D. Liu et al. / Journal of Molecular Liquids xxx (xxxx) xxx
3
can be determined by a simple titration method with a hydrochloric
acid solution using bromophenol blue as the indicator. The conversion
of the quaternization reaction was calculated by Eqs. (1) and (2):
cotton fabric were studied by scanning electron microscope (SEM)
(Phenom LE) at an accelerating voltage of 10 kV, a thin gold layer was
coated on the fabric before measurements. Whiteness (expressed as
whiteness index) and softness (expressed as bending rigidity) of
treated cotton fabric were measured by a WSB-2 digital whiteness
meter and a LLY-01B electric rigidity tester, respectively. Rewetting abil-
ity of treated cotton fabric was measured using the Chromate-Method.
Pretreated white cotton fabric was cut into pieces of 250 mm × 20 mm
each. Then, it was vertically immersed in a potassium chromate solution
with the short side 10 mm into the solution. After 20 min, the maximum
height that the yellow potassium chromate solution reached on the
treated fabric was measured, and the value was obtained by averaging
over five parallel measurements for each sample.
VH ꢀ cH ꢀ 56:1
AV ¼
ð1Þ
m
where VH, cH, m, and AV are the required volume of hydrochloric acid so-
lution (expressed in mL), the concentration of the hydrochloric acid so-
lution (expressed in mol/L), the sample quality (expressed in g), and the
reaction amine value of equivalent potassium hydroxide (expressed in
mg KOH g−1), respectively.
ðAVÞ −ðAVÞ2
ð1AVÞ1
CR ¼
ð2Þ
3. Results and discussion
where (AV)1, (AV)2 and CR represent the initial reaction amine value
(given in units of mg g−1), the final reaction amine value (given in
units of mg g−1) and the conversion of DAP of the synthetic route,
respectively.
3.1. Effect of synthetic conditions on DAP conversion
Univariate analysis was used to optimize the synthetic conditions for
preparation of the gemini ester surfactant. The parameters of mole ratio
of raw materials, reaction time, reaction temperature and solvent vol-
ume were studied. Fig. 2a presents the conversion of DAP versus reac-
tion temperature, when the reaction conditions were set up as
follows: reaction time was 6 h, solvent volume was 0.3 L/mol and the
molar ratio of DAP to 1,4-dibromobutane was 2.05:1. The conversion in-
creases with the reaction temperature at first, and then decreases with
further increase in the reaction temperature. The maximum conversion
(~94%) is obtained at around 100 °C. This is probably because the
quaternization reaction is an endothermic reaction. The initial increase
in the temperature can provide more kinetic energy for the reactants,
thus increases the collision probability between the reactant molecules,
and improves the conversion of DAP significantly. However, when the
reaction temperature was higher than 100 °C, the DAP conversion de-
creased to some extent. Therefore, the selected reaction temperature
was set around 100 °C.
2.4. Benzene solubilization capacity
A certain amount of benzene was added to a 100-mL volumetric
flask with the surfactant solution (0.001 mol/L, 10 mL). Then, water
was added to the tick mark. The absorbance of each solution was mea-
sured at 560 nm on a UV-1800PC UV spectrometer. The solubilization
capacity (X) was obtained by the following equation (Eq. (3)).
A
c ꢀ V
X ¼
ð3Þ
where A, V, and c are the solubilization limit of benzene (expressed in
mL), the amount of surfactant solution (expressed in mL) and the con-
centration of surfactant solution (expressed in mol/L), respectively.
2.5. Employment of TBDB as a softener of cotton fabric
To explore the solvent effect on the conversion, various amounts
of solvent volume per molar DAP were examined. The reaction con-
ditions were set up as follows: the reaction time was 6 h, reaction
temperature was 100 °C and the molar ratio of DAP to 1,4-
dibromobutane was 2.05:1. Fig. 2b presents the conversion of DAP
versus solvent volume. It can be seen that the conversion increases
from 86% to 94% with the increase of the solvent volume from 0.2
to 0.3 L/mol, and decreases with further increase of the solvent vol-
ume. When the solvent volume was around 0.1 L/mol, the solution
would become very viscous as the reaction progressed and gradually
turned dark brown. This is probably because high concentration of
quaternary ammonium salt can result in high viscosity of the solu-
tion, which leads to a decrease in heat transfer efficiency in the sys-
tem, causing local overheating of the solution. When the solvent
volume was 0.2 L/mol, the solution gradually became viscous with
reaction time and the product gradually turned yellow. Adding a rea-
sonable amount of solvent can not only control the viscosity of the
system, but also improve the heat and mass transfer efficiency of
the system, and thus increase the conversion of the reaction. How-
ever, when the amount of the solvent added was further raised
above 0.3 L/mol, the conversion of DAP was decreased, possibly
due to the decrease of the reactant concentration in the system.
Therefore, the selected solvent volume per molar DAP was around
0.3 L/mol.
2.5.1. Preparation of quaternary ammonium salt emulsion
Quaternary ammonium surfactant, emulsifiers (weight ratio of
Tween-20:Tween-60 = 1:3) and isopropyl alcohol, with the mass
ratio of 10%, 5% and 1% respectively, were stirred to dissolve in water
in a 500-mL conical flask at 60 °C. After stirring for 2.5 h, the solution
was cooled to room temperature to obtain a quaternary ammonium
salt emulsion having a mass fraction of the surfactant of ~10%.
2.5.2. Treatment on fabric
The pre-weighted raw fabric was soaked in the 1 g/L quaternary am-
monium salt emulsion (weight ratio of fabric to bath = 1:20) at 50 °C
for 30 min and then padded. After that, the fabric was dried at 100 °C
for 10 min and then kept in a dry container to equilibrium for 24 h.
2.6. Characterization
The structures of the prepared compounds were identified by
Fourier-Transformed Infrared (FT-IR) spectra, 1H NMR spectra and
Mass spectra. FT-IR spectra were recorded by a Brucker Tensor-27 FT-
IR spectrometer in the wavenumber range from 400 to 4000 cm−1
,
with an average of 32 scans at the resolution of 4 cm−1. 1H NMR spectra
were recorded by a Brucker AVIII/Ascend500HD NMR spectrometer
using DMSO‑d6 as the solvent. Mass spectra were recorded by an Agilent
1290-6545 liquid chromatography with mass spectrometer (LC-MS).
The surface tensions of surfactant solutions were measured with a
Krüss (Hamburg, Germany) Processor K100 Tensiometer. The CMC
and the surface tension at the CMC were determined from the breaking
point on the curve of surface tension plotted against the logarithm of the
concentration. The surface morphologies of untreated and treated white
To examine the effect of the molar ratio between 1,4-
dibromobutane and DAP on the conversion, the reaction conditions
were set up as follows: reaction temperature was 100 °C, solvent vol-
ume per molar DAP was 0.3 L/mol and the reaction time was 6 h.
Fig. 2c presents the conversion of DAP versus the molar ratio of
DAP to 1,4-dibromobutane. It shows that the conversion increases
with the molar ratio of DAP to 1,4-dibromobutane no more than
Please cite this article as: D. Liu, X. Yang, P. Liu, et al., Synthesis and characterization of gemini ester surfactant and its application in efficient fabric