Thermodynamics properties of micellization of organosilicone modified gluconamide-type surfactant

Article abstract of DOI:10.14233/ajchem.2013.15527

Thermodynamic properties of micellization of N-3-propylmethyltrisiloxane-N- glucosylamine in water over a temperature range of 298 to 313 K been studied with surface tension method. On the basis of these results, the thermodynamic parameters i.e., Gibbs energy (δG? m), enthalpy (δS? m) and entropy (δH? m) of micellization have been evaluated.

Full text of DOI:10.14233/ajchem.2013.15527

Asian Journal of Chemistry; Vol. 25, No. 17 (2013), 9865-9868
http://dx.doi.org/10.14233/ajchem.2013.15527
Thermodynamics Properties of Micellization of
Organosilicone Modified Gluconamide-Type Surfactant
LEI TAO
School of Environment and Safety, Taiyuan University of Science and Technology, Taiyuan 030006, Shanxi Province, P.R. China
Corresponding author: E-mail: leitao030006@126.com
(Received: 23 March 2013;
Accepted: 25 October 2013)
AJC-14292
Thermodynamic properties of micellization of N-3-propylmethyltrisiloxane-N-glucosylamine in water over a temperature range of 298 to
313 K been studied with surface tension method. On the basis of these results, the thermodynamic parameters i.e., Gibbs energy (∆Gom),
enthalpy (∆Som) and entropy (∆Hom) of micellization have been evaluated.
Key Words: Thermodynamics Properties, Micellization, Organosilicone, Gluconamide, Surfactant.
Infrared spectroscopy was performed with a Fourier
Transform Infrared Spectrometer (Hitachi 270-30). The
surfactants were smeared directly onto a KBr plate. Proton nuclear
magnetic resonance (1H and 13C NMR) spectroscopy was
recorded in CDCl3 with aVarian INOVA-400 MHz spectro-
meter. Since TMS cannot easily be used as internal standard
because of the overlapping with other methyl signals, we used
the residual protons of the solvent at 7.26 ppm as the reference.
Measurement of surface tension: Equilibrium surface
tension values of the surfactants in aqueous solution were
obtained by the Wilhelmy plate method using a model K12
Krüss tensiometer (Hamburg, Germany). Prior to measurement,
the surface tension of the distilled, deionized water was measured.
These values were in the range of 72.3 0.3 mN/m. Surfactant
solutions were then prepared with this water and the samples
were left for 15 min prior to surface tension measurement.
Synthesis of 3-aminopropyltrisiloxane: The mixture of
3-aminopropylmethyldiethoxysilane (28.79 g, 0.15 mol),
hexamethyldisiloxane (121.89 g, 0.75 mol) and tetramethyl
ammonium hydroxide (0.735 g, 0.008 mol) was heated for
2 h at 90 °C under nitrogen atmosphere, with stirring. The
resulting quaternary ammonium hydroxide was then deacti-
vated by heating for 0.5 h at 130 °C and the excess hexamethyl-
disiloxane was simultaneously distilled from the mixture. The
liquid product was purified by fractional distillation. Colourless
liquid, 22.2 g (yield: 52.9 %), boiling point (b.p.) 85 °C/1.5
mmHg. IR (KBr, νmax, cm-1): 3300 (O-H), 1260 (Si-Me3), 1100
(Si-O-Si), 840 (Si-Me3), 760 (Si-Me3). 1H NMR(CDCl3, ppm)
δ: 0.004 (s, 3H, SiCH3), 0.08 (s, 18H, Si(CH3)3 × 2), 0.44 (t,
INTRODUCTION
With an increasing environmental concern, sugar-based
surfactant with hydrophilic sugar groups has attracted the
attention of researchers worldwide, because sugar-based
surfactants have good excellent biodegradability, good derma-
tological compatibility and the absence of toxic effects1.
Generally silicone surfactant with hydrophobic siloxane
group can produce lower surface tension than hydrocarbon
surfactant. Because the flexible siloxane backbone can adopt
orientations while it lies flat on the surface of the water,
favouring exposing the low surface energy methyl groups
substations to the air2,3.
These unique properties prompted a lot of researchers to
integrate sugar and siloxane's advantage. In spite of a few
papers and patents have reported siloxane modified sugar based
surfactants4-10, relatively little is known about the thermody-
namics properties of micellization of this interesting class of
compounds. In this work, we reported the thermodynamics
properties of micellization of N-3-propylmethyltrisiloxane-
N-glucosylamine [abbreviated as Si(3)N-GA] in water over a
temperature range of 298 to 313 K
EXPERIMENTAL
3-Aminopropylmethyldiethoxysilane, hexamethyldisi-
loxane were purchased from Beijing Chemical Reagents
Company and were used without further purification. Double
distilled water was used for the analysis and for the measure-
ments of primary properties.

