New Values of the Required Hydrophilic-LipophilicBalance for Oil in Water Emulsions of Solid Fatty Acidsand Alcohols Obtained from Solubility Parameter andDielectric Constant Values

Ricardo C. Pasquali, Carlos Bregni, and Melina P. TaurozziDepartamento de Tecnologıa Farmaceutica, Facultad de Farmacia y Bioquımica, Universidad deBuenos Aires, Buenos Aires, Argentina

The goals of this articles are to find a correlation between the required HLB values and the solu-bility parameters of oils; find a more precise correlation between the required HLB values and thedielectric constant, than the one obtained by other authors; and to determine the required HLBvalues for o/w emulsions of solid fatty acids and alcohols from the values of the solubility para-meters and dielectric constants, that could be more trustful than the ones obtained by the meth-odology proposed by Griffin. It was obtained lineal relation between required HLB and solubilityparameter (r¼ 0.995). Also it was observed lineal relations between required HLB and dielectricconstants or logarithm of the dielectric constant more precise than the one obtained by otherauthors.

Keywords Dielectric constant, fatty acids, fatty alcohol, required HLB, solubility parameter

INTRODUCTION

The hydrophilic-lipophilic balance (HLB) for theclassification and selection of surface-active agents was firstissued in 1948 in a brochure of the Atlas Powder Com-pany.[1] The following year, William Griffin, one of thecompany’s Chemists, formally presented the HLB conceptin an article published in the first volume of the Journal ofthe Society of Cosmetic Chemists.[2] In this article, Griffinintroduced the concepts of the required HLB values for oilin water (o=w) and for water in oil (w=o) emulsions anddescribed the methodology used for its experimental deter-mination. Griffin detailed a list of the required HLB valuesthat included solid products such as cetyl alcohol, beeswax,carnauba wax, candelilla wax and stearic acid. The experi-ments for the determination of the required HLB values ofsolids were carried out at 60–70�C. As the water affinity(and the HLB value) of the nonionic surfactants with poly-oxyethylene chains decrease as the temperatures rise, therequired HLB values of these solids are consequentlyaffected by an error in excess.

Gorman and Hall[3] found a lineal correlation (r¼ 0.85)between the required HLB values and the logarithm of the

dielectric constant of oils and between the HLB value andthe logarithm of the dielectric constant of nonionic surfac-tants. Schott[4] demonstrated a nearly lineal correlationwhen the solubility parameter of nonionic surfactants, cor-rected for hydration by including a hydrogen-bondingcomponent, was plotted versus the HLB values. Theseresults and the fact that there exists correlation betweensolubility parameters and dielectric constants[5] suggestthat a correlation between the required HLB values andthe solubility parameters of oils could be established. Hav-ing a mathematic formula that would enable to calculatethe required HLB of an oil from its solubility parameterwould avoid its experimental determination. The latter,apart from being quite laborious, could be affected byerrors, such as the one mentioned before in the case of solidproducts. Thus, for instance, the published HBL requiredvalues for the cetyl alcohol obtained experimentally were:13,[2] 15,[6] 16,[7] 15.5,[8] and 14.78.[9] On the other hand,the knowledge of a more precise correlation between therequired HLB and the dielectric constant than the oneobtained by Gorman and Hall[3] would allow calculatingmore trustworthy HLB required values for productsformed by complex mixtures, such as oils and naturalwaxes or for the oily phase of an emulsion, all of themobtained from the determination of its dielectric constants.The dielectric constants are more trustful and easier todetermine than the required HLB values using the techni-ques that evaluate the emulsion’s stability or the size of

Received 18 November 2007; accepted 8 December 2007.Address correspondence to Ricardo C. Pasquali, Departa-

mento de Tecnologıa Farmaceutica, Facultad de Farmacia y Bio-quımica, Universidad de Buenos Aires, Junın 956, 6� piso (1113),Buenos Aires, Argentina. E-mail: rcpasquali@yahoo.com

Journal of Dispersion Science and Technology, 30:328–331, 2009

Copyright # Taylor & Francis Group, LLC

ISSN: 0193-2691 print=1532-2351 online

DOI: 10.1080/01932690802540517

328

the drops in the oily phase versus the HLB value of theemulsifier.[2,10–13]

The aims of this article are to find a correlation betweenthe required HLB values and the solubility parameters ofoils; find a more precise correlation between the requiredHLB values and the dielectric constant, than the oneobtained by Gorman and Hall;[3] and to determine therequired HLB values for o=w emulsions of solid fatty acidsand alcohols from the values of the solubility parametersand dielectric constants published, that could be moretrustful than the ones obtained by the methodology pro-posed by Griffin.

MATERIAL AND METHODS

The required HLB, the solubility parameters and thedielectric constants of the oils and the solids are listed,respectively, in Tables 1 and 2. The solubility parameterswere obtained from Vaughan,[14] the dielectric constantsfrom Gorman and Hall[3] and Lide,[15] and the requiredHLB values from Gorman and Hall,[3] Griffin,[2,6]

ICI,[7,8,16] and Croda.[9]

RESULTS AND DISCUSSION

The required HLB values of oils are related to thesolubility parameter (d), in J1=2 cm3=2, (Figure 1) by theEquation (1), and with the dielectric constant (e) (Figures 2and 3) by the Equations (2) and (3). SHLB is the typicaldeviation of the required HLB values.

Required HLB ¼ 0:8770d� 2:79

r ¼ 0:995

SHLB ¼ 0:2

½1�

Required HLB ¼ 0:8149 eþ 8:73

r ¼ 0:984

SHLB ¼ 0:4

½2�

Required HLB ¼ 8:34551 log eþ 7:34

r ¼ 0:989

SHLB ¼ 0:4

½3�

Table 3 Provides the values of the required HLB fatty acidsand fatty alcohols calculated in Equations (1), (2), and (3).

