Suspoemulsions in Sunscreens and Colour Cosmetics

The formulation of suspoemulsions for sunscreens and colour cosmetics remains a challenge for the chemist due to the complex interactions between the particles and droplets that may result in heteroflocculation [4]. One of the main challenges here is to ensure that the small submicron particles remain individually dispersed in the formulation in order to achieve maximum UV protection for sunscreens and optimum colour properties for make-up products. To achieve maximum dispersion 

The process of wetting involves replacing the solid/vapour interface (with interfacial tension ygy) with a solid/liquid interface (with interfacial tension yg ). Wetting can be described in equilibrium thermodynamics in terms of the contact angle 0 by Young s equation at the wetting line [5]. 

The energy required to achieve dispersion wetting, is given by the product of the external area of the powder, A and the difference between ncl ygy. 

wetting of the external surface of the powder depends on the liquid surface tension and the contact angle. i 9 90°, cos9 is positive and the work of dispersion is negative - that is, wetting will be spontaneous. 

In order for liquid penetration to occur, Ap must be positive and hence 9 should be less than 90°. 

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