Relationship between the hardness of an oil–wax gel and the surface structure of the wax crystals

The hardness of an oil–wax gel consisting of a solid paraffin wax (C32) and an oil varies with the oil properties. To clarify the mechanism of this hardness variation, a relationship between the gel hardness and the surface structure of the wax crystals has been studied. The hardness of the gel was affected by the oil polarity; a higher polarity oil produced a harder gel. It was found that in a higher polarity oil gel, the surface of the wax crystals were rougher and contained many steps. These steps on the crystal surface were probably induced by the disordering of the lamellar structure on a nanometer scale (small angle X-ray scattering (SAXS) measurement). Actually, when two kinds of paraffin waxes (C32 and C30) were admixed to purposely disorder the lamellar structure, the wax crystals possessed many steps even in a lower polarity oil and the obtained gel was harder compared with the single paraffin gels.