Indian Journal of Chemistry Yol. 38A, January l 999, pp. IO- 1 6

Clouding behaviour of binary mixtures of Triton X- 100/ Tween-80 as well as

Tween-20IBrij-35, and the influences of the ionic surfactants (SDS and CTAB) and

water soluble polymers (PVA and PVP) on their cloud points

Sou men Ghosh & S P Moulik * Centre for Surface Science, Department of Chemistry, Jadavpur University,Calcutta 700 032, India

Received 17 July 1998; revised 5 NOI'ember 1 998

The clouding behaviour of binary mixtures of non-ionic surfactants, Triton X-I OO I Tween-80 and Tween-20 I Brij-35 at different molar ratios have been studied. The effects of ionic surfactants, CTAB and SDS on the clouding features of these binary mixtures have also investigated. Similar investigations using the water soluble polymers, PYA and PYP have been made. The interac­tions of SDS with PYA and PYP as well as that of the ternary mixtures ofTween-20 / Brij-35 / SDS with PYA have been viscometrically examined. Rationalization of the results (cloud points) in terms of surfactant composition and polymer concentration in solution has been attempted.

Investigations on mixtures of surfactants, and surfactants and polymers in aqueous solutions are of interest for fundamental understanding of their interactions with regard to their chemi­cal, pharmaceutical, mineral processing and petroleum engi­neering applicationsl.7• In mixed state, the aqueous solution is not only composed of singly dispersed surfactant and polymer molecules but also of surfactant aggregates (such as micelles and vesicles) as well as complexes of polymer and surfactant. The stability of mixed surfactants and surfactant-polymer com­binations with respect to temperature needs to be known with reference to their multifold applications mentioned above. This can be fairly understood by measuring their cloud points.

The cloud point (CP) is an important property of non­ionic surfactants; below CP, a single phase of molecular or micellar solution exists, above it water solubility of surfactant is reduced and a cloudy dispersion resultsX by the formation of giant molecular aggregates in the state of a separate phase 9-12. Water soluble polymers also exhibit clouding by a similar mechanism. The phenomenon is reversible and the CP stands for the transition from water soluble state to oil soluble stateD The CP value for a polymer- surfactant mixture may be a guide to its hydrophilic / hydrophobic character. This information is useful in the preparation of emulsions, dispersions, etc., where nonionic surfactant as well as surfactant and polymer are of­ten used in combination .

The CP's of polymers and non ionic surfactants (which are related to their interactions with the water molecules in the medium) arc also affected by the addition of other substancesiJ. The effect of added ionic surfactants on the cloud point of

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some polymers in aqueous solution have been studied by sev­eral workersI4-IX• It has been reported that the Flory-Huggins theory for polymer solutions can describe the clouding phe­nomenon 19-21. According to this theory, the phase separation above the clouding temperature of nonionic surfactants in the presence of a polymer'can be correlated with the surfactant structure with reference to the temperature effect on the aggre­gation number. The formation of polymer-micelle complex gives rise to conformational changes in the polymer molecule and the measurement of viscosity of the solution may provide with the idea of polymer-micelle association.

In this paper, we have reported the clouding of surfac­tants in binary and ternary mixtures as well as the effects of water soluble polymers on the phenomenon. The binary mix­tures are Triton X- I 00rrween-80 and Tween-20IBrij-35. for ternary combinations, ionic surfactants, CTAB and SDS have been employed with the binary mixtures. The water soluble polymers, PVP and P YA have been also used with the binary mixtures . The effect of PYA on the viscosity of the ternary mixture of Tween-20/ Brij-35/SDS has been also investigated.

Materials and Methods

The surfactants, cetyltrimethylammonium bromide (C TAB), tert-octylphenyl polyoxyethyleneether (Triton X- I 00 or TX-l 00), polyoxyethylene(20) sorbitanmonooleate ( Tween-80 or Tw-80), polyoxyethylene (20) sorbitanmonolaurate (Tween-20 or Tw-20), polyoxyethylene (23) laurylether (Brij-35 or Bj-35) and sodium dodecyl sulphate (SDS) were the same samples as used previously 1.2. The water soluble poly­mers, polyvinyl pyrrolidone (PVP) and polyvinyl alcohol

GHOSH et al. : CLOUDING BEHAVIOUR OF B INARY MIXTURES OF SOME NON-IONIC SURFACTANTS II

(PVA) were products of Sigma, USA (M" = 40,000) and Aldrich, USA (M" = 35,000) respectively.

