Supplementary Materials for
Effect of Hydrophilic Head Group on Krafft Temperature, Surface Activities and Rheological Behaviors of Erucyl Amidobetaines
Yuejiao Wang,1,4 Yongmin Zhang,1,4 Xingli Liu,2 Jiyu Wang,1 Limin Wei,1 Yujun Feng1,3 ()
1 Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, P. R. China
2 College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
3 Polymer Research Institute, State Key Laboratory of Polymer Materials Engineering, Chengdu 610065, P. R. China
4 University of the Chinese Academy of Sciences, Beijing 100049, P. R. China
1. Materials
Erucic acid (Sipo, China, 97.5 %), N,N-dimethylpropanediamine (Feixiang Chemicals, China, AR), sodium fluoride (Kelong, China, AR), sodium chloroacetate (Kelong, China, AR), 1,3-propanesultone (Alfa Aesar, ≥ 99.0 %, GC), sodium 3-chloro-2-hydroxypropanesulfonate (Yacoo, AR), were used without further purification. All other chemicals used were reagent grade.
2. Characterizations
1H NMR spectra was recorded on a Bruker Avance 300 spectrometer (300 MHz) in CD3OD at room temperature. ESI HRMS was obtained by Bruker Daltonics Data Analysis 3.2 system.
EHSB: yield 92 %; 1H NMR (300 MHz, CD3OD) (Figure S1): 0.90 (t, J = 6.96 Hz, 3H), 1.30 (m, 28H), 1.60 (m, 2H), 2.00–2.04 (m, 6H), 2.15–2.23 (m, 2H), 3.00 (m, 2H), 3.19 (s, 6H), 3.25–3.44 (m, 4H), 3.75 (m, 2H), 4.57 (m, 1H), 5.33 (m, 2H). ESI HRMS (Figure S2): Calc., 583.4121 (M + Na+); Found: m/z = 583.4124.
Figure S1 1H NMR spectrum of hydroxyl-sulfobetaine surfactant EHSB (CD3OD, 300 MHz, TMS)
Figure S2 ESI-HRMS spectrum of hydroxyl-sulfobetaine surfactant EHSB
EDAS: yield 91 %; 1H NMR (300 MHz, CD3OD) (Figure S3): 0.90 (t, J = 6.91 Hz, 3H), 1.30 (m, 28H), 1.61 (m, 2H), 2.00–2.04 (m, 6H), 2.18–2.23 (m, 4H), 2.87 (t, J = 6.87 Hz, 2H), 3.10 (s, 6H), 3.25–3.36 (m, 4H), 3.53 (m, 2H), 5.34 (m, 2H). ESI HRMS (Figure S4): Calc., 567.4172 (M + Na+); Found: m/z = 567.4169.
Figure S3 1H NMR spectrum of sulfobetaine surfactant EDAS (CD3OD, 300MHz, TMS)
Figure S4 ESI-HRMS spectrum of sulfobetaine surfactant EDAS
EDAB: yield 72 %; 1H NMR (300 MHz, CD3OD) (Figure S5): 0.90 (t, J = 6.93Hz, 3H), 1.30 (m, 28H), 1.60 (m, 2H), 1.94–2.04 (m, 6H), 2.16–2.21 (m, 2H), 3.23–3.26 (s, 6H), 3.29–3.31 (m, 2H), 3.56–3.62 (m, 2H), 3.79 (s, 2H), 5.34 (m, 2H). ESI HRMS (Figure S6): Calc., 503.4189 (M + Na+); Found: m/z = 503.4189.
Figure S5 1H NMR spectrum of carboxybetaine surfactant EDAB (CD3OD, 300MHz, TMS)
Figure S6 ESI HRMAS spectrum of carboxybetaine surfactant EDAB
3. Determination of Krafft temperature
The more easily accessible methods, for example, visual observation [1] and spectrophotometry [2, 3], electrical conductivity [2], have been proposed to determine TK at which the surfactant solution with concentration far above the CMC (normally 1 wt%) suddenly becomes clear. TK is normally determined by electrical conductivity for saturated surfactant solution as a function of temperature. However, such a process is time-consuming and not suitable for the uncharged species such as amidobetaines in this work. And the high NaCl content in the solution also limits this process. The spectrophotometric technique is more suitable for metastable crystalline phase other than solution with solid precipitate in this work. Therefore, the TK of erucyl amidobetaines in this work was determined by visual observation which was reported previously [2].
