G. Marti-mestres et al., Effect of the addition of oxybenzone or octyl-methoxycinnamate on particlesize of submicron emulsions, DRUG DEV IN, 26(3), 2000, pp. 349-356
The formulation of sunscreen products requires understanding of the solubil
ization of these products in different vehicles to obtain aesthetic prepara
tions and to evaluate long-term stability. For this study, two different ul
traviolet (UV) filters were selected: oxybenzone (powder) and octyl-methoxy
cinnamate (liquid). First the solubility of these UV filters was tested usi
ng a three-component simplex-centroid design strategy. The mixtures were pr
epared with three oily phases used in this field of cosmetics: liquid paraf
fin, isopropyl myristate, and coconut oil. A phase diagram method was used
to carry out a systematic study of submicron oil-in-water emulsions. Phase
diagrams were produced by diluting fixed binary mixtures with water. The su
rfactant consisted of polyoxyethylene-20-sorbitan monostearate/sorbitan mon
ostearate (50/50, w/w). The oily phase contained equal quantities of each o
il studied. From this water/surfactant/oil ternary system, we selected two
reference emulsions with receptively 75/5/20 and 68/7/25 proportions. Photo
n correlation spectroscopy (PCS) was used to investigate the influence of t
hese two UV filters at several concentrations on droplet size and distribut
ion of the oil droplets in the material. All emulsions were stored and chec
ked every month for 6 months.