The Effect of Shear and Oil Wa

8/4/2019 The Effect of Shear and Oil Wa

1/6

ABSTRACT: Required hydrophile-lipophile balance (HLB)values were examined in terms of the nature of kerosenewater, both oil-in-water (O/W) and water-in-oil (W/O), emul-sions formed using Span 80/Tween 80 surfactant blends. Boththe nature of the emulsification method and the oil/water ratiowere critical in determining the resulting emulsion type. Bothhigh- and low-shear conditions were investigated. Under highshear, low internal phase emulsions formed using the surfac-tant mixtures that corresponded to the required HLB values foremulsification involving kerosene (6 for W/O and 14 for O/W).However, at low shear, high internal phase (concentrated)emulsions resulted. Furthermore, depending on the oil/waterratio, some of the high internal phase emulsions were oppo-site to the type expected, given the HLB of the surfactantblend used. From these results, it appears that the emulsifica-tion technique (applied shear and oil/water ratio) used can beof greater importance in determining the final emulsion typethan the HLB values of the surfactants themselves.

Paper no. S1223 in JSD 5, 1924 (January 2002).

KEY WORDS: Effect of shear, emulsification methods,emulsion-forming requirement, hydrophile-lipophile balance(HLB), technical-grade nonionic surfactants.

The hydrophile-lipophile balance (HLB) concept was firstintroduced by Griffin (1) as an empirical scale to describe

the balance of the size and strength of the hydrophilic andlipophilic groups in an emusifier molecule. In Griffins pro-posed HLB system (1) both surfactants and oil phases couldbe classified. The latter are described in terms of a re-quired HLB value for their emulsification. In this sense,every oil phase has two required HLB values, one each for

water-in-oil (W/O) and oil-in-water (O/W) emulsification.Griffins original work (1) focused on the creation of

O/W emulsions. In order to evaluate the required HLB for

O/W emulsion formation, a bottle test series was createdusing a 50:50 oil/water ratio (by weight) and 15% surfactant(of the oil phase) that was predissolved in the oil phase. Astable emulsion was judged to occur for bottles where no oilor water separated over a period of at least 24 h. The surfac-tant mixture HLB that created the stable emulsion was takento correspond to the required HLB value for O/W emulsifi-

cation of the oil phase employed. In a later publication (2)from ICI Americas (Bridgewater, NJ), Griffins method wasmodified through the use of an oil/water ratio of 20:80 orsmaller and a surfactant concentration that was 1020% by

weight of the oil phase. Low internal phase emulsions werethen formed as the continuous phase was added under pro-

peller agitation. In both of these publications, only a few re-quired HLB values for W/O emulsification were reported.Most of the published work done by Griffin (1) and ICI (2)to determine required HLB values was carried out with thenonionic ICI surfactant series of Spans and Tweens.

Whereas the HLB classification of surfactants has been

the focus of many researchers, only a few groups have ex-amined required HLB experimentally, in terms of emulsioninversion points (35), turbidity (6), and conductivity (7).

At the present time, there appear to be no published re-ports of attempts to repeat Griffins work.

Both Griffins (1) and ICIs (2) studies introduced rela-

tively high shear into the oil/water/surfactant systems. Lowinternal phase emulsions typically result when high-shear con-ditions are used for emulsification, and low-shear mixing can

lead to high internal phase, or concentrated, emulsions (8).Several conditions are needed to form a concentrated emul-sion. First, it is generally accepted that low-shear mixing is re-quired while the internal phase is slowly added to the contin-uous phase (811). Second, the surfactants used to create theemulsion need to be able to form elastic films (8,11). The for-mation of concentrated emulsions has been linked to surfac-tantoil phase interactions (9) and therefore to oilwater in-terfacial tension and the potential for surfactantsurfactant

interactions (12). The combined influence of these factors

may encourage the inversion of low internal phase to concen-trated emulsions during the emulsification process.

