chapter 3 surface activity of bisphosphate gemini...

Chapter 3

Surface Activity of Bisphosphate

Gemini Surfactants

43

3.1 Introduction

This chapter deals with the investigation of interfacial properties of anionic gemini sur-

factants at the air/water interface. The static or equilibrium surface tension was mea-

sured and estimated the surface activity of newly synthesized m−3−m and m−5−m

types of geminis. The critical micellar concentration (CMC) values were confirmed in-

vestigates using specific conductance studies and also by dye solvatochromism method.

The Dynamic behaviour of aqueous solutions of geminis was also investigated. The

equilibrium and dynamic surface tension parameters were correlated to the foamability

of these surfactants.

3.2 Materials and Methods

In this study the bisphosphate geminis were used, the synthesis procedure was discussed

in earlier chapter. The aqueous solutions were prepared using distilled water. Eosin-Y

dye was used for dye micellization. Eosin-Y was obtained from M/s. Acros, Belgium.

3.3 Equilibrium Surface Tension

The equilibrium surface tension was measured on a Kruss K-11 automated tensiometer

with an accuracy of ±0.2 mN/m, using Wilhelmy Plate Method. In this method a

Platinum plate is attached to a very sensitive balance. A height adjustable sample carrier

is used to bring the liquid to be measured in contact with the probe. A test sample

(liquid), was poured in the sample vessel. The sample vessel is made of Quartz. When

the platinum plate is immersed in the liquid, a force acting on the plate is traced by the

balance. If the wetting length of the plate is known, the force measured by the balance

can be used to calculate the surface tension. The surface tension can be calculated by

equation;

γ =F

Lcosθ(3.1)

44

Considering the plate is completely wet, the contact angle of the plate, θ = 00, cosθ

is approximately 1.

The instrument was calibrated using distilled water. All the measurements were

performed at 25.0±0.10 C. All the measurements were repeated thrice. Measurements

were carried out using aqueous solutions of gemini surfactants. Distilled water was

used to prepare the solutions. CMC values of the gemini surfactants were estimated

from the surface tension versus surfactant concentration plots. The maximum surface

excess concentration Γmax, was estimated, by fitting Szyskowski equation (3.2), to the

surface tension plots.

(γ0− γ) = π = nRT Γmax× ln(1+K× c) (3.2)

In this equation, γ0 is the surface tension of pure water, γ the surface tension of

surfactant solution, π is the surface presssure, Γmax the maximum surface excess con-

centration of surfactant, c concentration of surfactant solution, R the universal gas con-

stant, T the absolute temperature, K adsorption constant and n the number of ionic

species whose concentration at the interface varies with the change in the surfactant

concentration in the solution. In the case of dimeric surfactant having divalent surfac-

tant ion and two univalent counter ions, the value of n employed is 3. The minimum

surface area per molecule (Amin), was calculated using the equation (3.3).

Amin =1016

(Γmax×NA)(3.3)

Where, NA is the Avogadro number.

The efficiency i.e. pC20, of the synthesized gemini surfactants was also estimated,

the pC20 value is the negative logarithm of surfactant concentration (C20), required to

depress the surface tension by 20 mN m−1.

45

3.3.1 Dye Micellization

The CMC measurements was carried out using dye micellization technique. It was stud-

ied using a water soluble, Eosin-Y dye. The ultraviolet visible spectrums were recorded

on a single beam UV-Visible spectrophotometer (Agilent-8453). The Eosin dye shows

shift in absorbance due to the presence of micelles. Plot of surfactant concentration

versus the absorbance, at wavelength (λmax) 517 nm and fixed dye concentration (0.01

mM) was used to estimate the CMC values of synthesized gemini surfactants.

3.3.2 Conductivity measurements

The electrical conductivity method is widely used for studying the micellization be-

havior of ionic surfactants in aqueous and non aqueous media. In this method critical

micellization concentration (CMC) values of ionic surfactants are determined generally

by plotting specific conductivity versus concentration. Besides this graphical approach,

different analytical approaches are also used to determine the micellization parameters

of ionic surfactants from their specific conductivity data. Since cmc values of surfac-

tants lie in the low concentration region, normally measurement of specific conductiv-

ity of ionic surfactants in different media is made in the low concentration region only

[Seredyuk and Holmberg, 2001; Boda et al. , 2000; Sikiri et al. , 2002; Sugimoto et al. ,

1996]. Extension of specific conductivity measurements of ionic surfactants to the high

concentration region is, however, restricted due to low solubility of these surfactants,

especially in water and pure non aqueous liquids.

Conductivity of the gemini surfactant solutions was measured as a function of con-

centration with a low frequency conductivity analyzer LT-23 conductometer (Labtron-

ics, India Ltd., accuracy of ±1%) at 25.0±0.10C.

