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Notes: Oil-in-water (o/w) emulsions for cosmetic use, such as lotions and creams, are complex multiple-phase systems, which may contain a number of interacting surfactants, fatty amphiphiles, polymers and other excipients. This study investigates the influence of two synthetic cationic polymers, Polyquaternium-7 and Polyquaternium-11, and the natural anionic polymer, gum of acacia, on the rheology and microstructure of creams prepared with a non-ionic mixed emulsifier (cetyl stearyl alcohol-12EO/cetyl alcohol) using rheology (continuous shear, and viscoelastic creep and oscillation), microscopy and differential scanning calorimetry (DSC). A control cream containing no polymer was also investigated. The semisolid control cream was structured by a swollen lamellar gel network phase formed from the interaction of cetyl alcohol and the POE surfactant, in excess of that required to stabilize oil droplets, with continuous phase water. Endothermic transitions between 25 and 100 °C were identified as components of this phase. Incorporation of cationic polymer into the formulation caused significant loss of structure to produce a mobile semisolid containing larger oil droplets. The microscopical and thermal data implied that the cationic polymer caused the swollen lamellar gel network phase to transform into non-swollen crystals of cetyl alcohol. In contrast, incorporation of gum of acacia produced a thicker cream than the control, with smaller droplet sizes and little evidence of the gel network. Microscopical and thermal data implied that although there were also interactions between gum of acacia and both the surfactant and the swollen gel network phase, the semisolid properties were probably because of the ability of the gum of acacia to stabilize and thicken the emulsion in the absence of the swollen lamellar network.

Notes: Theories of emulsion stability are discussed in relation to dilute, concentrated and semisolid emulsions. It is shown that whilst a unified theory cannot be applied quantitatively to emulsion systems, a better understanding of the various mechanisms of stabilization and breakdown is emerging. Established concepts, eg, the HLB concept, are now given a less empirical gloss.The application of colloid stability theory, even to very dilute emulsions, is difficult. This is because of the polydispersity of the systems and because surfactant and stabilizers may be free to move on the globule surfaces, as well as dissolve in the dispersed or continuous phases. Further difficulties arise because flocculation is not necessarily a sign of emulsion instability in the practical sense, as creamed or flocculated emulsions often may be redispersed by shaking. Crucial to emulsion stability is the prevention of coalescence, and this is governed by the nature of the adsorbed emulsifier film.The flocculation and coalescence that can be understood in dilute emulsions from the DVLO theory and the metastability of thin films against rupture do not address themselves to flocculation and coalescence in concentrated, structured or semi-solid emulsions. These may possess surfactant multilayers rather than monolayers at the oil/water interfaces and the bulk phases are frequently structured. Some emulsions invert at critical temperatures. In semi-solid emulsions, stability is controlled by the phase behaviour of the emulsifier components, rather than by the forces governing stability in dilute colloids and thin films. Stability is usually considered to be product stability during storage. The stability of an emulsion in use, eg, during and after application to the skin, is a topic of equal importance but little documented. This related problem is also discussed. Application de la theorie des emulsions aux systemes complexes et reels On discute les théories de la stabilité des émsions diluées. concentrées et semi solides. Bien qu'une théorie unique ne puisse s'appliquer de façon quantitative á tous les systemes d'emulsions, il ne s'en dégage pas moins une meilleure compréhension des mécanismes de stabilisation et de rupture. Les concepts établis, tels que la valeur HLB apparaîssent maintenant moins empirique.L'application de la théorie de la stabilité des colloïdes est difficile même pour les émulsions diluées. Cela est dûá la diversité des systèmes et au fait que les surfactifs et les agents de stabilisation sont libres de se mouvoir sur la surface des globules comme de se dissoudre dans les phases dispersée et continue.Des difficultés supplémentaires surviennent du fait que la floculation n'est pas obligatoirement synonyme de l'instabilité de l'émulsion et que des émulsions eremeuses ou floculées peuvent souvent être redispersées par agitation. Le paramétre important pour la stabilité des émulsions est la prévention de la coalescence ce qui est liéà la nature du film d'émulsif adsorbé.

Notes: Liquid paraffin in water emulsions stabilized by PEG 1000 monostearate and alcohols cetostearyl (c/s) myristyl (C14), cetyl (C16) or stearyl (C18) and ternary systems prepared by dispersing each fatty alcohol and surfactant in water were examined during 30 days using a Ferranti-Shirley cone and plate viscometer. Microscopical diffusion experiments investigated interaction between PEG 1000 monostearate solution and each alcohol at high and low temperature.The rheological properties of each ternary system and corresponding emulsion were similar. Formulations prepared from pure C14, C16 or c/s alcohols were semisolid immediately after preparation. Flow curves were in the form of anticlockwise hysteresis loops with spur points. On ageing for 24 h, structure built-up over a time scale similar to that observed in diffusion experiments, so that apparent viscosities increased. However, on further ageing the pure C14 and C16 alcohol systems were not as stable as those prepared with c/s alcohol. In contrast, the pure C18 systems were mobile liquids and the emulsion cracked within days. This correlated with diffusion experiments where little interaction was observed between stearyl alcohol and PEG 1000 monostearate.Emulsion consistencies and stabilities were related to the low temperature structures formed in the continuous phases. L'influence des alcools gras sur la structure et la stabilité des crèmes préparées à partir de systèmes monostéarate de polyéthylène glycol 1000/alcools gras.