Journal of Chemical & Engineering Data
Article
ionics. Before the critical micelle concentration, ionic
surfactants become insoluble in solution. The solubilities of
micelle forming surfactants show a strong increase above a
certain temperature, termed as Krafft temperature, TK (also
known as Krafft point or critical micelle temperature).23 Below
TK, the solubility of the surfactant is too low for micellization;
therefore, solubility alone determines the surfactant monomer
concentration. Above TK a relatively large amount of surfactant
can be dispersed in micelles, and solubility increases greatly. A
surfactant with a low Krafft point is more soluble than a
surfactant with a high Krafft point.
In this study, a series of N,N-dialkyl-N,N-diethyl ammonium
bromide, two tail−one head surfactants, abbreviated as “m-0-m”
(m = 10, 12, and 16) and N,N′-dialkyl-N,N,N′,N′-tetramethyl-
N,N′-ethanediyl-diammonium dibromide, two tail−two head
surfactants, abbreviated as “m-2-m” (m = 12 and 16) were
synthesized in our laboratory. Critical micelle concentrations
(CMCs), degree of micelle ionization (α), Krafft temperatures
(TK) of 1 wt % aqueous solutions of these surfactants, and
melting points (TM) were determined. The Krafft temperatures
of some monomeric, dimeric, and double chain cationic
surfactants have been systematically investigated by using a
conductometer. The effects of the hydrophobic alkyl chain,
headgroup, and spacer on cationic surfactants are explained by
using the CMC and TK values which were found for the studied
surfactants. In addition, the effects of NaCl molality on the
Krafft temperature of various cationic surfactants have been
examined.
Supporting Information). The chemicals as well as their
purities and suppliers are listed in Table 1.
Synthesis of Cationic Gemini Surfactants. Cationic Gemini
surfactants used in this work were synthesized as described by
Zana et al.24 and are shown in Scheme 2. Acetone is used as
solvent.25 The reaction products were obtained in yields of
about 90−97%, and these products were purified and
recrystallized.
1
Spectral Characteristics for 12-2-12. H NMR (300 MHz,
CDCl3): δ = 0.86 (t, 6H), 1.17−1.30 (m, 36H), 1.81 (m, 4H),
3.47 (s, 12H), 3.70 (m, 4H), 4.70 (s, 4H).
13C NMR (75 MHz, CDCl3): δ = 14.38, 22.92, 23.28, 26.48,
29.42, 29.60, 29.77, 29.80, 29.88, 32.15, 51.30, 57.02, 66.09.
1
Spectral Characteristics for 16-2-16. H NMR (300 MHz,
CDCl3): δ = 0.86 (t, 6H), 1.23−1.34 (m, 52H), 1.82 (m, 4H),
3.46 (s, 12H), 3.70 (m, 4H), 4.69 (m, 4H).
13C NMR (75 MHz, CDCl3): δ = 14.38, 22.93, 23.27, 26.47,
28.40, 29.00, 29.43, 29.60, 29.62, 29.67, 29.79, 29.83, 29.92,
29.98, 32.16, 51.26, 57.07, 66.02.
Synthesis of Double-Chain Cationic Surfactants. The
double chain cationic surfactants didecyldiethylammonium
bromide, didodecyldiethylammonium bromide, and dihexade-
cyldiethylammonium bromide synthesized from diethyl amine
and corresponding alkyl halide by two-stage reaction are shown
in Schemes 3 and 4.
To a solution of diethylamine (0.2 mol) in dry acetone was
added alkyl halide (0.1 mol), and the solution was stirred for 6
h at reflux temperature. Then, the reaction mixture was cooled
to room temperature and was quenched with 1% KOH
solution. The aqueous layer was extracted with diethyl ether
three times and was washed in brine solution. The organic
layers were collected and dried over anhydrous Mg2SO4
(Scheme 3).
2. EXPERIMENTAL SECTION
2.1. Materials. Hexadecyltrimethylammonium bromide
(CTAB) and dodecyltrimethylammonium bromide (DTAB)
cationic surfactants were obtained from Merck. N,N′ didodecyl-
N,N,N′,N′-tetramethyl-N,N′-ethanediyldiammonium dibro-
mide (12-2-12), N,N-hexadecyl-N,N,N′,N′-tetrametyl-N,N′-
ethanediyldiammonium dibromide (16-2-16) Gemini cationic
surfactants and N,N-didecyl-N,N-diethylammonium bromide
(10-0-10), N,N-didodecyl-N,N-diethylammonium bromide (12-
0-12), and N,N-dihexadecyl-N,N-diethylammonium bromide
(16-0-16) double chain cationic surfactants have been
synthesized and purified in our laboratory. Structures of
surfactant molecules used in this study are given in Scheme
In the next stage, reaction of diethylalkylamine with the same
alkyl halide in acetone gave dialkyldiethylammonium bromide
(Scheme 4).
1
Spectral Characteristics for 10-0-10. H NMR (300 MHz,
CDCl3): δ = 0.86 (t, 6H), 1.20−1.70 (m, 38H), 3.20−3.30 (t,
4H), 3.50−3.60 (quartet, 4H).
13C NMR (75 MHz, CDCl3): δ = 8.40, 14.30, 22.40, 22.90,
26.70, 29.40, 29.50, 29.60, 32.00, 54.40, 58.40.
1
Spectral Characteristics for 12-0-12. H NMR (300 MHz,
CDCl3): δ = 0.88 (t, 6H), 1.20−1.80 (m, 46H), 3.20−3.30 (t,
1
1, and H and 13C NMR spectra of surfactants were recorded
4H), 3.50−3.60 (quartet, 4H).
13C NMR (75 MHz, CDCl3): δ = 8.40, 14.30, 22.30, 22.90,
26.70, 29.40 29.50, 29.60, 29.70, 29.80, 32.10, 54.40, 58.30.
with Varian Mercury Plus 300 MHz spectrometer (see
1
Spectral Characteristics for 16-0-16. H NMR (300 MHz,
Scheme 1. Structures of Surfactant Molecules Used in This
Study: (a) Double-Chain Cationic Surfactants, (b) Gemini
Surfactants, and (c) Conventional Surfactants
CDCl3): δ = 0.88 (t, 6H), 1.20−1.70 (m, 62H), 3.20−3.30 (t,
4H), 3.50−3.60 (quartet, 4H).
13C NMR (75 MHz, CDCl3): δ = 8.40, 14.40, 22.30, 22.90,
26.70, 29.40 29.60, 29.62, 29.70, 29.82, 29.89, 29.92, 32.20,
54.37, 58.27.
2.2. Apparatus and Procedure. Conductivity Measure-
ments. The conductivity measurements of surfactant solutions
were taken with a conductometer WTW Terminal 740 using a
dip-type cell with a cell constant of 0.485 cm−1. Equipment was
initially calibrated by standard KCl solutions. Conductivity
values were for to find three different physicochemical
characteristics: critical micelle concentration (CMC), degree
of micelle ionization (α), and Krafft temperatures (TK).
Deionized double distilled water was used in all experimental
work, and its specific conductivity value was about 1−2 × 10−6
S cm−1. All the experimental data were taken at 30.0 0.1 °C.
B
J. Chem. Eng. Data XXXX, XXX, XXX−XXX