3.3.2.1 The Degree of Micelle Ionization (α)

The counterion distribution in a micellar solution can be assessed from electrical con-

ductivity versus surfactant concentration plots. The counterion binding to micelles was

determined from the ratio between the slopes above and below the CMC [Bradley et al.

46

, 1988; Thomas and Penfold, 1996; Lu et al. , 1993; Rosen et al. , 1999; Lu, 1997;

Cheah and Cilliers, 2005]. In the low concentration domain, the change of (k) is due to

a larger concentration of free cations and anions of surfactants solutions, whereas the

break in the plot account for onset of micellization.

3.4 Dynamic Surface Tension

Dynamic behavior of surfactants can be investigated by dynamic surface tension mea-

surements. The equilibrium surface tension of a surfactant solution is not achieved

instantaneously. For example, when a fresh interface is formed, surfactant molecules

must first diffuse from the bulk to the interface, and then adsorb, whilst also achieving

the correct orientation. A freshly formed interface of a surfactant solution has a surface

tension, very close to that of the solvent. Over a period of time, surface tension will

decay to the equilibrium value, and this period of time can range from milliseconds to

days depending on the surfactant type and concentration. This dynamic surface tension

is an important property as it governs many important industrial and biological pro-

cesses[Fainerman, 1991; Frese et al. , 2004; Patist et al. , 1998]. In the photographic

industry the formulation of thin gelatin films requires high flow velocities, and hence

DST needs to be monitored during the fabrication process to prevent film deformation

and irregularities. DST is also important in the printing industry [Hua and Rosen, 1988;

Fielden et al. , 2001; Fainerman and Miller, 1994]. It is also of importance in agrochem-

icals where fast wettability plays a role in the easy spreading of pesticides onto leaves.

DST also plays a crucial part in metal, paper and textile production. Coating is also a

one of the important application [Zana, 2002a; Zana, 2002b; Patist et al. , 1998]. One

biological process where the control of DST is essential is in the lung, where low DST

is necessary for effective functioning of the alveoli, and phospholipids are the main sur-

face active ingredients. It is, of course, important in other emulsifiers, wetting agents

and foaming agents [Zana, 2002a; Nagayama et al. , 1974; James Smith et al. , 2007;

Buzzacchi et al. , 2006].

47

The dynamic surface tension measurements were carried out using maximum bub-

ble pressure method. The maximum bubble pressure method involves measurement of

the pressure in the bubble as a function of bubble size. It is possible to measure the

surface tension as a function of time by measuring pressure in the bubble at different

times [Reymond, 1971; Kalekar and Bhagwat, 2006; Kalekar and Bhagwat, 2007] i.e.

dynamic surface tension. In this method, a gas is allowed to flow in to the needle, while

monitoring its pressure [Fainermann et al. , 1998]. A sample quantity of 20 ml liq-

uid was used for this study. The bubble formation rate was controlled by adjusting the

airflow rate. The pressure was measured by a pressure transducer connected to an oscil-

loscope. In this method, a curved liquid-gas interface forms inside the needle. Pressure

in the system rises until the bubble forms a hemisphere at the tip of the needle. The

maximum pressure (corresponding to a hemispherical bubble) is directly proportional

to the surface tension. As soon as the bubble diameter increases, the pressure falls

dramatically. When the bubble has formed fully and it breaks away (Figure 3.1), the

liquid momentarily surges back up into the needle. Area of the interface (once formed)

remains constant. Surface age can be varied by varying the bubble frequency. Measure-

ments were conducted with effective surface ages from 1 ms to 30 s. Young Laplace

equation (3.4), was used to calculate the dynamic surface tension.

Pmax =2γ f

r+hρg (3.4)

where, f is the correction factor for nonsphericity of the bubble.

48

Figure 3.1: Working principle of Maximum Bubble Pressure Method(rb is the radius of bubble & rc is the radius of capillary)

49

3.4.1 Experimental set up for Maximum Bubble Pressure Method

The setup essentially consists of three major units.

1) Gas introduction unit (bubble formation unit),

2) Pressure sensing unit and

3) Data acquisition unit.

Figure 3.2: Setup of Maximum Bubble Pressure method

1) Gas introduction unit:

The gas introduction unit consists of three components.

a) Pressure vessel (gas source),

b) Flow controllers and

c) Needle (for bubble formation).

a) Pressure vessel:

A thick walled conical flask is used as gas source. It is made air tight by means of a

rubber stopper. Manometer attached to the flask shows the pressure inside the flask. As

air used was atmospheric air, it contains water vapors, which may harm the electronic

pressure sensor. To avoid this, flakes of calcium chloride were kept in the flask which

50

absorbs water vapors from moist air, and supplies relatively dry air to bubble formation

unit and to sensor.

b) Flow controllers: Close controlling device is necessary to regulate the air flow

rate. Needle valve is used in the setup, which satisfactorily controls the air flow rate.

