Abstract
Alkyl phosphates are well known and have been commonly used for a long time in the cosmetic and detergent fields as a mild surfactant. However, many of the general industrial products of alkyl phosphate in the market are the mixtures of mono-, di- and tri-esters which do not have the specific features of mono-esters. If we use the alkyl phosphate which has highly purified mono-ester, it is expected to form a new beautiful self-assembling structure. In this study, by increasing the mono alkyl content, we tried to discover such a new functional behavior and structure using highly purified hexadecyl alkyl phosphate. Among the compounds studied, hexadecyl phosphate neutralized with L-arginine (R16MP-Arg) in an aqueous system showed characteristic solution properties and association behavior below the Krafft temperature. Spontaneous swelling of R16MP-Arg was observed below the Krafft temperature, and a gel structures composed of R16MP-Arg and water was formed without heating or shaking. This gel was identified as a thermodynamically stable “α-gel” based on the results of DSC and SAXS measurements. In this study, we revealed that highly purified mono hexadecyl phosphate with L-arginine organized a very stable α-gel structure. Cosmetics in which this α-gel is used as the base give a refreshing and smoothing sensation when applied to the skin. The unique property of R16MP-Arg is that it affords a stable gel structure even when mixed with fatty alcohol.
