CHAPTER V

Effect of Additives on the Phase Separation Behavior of

Triblock Polymers and Tritons: A Cloud Point Study

5.1 Introduction

5.2 Present Work

5.3 Results and Discussion

5.3.1 Effect of Amino Acids on the Cloud Point of Triblock Polymers/Tritons

5.3.2 Effect of Dipeptides on the Cloud Point of Triblock Polymers/Tritons

5.3.3 Effect of Amino Alcohols on the Cloud Point of Triblock Polymers/Tritons

5.3.4 Effect of Sugars on the Cloud Point of Triblock Polymers/Tritons

5.3.5 Effect of Hydroxy Acids on the Cloud Point of Triblock Polymers/Tritons

5.3.6 Effect of Dicarboxylic Acids on the Cloud Point of Triblock Polymers/

Tritons

5.4 Conclusions

References

125

5.1 Introduction

Phase transition is an important physicochemical property of nonionic

surfactants which significantly affects their self assembly behavior and consequently

their selection for application in diverse fields like bioprocessing, agricultural and

petrochemical industry etc.1-8

Phase transition phenomenon is preferable in certain

applications especially related to the extraction processes as it is considered to be a

convenient and environmentally safe alternative to extraction with organic solvents.

Phase transition is a thermorheologically reversible process that is dependent upon

balance between hydrophilic and hydrophobic interactions of the system and it can be

induced with variation in temperature of the micellar solution. Critical temperature at

which phase transition takes place is known as cloud point (CP) temperature.9

Cloud

point study can prove to be an important tool for the estimation of shelf life and

appropriate storage conditions required for nonionic surfactants based commercial and

industrial products.

Several factors have been considered to be responsible for CP phenomenon like

structure of surfactant molecule, concentration, temperature and the presence of third

component known as additive. Additive modifies the clouding behavior of a nonionic

surfactant as it effects the surfactant-solvent interactions by modifying solvent structure

and the extent of solvation of the clouding species. It consequently affects other

physicochemical properties of the micellar solution like critical micellar concentration

(cmc), micellar shape and size. Acquiring knowledge of phase transition phenomena

under varied thermal conditions therefore carries practical and theoretical interest as it

induces dramatic changes in the physical properties and the performance of surfactant.

Study of interaction between nonionic surfactants and biomolecules as additives

is the focus of current research as the surfactants are not only being employed as

medium but are also being used as important constituents of systems that mimic living

systems in vitro. In view of this, a number of research groups are actively engaged in

revealing the secrets of surfactant-biomolecular interactions by investigating the

additive effect of different biomolecules on physicochemical properties of surfactants.

126

Rakshit and Sharma10

have studied the effect of amino acids: glycine, alanine

and valine on the physicochemical properties of decaoxyethylene dodecyl ether

(C12EO10). They have reported depression in cmc of the surfactant with increase in the

concentration of amino acid. Sharma et al11

have studied the effect of amino acids i.e

glycine, alanine and valine on the solution and morphological properties of

nonaoxyethylene dodecyl ether (C12EO9) by tensiometric, small angle neutron

scattering, dynamic light scattering and viscometric measurements. They have observed

that the presence of amino acids lowers the clouding temperature and cmc of C12EO9

surfactant. With increase in the concentration of amino acid and temperature, increase

in aggregation number of surfactant has been reported. In the concentration region

studied, amino acids do not have much effect on the hydrodynamic radius.

Jan et al12

have studied the clouding phenomena of nonionic surfactant Triton-

X-100 (TX-100) and its mixed systems with anionic surfactant sodium bis(2-

ethylhexyl)sulfosuccinate (AOT) and cationic surfactant dodecylpyridinium chloride

(DPC) in the presence of hydrophobic ions furnished by sodium salts of carboxylic

acids viz. sodium ethanoate, sodium propanoate, sodium butanoate, sodium hexanoate

and respective carboxylic acids like ethanoic acid, propanoic acid, butanoic acid and

hexanoic acid. They have explained the influence of salts on the cloud point (CP) on the

basis of salt effect as well as the solubilization of higher alkyl chain hydrophobic ions

furnished by these salts. Counterion effect was also taken into account to explain the

variation in CP of the mixed systems. Effect of acids on CP has been explained in the

light of their aqueous solubility and their partitioning ability between octanol and water.