Desired adsorption times can be obtained by precisely controlling air flow.

c) Needle (for bubble formation): It is one of the most important component of

the setup. Because, it’s size and shape affects the design of pressure sensing unit and

accuracy of experiments. Syringe microburette tips are convenient capillaries since they

have inside diameters of about 0.2 mm and have their bottom surface ground flat. In

this set-up steel needle is used. Needle is flared from the tip. Needle shape is made well

ground. Size of needle is 0.22 mm ID and length 40 mm.

2) Pressure sensing unit:

Pressure transducer of series ACX 01 DN is used in the set-up. With this size of nee-

dle, pressure difference that should be detected is about 10 N/m2 per unit change in

surface tension. Sensitivity of transducer is of 0.1 N/m2 and response time of 1 μ sec.

Transducers with these specifications does measurements satisfactorily. Input voltage

to transducer needed is 5 V. A battery of 9 V is used and a circuit is designed to reduce

the voltage to desired 5 V supply voltage. Output from transducer is in the form of

voltage which ranges from 0-5 V corresponding to the pressure sensed by transducer.

3) Data acquisition unit:

This unit analyzes output from the pressure transducer. Oscilloscope of 1 MHz data

acquisition rate is used. Oscilloscope displays pressure trace on the screen. The height

of pressure trace gives corresponding pressure difference and time scale between two

peaks of pressure trace gives time between two bubbles.

Needle tip is first cleaned with a polish paper to remove the rust if present at the

tapered tip.

• Needle is then washed with distilled water and subsequently with acetone.

51

• Surfactant solutions of desired concentration were prepared and small 3-4 glass

bottles were prepared of same concentration and used one after another. This is to insure

that the measurements are on the same concentration. If the bulk concentration is low,

it may happen that at fast bubble rate, within measurement time significant quantity of

surfactant may be carried with foam affecting the bulk concentration.

• Pressure vessel is filled with air till it reaches pressure up to 2600 N/m2 (20 mm

Hg) .

• Glass bottle containing sample is placed on set-up base in such a position that im-

mersion height of needle is 10 mm, which is kept constant throughout the experiments.

• Air is passed to the solution through needle by opening the valve. As pressure in

the vessel is higher, there is no need to make special arrangement for introduction of

gas to form bubbles.

• Bubble formation rate is controlled by the needle valve. Oscilloscope shows the

pressure trace as shown in Figure 3.1. The bubble formation rate is measured either by

means of stopwatch or by monitoring the time line on the oscilloscope.

• Peak height and time is measured on the oscilloscope screen during the experi-

mental run. The time between two peaks is the time between two successive bubbles,

and height of the pressure trace gives pressure difference across the bubble interface

which is in proportion with surface tension.

• For surface tension calculation, peak height is compared with height from known

surface tension. Peak height of water (surface tension = 72 mN/m, measured on K-

11) is determined and solving Young Laplace equation to account peak heights, surface

tension is calculated.

γsample =peak height (sample)peak height (water)

×72mN/m (3.5)

52

3.5 Foaming power

Foaming power of the synthesized gemini surfactants was measured by the Ross Miles

pour foam test method, as per standard ASTM designation D-1173-53. Foaming test

was carried out by pouring 50 ml of the test solution into a glass column (100 cm high,

ID 5.0 cm) from the side wall, so that it will not produce foam (initial solution was 50

ml). A 200-ml pipette is positioned in the centre so that its lower end lies exactly 90 cm

above the liquid surface in the glass. The orifice of the pipette has an ID of 2.9 mm and

breaks up the liquid flowing through it into drops. The test solution filled in the pipette

is allowed to fall by its own weight into the glass column, foam develops. The initial

height of the foam is read immediately and again after every 5 minutes till completion

of 30 minutes. Foam formation and foam stability was studied for all the phosphate

geminis at fixed concentration (2 mM).

3.6 Results and Discussions

3.6.1 Equilibrium surface tension

Surface tension measurements were carried out as mentioned in the section 3.1. The

surface tension versus surfactant concentration plots were used to find out CMC val-

ues. The CMC values were taken as the point of inflection in surface tension values,

as shown in Figure 3.4 - 3.9. It was observed that, m− 3−m type geminis, CMC in-

creases with the increasing chain length, which is quite unusual trend. The CMC varies

in the order 12-3-12>16-3-16>10-3-10 (0.51 mM, 0.30 mM, 0.12 mM respectively).

These CMC values were cross verified by dye micellization and conductivity methods.