TABLE 1Values of required HLB, solubility parameters and

dielectric constants of the oils used for obtaining thecorrelations

OilRequired

HLBHLB

references

Solubilityparameter

(J1=2

cm3=2)Dielectricconstant

Butyl stearate 11 (7) 15.71 3.14b

Castor oil 13a (3) 18.20 4.67b

(7)Cyclomethicone

D48.0 (8,16) 12.25 Not

availableCyclomethicone

D57.5 (8,16) 11.80 Not

availableDecyl alcohol 15 (7) 20.00 7.93c

Isopropylmyristate

11.5 (8,16) 16.40 Notavailable

Isopropylpalmitate

11.5 (8,16) 15.91 3.15b

Lauryl alcohol 14 (7) 19.45 6.5b

Mineral oil 10 (7) 14.46 2.1b

Oleyl alcohol 13.5 (7) 18.31 Notavailable

Oleic acid 11 (3) 16.18 2.46b

aMean value.bFrom (3).cFrom (15).

TABLE 2Values of required HLB, solubility parameters and dielec-

tric constants of solid fatty acids and alcohols

SolidRequired

HLBHLB

references

Solubilityparameter(J1=2 cm3=2)

Dielectricconstant

Cetylalcohol

13 (2) 18.29 3.69b

15 (6)16 (7)

15.5 (8,16)14.78 (9)

Stearylalcohol

15–16 (7) 18.20 3.38b

15.5 (8,16)13.93 (9)

Lauricacid

16 (7) 17.30 Notavailable

Myristicacid

Notavailable

16.57 Notavailable

Palmiticacid

Notavailable

16.14 2.417b

Stearicacid

17 (26) 15.83 2.29a

2.314b

aFrom (3).bFrom (15).

NEW VALUES OF REQUIRED HLB OF SOLID FATTY ACIDS AND ALCOHOLS 329

FIG. 1. Required HLB of oil versus solubility parameter in J1=2 cm3=2.

FIG. 2. Required HLB of oil versus dielectric constant.

TABLE 3Calculated required HLB values from Equations (1), (2), and (3).

Calculated required HLB

Solid Equation (1) (�0.2) Equation (2) (�0.4) Equation (3) (�0.4)

Cetyl alcohol 13.2 11.7 12.1Stearyl alcohol 13.2 11.5 11.8Lauric acid 12.4 — —Myristic acid 11.7 — —Palmitic acid 11.4 10.7 10.5Stearic acid 11.1 10.6 10.4

330 R. C. PASQUALI ET AL.

CONCLUSIONS

Equation (1) represents the best correlation out of thethree equations obtained that calculate the required HLBfor o=w emulsions. This equation would be the one recom-mended to calculate the required HLB values for o=wemulsions of oils or waxes when their solubility parametersare known. The values obtained from Equation (2) andEquation (3) are similar. These equations can be used withproducts whose composition is complex and also with themixture of all the components of an emulsion’s oily phaseafter the determination of its dielectric constant.

In the case of the oils, the use of these equations wouldallow to estimate the required HLB values in a simpler waythan using the methodology proposed by Griffin. In thesolid products, such as the fatty acids and alcohols, furtherto the latter advantage, the values obtained are more trust-ful than the ones obtained with Griffin’s technique due tothe dependence of the HLB values with the temperatureof the nonionic surfactants used in the experiments.

REFERENCES

[1] Atlas. (1948) Surface Active Agents; Wilmington, Delaware:Atlas Powder Company.

[2] Griffin, W.C. (1949) J. Soc. Cosmet. Chem., 1: 311–326.

[3] Gorman, W.G., and Hall, G.D. (1963) J. Pharm. Sci., 52:442–446.

[4] Schott, H. (1984) J. Pharm. Sci., 73: 790–792.[5] Paruta, A.N., Sciarrone, B.J., and Lordi, N.G. (1962)

J. Pharm. Sci., 51: 704–705.[6] Griffin, W.C. (1974) In Cosmetics. Science and Technology,

edited by M.S. Balsam; New York: John Wiley & Sons,pp. 573–629.

[7] ICI. (1976). The HLB System; Wilmington, DE: ICI United

States of America Inc.[8] ICI. (1982). Emulsification of Selected Cosmetic Emollients;

Wilmington, DE: ICI Americas Inc.

[9] Croda. (2000) Guide to High Purity Raw Materials forPharmaceutical and Nutritional Use; Parsippany, NJ:Croda.

[10] Griffin, W.C., Ranauto, H.J., and Adams, A.D. (1966) Am.Perf. Cosm., 81: 31–38.

[11] Robbers, J.E., and Bhatia, V.N. (1961) J. Pharm. Sci., 50:708–709.

[12] Orafidiya, L.O., and Oladimeji, F.A. (2002) Int. J. Pharm.,237: 241–249.

[13] Gullapallia, R.P., and Shethb, B.B. (1999) Eur. J. Pharm.Biopharm., 238: 233–238.

[14] Vaughan, C.D. (1985) J. Soc. Cosmet. Chem., 36: 319–333.[15] Lide, D.R. (2001) CRC Handbook of Chemistry and Physics;

Boca Raton, FL: CRC Press.[16] ICI. (1990) The HLB System; Wilmington, DE: ICI

Americas Inc.

FIG. 3. Required HLB of oil versus logarithm of dielectric constant.

NEW VALUES OF REQUIRED HLB OF SOLID FATTY ACIDS AND ALCOHOLS 331