HLB number

The HLB system has made it possible to organize a great deal of rather messy information and to plan fairly efficient systematic approaches to the optimiza-tion of emulsion preparation. If pursued too far, however, the system tends to lose itself in complexities [74]. It is not surprising that HLB numbers are not really additive their effective value depends on what particular oil phase is involved and the emulsion depends on volume fraction. Finally, the host of physical characteristics needed to describe an emulsion cannot be encapsulated by a single HLB number (note Ref. 75). 

Fig. XIV-10. The correlation between the HLB number and the phase inversion temperature in cyclohexane of nonionic surfactants. (From Ref. 71.)...

A surfactant mixture having an HLB number of 8 should give a good W/O emulsion in which the oil phase is lanolin. Suggest two possible surfactant mixtures that you, an aspiring cosmetic chemist, might use you have been told that your formulations must contain 10% cetyl alcohol. 

Nonionic surfactants are often characterized ia terms of their hydrophi1 e—1 ipophi1 e balance (HLB) number (see Emulsions). For simple alcohol... 

Furthermore, in a series of polyoxyethylene nonylphenol nonionic surfactants, the value of varied linearly with the HLB number of the surfactant. The value of K2 varied linearly with the log of the interfacial tension measured at the surfactant concentration that gives 90% soil removal. Carrying the correlations still further, it was found that from the detergency equation of a single surfactant with three different polar sods, was a function of the sod s dipole moment and a function of the sod s surface tension (81). 

One of the most important characteristics of the emulsifier is its CMC, which is defined as the critical concentration value below which no micelle formation occurs. The critical micelle concentration of an emulsifier is determined by the structure and the number of hydrophilic and hydrophobic groups included in the emulsifier molecule. The hydrophile-lipophile balance (HLB) number is a good criterion for the selection of proper emulsifier. The HLB scale was developed by W. C. Griffin [46,47]. Based on his approach, the HLB number of an emulsifier can be calculated by dividing... 

The performance of secondary alkanesulfonates in applications as emulsifiers in the widespread emulsion polymerization of vinyl monomers can be assessed by their hydrophilic-lipophilic balance (HLB) numbers. The HLB numbers can... 

The HLB numbers decrease with increasing chain length, e.g., from 13.25 for sodium decane 1-sulfonate to 9.45 for the C18 homolog [72]. Typical HLB numbers for positional isomers range from 12.3 for sodium dodecane 1-sulfonate to 13.2 for the more hydrophilic 6 isomer [73]. The HLB numbers of alkanesulfonates are less influenced by the isomeric position of the functional group and by substituents than the cM values [68]. HLB numbers can be correlated with partition coefficients for the distribution of a surfactant between the aqueous and oily phases, which emphasizes that the partition coefficient is dependent on the carbon number [68]. 

A variety of nonpolar to moderately polar solvents has been evaluated for their ability to form stable CLAs (Table 15.2) [68]. As can be seen, as the solvent becomes more polar the aphron size increases and it becomes more unstable. Hence, the influence of the surfactant HLB number was evaluated using a moderately polar solvent, -pentanol [68]. This demonstrated that if the HLB number of the surfactant is high enough, then it is possible to formulate stable CLAs. 

Williams [105] investigated the effect on stability of water-in-styrene/divinyl-benzene HIPEs, stabilised with nonionic surfactants, on addition of a range of cosurfactants. Generally, stability was reduced, with higher degrees of coalescence being observed with cosurfactant addition. The stability appeared to be inversely related to the HLB number of the cosurfactant. 

Experiments on the stability of the HIPEs indicated that one of the most important factors was the solubility of the emulsifier in the continuous (formamide) phase. Thus, the higher the surfactant solubility, the more stable the emulsion. The emulsifier concentration was also important stability increased to a maximum, then decreased, with increasing surfactant concentration. Surprisingly, the HLB number did not appear to have much effect on the stability of the emulsions, over the range studied (11 to 14). This was attributed to the high concentration of emulsifier in the continuous phase, although the narrow HLB value range is probably also a factor. 

Researchers at Unilever [128] discovered that the surfactant used to form the HIPEs must be of low HLB value (between 2 and 6), as would be expected for w/o emulsions. The optimum surfactant was sorbitan monooleate (Span 80), which has an HLB value of 4.3. However, the HLB number of the surfactant is not the only criterion for the preparation of stable HIPEs the chemical nature was also found to be of importance [105]. 

Variations in the relative polarity or nonpolarity of surfactants (hydrophilic or hydrophobic) signiLcantly inLuence its interfacial behavior. A measure of this parameter is useful to classify surfactants. An HLB number is a direct expression of the hydrophilic and hydrophobic character of surfactants and is a useful means for surfactant classiLcation. HLB numbers for surfactants may be either calculated using the following empirical equation ... 

The amphiphilic nature of many emulsifying agents (particularly non-ionic surfactants) can be expressed in terms of an empirical scale of so-called HLB (hydrophile-lipophile balance) numbers222 (see Table 10.1). The least hydrophilic surfactants are assigned the lowest HLB values. Several formulae have been established for calculating HLB numbers from composition data and they can also be determined experimentally - e.g. from cloud-point measurements123,125. For mixed emulsifiers, approximate algebraic additivity holds. 

The optimum HLB number for forming an emulsion depends to some extent on the nature of the particular system. Suppose that 20 per cent sorbitan tristearate (HLB 2.1) plus 80 per cent polyoxyethylene sorbitan monostearate (HLB 14.9) is the optimum composition of a mixture of these emulsifiers for preparing a particular O/W emulsion. The HLB of the mixture is, therefore, (0.2 x 2.1) + (0.8 x 14.9) — 12.3. The theory is that an HLB of 12.3 should be optimum for the... 

A useful index for choosing surfactants for various applications is the hydrophilic-lipophilic balance (HLB), which is based on the relative percentage of hydrophilic-to-lipophilic groups in the surfactant molecule(s). Surfactants with a low HLB number normally form W/O emulsions, whereas those with a high HLB number form a O/W emulsion. A summary of the HLB range required for various purposes is given in Table I. 

Griffin developed a simple equation for calculation of the HLB number of certain numbers of nonionic surfactants such as fatty acid esters and alcohol ethoxylates. For the polyhydroxy fatty the HLB number is given by the equation... 

For the simpler alcohol ethoxylates, the HLB number can be calculated from the weight percentages of oxyethy-lene E and polyhydric alcohol P, i.e.,... 

The solubility of the surfactant of polyethyleneglycol type in different phases can be described by the HLB (hydrophilic-lipophilic-balance) concept [ 27]. This concept attributes to the molecule a HLB number that represents the geometric ratios of the hydrophilic and the hydrophobic moieties. It should, however, be emphasized that the HLB does not represent a fundamental property of the system but is based on experience. For fatty alcohol ethoxylates... 

The second system was formed from Span-80 and Tween-80, solutions of 20% total concentration and different ratios. It contained also 1 mol dm 3 NaCl and octane or hydrocarbons from the kerosene fraction as an organic phase. Producing optically transparent water solutions with a high solubilising ability turned to be a complicate problem. Such a solution was obtained only in a narrow HLB number range. It was necessary to heat the systems up to 60-70°C in order to destruct the O/W emulsion, followed by cooling to 21°C. 

A surfactant HLB number can be estimated roughly by mixing a small portion of the surfactant with water and observing the nature of the mixture. On the basis of Table 9.15 an approximate HLB munber can be assigned for these observations. 

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