Surfactant hydrophilic-lypophilic balance

A system named HLB (hydrophilic-lypophilic balance) constitutes a useful guide to the selection of a suitable surfactant for a given dispersed phase [2, 25, 97, 102]. 

Aqueous solutions of many nonionic amphiphiles at low concentration become cloudy (phase separation) upon heating at a well-defined temperature that depends on the surfactant concentration. In the temperature-concentration plane, the cloud point curve is a lower consolution curve above which the solution separates into two isotropic micellar solutions of different concentrations. The coexistence curve exhibits a minimum at a critical temperature T and a critical concentration C,. The value of Tc depends on the hydrophilic-lypophilic balance of the surfactant. A crucial point, however, is that near a cloud point transition, the properties of micellar solutions are similar to those of binary liquid mixtures in the vicinity of a critical consolution point, which are mainly governed by long-range concentration fluctuations [61]. 

Surfactant plays an important role in the stabilization of the droplets before and after polymerization with the capsule formation. Moreover, after polymerization the PBCA nanocapsules are going to be isolated from the oil phase and redispersed in the aqueous phase. Therefore, the choice of surfactant is very crucial. Generally for inverse systems, non-ionic surfactants with a low hydrophilic-lypophilic balance (HLB) values are well-suited. However, after redispersion in water, PBCA capsules stabilized with a water-soluble non-ionic surfactant would better resist the agglomeration process during centrifugation. 

Watanabe et al. [35] tried to use a more hydrophilic and commercially available protein, gelatin, as a substrate instead of asi-casein. The lypophiles used in this case were luecine n-alkyl esters with alkyl carbon numbers ranging from 2 to 12 in order to produce proteinaceous surfactants with a different hydrophilicity-lipophilicity balance. All of the enzymatically modified gelatin... 

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