Nanoemulsions polymeric surfactants

As most nanoemulsions are prepared using nonionic and/or polymeric surfactants, it is necessary to consider the interaction forces between droplets containing adsorbed layers (steric stabilisation). As this was described in detail in Chapter 10, only a summary will be given here [15, 16]. 

Nature of nanoparticle Emulsification method Nature of nanoemulsion Monomers Surfactants Polymerization and emulsification parameters Particle size (nm) References... 

This section, which is by no means exhaustive, will deal with the following topics (i) Surfactants used in cosmetic formulations, (il) Interaction forces between particles or droplets in a dispersion and their combination, (iil) Description of stability in terms of the interaction forces, (iv) Self-assembly structures and their role in stabilization, skin feel, moisturization and delivery of actives, (v) Use of polymeric surfactants for stabilization of nanoemulsions, multiple emulsions, liposomes and vesicles. 

The inherently high colloid stability of nanoemulsions when using polymeric surfactants is due to their steric stabilization. The mechanism of steric stabilization was discussed above. As shown in Fig. 1.3 (a), the energy-distance curve shows a shallow attractive minimum at separation distance comparable to twice the adsorbed layer thickness 28. This minimum decreases in magnitude as the ratio between adsorbed layer thickness to droplet size increases. With nanoemulsions the ratio of adsorbed layer thickness to droplet radius (8/R) is relatively large (0.1 0.2) when compared with macroemulsions. This is schematically illustrated in Fig. 1.28 which shows the reduction in with increasing 8/R. 

These surfactants have many uses, in particular as colloid and nanoemulsion dispersants, wetting agents, detergents and even additive to dehydrate crude oils. However, most polymeric surfactants are graft-type, particularly synthetic products such as polyelectrolytes, which are not strictly surfactants or are not used for their surfactant properties. It is the case of hydrosoluble or hydrodispersible polyelectrolytes which are utilized for the antiredeposition, dispersant and viscosity-enhancing properties such as carboxymethyl cellulose, polyacrylic acid and derivatives. 

The use of oil/water (OAV) emulsions has also been employed to fabricate PU NPs [162-165]. In this method, the diisocyanate (IPDI) is first dissolved in an oil/ surfactant mixture (90/10, saturated medium chain triglyceride/polysorbate 80 [polyoxyethylene 20-sorbitan monooleate]). Addition of the aqueous phase with PEG 400 (diamine or diol) to the 0/S mixture in dropwise fashion (to obtain 90% aqueous component) occurs under mechanical stirring to obtain nanoemulsions, followed by heating to 70 °C to allow polymerization and achieve PU or PU urea NPs, which can be isolated by ultracentrifugation [165]. This method works by having IPDI present in the core of oil nanodroplets in the 0/W nanoemulsion, which react with the diols or diamines at the surface of the oil droplet, resulting in the formation of the NPs with a size distribution from 40 to lOOnm. 

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