Doubly distilled conductivity water· (specific conduc­tance, 2-4 J..LS cm·1 at 303K) was used in all preparations.

The cloud point (CP) was determined by controlled heat­ing in a heating mantle of the stirred surfactant or surfactant! polymer system (taken in a stoppered container to its full ca­pacity without air gap and securedly glued to withstand the pressure generated during heating) until it clouded or got tur­bid. The sample was then allowed to slowly cool under stir­ring condition and the temperature for the disappearance of turbidity was also noted. The mean value of the appearance and disappearance of turbidity was considered as the CP. The reproducibility of the measurements was found to be within ± 0.2"e. Since the CP values are not small, the observed values have been rounded off to the nearest degree and presented in the Table I .

The viscosities of the polymer-ternary surfactant solu­tions were measured at 35"C using a calibrated Ubbelohde cap­illary viscometer placed in a water bath accurate within ± 0.2"C as reported earlier6•

Results and Discussion

Cloud points of binary mixtures The cloud points of the binary mixtures of TX-I 00 and

Tw-80 as well as of Tw-20 and Bj-35 of different composi­tions and at two overall concentrations are presented in Tables I A and I B respectively. It is seen from the data in the Tables that the CP's of the pure surfactants are not sensitive to the reported two concentrations (0.5 and 1% w/v ). In fact, the CP of TX-I 00 has been reported9.22 to change very slowly with concentration ; we have observed unchanged CP up to 4%. The changes in CP in the mixtures are also very mildly depen­dent on the overall concentration. It is seen from the tables that the CP of the TX-I 00 ITw-80 combination decreases with increasing proportion of TX-I 00; this is also observed for the Tw-20/Bj-35 combinations where CP decreases with increas­ing Tw-20. The calculated CP values on ideal basis have been obtained from the relations,

CP ""Ie = a CP TX.IOO + (I -a) CP Tw-KO

and CPeak = a CP Tw-20 + (I -a) CP Hj-:15

... ( I )

.. . (2)

where a is the mole fraction of either TX-I 00 or Tw-20 . The results are given in parentheses in Table I . The deviations from the experimental CP values are mild. It is more for the Tw-20 / Bj-35 system than the TX-100ITw-80 system. At high frac­tion of TX-I 00 / Tw-80, the system has shown ideality i.e. CP = CP . The molecules of TX-lOO and Tw-80 have the ohs t.:ak tend�ncy to associate (or mix), they have nearly similar hy-drophilic polyoxyethylene groups; they have the tendency to form mixed micelles. With increase in temperature, the sol­vated water molecules are stripped oil from the micelles and monomers by the thermal energy effect causing favourable free

Table 1 - The cloud points' of binary surfactant mixtures at different compositions and at two overall concentrations

(0.5% and 1 % w/v)

UTX_1OO

o 0.05 0. 1 0 0.20 0.33 0.50 0.67 0.80 0.90 1 .00

U Tw-20

o 0. 1 0 0.20

. 0.25 0.33 0.40 0.50 0.67

0.80 0.90 0.95 1 .00

A: TX-I OO and Tw-80

" CPt C 0.5%

97.0 9 1.0 88.0 86.5 85.0 80.0 76.0 72.0 67.5 65.0

B: Tw-20 and Bj-35

" CPt C 0.5%

1 30.0

1 29.0 1 27.0 1 24.5 1 1 8.0 1 1 9.5 1 1 6.0 1 1 3 .0

1 09.0 1 08.0 1 04.0 96.0

1 %

97.0 9 1 .5 (95.4) 88.5 (93.8) 87.5 (90.6) 87.0 (86.3) 80.0 (8 1 .0) no (75.7) 72.0 (7 1 .4) 68.5 (68.2) 65.0