The horizontal line in Figures 3.18-3.20, shows the absorbance of Eosin-Y dye in the

absence of surfactant. A line was drawn from the inflection point of absorbance and

extrapolated to the horizaontal line. The intercept was taken as CMC point. The CMC

values obtained was found to be in the order of 12-3-12>16-3-16>10-3-10 (0.44 mM,

0.30 mM, 0.2 mM respectively). These values are in close agreement with the CMC

53

values obtained from the surface tension measurements. Specific conductivity mea-

surements were also carried out to find CMC values. The CMC values were found to

be 0.11 mM, 0.22 mM, and 0.10 mM for 10-3-10, 12-3-12, 16-3-16 gemini surfactants

respectively.

In the case of m− 5−m geminis, the CMC values decreases linearly with the in-

creasing number of carbon atoms in the tail group, as 10-5-10>12-5-12>16-5-16 (0.76

mM, 0.26 mM, 0.11 mM respectively). The CMC values obtained from the conductiv-

ity method also follows the same trend, 10-5-10 > 12-5-12 > 16-5-16 (0.79 mM, 0.33

mM, 0.11 mM respectively). The two phosphate head groups connected by the short

chain spacer group causes electrostatic repulsion between the head groups so the gemi-

nis fold back at the air-water interface [Tyagi and Tyagi, 2011], thereby decreasing the

CMC value. This effect was also observed through large variance between the Amin

values for the m− 3−m and m− 5−m geminis. The increased hydrophobicity of the

gemini molecules influence the adsorption, as the Γmax decreases and consequently Amin

increases. The minimum area per molecule was found to be abruptly changed for 12-3-

12 and 10-5-10 gemini. A theoretical explaination suggested to the variation of the Amin

with the spacer chain is the balance of attractive interactions between the hydrophobic

tails, the repulsive interactions between the head groups, and the conformational en-

tropy of the sapcer chain [Diamant and Andelmann, 1994; Diamant and Andelmann,

1995]. the low Γmaxvalues for the geminis with C10 chain lengths indicate that in ad-

sorbing at the interface, these molecules are the most effective and efficient among the

six geminis. The CMC of monodecyl phosphate (MAP) surfactant, as reported in liter-

ature is 53 mM, at 200C [Schulz, 1976] and that of disodium dodecyl phosphate (SDP),

is 57 mM at 250C [Arakawa and Pethica, 1980]. Where as the geminis 10-3-10, 10-5-10

has CMC values (0.12 mM and 0.76 mM), several fold lower than the monomeric sur-

factants having same carbon chain lengths. Geminis 12-3-12 and 12-5-12 also possess

CMC, (0.51 mM and 0.26 mM), far lower than that of SDP. The effect of carbon num-

bers in the spacer group of geminis m−5−m over m−3−m can be seen as the addition

of two methyl groups in the spacer of m−5−m geminis makes them hydrophobic than

54

the m− 3−m geminis. Usually for the ionic surfactants, efficiency pC20, decreases

with the increase in alkyl chain length, reflecting the negative free energy of transfer of

methylene group from bulk to the interface [Rosen, 1978]. The efficiency, pC20 value

of the m− 3−m geminis found to be in the order of 10-3-10>16-3-16>12-3-12. Sim-

ilarly for m−5−m geminis, the efficiency increases with the increase in alkyl length,

which is in the order of 10-5-10>16-5-16>12-5-12. This indicates, unlike the conven-

tional monomeric surfactants, the increasing chain length of m−5−m geminis results

in the energetically less favorable diffusion of these gemini molecules at the interface.

12-3-12 was found to be more efficient than rest of the geminis. Surfactant effective-

ness is the maximum reduction in surface tension attainable, γcmc. Initially for both the

m−3−m and m−5−m type of geminis it decreases gradually and increases for gemini

with C16 chain length. The gemini with C12 chain lengths, are found to have low γcmc,

that is, more effective than the rest of the geminis.

The conductivity plots for m−3−m and m−5−m gemini surfactants were shown in

figures 3.10 - 3.15. Above the cmc, the change in the specific conductivity has a smaller

slope. The decreased slope may be due to two reasons: (1) the detention of a fraction

of the counter ions around micelle surface and consequently there is an effective loss

of free ions or (2) the micelles can also contribute to charge transport to a lesser extent

than the free ions due to their lower mobility. The degree of counter ion dissociation

(α) were obtained from the ratio of the slope above and below the break indicative of

the cmc and the degree of counter ion binding (β ) to micelles is equal to 1 −α [Bradley

et al. , 1988; Buijnsters et al. , 2002; Menger et al. , 2000; Seredyuk and Holmberg,

2001; Esumi et al. , 1996]. The larger the α smaller the β , means the weaker ability

of counter ion binding to micelles. The values of the degree of micelle ionization, α ,

for m− 3−m geminis found to be in the order of 16-3-16 > 12-3-12 > 10-3-10 (0.91,

0.76, 0.59 respectively) and the αvalues for m−5−m geminis found to be in the order

of 10-5-10 > 16-5-16 > 12-5-12 (0.49 > 0.30 > 0.25). The counter ion binding for the

m− 5−m geminis increased probably due to a decrease in the charge density at the

micellar surface caused by the decrease in the aggregation number of the micelles.