Sharma et al13

have studied the effect of sugars: (D-ribose, D-glucose and

sucrose) on the micellar solution of nonionic surfactant decaoxyethylene dodecyl ether

(C12EO10) at different temperatures 30 ˚C, 45 ˚C and 60 ˚C using small-angle neutron

scattering measurements. By determination of various structural parameters like micelle

shape and size, aggregation number and micellar density, they have reported that the

micellar structure of surfactant significantly depends on the temperature and

concentration of sugars. Micelles were found to be prolate ellipsoids at 30 oC and their

axial ratio increased with increase in temperature and sugar concentration. Study infers

127

that the effect of sugar and temperature on C12EO10 surfactant was additive, however,

the micellar structure remains independent of the nature of sugars used.

Ali et al14

have carried out volumetric, viscometric, refractive index,

conductometric and fluorescence probe studies on the interaction of glycine with

cationic surfactant hexadecyltrimethylammonium bromide (HTAB), anionic surfactant

sodium dodecyl sulphate (SDS) and nonionic surfactant Triton-X-100 (TX-100) at

different temperatures. Results indicate that ion-ion and ion-hydrophilic group

interactions are dominant over hydrophobic-hydrophobic and hydrophilic-hydrophobic

group interactions at temperatures 308.15 K and 313.15 K. At lower temperature,

298.15 K, hydrophobic-hydrophilic and hydrophobic-hydrophobic interactions were

reported to be dominating over ion-ion and ion-hydrophilic interactions in aqueous

SDS/HTAB solutions. Similar behavior was observed in TX-100 solution and the

sequence of strength of ion-ion or ion-hydrophilic interactions of glycine with the

surfactant molecules in the solution was found to be SDS > HTAB > TX-100.

Murakani et al15

have examined the effect of different sugars: sucrose, D-

glucose, D-maltose on hydrophobic-lipophilic balance and cloud point of

polyoxyethylene sorbtian monooleate (MOPS) and D-phase emulsification of

triglyceride by MOPS. All these sugars have been reported to decrease the cloud point

indicating the enhanced hydrophobicity of MOPS.

Yu et al16

have studied the effect of amino acids on the micellization of HTAB

by surface tension measurements. In the study, they have concluded that effect of

additives depends on their nature and concentration at a fixed temperature. For glycine,

alanine and serine, the steric effect was predominant over hydrophobicity during their

interaction between themselves and with HTAB. Hydrophobicity and steric effect of

alanine were reported to be stronger than glycine and was similar to serine. The cmc and

surface tension at cmc of HTAB in the presence and absence of glycine decreased with

increase in temperature. The cmc of HTAB in the presence of amino acids followed the

order: alanine ≈ serine > glycine. Thermodynamic parameters of micellization like

negative free energy, largely positive enthalpy imply that there exists enthalpy-entropy

compensation in the micellization of HTAB in the presence and absence of amino acids.

128

Li et al17

have studied the effect of various additives including inorganic salts,

nonionic and ionic surfactants, water-soluble polymers and alcohols on the cloud point

of nonionic surfactants, Tergitol 15-S-7, Tergitol 15-S-9 and Neodol 25-7. They have

observed that ionic surfactants sodium dodecyl sulphate and hexadecyltrimethyl

ammonium bromide in the micellar solution of 1 wt% Tergitol 15-S-7 causes dramatic

increase in its cloud point when concentration of ionic surfactants approach their critical

micelle concentration. Addition of water-soluble polymers decreased the cloud point,

while inorganic salts either increased or decreased the cloud point. Effect of alcohol as

an additive on the cloud point was dependent on its chain length or water solubility.

Bharatiya et al18

have investigated the micellization of triblock polymer F88

(EO104PO39PO104) in the presence of lipophilic S104 (C14diol) using dynamic light

scattering and small angle neutron scattering. They have observed that F88 remains

molecularly dissolved at ambient temperature even at fairly high concentrations of 5 wt%

or more. Addition of S104 induces the micellization at lower concentration and the

micellar growth is accompanied by enhancement in the aggregation number of triblock

polymer.

Bhadane and Patil19

have studied clouding in non-ionic surfactant Brij-58 by

measuring the cloud point of pure surfactant and its mixed system with alanine (Ala)

and phenylalanine (PA). They have observed that CP of pure surfactant decrease with

increase in Brij-58, Ala and PA concentration due to increase in micelle concentration.

Phase separation results from micelle-micelle interaction support the macromolecule-

surfactant interactions in aqueous medium.

Prasad et al20

have studied the effect of hydrotropes and glycols on the clouding

behavior of nonionic surfactants TX-100, Brij-56, polyvinylmethyl ether and P85

(EO26PO40EO26). By evaluating thermodynamic parameters, they found that the

enthalpy behavior of TX-100 is different from polyvinylmethyl ether and P85.

Hydrotropes were found to decrease the cloud point of TX-100, Brij-56,

polyvinylmethyl ether and P85, however, sodium cholate and salicylate increased the

cloud point.

