ORIGINAL ARTICLE

Dilational Properties of an Anionic Gemini Surfactantwith a Hydrophobic Spacer

Xiao-Ming Jiang • Lu Zhang • Wen-Qian Zhang •

Sui Zhao

Received: 14 October 2013 / Accepted: 28 May 2014

� AOCS 2014

Abstract The dilational properties of the anionic gemini

surfactant, ethanediyl-1,2-bis(sodium N-decanoyl-b-alani-

nate), and the comparable conventional surfactant were

investigated via the oscillation barrier technique. The

oscillation frequency was varied between 0.0033 and

0.1 Hz. The dilational moduli of the gemini surfactant at

low surfactant concentration show less dependence on the

frequency at the air/water interface compared with the

decane/water interface. The interface layer is basically

elastic. The dilational moduli at the air/water interface are

remarkably higher than those at the decane/water interface.

The dilational moduli of the gemini surfactant show two

maxima with increasing concentration, originating from the

reorientation and compression of the surfactant molecules

adsorbed at the interfaces. A possible schematic diagram of

the adsorption of the gemini surfactant at the air/water and

decane/water interfaces is proposed.

Keywords Gemini surfactant � Dilational property �Dilational modulus

Introduction

Gemini surfactant consists of two hydrophilic groups and

two hydrophobic chains, which are connected by a spacer

group. It has been reported that the interfacial properties of

a gemini surfactant in aqueous media can be orders of

magnitude greater than those of the comparable conven-

tional surfactant [1, 2]. Gemini surfactants can be used in

diverse products such as detergents, cosmetics and flotation

collectors [3–5].

The dilational viscoelasticity originates from the

response of an interface to an extrinsic disturbance, which

is fundamental to many industrial processes such as

emulsification, detergency and foaming. It involves the

dynamic relaxation process at interface rather than the

equilibrium property [6]. The investigation of the dilational

properties can give an insight into the relaxation processes

of the interface, which provides accurate information about

the structure of the adsorption layers [7–12].

N-acylamino acid derivatives have been widely used in

cosmetics, due to their biodegradability and their skin

compatibility. We have synthesized a kind of anionic

gemini surfactant derived from an N-acylamino acid. In the

present work, we focused on the dilational properties of

this surfactant. The results derived from this paper may be

useful to understand the differences of the dilational

properties between the gemini surfactant and the conven-

tional surfactant.

Experimental Section

Materials

The structure of the anionic gemini surfactant, ethanediyl-

1,2-bis(sodium N-decanoyl-b-alaninate), referred to as

C10X2C10, is shown in Scheme 1. The procedure for the

synthesis of C10X2C10 has been reported. Its structure was

characterized by 1H-NMR and elemental analysis [13]. The

X.-M. Jiang (&) � L. Zhang � W.-Q. Zhang

Department of Chemistry and Chemical Engineering,

Guizhou University, Huaxi, Guiyang 550025, Guizhou,

People’s Republic of China

e-mail: ming1840@126.com

S. Zhao

Technical Institute of Physics and Chemistry, Chinese Academy

of Sciences, Beijing 100190, People’s Republic of China

123

J Surfact Deterg

DOI 10.1007/s11743-014-1604-3

mass fraction of the surfactant in the product was above

0.99. Sodium N-decanoyl-N-methyl-b-alaninate (SDMA)

from J&K Scientific Co., Ltd. was recrystallized from

aqueous ethanol. C10X2C10 is a ‘‘dimer’’ corresponding to

the ‘‘monomer’’ SDMA. Decane (Aldrich) was [99 %

pure. UV scans confirmed that there was no absorbance

above 250 nm.

Surface Tension Measurements

The surface tension was measured with a JK99A tensi-

ometer using the Wilhelmy plate technique at 30 ± 0.1 �C.

All the solutions were prepared in triply distilled water and

the experimental error was within 0.1 mN m-1.

Interfacial Tension Measurements

The interfacial tension was determined with an XZD-3

interfacial tensiometer using the spinning-drop technique at

30 ± 0.1 �C and the experimental error was within

0.1 mN m-1.

Interfacial Dilational Viscoelasticity Measurements

The interfacial dilational viscoelasticity meter JMP2000A

(Shanghai Powereach Co.) and the oscillation barrier

technique, used in this study, have been introduced else-

where [14–17]. The viscoelasticity meter has two slide

barriers which can periodically move in the Langmuir

trough. The measurement principle is similar to that of

Lucassen and Giles [18].

When we investigated the dilational properties of the

surfactants at the air/water interface, the distilled water

(90 mL) was put into the Langmuir trough to make the

Wilhelmy plate just touch the surface of the water phase.