1 %

1 30.0

1 29.0 ( 1 26.6) 1 27.0 ( 1 23.2) 1 25.0 ( 1 2 1 .5) 1 2 1.0 ( 1 1 8.7) 1 20.0 ( 1 1 6.4) 1 17.0 ( 1 13 .0) 1 14.0 ( 1 07.3)

1 1 0.0 ( 1 02.8) 1 09.0 (99.4) 1 05.0 (97.7) 96.0

• parentheted values are calculated according to Eqs I and 2 for A and B respectively

energy change for complexation/association leading to easier detachment from the aqueous environment or phase separa­tion 23:24. This is prevalent in all the combinations of Tw-20 and Bj-35 where CP,,,,, < CPeak•

Clouding of ternary combinations In Figs I A and B, the cloud points of binary mixtures of

TX- lOO / Tw-80 and Tw-20 / Bj-35 at different proportions in presence of increasing concentrations of CTAB and SDS re­spectively are presented. The concentrations of the ionic sur­factants have not exceeded their critical micellar concentra­tion or CMC. In the case of SDS, the concentrations are close

1 2

95

91

87

83

79 .u '-... a. 75 u

71

67

63

59

55 - 4

INDIAN J CHEM, SEC. A, JANUARY 1 999

B 140

U "-a. U '

0·21 0·35 0-49 R

0·7 0·27 0·45 0·63 R'

Fig. 1 - Effects of CTAB and SDS on the CP of binary mixtures of nonionic surfactants.

- 3

A : CP ofTX-I OO / Tw-80 vs. [ CTAB] / [ CTAB] CMC (R) plot. B : CP of Tw - 20 / Bj-35 vs [ SDS] / [SDS] CMC (R,) plot. Binary ratios (TX-IOO,

Tw-80 or Tw-20 : Bj-35 ):, 0, 4: 1 ; 0, 2:1 , �,I : I ,. , 1 :2; ® ,1 :4.

A

96

92

88

84 u . ""-b a. 80 u

c 76

e d 72

68

e o e 64

60 -2 -1 0 -4 -3 -2 -1 log CpVA (wt 010) log Cpvp (wt 0/.)

0·9

B

o

Fig. 2- Plots of CP vs. log CpVA (wt %) and CP vs. log Cpvp(wt %) in the binary mixture of TX-I OO / Tw-80. A : with PYA; B : with PYP A (a) , Tw-80 ; A (b,c,d,e,f) : TX-I 00 : Tw-80, I :4, I :2, I: 1 , 2: 1 ,4: I; A (g) , TX-I 00. B(h) , Tw-80 ; B (i,j,k,l,m):

TX-IOO : Tw-80, 1 :4; 1 :2; I: 1 ,2: I ,4: I; B (n) , TX·1 00.

•

Fig.

3.5

3.0

2.5

GHOSH et al. : CLOUDING BEHAVIOUR OF BINARY MIXTURES OF SOME NON-IONIC SURFACTANTS 1 3

B 130

125

120

115

e

105

100

95

90

p "-

130

125

120

115

0.. 110 u .

105

100

95

90

A

o o

8�4L----_� 3----_�2-- ---_Ll�--=0----�-" 85L----L----�--�----�---0�--� -5 -4 -3 -2 -1 log Cpvp (wt"to) log CpVA (wt"to)

Fig. 3 - Plots of CP vs. log CpVA (wt %) and CP vs. log Cpyp(wt %) in the binary mixture of Tw- 20 I Bj-35. A : with PVA ; B : with PVP A (a) , Bj-35 ; A (b,c,d,e,f) : Tw-20 : Bj-35, 1:4, I :2, I: 1 , 2: I ,4: I; A (g) , Tw-20. B (h) , Bj-35 ; B (i,j,k,l,m) : Tw-20 : Bj-35, 1:4; I :2; I: 1 , 2: I ,4: I; B (n) , Tw-20.

A

n; « 2.0 ii:

to the CMC only for a few combinations. The courses in the first set (Fig. I -A) are on the whole sigmoidal whereas they are monotonons in the second set (Fig. I -B) . It is seen from Fig. l that small concentrations of ionic surfactants have consider­able CP increasing potentials; CTAB (having CMC one tenth of that of SDS ) is relatively more effective on TX-lOOrrw-80 system than SDS on Tw-20IBj-35 system. The formation of mixed micelles with the ionic surfactants is considered to im­part stability to the nonionic binary systems. A minor pres­ence of ionic surfactants has a significant effect on the protec­tion from clouding of the nonionic surfactants. The ionic sur­factants hardly cloud by the application of temperature.