129

5.2 Present Work

In view of the importance of surfactant-biomolecular interactions, present study

is focused on the investigation of additive effect of different biomolecules like amino

acids, amino alcohols, sugars, hydroxy acids and dicarboxylic acids on the clouding

behavior of Triblock polymers: L64 (EO13PO30EO13), P84 (EO19PO43EO19) and Tritons:

Triton-X-100 (TX-100) and Triton-X-114 (TX-114). Different systems studied are:

L64/P84 + Amino Acids (Glycine, Proline, Valine, Serine, Threonine)

L64/P84 + Dipeptides (Glycylglycine, Glycyl-DL-Valine)

L64/P84 + Amino Alcohols (Leucinol, Isoleucinol, 2-Amino-1-butanol)

L64/P84 + Sugars (Fructose, Sucrose, Maltose)

L64/P84 + Hydroxy Acids (Citric acid, Lactic acid)

L64/P84 + Dicarboxylic Acids (Succinic acid, Oxalic acid)

TX-100/TX-114 + Amino Acids (Glycine, Proline, Valine, Serine, Threonine)

TX-100/TX-114 + Dipeptides (Glycylglycine, Glycyl-DL-Valine)

TX-100/TX-114 + Amino Alcohols (Leucinol, Isoleucinol, 2-Amino-1-butanol)

TX-100/TX-114 + Sugars (Fructose, Sucrose, Maltose)

TX-100/TX-114 + Hydroxy Acids (Citric acid, Lactic acid)

TX-100/TX-114 + Dicarboxylic Acids (Succinic acid, Oxalic acid)

Triblock polymers (TBPs) and Tritons represent an important class of nonionic

surfactant that possesses unique features like mild nature, structural polymorphism and

self assembly behavior.21-29

In case of triblock polymers, systems have been chosen in

such a way that the hydrophobicity of both the triblock polymers remains almost

constant while their EO (polyethylene oxide) and PO (polypropylene oxide) units vary.

Due to variation in EO and PO units, size of core and corona of the micelle vary. In case

of Tritons (TX-100 and TX-114), system selection has been carried out on the basis of

hydrophobicity variation.

130

5.3 Results and Discussion

Cloud point (CP) values of pure triblock polymers: L64, P84 and Tritons: TX-

100, TX-114 at fixed concentration level of 1 wt% are in good agreement with their

literature values30-32

. Effect of biologically important additives: amino acids, dipeptides,

amino alcohols, sugars, hydroxy acids and dicarboxylic acids on the cloud point

behavior has been investigated at the constant concentration of TBP and Tritons (1 wt%)

by varying the additive concentration. Cloud point values for triblock polymers (TBPs)

and Tritons in the pure state at fixed concentration of 1 wt% as well as in the presence

of 0.5 mol dm-3

concentration of different biomolecules are given in Table 5.1.

5.3.1 Effect of Amino Acids on the Cloud Point of Triblock Polymers/Tritons

Amino acids (AA) are one of the simplest biomolecules that act as prototypes of

complex biomolecules33,34

. In the present study, different amino acids (AA): glycine

(Gly), proline (Pro), valine (Val), serine (Ser) and threonine (Thre) have been employed

to study the additive effect on the cloud point of triblock polymers (L64/P84) and

Tritons (TX-100/TX-114). Variation in cloud point of L64/P84 in the presence of amino

acids has been given in Figure 5.1a-5.1b whereas variation in the cloud point of TX-

100/TX-114 in the presence of amino acids has been given in Figure 5.2a-5.2b. In case

of systems containing TBPs: L64/P84 and different amino acids: Gly/Pro/Val/Ser/Thre,

amino acids cause CP of TBPs to appear at relatively lower temperature. The observed

order for decrease in CP at the highest used concentration of 0.5 mol dm-3

of AA for

L64 has been found to be: Gly > Pro > Thre > Ser > Val, whereas the corresponding

order for P84 is Ser > Thre > Gly > Pro > Val as given in Table 5.1. In case of TX-100,

except proline and serine all other amino acids initially increased the CP at lower

concentrations used while at their higher concentration, a decrease in CP was observed.

Proline and serine decreased the CP of TX-100 at all the concentrations used as shown

in Figure 5.2a. For TX-100+AAs system, trend observed for the CP decrease at higher

concentration of AA was: Thre > Gly > Pro > Ser > Val. In case of TX-114+AA

system, all the amino acids except serine initially caused an increase followed by a

decrease in the CP with an increase in the concentration of amino acids. In TX-114+Ser

system, CP has been found to be showing a decrease at all the concentrations of serine.

