HLB method

In water, the surfactant solubility behavior can be shown in more detail as no dispersibility (HLB 1-4) poor dispersibilty (HLB 3-6, such surfactants may be applied as W/O emulsifiers) unstable milky dispersion after vigorous agitation (HLB 6-8, these may be applied as wetting agents) stable milky dispersion (HLB 8-10) from translucent to clear (HLB 10-13, these may be applied as O/W emulsifiers up to HLB 15) clear solution (HLB 14-18, these may be applied as detergents for HLB 13-15 and solubilizer for HLB 15-18). 

In summary, the HLB method is only an empirical approach which has made it possible to organize a great deal of rather messy information on emulsion preparation, in order to choose candidate surfactants in trial and error laboratory work for suitable emulsion selection. There are other surfactant selection methods such as the phase inversion temperature (PIT) and the hydrophilic-lipophilic deviation (HLD) methods used for the same purpose in the emulsion industry, but these are outside the scope of this book. 

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However, as pointed out by Rosen (1978) the HLB method is useful only as a rough guide to emulsifier selection since it indicates neither the efficiency of the emulsifier (i.e., the concentration required) or its effective ness (ije., the stability of the emulsion produced) and does not take into account the effect of temperature in varying tbe extent of hydration of hydrophilic groups such as polyoxyethylene, with consequent change In tbe action of the surfactant. 

Fifty year later, Griffin (101) introduced the HLB number in order to quantify this concept of hydrophilicity (water solubility) and vice versa. The introduction of the HLB method was quite a breakthrough at the time, and it... 

A major drawback to this method, however, is that Winsor s so-called R ratio could not be numerically calculated as in the HLB method, which made it difficult to use for practical emulsion formulations. 

To overcome the limitations of the HLB method to formulate microemulsions, a different approach called hydrophilic-lipophilic difference (HLD) was developed by Salager et al. (1983, 2000). The HLD approach captnres the impact of various factors on microemnlsion type. The HLD value for nonionic and ionic snrfactants can be calculated as follows (Acosta and Bhakta 2009) Nonionic surfactants ... 

Although the HLD method has a limited database (CC value is known only for a limited number of surfactants likewise the Nqq value is known for a limited number of oils) as compared with the HLB method, this concept can play an important role in the formulation design. 

Because of the drastic energy increase involved in the emulsification process, the resulting emulsion is not thermodynamically stable and the deemulsification process must be either slowed down to get stable goods or accelerated in separation operations. This chapter will focus on stabilizing emulsions. This stabilization can be explained using two different concepts the interfadai film using the hydrophilic-lipophilic balance (HLB) method and the Deijaguin, Landau, Verwey, and Overbeek (DLVO) theory. 

The hydrophilic and lijpophilic balance (HLB) method allows the selection of the right emulsifier with a minimum number of experiments. Refer to Sec. V.C. 

On the other hand, the HLB concept is of primary importance to select the right composition of the emulsion and is still used in the development work. The HLB method will be developed in detail later. 

In short, Griffin s method is too simple to fit the needs of real formulations. Nevertheless, if some improvements are made, the HLB method is one of the most effective for developing stable emulsions. 

In addition to the HLB method, another method can help in formulating emulsions It is based on CNEA (carbon number of equivalent alcane) and on CNPA (carbon number of... 

Table 7 Selection of the Suitable Emulsifier According to the HLB Method...

Figure 51 The right surface-active agent the HLB method content optimisation.

Testa and Vianello [101] applied the HLB method to the emulsion polymerization of VC. They plotted the rate of polymerization and some properties of the latex against the HLB of anionic emulsifiers or their blends with non-ionic emulsifiers (Empicol (HLB = 40), sodium laurate (20.8), Atlas G 3300 (11.7) and Span 20 (8.6)). No bell-shaped curves were obtained, as one would have expected. The properties of polymer latexes and/or the rate of polymerization seemed to be rather dependent upon the amount of the emulsifier. 

The authors [101] came to the conclusion that PVC insolubility in its monomer changes the latex properties to such an extent that it does not follow the emulsification laws on which the HLB method is based. This does not mean that the HLB approach is not useful in the vinyl chloride polymerization but its role is somewhat reduced. The polymerization lod are emulsifier monomer droplets or monomer-swollen micelles - their number is a function of the HLB nature. 

Because the PIT approach to surfactant evaluation is newer than the HLB method, the effects of variables on the relationship between PITs, surfactant structures, and emulsion stability have not been as clearly defined in a quantitative way. It has been found, however, that there is an almost linear correlation between the HLB of a surfactant under a given set of conditions and its PIT under the same circumstances. In essence, the higher the HLB of the surfactant system, the higher will be its PIT. 

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