?f! 1.5

1.0

0.5

nn 1).5 1.0 1.5 2.0 % PVP at IP

2.5 3.0

4- A test of correlation between the CP controlling activities of PYA and PVP by plotting % PYA at IP vs % PVP at IP. A: TX-l ()() I Tw-80 system (least squares slope = 1.23, inter­

cept = 0.20 , corr. coeff. = 0.99). B: Tw-20 I Bj-35 system ( least squares slope = 0.65, intercept

= 0.66, corr. coeff. = 0.89).

0, 0 indicate calculated values and. , • indicate observed values of A and B respectively.

Effects of polymers on the CP of binary surfactant mixtures In Figs 2 A and B , the effects of PYA and PVP on the

CP of mixed TX-100 / Tw-80 system at different composi­tions are presented. The polymers are seen to decrease the CP at higher concentration. P YA is more effective than PVP . Sur­factants are known to preferentially aggregate in the presence of polymers 25,26; pendent like products have been conjectured. In this model, flexible water soluble polymers can wrap the micellar aggregates. By the action of temperature, desolvated nonionic surfactant molecules or aggregates lodge on the poly­mer chain which also tends to phase out because of its self­desolvation, and the total entity thus becomes unstable and show clouding at lower temperature. The type of polymer, its

14 INDIAN J CHEM, SEC. A, JANUARY 1999

90 e

80

o

70 60

60�--�------�------�----� o 0·2 0·5 0·8 1.0 OO�--�------L------L--�

o 0·2 0·5 0·8 '.0

o(TX-100 o(Tw-20

Fig. 5- CP - cx,.X.ICXI (A) and CP- cx,.w.2(1 (8) profi les at 4% (w/v) PYP and PYA in each case. 0, PYP ; � , PYA. Lines are drawn according to equations 1 and 2.

, ·4 "---�--PV

PYA

'·1 0

1.0�--L---...L-_---L __ ....I-_--l o 0·02 0·04 0·06 0·08 0·1

[SDS]/mol dm3

Fig.6- Dependence of relative viscosi ty (ll) of PYA and PYP on [SDS] at 308 K.

molecular length, flexibility, solvation and configuration arc the major factors in the matter of destabilization of the cloud­ing surfactant systemsI4.IR. A comprehensive study in this di­rection would be worthwhile in view of uses of polymers and surfactants in combination in the tertiary oil recovery process where underground temperature is relatively much high.

In Figs 3 A and B , the effects of PYA and PVP on the CP of Tw-20 I Bj-35 mixed system at different compositions are presented. Here also at higher polymer concentration, PYA is more effective CP lowering agent than PVP. In all the curves presented in Figs 2 and 3, initial and final linear courses and their intersections can be distinctly located. The intersections in several curves are marked with 'cross signs' as indicators.

From the intersection points (IP) on the curves for the pure surfactants, the IP c.k values for the binary mixtures have been obtained from the relations,

(IP cak ) TX.J(XIlTw.XO = a (IP) TX.J(KI + (I-a) (lP) Tw.X(J . . . (3)

and (IP c.k) Tw·201 Bj·35 = a (IP) Tw.20 + ( I -a) (IP) Bj.,5 .(4)

In Fig. 4-A, (IP"h)TX.J(X}{fw.XIJ values for PYA are plotted against

(IP'lO'\X.lootrw.XO values for PVP along with the corresponding

(IPc.k\X.J(Xltrw.XO values for PVP and PYA. Similar results on Tw-20/Bj-35 system for PYA and PVP cases are depicted in Fig. 4-B. The agreements are fairly good. The least squares linear courses taking all the points calculated and observed follow the relations,

(IPlVA TX.J(XlfTw.X(J = 0.20 + 1.23 (lP)PVP TX.J(Jotrw.XIJ

and (IP)PVA Tw.20/Bj.35 = 0.66 + 0.65 (IP)PVP Tw.10/Bj.35

... (5)