131

320

322

324

326

328

330

332

0 0.1 0.2 0.3 0.4 0.5

L64+Gly

L64+Pro

L64+Val

L64+Ser

L64+Thre

[Amino acid]/ mol dm-3

CP

(K

)

(a)

325

330

335

340

345

350

0 0.1 0.2 0.3 0.4 0.5

P84+Gly

P84+Pro

P84+Val

P84+Ser

P84+Thre

CP

(K

)

[Amino acid]/ mol dm-3

(b)

Figure 5.1 Plots of CP variations of (a) L64 (b) P84 in the presence of amino acids

132

330

332

334

336

338

340

342

344

0 0.1 0.2 0.3 0.4 0.5

TX-100+Gly

TX-100+Pro

TX-100+Val

TX-100+Ser

TX-100+Thre

CP

(K

)

[ Amino acids ]/ mol dm-3

(a)

290

292

294

296

298

300

302

304

0 0.1 0.2 0.3 0.4 0.5

TX-114+Gly

TX-114+Pro

TX-114+Val

TX-114+Ser

TX-114+Thre

CP

(K

)

[ Amino acid ]/ mol dm-3

(b)

Figure 5.2 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

amino acids

133

Table 5.1 CP values of triblock polymers (L64 and P84) and Tritons (TX-100 and

TX-114) at highest concentration of additives (0.5 mol dm-3

)

Additive CP (K) of Nonionic surfactants

L64

(331.2 K)*

P84

(346.7 K)*

TX-100

(339.7 K)*

TX-114

(297.9 K)*

Glycine (Gly) 320.6 330.4 334.1 295.1

Proline (Pro) 322.9 334.1 336.6 292.2

Valine (Val) 325.1 336.9 337.6 299.3

Serine (Ser) 324.1 328.9 337.3 290.7

Threonine (Thre) 323.4 330.3 330.1 297.2

Glycylglycine (Gly-Gly) 326.5 328.5 330.9 296.2

Glycyl-DL-Valine

(Gly-DL-Val)

323.7 330.1 332.4 298.3

Leucinol 324.7 359.5 358.3 305.4

Isoleucinol 321.4 334.5 334.6 302.8

2-Amino-1-butanol 327.5 343.1 353.1 309.5

Fructose 324.7 333.9 341.7 297.8

Sucrose 326.2 330.2 343.4 293.1

Maltose 318.7 331.9 344.9 298.6

Citric acid 331.1 348.5 342.9 298.8

Lactic acid 331.4 343.5 344.4 297.7

Succinic acid 317.1 342.9 336.9 292.9

Oxalic acid 312.9 346.3 336.4 293.3

*Experimental value of pure TBP/Tritons

134

Decrease in CP for TX-114+AA system follows the order: Ser > Pro > Gly >

Thre > Val. Results obtained for the above systems can be explained by considering the

two factors which are effective in controlling the cloud point variation namely solvation

capacity and hydrophobicity of micelles in the aqueous environment.35,36

The observed

decrease in CP of TBPs/Tritons can be related to decreased solvation capacity of

micelles in the presence of amino acids. Amino acids being zwitterionic possess high

affinity for water molecules and are soluble in aqueous medium. In their mixed system,

a competitive interaction exists between TBPs/Tritons and amino acids for the water

molecules present around them. As a result, interaction between polyethylene oxide

group (EO) of TBPs/Tritons and water molecules decreases. It leads to the dehydration

of micelles of TBPs/Tritons that consequently reduces the CP of TBPs/Tritons+AA

system. It clarifies the fact that additives which lower the solvation of micelles cause a

decrease in CP. Results indicate that valine causes a minimum decrease in CP for all the

systems investigated due to its least solubility in water. An initial increase in CP

observed for Tritons at lower concentration of amino acids can be attributed to the

presence of the insufficient amount of amino acids to attract water molecules from the

micellar system and thereby water molecules remain primarily associated with EO

groups of Tritons. It facilitates the solvation of Triton micelles and consequently

increases its CP.

Results obtained for TBPs/Tritons+AA systems can also be explained in terms

of hydrophobicity. Being hydrophobic in nature, amino acids tend to get incorporated

into the interfacial layer that results into increase in hydrophobic interaction of

TBP/Tritons to varying extents. However, observed cloud point variation is not in

accordance with the order of hydrophobicity for different amino acids: Val > Gly >

Thre > Ser > Pro. It is to be noted hereby that although TBPs: L64 and P84 have similar

hydrophobicity, yet, order of CP variation on addition of amino acids is not same.

Similarly, a relevant order is not obtained for Tritons with varying hydrophobicity.