9866 Tao
Asian J. Chem.
2H, J = 8.4Hz, SiCH2), 1.40-1.44 (m, 2H, CH2CH2NH2), 1.5
(s, 2H, NH2), 2.64 (t, 2H, J=7.2Hz, CH2N). Elemental analy-
sis (%) calcd for C10H29NO2Si3: C, 49.26; H, 10.45; N, 5.01.
Found: C, 49.40; H, 10.28; N, 5.09.
Synthesis of N-3-propylmethyltrisiloxane-N-glucosyl-
amine: 3-aminopropyltrisiloxane (1.8 g, 0.0064 mol), was
dissolved in 50 mL of dry methanol. D-(+)-gluconic acid
δ-lactone (1.147 g, 0.0064 mol) was added and the mixture
was heated to reflux temperature for 6 h.After cooling to room
temperature and evaporation of the solvent the solid residue
was gently crushed, washed several times with hexane at 30 °C
and dried under reduced pressure to a constant mass. The yield
was white powder, 2.369 g.
(1)
(2)
IR (KBr, cm-1): 3300 ν(O-H), 1646 [ν(C=O) in amide],
1547 [δ(N-H) in amide], 1467cm-1 [ν(C-H) in -CH2-], 1260
ν(Si-Me3), 1146-1035 cm-1 [ν(C-O), δ(O-H) and ν(Si-O-Si)],
840 ν(Si-Me3), 760 ν(Si-Me3). 1H NMR (CDCl3, ppm) δ:0.03
(s, 3H, SiCH3), 0.10 (s, 18H, Si(CH3)3·2), 0.45 (t, 2H, J = 8.4
Hz, SiCH2), 1.54 (s, 2H, SiCH2CH2CH2), 3.26 and 3.13 (d,
2H, CH2N), 4.30 (s, 1H, H2), 4.13 (s, 1H, H3), 3.74 (m, 4H,
H4 + H5 + H6 + H6'). Elemental analysis (%) calcd for
C16H39NO8Si3: C, 41.98; H, 8.59; N, 3.06. Found: C, 42.10; H,
8.40; N, 3.19.
4000 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400
Fig. 1. FT-IR spectra of (1) 3-aminopropyltrisiloxane, (2) N-3-
propylmethyltrisiloxane-N-glucosylamine
primary amine proceeded in the presence of the methanol at
reflux temperature. The structure of amide was confirmed by
proton nuclear magnetic spectroscopy. The protons of the
carbon adjacent to the free amine (CH2-NH2) are seen at 2.64
ppm, while the same protons after amide formation through
coupling with the lactone (CH2-NHCO) shift to 3.26 and 3.13
ppm. This shift is observed in the spectrum (Fig. 2), verifying
the absence of free amino groups and indicating pure
glucosylamine surfactants up to the detection limit of the
analysis. In amide the hydrogen of C1 and C2 are adjacent to
the carbonyl function and shows a low-field shift, 4.30 ppm
and 4.13 ppm respectively. The signals of the hydrogen atoms
in C3-C6 were assigned according to the literature. All other
hydrogen atoms have observed in their normal positions. In
IR spectrum strong absorption at 1646 and 1547 cm-1 indicate
the formation of amide bonds.
Thermodynamic properties of micellization Si(3)N-
GA: The equilibrium surface tensions of dilute aqueous
solutions of N-3-propylmethyltrisiloxane-N-glucosylamine
were measured (Fig. 3). The surface tension of Si(3)N-GA
aqueous solution decreased with increasing the surfactant
concentration until the CMC above the CMC, the surface
tension became steady.As shown in Fig. 3, Si(3)N-GA is highly
RESULTS AND DISCUSSION
The glucosamide-based trisiloxane surfactant was
prepared by the two step process described in Scheme-I.
Amine intermediate was synthesized by the base-catalyzed
reaction of a silane monomer 3-aminopropylmethyl
diethoxysilane and hexamethyldisiloxane. The complete
1
substitution OCH3 by Me3SiO was checked by H NMR
spectroscopy, following the disappearance of OCH3 absorption
peak at 3.48 ppm as well as the appearance of Si-Me3 charac-
teristic absorption at 0.10 ppm. Similarly in IR spectrum, the
appearance of Si-CH3 deformation absorption at 1260 cm-1
and Si-Me3 characteristic absorption at 840 and 760 cm-1
(Fig. 1), respectively also support the formation of the 3-amino-
propylmethyltrisiloxane.
D-(+)-Gluconic acid δ-lactone was ring-opened by nucleo-
philic attack of the primary amine. The amidation of the
CH3
Si
CH3
Si
CH3
H3C
O
O
Si CH3
CH3
CH3
CH2
CH2
CH2
CH3
CH3
H3C Si
(Me Si) O
CH3
Si
CH3
H3CO Si OCH3
O
O
Si CH3
CH3
D-(+)-Glucose δ-lactone
CH3
CH2
CH2
CH2
NH2
H2C
3
2
NH
(CH ) NOH
MeOH
CH2
CH2
NH2
3 4
1
O
OH
HO
2
5
6
3
4
OH
Scheme-I: Synthesis of N-3-propylmethyltrisiloxane-N-glucosylamine
OH
OH