Sample solutions with concentration of 1 wt% were prepared by dissolving surfactant powders in distilled water or brine with desired concentration of NaCl, followed by gentle agitation while mildly heating. When completely solubilized at high temperatures, the solutions were cooled to induce precipitation, and then left to stand overnight for equilibrium prior to measurements. TK was determined by heating 10 mL of surfactant solution in a sealed tube until a clear solution was obtained [1, 4] and the reproducibility of three times for the same measurements was ±0.1 °C. In some cases, no precipitae was found when the clear solutions were cooled. Even the sealed tube containing the solution was placed in water bath containing ice water mixture (the temperature of the mixture is 0 °C ) for 2 h, no visible precipitation or turbidity was observed. If we contine to cool the tube, the solution will be frozen. On this occasion, the TK of the sample solution is regarded as below 0 °C.
4. Measurement of surface tension
Surface tension (γ) was measured with a Krüss K100 tensiometer by the automatic model of the du Noüy Ring technique at 25 ± 0.01 °C, and a cover was used to minimize water evaporation. Sample solutions with desired concentration were prepared by dissolving surfactant in 500 mM NaCl solution to ensure good solubility. A set of measurements to obtain equilibrium surface tension were taken until the change was less than 0.03 mN/m every 3 min [5]. The critical micelle concentration (CMC) and surface tension at the CMC (γCMC) were determined from the break point of the surface tension and logarithm of concentration curve.
5. Fluorescence spectroscopy
Sample solutions with desired concentration were prepared by dissolving surfactant and pyrene in 500 mM NaCl solution to ensure good solubility of the surfactants, followed by ultrasonic vibration for 48 h for purpose of solubilization. The concentration of pyrene in solution is 6 ´ 10-7 mol/L. Fluorescence spectra were recorded on a Varian Cary Eclipse spectrometer equipped with a Neslab circulating bath to controlling the temperature of the water-jacketed cell. All measurements were carried out at 25 °C. They were recorded with an excitation wavelength of 335 nm, excitation slit width of 10 nm and emission slit width of 2.5 nm. Fluorescence spectrometer was corrected by solution of pyrene with concentration of 6 ´ 10-7 mol/L in 500 mM NaCl.
Pyrene has been used as a fluorescent probe to determine critical micelle concentration (CMC) [6, 7] and it appears five vibronic peaks in the fluorescence spectrum. The ratio of the intensity of the first peak (I1) at 373nm to the intensity of the third peak (I3) at 384 nm was 1.8 in the measurement. The ratio I1/I3 is sensitive to solvent polarity, as the surfactant concentration is increased, a continuous decrease in I1/I3 is observed, reflecting the incorporation of the hydrophobic probe into the micellar environment _ENREF_15[8-10]. Critical micelle concentration of surfactants can be obtained by the relation of the ration I1/I3 and the surfactant concentration_ENREF_1 at the first turning point.
6. Rheology
Rheological experiments were performed on a Physica MCR 301 (Anton Paar, Austria) rotational rheometer equipped with concentric cylinder geometry CC27 (ISO3219) with a measuring bob radius of 13.33 mm and a measuring cup radius of 14.46 mm. Sample solutions were stored at the test temperature for at least 20 min before running experiments. Dynamic frequency spectra were conducted in the linear viscoelastic regimes, as determined from dynamic stress-sweep measurements. All experiments were done using stress controlled mode, and Cannon standard oil was used to calibrate the instrument before the measurements. The temperature was set to ±0.1 °C accuracy by a Peltier temperature control device, and a solvent trap was used to minimize water evaporation during the measurements. Sample solutions with desired concentration were prepared by dissolving surfactant in 500 mM NaCl solution to ensure good solubility of the surfactants. All measurements were carried out at 25 °C.
Figure S7 steady shear viscosity (η) plotted as a function of shear rate () for various concentrations of EDAB (A) and EDAS (B) in 500 mM NaCl at 25 °C
7. Calculation of packing parameter
Packing parameter P is calculated by the formula P=υ/al [11], where a is the effective headgroup area and υ is the volume of the lipophilic chain possessing maximum effective length l.
Generally, the l and υ can be calculated from Nagarajan’s procedure [12] for saturated alkyl chains. Considering both cis-double bond and amido bond coexisted in the hydrophobic tail chains for the three amidobetaie surfactants in this work, we approximately estimated l and υ by treating both cis-double bond and amido bond as saturated double carbon bonds, so 26 carbon atoms are contained in the hydrophobic tail chains. Based on these approximations, l and υ were calculated as as follows:
Å3 (1)
Å3 (2)
Å3 (3)
Å (4)
where T is in Kelvin, n is the number of carbon atoms in hydrophobic tails. At 25 °C, the value of υ(CH3) and υ(CH2) are 54.6 Å3 and 26.9 Å3, respectively. As the hydrophobic part for these three surfactants is completely the same, they have the same l and υ. The values of υ and l calculated are 727.1 Å3 and 34.39 Å, respectively. The parameter a is assumed to equal to ACMC [13]. So we calculated P for EHSB, EDAS and EDAB to be 0.38, 0.61, and 0.49, respectiely.
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