These observations reveal that hydrophobicity is not the only decisive criteria for cloud

point variation but structural and orientation aspects of different constituents in the

solution also account for this variation.

135

5.3.2 Effect of Dipeptides on the Cloud Point of Triblock Polymers/Tritons

Dipeptides act as building blocks for proteins and complex biological

compounds with enzymatic activities.37-40

Effect of dipeptides glycylgycine (Gly-GLy)

and glycyl-DL-valine (Gly-DL-Val) on the CP behavior of tribock polymer has been

given in Figure 5.3a-5.3b while effect of dipeptides on the CP behavior of Tritons has

been given in Figure 5.4a-5.4b. It is clear from Figure 5.3a-5.3b that decrease in CP

caused by dipeptides is relatively more pronounced in case of P84 than L64. Relatively

higher decrease obtained for P84 as compared to L64 can be accounted to the difference

in micellar structure of these TBPs. Both the TBPs: L64 and P84 have similar

hydrophobicity and percentage amount of EO content (EO% = 40), but, PO core of P84

is relatively larger in comparison to L64. Larger PO core in P84 facilitates the

solublization of dipeptides in comparison to L64.

Increase in solubilization of dipeptides increases the hydrophobicity of the

system and decrease in CP is observed for TBPs+Dipeptide systems. In case of

L64+Dipeptide systems, order of decrease in CP at higher concentration of dipeptide is

Gly-Gly > Gly-DL-Val. However, order gets reversed in P84+Dipeptide system. This

reversal in order of CP decrease can be attributed to the increase in hydrophobicity of

the system with increase in dipeptide concentration. In TX-100/TX-114+Gly-Gly

systems, an initial increase in CP at lower concentrations is followed by decrease at

higher concentration of dipeptides as shown in Figure 5.4a-5.4b. TX-100+Gly-DL-Val

system exhibits a decrease in CP for all the concentrations investigated. However, CP

decrease is not so prominent in TX-114+Gly-DL-Val system and an overall increase in

CP is observed over complete concentration range of Gly-DL-Val. Anomalous behavior

of TX-114+Gly-DL-Val system can be attributed to the inefficient packing of TX-114

and Gly-DL-Val in the mixed micelles. Although Gly-DL-Val has high hydrophobicity,

yet, steric factors play dominant role and raise the CP of TX-114+Gly-DL-Val system.

Variation in interaction of TX-100 and TX-114 with Gly-DL-Val is due to difference in

values of their hydrophilic-lipophilic balance (HLB of TX-100=13.5, TX-114=12.4). It

influences the surfactant-water interaction and promotes the hydrophobic interactions in

the aqueous medium. Reduction in CP at higher concentration of dipeptides can be

136

322

324

326

328

330

332

0 0.1 0.2 0.3 0.4 0.5

L64+Gly-Gly

L64+Gly-DL-Val

CP

(K

)

[ Dipeptide ]/ mol dm-3

(a)

325

330

335

340

345

350

0 0.1 0.2 0.3 0.4 0.5

P84+Gly-Gly

P84+Gly-DL-Val

CP

(K

)

[ Dipeptide ]/ mol dm-3

(b)

Figure 5.3 Plots of CP variations of (a) L64 (b) P84 in the presence of dipeptides

137

330

332

334

336

338

340

342

344

0 0.1 0.2 0.3 0.4 0.5

TX-100+Gly-Gly

TX-100+Gly-DL-Val

CP

(K

)

[ Dipeptide ]/ mol dm-3

(a)

296

297

298

299

300

301

302

303

0 0.1 0.2 0.3 0.4 0.5

TX-114+Gly-Gly

TX-114+Gly-DL-Val

CP

(K

)

[ Dipeptide ]/ mol dm-3

(b)

Figure 5.4 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

dipeptides

138

explained in terms of an increase in hydrophobicity of the mixed system. Mutually

different trend for CP variation followed by systems of TBPs and Tritons with

dipeptides can be related to the structural differences between Tritons (polar head and

nonpolar tail micellar structure) and TBPs (core and shell micellar structure).