Vol. 25, No. 17 (2013)
Micellization of Organosilicone Modified Gluconamide-Type Surfactant 9867


1
∂γ




Γmax = −
(1)
(2)
(3)
(4)
2.303RT ∂logc

T
1016
Asm =
NAΓmax
(1)
(2)
CMC




∆G0mic = RTln
55.5


Cπ



∆Ga0ds = RT In
– 6.022πAs
m


55.5

where R = 8.3144 J/mol K, NA is Avogadro's number and Am
s
in Å2 per molecule. π(= γ0-γ) the surface pressure in the region
of surface saturation and Cp the molar concentration of surfac-
tant in the aqueous phase at a surface pressure π (in mN/m).
The enthalpies of micellization were calculated using
eqn. 5:
8
7
6
5
4
3
2
1
0
-1
1H Chemical Shift (ppm)
Fig. 2. 400 MHz 1H NMR spectra in CDCl3, (1) N-3-propylmethyl
trisiloxane-N-glucosylamine, (2) 3-aminopropyltrisiloxane
45
∂In CMC
∂T



∆H0 = RT2In


m
(5)
298K

303k
308k
313k
40
35
30
25
20
15
Therefore, if the dependence of the CMC values on tempe-
rature is known, a plot of ln CMC vs. temperature can be
constructed. The slope can then be found at each temperature.
These plots were found to be best fit with a second-order
polynomial (r2 = 0.95). The plot is presented in Fig. 4. The
entropies of micellization were then calculated from eqn. 6
∆H0m – ∆G0m
∆S0m =
(6)
T
Thermodynamics of micellization were calculated for
Si(3)N-GA in aqueous solution. The parameter values obtained
are given in Table-2.
10
100
1000
Concentration (mg/L)
Fig. 3. Plots of equilibrium surface tensions of aqueous solutions of the
new trisiloxanes versus logarithm of molar concentration at different
temperature
-7.80
-7.85
-7.90
-7.95
effective aqueous surfactant reducing the surface tension of
water to approximate 21-22 mN/m. These values of γCMC are
significantly lower than those reported for hydrocarbon
surfactants11 and are comparable to those reported for other
low molecular weight silicone surfactants12.
By applying the approximate form of the Gibbs adsorption
isotherm equations (eqn. 1 and 2) to the steeply descending,
linear portion of the surface tension versus log concentration
plots (Fig. 2), the saturation adsorption values, Γmax, at the air/
water interface and the minimum area per surfactant molecule,
295
300
305
310
315
Am , at the air/water interface were obtained for each of the
s
Temperature (K)
novel trisiloxane surfactants. The adsorption data and Am are
s
Fig. 4. Variation of ln CMC with temperature
summarized in Table-1.
TABLE-1
AQUEOUS SURFACE ACTIVITY OF THE NEW TRISILOXANES AT DIFFERENT TEMPERATURE
∆G0mic (KJ/mol)
Γmax (mol/m2)
2.55 × 10-10
2.59 × 10-10
2.70 × 10-10
2.74 × 10-10
Temperature
CAC (mol/L)
Ams (Å2/molecule)
γcac(mN/m)
20.54
19.70
19.61
19.54
4.13 × 10-4
4.06 × 10-4
3.66 × 10-4
3.47 × 10-4
65.1
64.3
61.5
60.6
-29.25
-29.78
-30.04
-30.18
298
303
308
313

