Phytosphingosine for Skin Differentiation and Other Topics: Literature Findings

By: Charles Fox, Independent Consultant

Posted: December 1, 2009, from the December 2009 issue of Cosmetics & Toiletries.

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Earlier research of carboxymethyl starch as a thickener for this surfactant system indicated that the starch, with a different degree of substitution, could be used as a thickener for APG formulations—a surfactant class that is difficult to thicken without use of PEG derivatives.¹⁷ The disadvantage of carboxymethyl starch as a thickener for APG formulations is its low transparency.

Here, the researchers characterized a modified starch by 13C NMR spectroscopy. For detergent formulations, analysis of the starch-based thickener was conducted with static light scattering and viscosity measurements. The carboxymethyl starch was further modified with 2-hydroxyalkyl substituents to create a better interaction between the surfactant and modified starch; to improve this interaction, varying 1,2-epoxyalkanes were used.

Waxy maize starch was first hydrophobically modified through homogeneous reaction conditions using 1,2-epoxyalkanes. Then, it was hydrophilically modified under heterogeneous reaction conditions using monochloro acetic acid. Use of the modified starch at 0.5% w/w as a thickener in aqueous APG formulations showed, by a similar degree of substitution of the hydrophobic and hydrophilic substituents, that the transparency could be increased with the increasing alkyl chain length of the 2-hydroxyalkyl substituents, up to 75%. At the same time, the formula viscosity stayed in the range of 6,000 mPas. The viscosity and the transparency of the surfactant systems could thus be controlled by varying the ratio of hydrophobic and hydrophilic functional groups.

Liquid crystal-silica composite dispersions with improved stability: Shiseido Co. disclosed liquid crystal-silica composite dispersions with improved stability, in addition to their production.¹⁸ The dispersions contained an amphipathic substance, water and a fine-particle dispersant. The inverse bicontinuous cubic liquid crystal phase was formed when the amphipathic substance, i.e., tetramethyltrihydroxyhexadecane, and a portion of the water are dispersed in the remainder of water and the dispersant. The silica is formed inside the inverse bicontinuous cubic liquid crystal phase.

A method for producing the composite dispersion is also disclosed. For example, 75 parts tetramethyltrihydroxyhexadecane (phytantriol), 5 parts glycerin-substituted silane derivative, and 20 parts water were mixed to make a transparent gel composition having inverse bicontinuous cubic liquid crystal phase (V2 phase). The gel composition was added in a solution of 0.1% polyoxyethylene lauryl ether acetic acid sodium salt to obtain a liquid crystal-silica composite spherical fine particle dispersion. In addition, a lotion containing the dispersion was formulated.