.. . (6)

The non-ideality behaviours ofTX-1 00 I Tw-80 and Tw-20 I Bj-35 systems in respect ofCP in the PYA and PVP envi­ronments are depicted in Figs 5 A and B. In the case of the first binary mixture, the deviations are negative from the ideal line in the environment of 4% of PYA; in presence of 4% of PVP the results are nearly ideal. Positive deviations on the other hand have been observed for the other binary combina­tion in the presence of 4% of both the polymers. Similar trends have been observed (not presented) at other levels of polymer concentration. The negative deviation suggests destabilization of the system whereas positive deviation advocates stabiliza­tion. To what a degree the individual CP values are modified to deciding the resultant CP in the surfactant-polymer combi­nations is difficult to rationalize. Until more systematic data are not at hand, we refrain from conjecturing on this complex issue.

\ t

GHOSH et at.: CLOUDING BEHAVIOUR OF BINARY MIXTURES OF SOME NON-IONIC SURFACTANTS 15

,., r--------------.

1:2:4 2:1.:4

1·0 :--�=__-___:�-��.l----.J o 0-02 0·05 0·08 0.1 [SDS]/moldm-3

1:4:2

1.0�--:-'::-----1-___ ....l-_--.J o 0·02 0·05 0.08 0·1

[SDS]/moldrrf3 Fig.7- Dependence of relative viscosity (11,) of PYA on the ternary

surfactant systems (Tw-20 / Bj- 35/ SDS) at different ratios at 308 K plotted in terms of [SDS], Mole ratio compositions are shown on the curves.

Vis cosity of P VA alld P VP in presence of different ratios of SDS, Tw-20 and Bj-35

The cationic surfactants can interact with polymers pro­vided the biter is appreciably hydrophobic. But they are known not to interact with PYP and polyoxyethylene (PEO)27.2X . While eTAB interacts with PYAls, SDS can interact with both PYA and PypI4.29.'O. We have observed that relative viscosity of PYA

solution at 35"C increases with SDS and becomes maximum (1.26) at 15 mmol dm'] (-twi.:e its CMC) and then declines. The results with PYA and PYP are presented in Fig. 6. At 1000 ppm PYA, an expansion in the PYA molecular configuration by the atlachmenr of DS . anion or SDS and consequent repul­sion of the formed polyelectrolyte type entity enhances the viscosity up to [SDS] = 15 mmol dm·'. At higher [SDS], wrap­ping of the fonned micelles (CMCSDS == 8 mmol dm')) by the polymer chain causes reuuction of the chain Il:."ngth whereupon viscosity is reduced. AI a concentralioil 0f PYP of 10,000 ppm,

and at [SDS] =50 mmol dm') (6 times its CMC), the viscosity goes to a maximum)l. The relatively high concentration of the polymer demicellizes SDS and the polymer-attached charged monomers induce polyelectrolyte characteristics to the PYP

with a consequence of enhanced viscosity. In Fig. 7, the relative viscosity of 1000 ppm PYA solu­

tion in Tw-20/Bj-35/SDS at different molar ratios, 4: I :2, 1:4:2, 1:2:4, 2: 1:4 and I: I: I are presented as a function of [SDS] at each ratio. There are increment and decrement in viscosity with definite breaks in all the courses except for the ratios 4:2: I and I: 1: 1 for which the relative viscosity continuously declines. Different states of molecular configuration induced by the mixed bi-nonionic and mono ionic surfactants are envisaged. Deciphering of individual contributions would be an worth­while task for a future study.

Conclusions

The following conclusions can be made from the study: (i) With respect to the clouding behaviours, the binary mix­

tures ofTX-100 /Tw-80 are more ideal than Tw-20/Bj-35; (ii) the ionic surfactants SDS and CTAB at concentrations less than CMC can appreciably check the clouding of the afore­said non ionic binary mixtures; and (iii) the water soluble poly­mers PYA and PYP at low concentrations can undergo inter­action with the above binary mixtures and significantly pre­vent them from clouding .

Acknowledgement

S. O. thanks the UOC, New Delhi for financial support to conduct the work.

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.\ • t