5.3.3 Effect of Amino Alcohols on the Cloud Point of Triblock Polymers/Tritons

Amino alcohols are important constituents of cancer and HIV drugs.41

Figure

5.5a-5.5b and Figure 5.6a-5.6b represents the plots for additive effect of Leucinol,

Isoleucinol and 2-Amino-1-butanol on the CP of triblock polymers: L64/P84 and

Tritons: TX-100/TX-114 respectively. Decrease in CP of L64 on addition of amino

alcohols has been observed over the complete concentration range with an order:

Isoleucinol > Leucinol > 2-Amino-1-butanol as revealed from Figure 5.5a. In case of

P84, isoleucinol has been found to be decreasing the CP over all the concentrations

while, leucinol and 2-amino-1-butanol cause decrease in CP at low concentration as

given in Figure 5.5b. However, at higher concentrations of leucinol and 2-amino-1-

butanol, an abrupt rise in CP of P84 is observed. On an average, decrease in CP is

observed for P84+2-Amino-1-butanol system. Addition of amino alcohol to TX-

100/TX-114 causes CP to appear at higher temperature over complete concentration

range with an exception of TX-100+Isoleucinol system where a decrease in CP is

obtained as shown in Figure 5.6a-5.6b. Observed CP variation can be explained on the

basis of polar nature of amino alcohols and their tendency to form hydrogen bond with

water molecules. Due to this property of amino alcohols, availability of non-associated

water molecules for the hydration of EO groups decreases that result in lowering of CP.

In L64, this lowering occurs over the complete concentration range, however, in P84,

similar behavior is observed only at lower concentrations of amino alcohols. At higher

concentrations of amino alcohols in P84 system, steric hindrance produced by excess

amino alcohol molecules raises the CP of system. A continuous increase in the CP for

Tritons can be attributed to the tendency of amino alcohols to provide the sufficient

polar medium which increases the solubility of Tritons in aqueous medium and

consequently rise in CP is observed. Leucinol and isoleucinol form hydrogen bond with

water molecules that causes dehydration of EO groups and lowers the CP.

139

320

322

324

326

328

330

332

0 0.1 0.2 0.3 0.4 0.5

L64+Leucinol

L64+Isoleucinaol

L64+2-Amino-1-butanolC

P (

K)

[ Amino alcohol ]/ mol dm-3

(a)

330

335

340

345

350

355

360

0 0.1 0.2 0.3 0.4 0.5

P84+Leucinol

P84+Isoleucinol

P84+2-Amino-1-butanol

CP

(K

)

[ Amino alcohol ]/ mol dm-3

(b)

Figure 5.5 Plots of CP variations of (a) L64 (b) P84 in the presence of amino alcohols

140

330

335

340

345

350

355

360

0 0.1 0.2 0.3 0.4 0.5

TX-100+Leucinol

TX-100+Isoleucinol

TX-100+2-Amino-1-butanol

CP

(K

)

[ Amino alcohol ]/ mol dm-3

(a)

296

298

300

302

304

306

308

310

312

0 0.1 0.2 0.3 0.4 0.5

TX-114+Leucinol

TX-114+Isoleucinol

TX-114+2-Amino-1-butanol

CP

(K

)

[ Amino alcohol ]/ mol dm-3

(b)

Figure 5.6 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

amino alcohols

141

However, due to structural differences, this interaction is developed to varying

extents in TX-100 and TX-114. This differential behavior ultimately results in decrease

in CP of TX-100+Isoleucinol and increase in CP of TX-114+Isoleucinol system.

Besides this, lower solubility of TX-114 in comparison to TX-100 also affects the CP

behavior of Tritons+Isoleucinol system. Due to differential solubility, similar results are

not obtained for variation in CP of TX-100 and TX-114.

5.3.4 Effect of Sugars on the Cloud Point of Triblock Polymers/Tritons

Sugars constitute an important part of complex biological systems. Additive

effect of sugars: fructose, sucrose and maltose on the cloud point of triblock polymers

(L64/P84) has been given in Figure 5.7a-5.7b while effect of sugars on the cloud point

of tritons (TX-100/TX-114) has been given in Figure 5.8a-5.8b. Variation in CP of

triblock polymer systems reflects water structure influencing tendency of these sugars.42

Continuous decrease in CP of TBP, with an increase in concentration of sugar has been

observed as shown in Figure 5.7a-5.7b.It can be accounted to the introduction of sugar

molecules into the micellar core that strengthens hydrophobic interactions and cause

micellar growth. As micellar size increases, water solubility of surfactant decreases and

phase separation takes place comparatively at lower temperature. In other words,

dehydration of EO groups of triblock polymers take place at comparatively lower

temperature thus lowering their CP. In case of TX-100/TX-114+Sugar system, there is

an initial increase in CP at low concentration of sugar, however, further increase in the

concentration of sugar decreases the CP. In case of TX-100/TX-114+Sugar system, an

overall increase in the CP is observed except for TX-114+Sucrose system. In TX-

100/TX-114+Sucrose systems, comparatively larger decrease in CP with increase in

concentration of sucrose is observed for TX-114 than TX-100. Results for TX-100/TX-

114+Sugar systems indicate that sugar molecules are contributing to the solvation of

micelles at lower concentrations and promoting the desolvation at higher

concentrations. At low concentration, orientation of constituents in the micelle might be

the reason behind inefficient packing that causes an increase in the CP of the system.