When we measured the dilational properties of the sur-

factants at the decane/water interface, the distilled water

(90 mL) and decane (50 mL) were added to the trough

successively. The Wilhelmy plate was completely sub-

merged under the decane surface. The solution in the

Langmuir trough was pre-equilibrated for 8 h. The inter-

face was periodically expanded and compressed at a fixed

amplitude (DA/A, 10 %). The oscillation frequency was

varied between 0.0033 and 0.1 Hz at 30 �C. The standard

deviation did not exceed 3 % in the experiments.

Results and Discussion

Surface Properties

The surface tension (c), versus the log surfactant molar

concentration (C) for C10X2C10 and SDMA in water at

30 �C is plotted in Fig. 1. The values of the CMC for

C10X2C10 and SDMA are 1.5 9 10-4 and 1.4 9 10-3

mol L-1, respectively. The gemini CMC value is roughly

one order of magnitude lower than the conventional sur-

factant CMC. The cCMC values are approximately the

same (*30 mN m-1) for conventional and gemini

surfactants.

(CH2)2

C10X2C10

C9H19CON(CH2)2COONa

C9H19CON(CH2)2COONa C9H19CON(CH2)2COONa

CH3

SDMA

Scheme1 Structures of the gemini and conventional surfactants

-4.4 -4.2 -4.0 -3.8 -3.6 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 -2.2

30

35

40

45

50

55

60

65

log C (mol/L)

Sur

face

Ten

sion

(mN

/m)

SDMA C10X2C10

Fig. 1 Plot of surface tension versus the log surfactant concentration

-3.6 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 -2.2 -2.02

4

6

8

10

12

14

16

18

20

22

24

log C (mol/L)

Inte

rfac

ial t

ensi

on(m

N/m

) SDMA C

10X

2C

10

Fig. 2 Plot of interfacial tension versus the log surfactant concen-

tration (oil phase: decane)

J Surfact Deterg

123

Interfacial Properties

Equilibrium interfacial tension curves for C10X2C10 and

SDMA are plotted in Fig. 2. The cCMC values at the dec-

ane/water interface are much lower than those at the air/

water interface. It reflects the fact that the hydrophobic

chain and the decane have a similar nature. The CMC

values in the decane/water system are all greater than the

corresponding CMC values in the air/water system due to

partitioning of the decane into the bulk surfactant phase.

Oscillation Frequency Dependence of the Dilational

Modulus

The dilational modulus (E) is defined as the change of the

interfacial tension (dc) upon the interfacial area change

(dlnA):

E ¼ dc=d ln Að Þ

Variation of the dilational modulus with the oscillation

frequency reflects the dilational viscoelasticity of the

interfacial film. Figure 3 shows the effect of the oscillation

frequency (x) on the dilational modulus of the surfactants

at the air/water interface. The curves of log E - log x are

quasi-linear. It indicates that the characteristic frequency of

the relaxation process exceeds the highest frequency

employed in the experiments [19].

The dilational modulus of SDMA increases with

increasing oscillation frequency; this is expected behavior

for the surfactants. At higher frequencies, the surfactant

molecule does not have enough time to diminish the

interfacial tension gradient which results from the com-

pressed interface. So the dilational modulus increases with

increasing oscillation frequency.

The dilational modulus of C10X2C10 at the air/water

interface does not exhibit an obvious dependence on the

frequency until the surfactant concentration increases to

5.00 9 10-4 mol L-1 (Fig. 3). The interface layer is

basically elastic. But the dilational modulus increases

gradually with increasing frequency at higher concentra-

tions because the exchange of the surfactant molecules

between the bulk and the interface does play a role in the

viscoelasticity of the air/water interface.

The dilational moduli of SDMA and C10X2C10 at the

decane/water interface show a frequency dependence in the

concentration range examined (Fig. 4).

Concentration Dependence of the Dilational Modulus

Figure 5 shows the variation of the dilational modulus at

the air/water interface with surfactant bulk concentration.

The curves of SDMA pass through one maximum resulting

from two competitive factors: molecular diffusion and

intermolecular interaction [6, 20]. Increasing concentration

leads to fast molecular diffusion and strong intermolecular

interaction. The effect of two competitive factors may

account for the maximum of the dilational modulus.

It is noteworthy that the curves of the gemini surfactant

at the air/water interface pass through two maxima. It was

reported that the dilational modulus of Triton surfactants

could also show similar curves with increasing concentra-

tion [21]. According to the reference, we can deduce that

the first maximum can be attributed to the transition of the

adsorbed surfactant molecules from the expanded state to

the compacted state. The second maximum originates from

the internal compression of surfactant molecules.

The curve of SDMA at the decane/water interface shows

a typical shape with one maximum and that of C10X2C10

has a shape with two maxima (Fig. 6). The results are

similar to those at the air/water interface.