Many industrial processes exist in which the formationof low internal phase or concentrated emulsions needs tobe controlled, whether in terms of formation, stability, de-struction, or prevention. Examples range from asphaltemulsions to personal-care products to food products. Suc-cess in emulsion control requires achieving the right physi-

cal chemistry and also the right fluid mechanics. The focusof the present work is on the formation of low internalphase and concentrated emulsions made with kerosene/

water, Span/Tween surfactant systems. The emulsion types

created from the use of different oil/water ratios and shear

Copyright 2002 by AOCS Press Journal of Surfactants and Detergents, Vol. 5, No. 1 (January 2002) 19

*To whom correspondence should be addressed at Saskatchewan Re-search Council, 15 Innovation Blvd., Saskatoon, SK, Canada S7N 2X8.

E-mail: [email protected]

The Effect of Shear and Oil/Water Ratio on the Required

Hydrophile-Lipophile Balance for EmulsificationJana Vander Kloeta and Laurier L. Schramma,b,*

aChemistry Department, University of Calgary, Calgary, AB, Canada, T2N 1N4, and bPetroleum Recovery Institute,Alberta Research Council, Calgary, AB, Canada, T2L 2A6


2/6

intensities applied in the emulsification process are com-pared to the surfactant blend HLB employed.

EXPERIMENTAL PROCEDURES

The surfactants chosen were Span 80 and Tween 80 (ICISurfactants, used as received). These sorbitan monooleates

fall into the category of elastic film-forming surfactants(11). Span 80 (HLB 4.3) and Tween 80 (HLB 15) wereblended using different weight percentages to produce mix-tures of varying HLB ranging from 5.4 to 13.9. Kerosene waschosen as the reference oil phase since kerosene was one ofthe few oil phases Griffin had examined in terms of re-quired HLB values for both W/O and O/W emulsification,

which allowed for verification of the emulsion preparationmethod. Triple-distilled, deionized water was used as the

aqueous phase.The method used to determine the required HLB values

for emulsification was essentially that of ICI (2). Emulsions

formed under low shear were created using a magnetic stirplate/stir bar combination; this kind of mixing involvesmaximal shear rates in the range 10 to 103 s1 (13). Emul-sions formed under high shear were created using a Waringblender; this kind of mixing involves maximal shear rates inthe range 104 to 105 s1 (13). The produced emulsions were

examined under an optical microscope (Jenalumar; Zeiss,Jena, Germany) after being placed, dropwise, on glass slidesthat had been pretreated with Desicote (Beckman, Fuller-ton, CA) to render the glass surfaces hydrophobic. This wasnecessary to inhibit the water droplets in W/O emulsionsfrom coating the glass surface (14). A stable emulsion was

judged to occur for bottles where no oil or water separatedover a period of at least 24 h; the emulsions meeting this sta-bility criterion actually tended to be stable for several days.

All HLB values obtained were the result of at least two sepa-rate experiments. The error associated with all requiredHLB values determined in this work was 1.

RESULTS AND DISCUSSION

Various combinations of kerosene, deionized water, and theSpan 80/Tween 80 blends were tested to find the bestmethod for creating accurate and reproducible emulsion

series. Initially, the kerosene/water ratio was kept at 50:50;

the surfactant, as a percentage of the oil phase, was held

constant at 15%. Five methods of agitation were tested: vor-tex, stirring, blender, wrist-action shaker, and stirringduring addition of water. With the exception of the lastmethod, the various Span80/Tween 80 mixtures wereblended first with kerosene (as advised by Griffin) followedby the addition of the deionized water, and then the agita-tion method was applied. The only alteration in the stir-

ring during addition method was that the water additionand applied shear occurred simultaneously. The high shearintroduced by vortex and blender methods required onlyshort application times, less than 2 min, whereas stirringand wrist-action shaking were employed for 10 min. Thelonger mixing times for stirring and wrist-action shaking

were needed to ensure emulsion homogeneity. Of the fivemethods tested, stirring during the addition of water ap-peared to give the best results for required HLB determina-

tions for both W/O and O/W emulsions.The formation of both W/O- and O/W-type emulsions,

through lower internal (or dispersed) phase quantities, was

encouraged by adjusting the kerosene/water ratio to 80:20and 20:80, respectively. Table 1 outlines some of the varia-tions made with these ratios to further pinpoint the exactorder of combination necessary for successful emulsifica-tion within the HLB series. All these trials were performedby the stirring under addition method.