55

3.6.2 Dynamic surface tension

The dynamic surface tension i.e., the change in surface tension (with time) until it

reaches to equilibrium value, was measured by using maximum bubble pressure method.

It involves the measurement of maximum pressure needed to detach a bubble from the

tip of a capillary. The surface tension was determined from Young-Laplace equation

(3.4) for a bubble. The change in surface tension reduction with time contains four re-

gions: An induction region (I), Rapid fall region (II), Mesoequilibrium region (III), and

Equilibrium (IV). This is schematically illustrated in figure 3.3. Equation 3.6 fits the

three dynamic regions.

I

II

III

IV

72

0

log t

Surf

ace

tens

ion

(mN

/m)

Figure 3.3: Effect of surface age on dynamic surface tension

Dynamics of the aqueous soluitions of gemini surfactants was studied by means

of adsorption rate at fixed concentration, (1mM) that is above the CMC value for all

geminis. It was observed that, with increasing surface age, the dynamic surface tension

tends to reduce, approaching the equilibrium surface tension at long time. The change

in the surface tension with respect to time is represented in Figure 3.21. The rate of

adsorption for both type of geminis m−3−m and m−5−m, decreases with increasing

hydrophobicity in the molecule, i. e. increasing the carbon number in alkyl tail groups.

The meso equilibrium surface tension, γm, of the system can be obtained from long time

data by extrapolation of a plot of dynamic surface tension, i. e. γt versus t−1/2 to the

56

ordinate (t=infinity). Geminis 16-3-16 and 16-5-16 showed very slow dynamics, as the

t∗ values are very high, beyond the range measured, possibly more than 1000 sec. The

n and t∗ values were obtained by the equation (3.6) [Gao and Rosen, 1994; Hua and

Rosen, 1998].

log(γ0− γt)(γt− γm)

= nlog( t

t∗

)(3.6)

where γm is the mesoequilibrium surface tension of the solution (where γt shows

only a small change with time), γ0 is the equilibrium surface tension of the solvent

(72 mN/m for water), t∗ is the time when the variation of γt is maximum and n is

a dimensionless constant. The values for t∗, n and were obtained from the plots of

log[(γ0− γt)/(γt − γm)] i.e. reduced dynamic surface tension (RDST) versus log t (Fig-

ure 3.21) and are reported in Table 3.1. From Table 3.1, the value of t∗ is the time

required for the gt to reach half of the value between γ0 and γm and is related to the

surfactant concentration, as the surfactant concentration increases t∗ decreases. It has

been suggested that n is related to the difference between the energies of adsorption and

desorption of the surfactant [Hua and Rosen, 1998]. The n and t∗ values increases with

increasing hydrophobicity of the molecule [Rosen and Gao, 1995]. The effect of spacer

groups and the increasing carbon chain length of the gemini molecules, can be seen as

the t∗ values increases with increasing hydrophobicity of the molecules.

3.6.3 Foaming Power

The monoalkyl phosphate surfactants (MAPs), possess good foaming power at low con-

centration. The MAPs at 5 mM concentration produces good foam (C10MAP = 44 mm,

C12MAP = 213 mm, C16MAP = 50 mm). The percent foam stability after 10 minutes

was found to be very low i.e. 52.3, 30 and 74 [Imokawa and Tsutsumi, 1978]. How-

ever the geminis at higher concentration (2 mM), showed very low foam height with

stable foam, compared to MAPs. The foamability parameters were listed in Table 3.2.

The overall foaming power of these geminis compared to that of monomeric surfac-

57

tants [Imokawa and Tsutsumi, 1978], was found to be very low that is only about 8

to 10 percent that of MAPs. Authors Zhu et al. [Zhu et al. , 1991] had reported the

diphosphonate gemini surfactants with small, oxyethylene spacer groups showing low

foamability.

Gemini 10-5-10 shows better foam stability than the rest of the geminis. This ob-

servation tallies with the very low t∗ value of 10-3-10 gemini surfactant. The faster

(within less time) a molecule adsorbs at the micelle-water interface, it stabilizes the

foam film better, which results in stable foam. Whereas the slow adsorption of sur-

factant molecules to the interface allows rupture of foam film and the foam stability

reduces consequently. The foam stability was found to decrease with increasing carbon

number in the tail group. The t∗ values also increase with the chain length for both

the m− 3−m and m− 5−m geminis. A high surface density results in higher foam

stability, as more number of adsorbed monomers are available at the interface. This

was observed for m−5−m geminis. The foamability studies revealed that, the synthe-

sized bisphosphate geminis are of a class of low foam producing surfactants. The low

foamability can be the result of small, branched spacers and the increased electrostatic

repulsion between the head groups of surfactant molecules adsorbed at the foam film.

