Hydrophile—lipophile balance scale

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... 

Particularly useful is the physical classification of surfactants based on the hydrophile-lipophile balance (HLB) system [67,68] established by Griffin [69,70]. More than 50 years ago he introduced an empirical scale of HLB values for a variety of nonionic surfactants. Griffin s original concept defined HLB as the percentage (by weight) of the hydrophile divided by 5 to yield more manageable values ... 

Griffin suggested an empirical quantitative hydrophile-lipophile balance (HLB) scale which characterizes the tendency of a surfactant to form water-in-oil or oil-in-water emulsions [544], The HLB is a direct measure of the hydrophilic character of a surfactant the... 

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 type of emulsion formed (normally water-in-oil or oil-in-water, commonly expressed as wlo or olw, w denoting the aqueous phase and o the organic phase) is determined by the volume ratio of the two liquids and also by the phase addition sequence and the nature of any additives used to promote emulsification [29] the affinity of emulsifiers for oil and water is measured on the hydrophile-lipophile balance (HLB) scale [30]. Oil-in-water emulsions are most common in all application fields. 

An empirical scale developed for categorizing single-component or mixed (usually nonionic) emulsifying agents, using this principle, is the hydrophile-lipophile balance or HLB scale. This dimensionless scale ranges from 0 to 20 a low HLB (<9) refers to a lipophilic surfactant (oil-soluble) and a high HLB (>11) to a hydrophilic (water-soluble) surfactant. In gen-... 

Hydrophile-Lipophile Balance (HLB) Scale An empirical scale categorizing surfactants in terms of their tendencies to be mostly oil soluble or water soluble, hence their tendencies to promote WO or QW emulsions, respectively. 

Griffin devised the concept of hydrophile-lipophile balance (HLB) and its additivity many years ago for selection of non-ionic emulsifiers and this rather empirical method is still widely used. The enormous literature on the HLB of surfactants has been reviewed by Becher. Each surfactant is allocated an HLB number usually on a scale of 0-20, based on the relative proportions of the hydrophilic and hydrophobic part of a molecule. Water-in-oil emulsions are formed generally from oil-soluble surfactants of low HLB number and oil-in-water emulsions from more hydrophilic surfactants of high HLB number. The method of selection is based on the observation that each type of oil will require an emulsifying agent of a specific HLB number to produce a stable emulsion. Thus, oils are often designated two required HLB numbers, one low and one high, for their emulsification to form water-in-oil and oil-in-water emulsions respectively. A series of emulsifiers and their blends with HLB values close to the required HLB of the oil are then examined to see which one forms the most stable emulsion (c.f. Fig. lA). 

The amphiphilic nature of nonionic surfactants is often expressed in terms of the balance between the hydrophobic and hydrophilic portions of the molecule. An empirical scale of ffLB (hydrophile-lipophile balance) numbers has been devised (see Chapter 7, section 7.3.2). The lower the ffLB number, the more lipophilic is the compound and vice versa. ffLB values for a series of commercial nonionic surfactants are quoted in Tables 6.7 and 6.8. The choice of surfactant for medicinal use involves a consideration of the toxicity of the substance, which may be ingested in large amounts. The following surfactants are widely used in pharmaceutical formulations. 

The selection of different surfactants in the preparation of either O/W or W/O emulsions is often still made on an empirical basis. A semi-empirical scale for selecting surfactants, the hydrophilic-lipophilic balance (HLB number) was developed by Grifhn [18]. This scale is based on the relative percentage of hydrophihc to lipophilic (hydrophobic) groups in the surfactant molecule(s). For an O/W emulsion droplet the hydrophobic chain resides in the oil phase, whereas the hydrophilic head group resides in the aqueous phase. In contrast, for a W/O emulsion droplet the hydrophilic group(s) reside in the water droplet while the lipophilic groups reside in the hydrocarbon phase. 

Hydrophile—Lipophile Balance (HLB scale) An empirical scale categoriz-... 

The idea that the best steric stabilizers are amphipa ic in character has long been recognized by manufacturers of commercial nonionic surfactants. These are classified by the empirical HLB (an acronym for hydrophilic-lipophilic balance) scheme which endeavours to scale the relative solubilities of the two contrasting components in aqueous and nonpolar dispersion media. 

There are a large number of emulsifiers available and making a choice for a new formulation or product is difficult. The use of the hydrophilic-lipophilic balance (HLB) concept originated by Griffin in 1949 can be a useful empirical method of preliminary selection. The HLB number quantifies the balance of hydrophilic-lipophilic characteristics of the surfactant molecule on an arbitrary numerical scale. The least hydrophilic surfactants are assigned the lowest HLB (see Table 14.2). The use of the HLB balance is also well described by Davies and Rideal. ... 

In conclusion, the amphiphilicity factor is important for the understanding of microemulsion structuring. It was also suggested as an additional means of classifying surfactants, together with the packing parameter or the hydrophilic-lipophilic-balance (HLB) scale [84],... 

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