The results of trials 1 and 2 successfully correlated withthe correct required HLB values for each of W/O and O/Wemulsification, respectively. In both of these trials, the sur-factant was premixed with the dispersed phase, and the con-tinuous phase was added under stirring. When surfactant

was added to the continuous phase (trials 3 and 4) before

addition to the dispersed phase, no stable emulsions devel-oped. Similarly, if surfactant was added to the internal phase

(trials 5 and 6) and then mixed into the continuous phase,success in obtaining the required HLB was not possible dueto the instability of the potential emulsions.

The W/O and O/W emulsions created from trials 1 and 2were very viscous and exhibited long-term stability. Figure 1illustrates a typical bottle series done to determine the W/O-and O/W-required HLB (trials 1 and 2 of Table 1, respec-tively). The experimental details for the bottle series in Fig-ure 1 are given in Table 2 and are discussed below.

In bottles 16 (Fig. 1), 12 g of deionized water was pre-mixed with 1.8 g of a Span 80/Tween 80 emulsifier blend

followed by the addition of 48 g of kerosene. For bottles

20 J. VANDER KLOET AND L.L. SCHRAMM

Journal of Surfactants and Detergents, Vol. 5, No. 1 (January 2002)

TABLE 1Test Emulsification Procedures for Required HLBa Determinations

Surfactant Phase added StableWater Kerosene Surfactant premixed under emulsion

Trial (%) (%) (% of oil phase) with stirring formed

1 20 80 15 Water Kerosene Yes2 80 20 15 Kerosene Water Yes3 20 80 15 Kerosene Kerosene No4 80 20 15 Water Water No5 20 80 15 Water Water No6 80 20 15 Kerosene Kerosene No

aHLB, hydrophilic-lipophilic balance.


3/6

711, 12 g of kerosene was premixed with 1.8 g of a Span80/Tween 80 emulsifier blend followed by the addition of

48 g of deionized water. The oil/water ratio was changed inthe middle of the bottle series (Fig. 1) since preliminary re-sults had shown that at higher HLB values with an oil/waterratio 80:20, or at lower HLB values with an oil/water ratio20:80, no stable emulsions resulted. Figure 1 shows thatcreamy, stable emulsions were formed in bottles 2 and 3(emulsifier blend HLB 6 1) and bottle 10 (emulsifierblend HLB 14 1). Although Figure 1 shows an apparently

homogeneous emulsion in bottle 5, that this sample was un-stable went undetected by the camera. Given that bottles 2and 3 each had an oil/water ratio of 80:20, these emulsions

were first presumed to be W/O. Conversely, it was initiallyassumed that bottle 10 was an O/W emulsion.

Several 23 g samples of the stable emulsion producedin bottle 2 were diluted with either water or kerosene to de-termine which phase was the continuous phase (14,15).That the emulsion diluted spontaneously with water and

not kerosene was surprising. The reverse observation wasnoted for the bottle 10 emulsion, which diluted sponta-neously with kerosene and not water. These results indi-

cated that the bottle 2 emulsion was actually O/W and thebottle 10 emulsion W/O.Given this unexpected result, fresh emulsions were made

incorporating a blue dye (food coloring, Food Club, ScottBathgate Ltd., Winnipeg, Canada) into the aqueous phase(the dye was completely insoluble in the kerosene). This al-

lowed for microscopic examination of the emulsion to sub-stantiate the assignments of kerosene or water as the exter-nal (continuous) emulsion phase. Microscopic examinationof the emulsions confirmed the results of the dilution tests.

The unexpected emulsions were high-internal phase, or

concentrated, emulsions. The explanation for this behaviorcan be understood in terms of the shear applied in theemulsion formation and the description that follows.