3.6.4 Wettability

The term wetting agent is applied to any substance that increases the ability of water or

an aqueous solution to displace air from a liquid or solid surface. Wetting is a process

involving surfaces and interfaces, and the modification of the wetting power of water

is a surface property shown to some degree by all surface-active agents, although the

extent to which they exhibit this phenomenon varies greatly [Rosen, 1989]. The wetta-

bility alteration of hydrophobic surfaces such as glass, teflon and stainless steel, using

aqueous gemini surfactant solutions (of fixed concentration i.e. 2 mM) was studied, by

contact angle measurement technique, using Kruss K-10 goniometer. Contact angles

on finely divided solids are more difficult to measure, but are often more desired and

more important than those on large solid surfaces. Generally, if the contact angle of

58

pure water is smaller than 90°, then the surface is called hydrophilic and if the contact

angle is larger than 90°, the solid surface is considered hydrophobic. It was observed

that gemini 16-5-16 has very low contact angle (17°) on glass surface than rest of the

geminis, the contcat angle of pure water on glass surface was found 30°. The contact

angle of 10-3-10, 12-3-12 and 10-5-10 geminis on the teflon surface, found very less

than that of pure water on teflon surface which comes 120°. 12-3-12 and 12-5-12 gem-

inis found to wet the stainless steel surface more than rest of the geminis. The contact

results were taken as an average of five measurements and was listed in Table 3.3.

59

Table 3.1: Surface active parameters of gemini surfactants

Gemini CMC (mM) γcmc(mN/m) Γmax(1010mol/cm2) Amin(A2) pC20 n t∗

10-3-10 0.12 ±0.2 31.3 2.49 66 1.24 1.06 0.8512-3-12 0.51 ±0.2 25.1 0.39 425 1.65 0.24 11.8416-3-16 0.30 ±0.2 30.6 0.60 276 1.23 – –10-5-10 0.76 ±0.2 28.0 0.70 237 0.88 0.08 0.1412-5-12 0.26 ±0.2 26.2 1.00 166 1.10 2.6 2.5316-5-16 0.11 ±0.2 31.0 0.74 244 1.07 – –

CMC values of m-3-m geminis, obtained by dye micellization for 10-3-10 ,12-3-12 ,16-3-16 are (0.21 mM), (0.44 mM), (0.3 mM) respectively; and by conductivity mea-surement, (0.11 mM), (0.22 mM), (0.10 mM)

Table 3.2: Foaming parameters of the geminis

Gemini Foam height (mm) Foam stability (%)0 min 30 min

10-3-10 35 9412-3-12 39 9016-3-16 32 9410-5-10 48 10012-5-12 29 9016-5-16 18 89

Table 3.3: Contact angles of aqueous m−3−m and m−5−m gemini surfactants

Gemini Contact angle (θ )surfactant Glass Teflon Stainless Steel10-3-10 23 59 6812-3-12 29 66 5716-3-16 39 95 9110-5-10 32 56 6412-5-12 33 89 5816-5-16 17 89 85

60

0.01 0.1 1Concentration (mM)

20

30

40

50

60

70Su

rfac

e te

nsio

n (m

N/m

)10-3-10

Figure 3.4: Equilibrium surface tension plot of 10-3-10 gemini surfactant

0.001 0.01 0.1 1 10Concentration (mM)

20

30

40

50

60

70

Surf

ace

tens

ion

(mN

/m)

12-3-12


61

0.0001 0.001 0.01 0.1 1Concentration (mM)

20

30

40

50

60

70

Surf

ace

tens

ion

(mN

/m)

16-3-16


62


20

30

40

50

60

70Su

rfac

e te

nsio

n (m

N/m

)10-5-12



20

30

40

50

60

70

Suur

face

tens

ion

(mN

/m)

12-5-12


63

0.001 0.01 0.1 1Concentration (mM)

20

30

40

50

60

70

Surf

ace

tens

ion

(mN

/m)

16-5-16


64

0 0.5 1 1.5 2 2.5Concentration (mM)

0

0.2

0.4

0.6

0.8

Spec

ific

con

duct

ance

(x

10-3

S cm

-1)

10-3-10

slope 1 = 0.706

slope 2 = 0.421

Figure 3.10: Conductivity plot of 10-3-10 gemini surfactant


65

0 0.2 0.4 0.6 0.8 1Concentration (mM)