We try to provide information about the adsorption layer

for the gemini surfactant. We know that the cCMC values of

C10X2C10 and SDMA are approximately the same. It

indicates that both surfactants have approximately the same

1.151.201.251.301.351.401.451.501.551.601.651.701.751.80

SDMA

log|

E|

log

1.0 x10-6

1.0 x10-5

1.0 x10-4

5.0 x10-4

1.0 x10-3

5.0 x10-3

-2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

log

1.0 x10-6

1.0 x10-5

1.0 x10-4

5.0 x10-4

1.0 x10-3

5.0 x10-3

log|

E|

C10 X2 C10

Fig. 3 Influence of oscillation frequency on the dilational modulus at the air/water interface (C: mol/L)

J Surfact Deterg

123

density of hydrophobic chains in the adsorption layers [2].

Amin is the minimum adsorption area per molecule at the

surface, which can be calculated from an equilibrium sur-

face tension curve. The Amin values for C10X2C10 and

SDMA are 0.72 nm2 and 0.83 nm2, respectively. The value

for C10X2C10 is slightly smaller than that for SDMA

although C10X2C10 is a dimer corresponding to SDMA. So

we can speculate that the hydrophobic spacer chain of

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

log|

E|

log

SDMA

1.0 x10-4

5.0 x10-4

0.0010.0050.01

-2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

log

log|

E|

C10 X2 C10

1.0 x10-6

5.0 x10-6

1.0 x10-5

1.0 x10-4

5.0 x10-4

0.001 0.005

Fig. 4 Influence of oscillation frequency on the dilational modulus at the decane/water interface (C: mol/L)

20

25

30

35

40

45

50

55

60

Concentration (mol/L)

SDMA

Dila

tiona

l mod

uius

(m

N/m

)

0.10Hz 0.050Hz 0.0333Hz 0.025Hz 0.020Hz 0.0166Hz 0.0143Hz 0.0125Hz 0.0111Hz

E-6 E-5 E-4 5E-4 E-3 0.005 -- -- E-6 5E-6 E5 5E-5 E-4 5E-4 E-3 0.0050

10

20

30

40

50

60

Dila

tiona

l mod

uius

(m

N/m

)

Concentration (mol/L)

C10 X2 C10

0.10Hz 0.050Hz 0.0333Hz 0.025Hz 0.020Hz 0.0166Hz0.0143Hz 0.0125Hz0.0111Hz

Fig. 5 Influence of the surfactant concentration on the dilational modulus at the air/water interface

0

1

2

3

4

5

6

7

8

9

10

11

0.10Hz 0.050Hz 0.0333Hz 0.025Hz 0.020Hz 0.0166Hz 0.0143Hz 0.0125Hz 0.0111Hz

SDMA

Dila

tiona

l mod

uius

(m

N/m

)

Concentration (mol/L)E-4 5E-4 E-3 0.005 E-2 0.02 5E-7 E-6 E-5 5E-5 E-4 5E-4 E-3

0

2

4

6

8

10

12

14 C10 X2C10

Dila

tiona

l mod

uius

(m

N/m

)

Concentration (mol/L)

0.10Hz 0.050Hz 0.0333Hz 0.025Hz 0.020Hz 0.0166Hz0.0143Hz 0.0125Hz0.0111Hz

Fig. 6 Influence of surfactant concentration on the dilational modulus at the decane/water interface

J Surfact Deterg

123

C10X2C10 may bend towards the hydrophobic chains in

order to reduce the Amin value.

The values of the moduli for the two surfactants at the

air/water interface are much higher than those at the dec-

ane/water interface (Figs. 5, 6). We can deduce that the

insertion of decane molecules may weaken intermolecular

interaction dramatically because dilational moduli are

mainly controlled by the interaction between hydrophobic

chains of surfactants. A possible schematic diagram of

adsorbed C10X2C10 at the air/water and decane/water

interfaces is shown in Fig. 7.

