Nanotechnology plays an important role in personal care and cosmetic applications. Many products, such as sunscreens, contain particles or droplets in the nano size range from 5 nm to a few hundred nm. Examples are shown in Table 1.
These nanodispersions require special methods for their preparation and stabilization against flocculation (aggregation), Ostwald ripening (disproportionation) and coalescence. This article describes the methods for stabilizing nanodispersions against these break-down processes. It also describes the advantages offered by each type of nanodispersion in personal care and cosmetic applications.
Several methods can be applied to stabilize the dispersions against flocculation, Ostwald ripening and coalescence. Stabilization against flocculation can be achieved using either electrostatic or steric stabilization or a combination of both.
Electrostatic stabilization against flocculation: Electrostatic repulsion is produced when using ionic surfactants that adsorb at the interface, producing double layers. When two particles or droplets approach each other to a separation distance comparable to twice the adsorbed layer thickness, repulsion occurs as a result of overlap of the double layers.1 This repulsion overcomes the van der Waals attraction, thus preventing any flocculation. The repulsive energy increases with increase of the surface (or zeta) potential and decrease of electrolyte concentration and valency.
Excerpt Only This is a shortened version or summary of the article that appeared in the Aug. 1, 2004 issue of Cosmetics & Toiletries magazine. The full content is not currently available online.