Scanning electron microscopic observation of oil/wax/water/surfactant system

Abstract

We observed the internal structure of an oil/wax/water/surfactant system using a scanning electron microscope to investigate the relationship between its hardness and state of wax crystal. The molten wax (hydrogenated jojoba oil, ceresin, polyethylene wax, carnauba wax, or microcrystalline wax) was cast in a home‐made spiral mold of aluminum foil for preparing the test specimen for SEM observation. In hydrogenated jojoba oil a fine frame‐like crystal structure, the so‐called ‘card‐house structure,’ was observed but not in other waxes. The mixture of hydrogenated jojoba oil and water showed a few small droplets deposited on the roundish wax frame‐like structure. On the other hand, waxes other than hydrogenated jojoba oil did not change their internal structure when they were mixed with water. This result suggested that hydrogenated jojoba oil showed uniquely high affinity for water. In the system of oil, water, surfactant, and various kinds of waxes, their crystal structure, hardness, and the shape of dispersed water particles were remarkably changed with the combination of waxes. In the system with ceresin and carnauba wax, the hardness measured by a card‐tension meter was high, and the internal crystal structure was fine and amorphous. The water particle in the ceresin and carnauba wax system had a smaller diameter than that in the system containing hydrogenated jojoba oil. The system containing hydrogenated jojoba oil showed a card house‐like wax crystal structure without high hardness. It was considered that the wax crystal structure played an important role in providing hardness and in contributing to the water distribution in the oil/wax/water/surfactant system.