Surfactant molecules are self-organized in solution to form various aggregates such as micelles, reversed micelles, and liquid crystals (1). These aggregates are affected by concentration of surfactant, oil-water ratio, critical packing parameter (molecular shape) (2), hydrophile-lipophile balance (HLB), and other factors. Consequently, the phase behaviors of surfactant systems are complicated (3,4). Understanding the phase behaviors is considered very important to have pre-dictability in practical applications.Microemulsions are optically isotropic, transparent, and low viscous (5-15). They are thermodynamically stable solubilization systems. They are classified into three types: aqueous continuous micellar type, bicontinuous type, and oil continuous reversed micellar type. The type of microemulsion depends mainly on the HLB of the system.Earlier papers focused mainly on the solubilization of hydrocarbon oil in microemulsions. Thereafter, studies on phase behavior have been reported on so-called 537 JOS

No abstract

Removing makeup is considered to be the first step in the skincare process. Makeup that has served its purpose is a kind of impurity that should ideally be removed completely to maximize the effects of skincare products applied afterwards. However, the use of silicone resins has significantly improved the long‐lasting property of makeup with the result that makeup can hardly be removed efficiently either with surfactant‐type cleansers like soaps or with oil‐based cleansers like liquid crystalline cleansers. Furthermore, oil‐based makeup removers do not leave the skin feeling fresh but oily, and often have been used in combination with surfactant‐type cleansers. In other words, complete makeup removal and a fresh skin feel are considered to be incompatible in conventional formulation technologies. To obtain compatible systems, we investigated the applicability of a system known as the bicontinuous phase and eventually succeeded in developing a novel system for a makeup remover. This phase can be prepared with a specific composition with a complete hydrophilic‐lipophilic balance in an oil/surfactant/water system by using cyclo‐siloxane, which dissolves silicone resin well. The bicontinuous phase has an oil‐ and water‐continuous microstructure, showing affinity for both aqueous and oily substances. This bicontinuous phase was applied to the development of a novel makeup remover. Determination of remover cap‐ability and fresh skin feel revealed that the makeup could be completely removed and that the amount of oil remaining on skin surface after wash‐off was much less than with previous oil‐based removers. The results of the sensory test also supported the finding that the remover was far superior to conventional products. This makeup remover is the first example of the application of the bicontinuous phase technology to a cosmetic product and clearly seems to provide the best conditions for subsequent skin care, meaning that it is suitable for the first step in the skincare process.