
13C NMR (100 MHz, CDCl3): δ 13.94, 21.61, 22.50, 22.75, 24.48,
26.19, 29.12, 29.15, 29.26, 29.32, 29.42, 31.72, 50.88, 64.02, 64.58.
2.1.5. Bis-N,N,N-dodecyldimethyl-m-phenylenediammonium Di-
bromide [12-m-Φ-12]. R,R0-Dibromo-m-xylene (1.00 g, 3.79 mmol)
was dissolved in ethanol (50 mL) in a round-bottomed flask. N,N,N-
Dodecyldimethylamine (1.98 g, 9.28 mmol, 20% excess) was added
dropwise under stirring. The mixture was refluxed for 48 h. The solvent
was removed under vacuum, and the product was recrystallized from a
1:9 mixture of ethanol and diethyl ether. Yield: 76%
1H NMR (400 MHz, CDCl3): δ 0.87 (t, 6H), 1.21ꢀ1.3 (m, 32H),
1.3ꢀ1.4 (m, 4H), 1.83 (m, 4H), 3.23 (s, 12H), 3.55 (t, 4H), 5.02 (s, 4H),
7.51 (t, 1H), 7.85 (d, 2H), 8.60 (s, 1H).
2. EXPERIMENTAL SECTION
13C NMR (100 MHz, CDCl3,): δ 13.8, 22.45, 22.9, 26.11, 29.2, 29.38,
29.41, 29.50, 31.7, 52.8, 66.6, 68.8, 126.3, 129.8, 135.0, 137.5.
2.1.6. Bis-N,N,N-dodecyldimethyl-p-phenylenediammonium Dibro-
mide [12-p-Φ-12]. R,R0-Dibromo-p-xylene (1.00 g, 3.79 mmol) was
dissolved in ethanol (30 mL) in a round-bottomed flask. N,N,N-
Dodecyldimethylamine (1.98 g, 9.28 mmol, 20% excess) was added
dropwise under stirring. The mixture was refluxed for 48 h. Then the
solvent was removed under vacuum, and the product was recrystallized
from a 1:9 mixture of ethanol and diethyl ether. Yield: 73%
1H NMR (400 MHz, CDCl3): δ 0.85 (t, 6H), 1.18ꢀ1.28 (m, 36H),
1.3ꢀ1.4 (m, 4H), 1.84 (m, 4H), 3.21 (s, 12H), 3.52 (t, 4H), 5.18 (s, 4H),
7.80 (d, 4H).
2.1. Material and Synthesis. 2.1.1. Materials. Acetone (Aldrich,
g99%), diethyl ether (Aldrich, g99%), ethanol (Kemetyl AB, 99.5%),
dodecylbromide (Aldrich, 97%), N,N,N-dodecyldimethylamine (Acros,
95%), N,N,N0,N0-tetramethyl-1,2-ethylenediamine (Aldrich, g99%), 1,4-
dibromobutane (Aldrich, 99%), 1,6-dibromohexane (Aldrich, g97%), R,
R0-dibromo-m-xylene (m-phenylene dibromide, Aldrich, g97%), R,R0-
dibromo-p-xylene (p-phenylene dibromide, Aldrich, g98%), and hexade-
canethiol (Aldrich, 99%) were used as purchased. N,N,N,-Dodecyldi-
methylammonium bromide (DTAB, Aldrich, g98%) was recrystallized
twice from ethanol and dried under vacuum prior to use. 16-Hydroxyhex-
adecanethiol were from prepared from 15-carboxyhexadecanethiol
(Aldrich, 90%) according to a protocol described elsewhere.21
13C NMR (100 MHz, CDCl3): δ 14.0, 22.4, 22.9, 26.24, 29.2, 29.36,
29.4, 29.5, 31.8, 51.2, 64.6, 66.2, 103.3, 133.0.
Milli-Q water (resistance >18 MΩ cm) was used for the preparation
3
2.2. NMR. 1H NMR and 13C NMR analyses were carried out on a
Jeol 400 MHz spectrometer at 25 °C. Deuterated solvents were
purchased from Armar Chemicals.
of aqueous solutions.
2.1.2. N,N0-Didodecyl-N,N,N0,N0-tetramethyl-N,N0-ethanediyl-dia-
mmonium Dibromide [12-2-12]. Dodecyl bromide (11.96 g, 48 mmol,
20% excess) was dissolved in acetone (30 mL) in a round-bottomed
flask. N,N,N0,N0-Tetramethyl-1,2-ethylenediamine dissolved in 20 mL
of acetone (2.32 g, 20 mmol) was added dropwise under stirring. The
mixture was refluxed for 48 h and cooled to room temperature, and then
a white solid was collected by filtration and washed with acetone. The
product was recrystallized from a 1:9 mixture of ethanol and diethyl
ether. Yield: 58%
2.3. Tensiometry. Surface tension measurements were carried out
on a Sigma 70 tensiometer (KSV) using the du No€uy ring method. The
temperature was kept at 25 °C ((0.01 °C) by a cryostat Neslab RTE-
200. The glassware was cleaned with chromosulfuric acid, and the ring
was flame treated prior to use. The measurements were conducted from
low to high concentrations.
2.4. Conductometry. The cmc and the degree of ionization were
determined by conductivity measurements according to the method
described by Zana.22 The conductometer was a CDM 210 (Radiometer
1H NMR (400 MHz, CDCl3): δ 0.86 (t, 6H), 1.21ꢀ1.3 (m, 32H),
1.36 (m, 4H), 1.8 (m, 4H), 3.49 (s, 12H), 3.68 (t, 4H), 4.70 (s, 4H).
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dx.doi.org/10.1021/la200539a |Langmuir 2011, 27, 7549–7557