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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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