Characterization of a Cosmetic Colloidal Dispersion of Plate-Shaped Inorganic Compounds Prepared by the Use of an Ultrahigh-Pressure Homogenizer

Abstract

An ultrafinely dispersed O/W emulsion as cosmetics was made from an aqueous mixture between plate-shaped inorganic compounds and oily substances without any surfactant. A Na-Type colloidal silicate of the 3-octahedral smectite structure was used as a plate-shaped inorganic compound. Polyethylene glycol (PEG) was used as a water-soluble polymer.
The PEG adsorption onto the surface of inorganic compound was to be expected for the effects of a steric stabilization mechanism. The mixtures of the silicate and PEG with both oil agents and water-soluble agents were homogenized by an ultrahigh-pressure homogenizer (more than 100MPa).
The dynamic rheological measurements of the emulsions thus prepared were carried out using a parallel-plate rheometer and then storage moduli (G′), loss moduli (G″), and loss tangent (tan ∂) were obtained. The specific bulky structures, such as card-house structures, were formed throughout the emulsion as judged by a Cryo-SEM electron microscopic observation. These structures were broken down by higher shear-rate and easily reformed with decreasing shear-rate again.
It was concluded that these structures were responsible for rheological properties of the cosmetic emulsions.