Effect of shear and oil/water ratios on the required HLB for

kerosene. Figure 2 illustrates what would normally be the ex-pected HLB behavior, without regard to either the shearused to create the emulsions or the oil/water ratio. To as-sess the difference in emulsification between low- and high-shear mixing, a number of kerosene/water/surfactant se-

ries were produced using a Waring blender. In these experi-ments, oil/water ratios were altered while using only the twosurfactant mixtures (HLB 6 1 and HLB 14 1) that corre-sponded to the required HLB values for kerosene. Table 3gives a summary of these experiments.

All samples listed in Table 3 were prepared by first mix-ing the surfactant with the designated phase, followed by aone-step addition of the other phase. The two phases were

then blended for 15 s. The emulsion formation methodused for the original kerosene/water reference system in-

volved adding the 80% phase to the 20% phase under stir-ring. Therefore, preparation of the samples of Table 3 was

repeated by slowly introducing the added phase with a 40mL glass syringe viaa hole in the lid during the 15-s blend-ing period. The results were identical to those in Table 3,attesting to the importance of high shear over stepwise ad-dition of one phase into another.

The emulsion information provided by these tests ismapped in Figure 3. This phase diagram nearly matches theexpected emulsification behavior of Figure 2. Thus, the re-quired HLB assignment system remained valid across thephase map at high shear.

EFFECT OF SHEAR AND O/W RATIO ON THE REQUIRED HLB 21


FIG. 1. Required hydrophilic-lipophilic balance (HLB) determination for water-in-kerosene and kerosene-in-water emulsions (details in text).

TABLE 2Experimental Description for Bottle Tests Shown in Figure 1

(kerosene/deionized water, Span 80/Tween 80 systems)Oil/aq. ratio Surf. Wt. surfactant (g) Surfactant Phase added

Bottle %/% [g/g] HLBa (15% of 20% phase) premixed with under stirring

1 80:20 [48:12] 4.3 1.8 Water Kerosene2 80:20 [48:12] 5.4 1.8 Water Kerosene3 80:20 [48:12] 6.4 1.8 Water Kerosene4 80:20 [48:12] 7.6 1.8 Water Kerosene5 80:20 [48:12] 8.6 1.8 Water Kerosene6 80:20 [48:12] 9.7 1.8 Water Kerosene7 20:80 [12:48] 10.7 1.8 Kerosene Water8 20:80 [12:48] 11.8 1.8 Kerosene Water9 20:80 [12:48] 12.9 1.8 Kerosene Water

10 20:80 [12:48] 13.9 1.8 Kerosene Water11 20:80 [12:48] 15 1.8 Kerosene Water

aFor abbreviation see Table 1.


4/6



FIG. 2. The expected emulsion tendencey as a function of HLB and oil/water ratio forkerosene/water emulsions (based on the definition of required HLB values for kerosene).O/W, oil-in-water; W/O, water in oil; for other abbreviation see Figure 1.

FIG. 3. Observed emulsion tendency as a function of HLB and oil/water ratio forkerosene/water emulsions prepared under high shear (Waring blender) (data from Table 3).

For abbreviations see Figures 1 and 2.

TABLE 3Emulsions Formed by Means of a Waring Blender (kerosene/water,Span 80/Tween 80 combinations)a

Kerosene/water Span 80/Tween 80 Surfactant Emulsionratio ratio HLB premixed with formed

20:80 10:90 13.9 Kerosene O/W80:20 10:90 13.9 Water Unstable50:50 10:90 13.9 Kerosene O/W20:80 80:20 6.4 Kerosene Unstable80:20 80:20 6.4 Water W/O50:50 80:20 6.4 Kerosene Unstable

aO/W, oil-in-water; W/O, water-in-oil; for other abbreviation see Table 1.


5/6


6/6

terpretations based on the classical HLB system appear toremain valid. However, at other phase volume ratios and es-pecially under low-shear emulsification conditions, in-

verted, concentrated emulsions may form at HLB valuesthat were not predicted. Future work should involve investi-gating the effects of mixing time and energy.

ACKNOWLEDGMENTS

The authors wish to express their thanks and appreciation to theNatural Sciences and Engineering Research Council of Canada,Syncrude Canada Ltd., and the Petroleum Recovery Institute of Al-berta Research Council Inc. for funding and other support of thisresearch.