0

50

100

150

200

250

300

Spec

ific

con

duct

ivity

(10

-6 S

cm

-1)

16-3-16

slope 2 = 206.02

slope 1 = 225.12


0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Concentration (mM)

0

50

100

150

200

Spec

ific

con

duct

ance

(10

-6 S

cm

-1)

10-5-10

slope 2 = 63.185

slope 1 = 128.27


66

0 1 2 3Concentration (mM)

0

50

100

150

200

Spec

ific

con

duct

ivity

(10

-6 S

cm

-1)

12-5-12

slope 2 = 40

slope 1 = 154.78


0.2 0.4 0.6 0.8 1Concentration (mM)

0

50

100

150

200

250

300

Spec

ific

con

duct

ance

(10

-6 S

cm

-1)

16-5-16

slope 2 = 270.73

slope 1 = 896.16


67

Figure 3.16: UV-visible spectrum of Eosin-Y dye

O

COO

HO

Br

Br

Br

O

Br

Figure 3.17: Structure of Eosin -Y dye

68

0.001 0.01 0.1 1Concentration (mM)

0.1

0.15

0.2

0.25

0.3

0.35

0.4A

bsor

banc

e (a

t 517

nm

)10-3-10

(Horizontal dashed line represents absorbance value of Eosin-Y dye, without surfactant)

cmc

Figure 3.18: Dye micellization plot of 10-3-10 gemini surfactant


0

0.1

0.2

0.3

0.4

0.5

Abs

orba

nce

( at

517

nm

)

12-3-12

cmc

(The horizontal dashed line represents absorbance value of Eosin-Y, without surfactant.)


69


0

0.1

0.2

0.3

0.4

0.5

0.6

Abs

orba

nce

(at 5

17 n

m)

16-3-16

cmc


70

0.1 1 10 100Time (sec)

55

60

65

70

Surf

ace

tens

ion

(mN

/m)

10-3-1012-3-1216-3-16

0.1 1 10 100Time (sec)

30

40

50

60

70

80

Surf

ace

tens

ion

(mN

/m)

10-5-1012-5-1216-5-16

Figure 3.21: Dynamic surface tension plots of m-3-m and m-5-m gemini surfactants

0.1 1 100.1

1

10

0.1 1 100.1

1

10

0.1 1 100.1

1

1 100.1

1

10

Red

uced

dyn

amic

sur

face

tens

ion

Time

10-3-10 10-5-10

12-3-1212-5-12

Figure 3.22: Reduced dynamic surface tension plots of m-3-m and m-5-m geminis

71

Table 3.4: Esquilibrium surface tension data of m−3−m gemini surfactants

10-3-10 12-3-12 16-3-16Conc. γ Conc. γ Conc. γ

(mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.03 67.59 0.005 68.62 0.001 69.760.05 52.41 0.009 63.76 0.003 69.480.07 47.08 0.012 54.96 0.005 69.440.09 41.47 0.025 48.52 0.007 67.730.1 38.13 0.07 39.20 0.01 67.730.3 31.73 0.09 37.49 0.03 60.750.5 30.45 0.12 36.95 0.05 54.490.7 29.13 0.25 31.32 0.07 48.711 30.16 0.5 27.61 0.09 43.48

1.3 29.20 0.7 25.12 0.1 42.971.5 29.44 1 25.90 0.2 39.561.7 30.77 1.3 25.49 0.3 30.732 29.36 1.5 24.44 0.5 29.32

1.7 24.51 0.7 30.492 25.00 1 29.60

Table 3.5: Esquilibrium surface tension data of m−5−m gemini surfactants

10-5-10 12-5-12 16-5-16 16-5-16Conc. γ Conc. γ Conc. γ Conc. γ

(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.007 64.59 0.01 60.67 0.009 60.34 0.1 31.730.015 64.42 0.015 59.81 0.01 58.67 0.2 29.730.03 61.88 0.03 57.38 0.02 54.98 0.3 28.480.06 56.45 0.06 48.36 0.03 51.27 0.4 27.90.12 51.87 0.12 37.78 0.04 47.64 0.5 27.460.25 42.62 0.25 26.54 0.05 44.55 0.6 26.730.5 32.44 0.5 25.59 0.06 41.55 0.8 26.090.7 28.7 1 23.86 0.07 39.82 0.9 26.571 28.98 2 23.97 0.08 37.73 1 26.052 29.31 4 23.73 0.09 32.64

