New Oil Gelling Agents for Cosmetics: Formation Mechanism of Oil Gels

We developed new oil gelling agents composed of a long-chain dialkyl phosphate (DP) surfactant and aluminum ion or multinuclear aluminum ion (MAI) which provide the ideal oil-gel systems. One such gelling agent is the aluminum salt of DP (DP-Al) prepared as a precipitate by mixing DP with aluminum chloride in aqueous solutions. Addition of small amounts of the salt to nonpolar oils led to hardening of the oil solutions at temperature below the melting point of alkyl chain (Tc) of DP-Al. Results obtained by X-ray diffraction techniques and with scanning electron microscopy (SEM) revealed that linearly-polymerized assemblies of DP-Al expand in oils three-dimensionally, which suggests that the excellent stability of the gel systems arises from the highly ordered structure. The gelling agent of DP-Al offered the ideal rheological property of waxy cosmetic products such as lip sticks. The complexes of DP with MAI particles (1nm diameter) of aluminum chlorohydrate, Al13O4(OH)24(H2O)12Cl7, provided the ideal thixotropic behavior in non-polar oils. The DP-MAI particle complexes were found to weakly interact by cohesive forces which makes a highly ordered structure of the DP-MAI particle complexes. The DP-MAI particle complexes offered the excellent stability and transparency of cosmetic products such as W/O creams.