References

1. Rosen MJ, Tracy DJ (1998) Gemini surfactants. J Surfactants

Deterg 4:547–554

2. Zana R (2003) Gemini (dimeric) surfactants in water. Marcel

Dekker, New York, pp 212–233, 309–314

3. Zana R, Xia JD (2004) Gemini surfactants: synthesis, interfacial

and solution-phase behavior, and applications. Marcel Dekker,

New York

4. Kumar N, Tyagi R (2014) Industrial applications of dimeric

surfactants: a review. J Dispers Sci Technol 35(2):205–214

5. Xia L, Zhong H, Liu G, Huang Z, Chang Q (2009) Flotation

separation of the aluminosilicates from diaspore by a gemini

cationic collector. Int J Miner Process 92:74–83

6. Miller R, Wustneck R, Kragel J, Kretzschmar G (1996) Dilational

and shear rheology of adsorption layers. Colloids Surf A

111:75–118

7. Kovalchuk VI, Miller RT, Fainerman VB, Loglio G (2005) Di-

lational rheology of adsorbed surfactant layers-role of the

intrinsic two-dimensional compressibility. Adv Colloid Interface

Sci 115:303–312

8. Monroy F, Giermanska JK, Langevin D (1998) Dilational vis-

coelasticity of surfactant monolayers. Colloids Surf A

143:251–260

9. Lucassen EH, Cagna A, Lucassen J (2001) Gibbs elasticity,

surface dilational modulus and diffusional relaxation in nonionic

surfactant monolayers. Colloids Surf A 186:63–72

10. Ravera F, Ferrari M, Santini E, Liggieri L (2005) Influence of

surface processes on the dilational viscoelasticity of surfactant

solutions. Adv Colloid Interface Sci 117:75–100

11. Ravera F, Ferrari M, Liggieri L (2006) Modelling of dilational

viscoelasticity of adsorbed layers with multiple kinetic processes.

Colloids Surf A 282:210–216

12. Fainerman VB, Lylyk SV, Aksenenko EV, Petkov JT, Yorke J,

Miller R (2010) Surface tension isotherms, adsorption dynamics

and dilational viscoelasticity of sodium dodecyl sulphate solu-

tions. Colloids Surf A 354:8–15

13. Jiang XM, Chen XM, Xie T (2010) Synthesis and flotation

property of gemini anionic surfactants. Chin J Appl Chem

6:742–744

14. Zhao RH, Zhang L, Zhao S, Yu JY (2010) Effect of the hydro-

philic-lipophilic ability on dynamic interfacial tensions of alkyl-

benzene sulfonates. Energy Fuels 24:5048–5052

15. Wang YY, Dai YH, Zhang L, Tang K, Luo L, Gong QT, Zhao S,

Li MZ, Wang EJ, Yu JY (2004) The interfacial dilational prop-

erties of hydrophobically modified associating polyacrylamide

studied by the interfacial tension relaxation method at an oil–

water interface. J Colloid Interface Sci 280:76–82

16. Wang YY, Dai YH, Zhang L, Luo L (2004) Hydrophobically

modified associating polyacrylamide solutions: relaxation pro-

cesses and dilational properties at the decane–water interface.

Macromolecules 37:2930–2937

17. Liu K, Zhang L, Cao XL, Song WX, Luo L, Zhang L, Zhao S

(2011) Dilational properties of N-acyltaurates with aromatic side

chains at water–air and water–decane interfaces. J Chem Eng

Data 56:3925–3932

18. Lucassen J, Giles D (1975) Dynamic surface properties of non-

ionic surfactant solutions. J Chem Soc Faraday Trans 71:217–232

19. Fainerman VB, Miller R, Kovalchuk VI (2002) Influence of the

compressibility of adsorbed layers on the surface dilational

elasticity. Langmuir 20:7748–7752

20. Zhang HX, Xu GY, Wu D, Wang SW (2008) Aggregation of

cetyltrimethylammonium bromide with hydrolyzed polyacryl-

amide at the paraffin oil/water interface: interfacial rheological

behavior study. Colloids Surf A 317:289–296

21. Fainerman VB, Aksenenko EV, Lylyk SV, Makievski AV, Ra-

vera F, Petkov JT, Yorke J, Miller R (2009) Adsorption layer

characteristics of Triton surfactants: 3. dilational viscoelasticity.

Colloids Surf A 334:16–21

Xiao-Ming Jiang obtained his Ph.D. degree in physical chemistry

from the Chinese Academy of Sciences in 2005. He is an associate

professor in the Department of Chemistry and Chemical Engineering,

Guizhou University, Guiyang, People‘s Republic of China. His

research interests include the preparation and application of

surfactants.

Lu Zhang graduated in chemistry from the Tangshan Normal

University in 2012. She is a postgraduate at Guizhou University and

her research is dedicated to the preparation of surfactants.

Wen-Qian Zhang graduated in chemistry from the Heze University

in 2011. She is a postgraduate at Guizhou University and her research

interest is the application of surfactants in flotation.

Sui Zhao obtained his M.Sc. degree in physical chemistry from the

Chinese Academy of Sciences in 1988. He is a research fellow of the

Technical Institute of Physics and Chemistry, Chinese Academy of

Sciences. His main research area is application of surfactants in

enhanced oil recovery.

COO--OOC

N N

O O

Fig. 7 Schematic diagram of the gemini surfactant at the interface

J Surfact Deterg

123