9868 Tao
Asian J. Chem.
TABLE-2
THERMODYNAMIC PARAMETERS OF Si(3)N-GA
∆Hom (KJ/mol)
∆Som (J·K-1/mol)
-∆Gom (KJ/mol)
T·∆Som (KJ/mol)
Temperature(K)
298
303
308
313
2.510
9.236
12.38
8.634
106.0
128.0
137.7
124.0
29.247
29.781
30.042
30.177
31.588
38.784
42.412
38.812
The data available indicate that the negative values of ∆Gom
are mainly due to the large positive values of ∆Som. ∆Hom is
positive and is much smaller than the value of T∆Som. There-
fore, the micellization process is governed primarily by the
entropy gain associated with it and the driving force for the
process is the tendency of the hydrophobic group of the
surfactant to transfer from the solvent environment to the
interior of the micelle.
This large entropy increase on micellization in aqueous
medium has been explained in two ways: (1) structuring of
the water molecules surrounding the siloxane chains in
aqueous medium, resulting in an increase in the entropy of
the system when the siloxane chains are removed from the
aqueous medium to the interior of the micelle-hydrophobic
bonding; (2) increased freedom of the hydrophobic chain in
the nonpolar interior of the micelle compared to the aqueous
environment
of the system. The enthalpy entropy compensation plots for
the Si(3)N-GA in all the solvent mixtures showed a good corre-
lation between the thermodynamic parameters. The plots
indicate that the change in ∆Hom is effectively balanced by a
corresponding change in ∆Som.
Free energy and enthalpy were negative whereas entropy
was positive. The minimal effect of temperature on the thermo-
dynamic parameters indicates that the process of micellization
was spontaneous in nature.
Conclusion
By using Wilhelmy plate method, the surface tension of
Si(3)N-GA at different temperatures (298-313 K). The results
show that with the increase of temperature, the critical
micelle concentration (CMC) of Si(3)N-GA slightly decreases,
but the maximum surface excess concentration at the air/
water interface increases. The micellization free energies
(∆G°mic) are in the range -29.247--30.177 kJ mol-1 in the studied
ranges of temperature. The process of micellization of Si(3)N-
GA in aqueous solution is mainly driven by the entropy.
An increase in temperature seems to cause both ∆Hom and
∆Som to become more positive, presumably because both the
amount of water structured by the hydrophobic chain and the
amount of water bound by the hydrophilic sugar group in the
nonmicellar species increase with increase in temperature,
resulting in a increase in ∆Hom and ∆Som, respectively. Since
these two parameters have opposite effects on ∆Gom, it may
become more negative or less negative with temperature
change, depending on the relative magnitude of the changes
in ∆Ho and ∆So . From the above data, ∆Go appears to
ACKNOWLEDGEMENTS
The authors acknowledged the financial support ofYouth
Fund of Taiyuan University of Science and Technology (No.
20113009) and the National Natural Science Foundation of
China.
m
m
m
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The values of ∆Hom in Table-2 indicate that the micelli-
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