REFERENCES

1. Griffin, W.C., Classification of Surface-Active Agents by HLB,J. Soc. Cosmetic Chem. 1:311 (1949).

2. The HLB System, ICI United States, Inc. (now ICI Americas,Inc.), Wilmington, 1976.

3. Marszall, L., Emulsion Inversion Point and Required HLB of

Oil-in-Water Emulsions, Cosmet. Toilet. 91:21 (1976).4. Marszall, L., Emulsion Inversion Point as an Accelerated

Method for Evaluating Required HLB, Cosmet. Toilet. 92:32(1977).

5. Marszall, L., Cloud Point and Emulsion Inversion Point,FetteSeifen Anstrich. 79:41 (1977).

6. Frenkel, M., R. Shwartz, and N. Garti, Turbidity Measurementsas a Technique for Evaluation of Water-in-Oil Emulsion Stabil-ity,J. Dispersion Sci. Technol. 3:195 (1982).

7. Prinderre, R., P. Piccerelle, E. Cauture, G. Kalantzis, J.P.Reynier, and J. Joachim, Formulation and Evaluation of O/WEmulsions Using Experimental Design, Int.. J. Pharm. 163:73(1988).

8. Lissant, K.J., inEmulsions and Emulsion Technology, Part I, Mar-cel Dekker, New York, 1974.

9. Chen, H.H., and E. Ruckenstein, Effect of the Nature of theHydrophobic Oil Phase and Surfactant in the Formation ofConcentrated Emulsions,J. Colloid Interface Sci. 145:260 (1991).

10. Cameron, N.R., and D.C. Sherrington, Non-aqueous High

Internal Phase Emulsions,J. Chem. Soc., Faraday Tran. 92:1543(1996).

11. Aronson, M.P., and M.F. Petko, Highly Concentrated Water-in-Oil Emulsions: Influence of Electrolyte on Their Propertiesand Stability,J. Colloid Interface Sci. 159:134 (1993).

12. Kirikou, M., and P. Sherman, The Influence of Tween40/Span 80 Ratio on the Viscoelastic Properties of Concen-trated Oil-Water Emulsions,J. Colloid Interface Sci. 71:51 (1979).

13. Hiemenz, P.C., and R. Rajagopalan, Principles of Colloid and Sur-face Chemistry, 3rd edn., Marcel Dekker, New York, 1997.

14. Schramm, L.L. (ed.),Emulsions, Fundamentals, and Applicationsin the Petroleum Industry,American Chemical Society, Washing-ton, DC, 1992.

15. Briggs, T.L., Experiments on Emulsions,J. Phys. Chem. 18:34(1914).

16. Brooks, B.W., and H.N. Richmond, Dynamics of LiquidLiquidInversion Using Non-Ionic Surfactants, Colloids Surf. 58:131(1991).

17. Brooks, B.W., and H.N. Richmond, Phase Inversion in Non-ionic Surfactant-Oil-Water SystemsII. Drop-Size Studies inCatastrophic Inversion with Turbulent Mixing, Chem. Eng. Sci.49:1065 (1994).

[Received September 25, 2000; accepted August 24, 2001]Jana Vander Kloet is a recent M.Sc. graduate (2000) in colloid and

interface chemistry from the University of Calgary, Canada, where

she studied the interfacial characteristics and other physical proper-

ties of bituminous froth emulsions systems. She earned her B.Sc.

(Hon.) from McMaster University (1995). Her research interests

include the areas of emulsifiers and demulsifiers in petroleum in-

dustry applications.

Dr. Laurier L. Schramm is president and CEO at the

Saskatchewan Research Council and adjunct professor of chemical

engineering at the University of Calgary, both in Canada. His re-

search interests lie in colloid and interface science and the petroleum

industry applications of suspensions, emulsions, foams, surfac-tants, and polymers. In these areas he has published seven books

and over 100 other scientific publications including 17 patents,

most of which have been adopted into commercial practice.



Documents

The Effect of Shear and Oil Wa