Sunscreen dispersions for UV protection

The active particles can be in either the oil phase, the water phase, or both as illustrated in Fig. 1.52. 

To keep the particles well dispersed (as single particles) high steric repulsion is required to overcome strong van der Waals attraction. A schematic representation of the layers required for stabilization and the resulting energy-distance curve for such sterically stabilized system is given in Fig. 1.53. 

The depth of the minimum in the energy-distance curve depends on the ratio of the adsorbed layer thickness 8 to peirticle radius R as illustrated in Fig. 1.54. 

It can be seen from Fig. 1.54 that by increasing (8/R) G decreases and this eliminates any weak flocculation. This ensures the effectiveness of the Ti02 for sunscreen protection. 

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