If the hydrophile consists only of oxyethylene groups (CH2CH2O, mol. wt. = 44), a simpler version of the equation is

giving the upper end of the scale (20) for polyoxyethelene glycol itself.

Some HLB values of typical surfactants used in pharmacy are given in Table 7.2. A more detailed list is given in Tables 6.7 and 6.8.

Group contribution

The HLB system has been put on a more quantitative basis by Davies, who calculated group contributions (group numbers) to the HLB number such that the HLB was obtained from

HLB = X (hydrophobic group numbers) -X (lyophilic group numbers) + 7 (7.17)

Table 7.2 Typical HLB numbers of some



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