72

Table 3.6: Conductivity data of m−3−m geminis

10-3-10 12-3-12 16-3-16Conc. k Conc. k Conc. k(mM) (µScm−1) (mM) (µScm−1) (mM) (µScm−1)0.03 4 0.005 10 0.001 40.05 16 0.007 24 0.005 50.07 30 0.009 28 0.007 50.09 44 0.012 29 0.009 60.1 54 0.025 40 0.01 70.3 144 0.05 76 0.03 80.5 227 0.07 107 0.05 130.7 298 0.09 136 0.07 171 427 0.12 162 0.09 23

1.3 571 0.25 295 0.1 291.5 659 0.5 575 0.2 501.7 719 0.7 801 0.3 662 853 1 1336 0.5 110

1.3 1536 0.7 1521.5 1692 1 210

73

Table 3.7: Conductivity data of m−5−m geminis

10-5-10 12-5-12 16-5-16Conc. k Conc. k Conc. k(mM) (µScm−1) (mM) (µScm−1) (mM) (µScm−1)0.007 7 0.01 7 0.009 70.015 8 0.015 10 0.01 100.03 9 0.03 13 0.02 130.06 12 0.06 15 0.03 160.12 18 0.12 28 0.04 260.25 39 0.25 45 0.05 380.5 69 0.5 64 0.06 460.7 95 0.1 84 0.07 580.9 112 1.5 107 0.08 691 122 2 126 0.09 75

1.2 134 2.5 146 0.1 891.5 152 3 163 0.2 1191.7 164 0.3 146

0.4 1700.5 2050.6 2270..8 278

74

Table 3.8: Absorbance data of m−3−m gemini surfactants at 517 nm

10-3-10 12-3-12 16-3-16Conc.(mM) Abs. Conc.(mM) Abs. Conc.(mM) Abs.

0.001 0.16190 0.005 0.18859 0.005 0.193540.005 0.16529 0.01 0.19996 0.01 0.190450.007 0.16617 0.03 0.19848 0.03 0.199610.01 0.16323 0.05 0.22559 0.05 0.205460.03 0.16549 0.1 0.20039 0.07 0.209940.05 0.17194 0.3 0.22334 0.09 0.204470.07 0.16520 0.5 0.22309 0.3 0.233040.1 0.16793 0.7 0.25151 0.5 0.311290.2 0.17572 0.9 0.30853 0.7 0.385670.3 0.19440 1 0.37357 0.9 0.444850.5 0.24553 1.2 0.40804 1 0.476880.7 0.32185 1.3 0.41460 1.2 0.541100.9 0.33912 1.5 0.51632 1.3 0.572471 0.33620 1.5 0.64091

75

Table 3.9: Dynamic surface tension data of m−3−m gemini surfactants

10-3-10 12-3-12 16-3-16t γ t γ t γ

(sec) (mN/m) (sec) (mN/m) (sec) (mN/m)0.1 67.2 0.14 63.11 0.11 69.460.3 67.2 0.16 63.32 0.12 69.46

0.41 67.2 0.2 63.53 0.27 68.40.5 67.2 0.22 63.53 2 67.8

0.53 67.2 0.3 61.84 3 67.71 67.2 0.61 57.6 4 67.7

1.15 67.2 1.12 55.91 5 67.73 65.6 2 54.85 6 67.75 65.6 2.85 54.21 8 67.7

6.8 62.4 4.08 54.21 10 67.77.4 62.4 5.27 53.36 15 67.710 62.4 6 53.36 20 67.715 60.8 8 53.36 25 67.7

20.5 60.8 9 53.36 30 67.722 59.2 10 53.36

25.4 56 15 53.3631.6 56 20 53.36

25 53.3630 53.36

76

Table 3.10: Dynamic surface tension data of m−5−m gemini surfactants

10-5-10 12-5-12 16-5-16t γ t γ t γ

(sec) (mN/m) (sec) (mN/m) (sec) (mN/m)0.12 50.82 0.13 60.56 0.12 61.840.26 47.44 0.19 60.99 0.5 61.840.39 46.59 0.25 60.99 0.93 61.840.62 42.35 0.35 60.99 1 61.840.82 41.51 1.31 55.06 2.6 61.841.02 40.66 1.34 55.91 3.75 61.841.97 37.69 1.35 55.06 3.77 61.842.14 37.27 1.64 53.36 4 61.84

5 35.2 1.69 52.52 4.24 61.848 35 1.79 51.67 4.62 61.84

10 35 2.07 49.13 4.97 61.8415 35 2.13 48.28 5.6 61.8420 35 3.24 44.89 6.49 59.2925 35 3.3 45.74 10.75 59.2930 35 6.07 38.96 13 59.29

6.3 38.12 15 59.296.43 38.12 17 59.298.9 34.73 18 59.2910 34.5 19 59.2913 34.3 20.7 59.2915 34.01 25 59.2920 34.01 30 59.2925 34.0130 34.01

77

chapter 3 surface activity of bisphosphate gemini...

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