Formation and properties of mini-emulsions formed by microemulsions dilution.

Mini-emulsions have been formed in quaternary systems water/hexanol/sodium dodecyl sulfate/decane by dilution of a microemulsion with an excess of water. We have investigated systematically the effect of composition variables in the droplet size and Ostwald Ripening rate. This droplet size has been investigated by using dynamic light scattering of samples submitted to further dilution in water. According to the dynamic light scattering results, the initial droplet size depends on the initial microemulsion water content, the larger the initial water concentration, the smaller the initial droplet size. This is probably related to the structure of the initial phase. The rate of Ostwald Ripening depends on the final surfactant concentration as expected for differences in interfacial tension. At high surfactant and dispersed phase contents, instability due to flocculation has been observed. Other experiments in which a fifth component (a more hydrophobic oil) was added to slow down Ostwald Ripening showed an initial droplet size increasing comparable to the systems without additive but after a relatively long time of approximately 2 h, a decrease was observed.

Selective incorporation of the polar ingredients on the formulation of clear gels through phase diagrams.

Synopsis This paper attempts to systematize the preparation of cosmetic formulations by means of phase diagrams. The general criteria used to adapt the usually complex cosmetic systems to simple ternary diagrams W/O/S, consists of grouping the different ingredients according to their functional characteristics (hydrophilics, lipophilics and amphiphilics) that are located respectively in the corresponding vertices W, O and S. Thus, the polar ingredients are always incorporated simultaneously as a single phase, over the initial combinations O/S according to the classical titration procedure. Selective incorporation of the polar ingredients by means of the so-called double-titration procedures was studied. Independent consideration of the polar ingredients leads to modelling of the system in a regular tetrahedron in which the components are located at the four vertices. Several possibilities of double-titration procedures are considered in the tetrahedron depending on the different sequences of incorporating the polar ingredients. The results obtained show a critical influence of the double-titration procedures on two main aspects: limits of existence of the transparent gel realms, and rheological behaviour of some selected compositions. The different possibilities compared with the fixed characteristics obtained by the conventional method of preparation constitute an advantage in adapting a final formulation to the specific needs.

Influence of the polar phase in the formulation of cosmetics.

Synopsis Frequently, the incoporation of the polar phase, as a second step in the formulation of a cosmetic, is considered as a simple dilution process. This work shows the influence of the polar phase on the final formulation, according to its constitution as well as the method of incorporation. Modelling the system through a regular tetrahedron suggests alternative ways to the usual method of incorporation (direct titration with a polar phase with a given composition), based on selective incorporation of the polar ingredients (double titration procedures). Depending on the constitution of the polar phase, it is possible to obtain different kinds of formulations (gel, liquids, ...), and, depending on the different possibilities of incorporation of the polar ingredients, identical compositions can be formulated in terms of percentage of their components, but showing different rheological characteristics, allowing an adaptation to the required specific needs of formulation.

Transparent gels: study of their formation and assimilation of active ingredients through phase diagrams.

Synopsis Multicomponent gel formulations capable of assimilating, simultaneously, several active ingredients of potential application in the cosmetic field were studied. The possibility of formation of a transparent gel was determined using a method which consisted in the optimization of several lipophilic basic compositions, composed of oil, a mixture of surfactants, a sunscreen agent, several vitamins and antioxidants situated in the base of a regular tetrahedron that symbolized the considered system. To this, a polar phase made of water, a cosolvent and urea in appropriate proportions and situated in the fourth vertex, was progressively added. It may be concluded, that the use of phase diagrams on cosmetic systems, constitutes a useful way to select the components and their mutual ratios, allowing an adaptation to the specific requested conditions of formulation.

Transparent formulations of a liposoluble sunscreen agent in an aqueous medium.

Synopsis Transparent formulations of a liposoluble sunscreen in an aqueous medium were studied, taking into account the different chemicals of a selected system situated in the vertices of a regular tetrahedron: sunscreen agent, co-solvent, (surfactants +/- mineral oil) mixture (in the tetrahedron base) and water as the fourth component. Several compositions were selected at optimized component ratios after which water was added progressively. Clear gel and liquid compositions were obtained yielding a sunscreen agent that it suitable for conventional use. The physico-chemical properties of some compositions were assessed in terms of water/sunscreen agent content.