142

318

320

322

324

326

328

330

332

0 0.1 0.2 0.3 0.4 0.5

L64+Fructose

L64+Sucrose

L64+Maltose

CP

(K

)

[ Sugar ]/ mol dm-3

(a)

330

335

340

345

0 0.1 0.2 0.3 0.4 0.5

P84+Fructose

P84+Sucrose

P84+Maltose

CP

(K

)

[ Sugar ]/ mol dm-3

(b)

Figure 5.7 Plots of CP variations of (a) L64 (b) P84 in the presence of sugars

143

339

340

341

342

343

344

345

346

347

0 0.1 0.2 0.3 0.4 0.5

TX-100+Fructose

TX-100+Sucrose

TX-100+Maltose

CP

(K

)

[ Sugar ]/ mol dm-3

(b)

292

294

296

298

300

302

0 0.1 0.2 0.3 0.4 0.5

TX-114+Fructose

TX-114+Sucrose

TX-114+Maltose

CP

(K

)

[ Sugar ]/ mol dm-3

(a)

Figure 5.8 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

sugars

144

5.3.5 Effect of Hydroxy Acids on the Cloud Point of Triblock Polymers/Tritons

Presence of hydroxy acids in shampoos, cosmetics, soaps and detergents

improve their physicochemical properties. Citric acid and lactic acid are frequently used

for the preparation of these products.43,44

Additive effect of these hydroxy acids on the

CP of triblock polymers: L64/P84 has been shown in Figure 5.9a-5.9b while effect of

hydroxy acids on Tritons: TX-100/TX-114 has been given in Figure 5.10a-5.10b. Plots

for triblock polymers reveal that CP of L64+Hydroxy acid systems initially decreases

and then increases as concentration of hydroxy acids increases in the bulk. At higher

concentration, these hydroxy acids behave as water structure breakers and lead to

increase in CP. Observed order of increase in cloud point is: Lactic acid > Citric acid as

shown in Table 5.1. Addition of hydroxy acids provide sufficient polar medium for the

hydration of EO group in TBPs which increases their CP. Similar behavior has been

observed for P84+Hydroxy acids systems, but, order gets reversed. These observations

may be attributed to the different PO and EO units present in L64 and P84. It was

observed that hydroxy acids increase the CP of TX-100 over complete concentration

range. However, CP of TX-114 initially decreases and then increases with an increase

in concentration of hydroxy acids. CP variation observed in Tritons clearly reflects the

influence of hydrophobicity of surfactants on the surfactant-hydroxy acid interactions as

TX-114 is more hydrophobic than TX-100.

145

327.5

328

328.5

329

329.5

330

330.5

331

331.5

0 0.1 0.2 0.3 0.4 0.5

L64+Citric acid

L64+Lactic acid

CP

(K

)

[ Hydroxy acid ]/ mol dm-3

(a)

334

336

338

340

342

344

346

348

350

0 0.1 0.2 0.3 0.4 0.5

P84+Citric acid

P84+Lactic acid

CP

(K

)

[ Hydroxy acid ]/ mol dm-3

(b)

Figure 5.9 Plots of CP variations of (a) L64 (b) P84 in the presence of hydroxy acids

146

339

340

341

342

343

344

345

0 0.1 0.2 0.3 0.4 0.5

TX-100+Citric acid

TX-100+Lactic acid

CP

(K

)

[ Hydroxy acid ]/ mol dm-3

(a)

296

296.5

297

297.5

298

298.5

299

299.5

0 0.1 0.2 0.3 0.4 0.5

TX-114+Citric acid

TX-114+Lactic acid

CP

(K

)

[ Hydroxy acid ]/ mol dm-3

(b)

Figure 5.10 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

hydroxy acids

147

5.3.6 Effect of Dicarboxylic Acids on the Cloud Point of Triblock Polymers/Tritons

Dicarboxylic acids find use in a variety of industrial applications in perfumery,

biodegradable solvents, lubricants, adhesives, powder coatings, pharmaceuticals and

corrosion inhibitors.45,46

Additive effect of dicarboxylic acids: succinic acid, oxalic acid

on CP of triblock polymers: L64/P84 has been shown in Figure 5.11a-5.11b while effect

of dicarboxylic acids on Tritons: TX-100/TX-114 has been shown in Figure 5.12a-

5.12b. For TBP/Tritons+Dicarboxylic acid systems, decrease in CP was observed over

the complete concentration range except for P84+Oxalic acid system. In P84+Oxalic

acid system, CP initially increases and then decreases with an increase in concentration

of oxalic acid. On the other hand, P84+Succinic acid system displays initial decrease

and then increase in CP with an overall decrease as shown in Figure 5.11b. In

L64+Dicarboxylic acid system, CP decreases but variation remains more or less

constant with increase in concentration of dicarboxylic acid as shown in Figure 5.11a.

CP of TX-100 decreases at all the concentrations of dicarboxylic acid and decrease was

more for oxalic acid than succinic acid as given in Table 5.1. Reversal in the order of

CP decrease is observed for TX-114+Dicarboxylic acid system. Decrease in CP of

TBP/Tritons+Dicarboxylic acid systems is due to tendency of dicarboxylic acids to

form hydrogen bond with water molecules that decreases the availability of water

molecules to hydrate the micelles and lowers the CP. Reversal in the order of CP

decrease on shifting from TX-100 to TX-114 in Tritons+Dicarboxylic acid systems can

probably be due to variation in hydrophobicity of Tritons. Observed anomalous

behavior of L64/P84+Oxalic acid systems can be accounted to the less hydrophobic

environment provided by oxalic acid in comparison to succinic acid.

148

310

315

320

325

330

335

0 0.1 0.2 0.3 0.4 0.5

L64+Succinic acid

L64+Oxalic acid

CP

(K

)

[ Dicarboxylic acid ]/ mol dm-3

(a)

340

342

344

346

348

350

0 0.1 0.2 0.3 0.4 0.5

P84+Succinic acid

P84+Oxalic acid

CP

(K

)

[ Dicarboxylic acid ]/ mol dm-3

(b)

Figure 5.11 Plots of CP variations of (a) L64 (b) P84 in the presence of dicarboxylic

acids

149

336

336.5

337

337.5

338

338.5

339

339.5

340

0 0.1 0.2 0.3 0.4 0.5

TX-100+Succinic acid

TX-100+Oxalic acid

CP

(K

)

[ Dicarboxylic acid ]/ mol dm-3

(a)

292

293

294

295

296

297

298

0 0.1 0.2 0.3 0.4 0.5

TX-114+Succinic acid

TX-114+Oxalic acid

CP

(K

)

[ Dicarboxylic acid ]/ mol dm-3

(b)

Figure 5.12 Plots of CP variations of (a) TX-100 (b) TX-114 in the presence of

dicarboxylic acids

150

5.4 Conclusions

In the present work, we have investigated the cloud point behavior of triblock

polymers (TBP): L64/P84 and Tritons: TX-100/TX-114 in the presence of biomolecules

as additives. Among various biomolecules employed as additives, amino acids were

found to be promoting desolvation of micelles of triblock polymers over the complete

concentration range and cause a decrease in CP. However, Tritons exhibited decrease in

CP at higher concentrations of amino acids except for proline and serine, where a

continuous decrease in CP has been observed. Dipeptides have been found to be causing

an increase in micellar core of the triblock polymers that disturbs hydrophilic-lipophilic

balance of the system and ultimately lead to decrease in CP of the system. Despite

similar hydrophobicity of L64 and P84, decrease in CP caused by dipeptides is

relatively more in P84 than L64 system due to larger PO core of P84. TX-100/TX-

114+Gly-Gly systems, exhibit increase in CP at lower concentrations and decrease at

higher concentration of dipeptides. TX-100+Gly-DL-Val system exhibits a decrease in

CP for all the concentrations investigated while in TX-114+Gly-DL-Val system an

overall increase in CP is observed over complete concentration range. Presence of

amino alcohols lowers the CP of triblock polymers L64 over the complete concentration

range of amino alcohols while in P84 decrease is observed at low concentration of amino

alcohols. A continuous increase in the CP for Tritons in the presence of amino alcohols

can be attributed to the tendency of amino alcohols to provide the sufficient polar

medium which increases the solubility of Tritons in aqueous medium and consequently

rise in CP is observed. Sugar brings variation in hydrophobicity and solvation/

desolvation properties of the micellar systems and decreases the CP of TBP/Tritons.

Higher concentration of hydroxy acids increases the CP of TBP/Tritons due to an

increase in polarity of the medium. Dicarboxylic acids have tendency to form hydrogen

bond with water molecules and were found to decrease the CP of TBP/

Tritons+Dicarboxylic acid systems over the complete concentration range with

exception of P84+Oxalic acid system. It can possibly be due to variation in the

hydrophobicity of system. Results discussed above reveal that molecular associations

(micellar structure), orientation aspects and hydrophobicity of the system collectively

augment the process of clouding.

151

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