Key factor of sponge phase formation in commercial polyethoxylated nonionic surfactant/cosurfactant/water systems and its unique feature at interface

A sponge phase is particularly interesting in terms of its features, such as its transparency, low viscosity, low interfacial tension and so on. However, most past research on the sponge phase have focused on pure surfactants, whereas little research exists on commercial polyethoxylated nonionic surfactants that are used in cosmetics and household products. The reason is attributed to the polyethyleneoxide, hydrophilic group of nonionic surfactants, having large distributions in polymerization degree, resulting in many irregular behaviors in the phase equi-librium. In this study, the phase sequence of the sponge phase formation in a commercial polyethoxylated nonionic surfactant/cosurfactant/water system was investigated based not only on HLB, but also on the distri-bution of polymerization degree of the hydrophilic group to reveal the irregularity of the phase sequence. As a result, in commercial nonionic surfactant systems, the important points for sponge phase formation were revealed to be (1) selecting a surfactant having intermediate HLB, and (2) selecting a structure with sufficient lipophobicity. These factors are for preventing cosurfactant phase separation that is attributed to the wide dis-tribution of polymerization degree of polyethyleneoxide groups. Furthermore, we demonstrated the phenomenal wetting behavior on a hydrophobic surface with unevenness and clarified that the low interfacial tension and low viscosity of the sponge phase among various self-assembling structures were the critical for the wetting behavior.

Automated summary

This study investigates the formation of the sponge phase in a commercial polyethoxylated nonionic surfactant system. The irregularity of the phase formation is revealed, and the important factors for sponge phase formation are identified. Furthermore, the study demonstrates the phenomenal wetting behavior of the sponge phase on a hydrophobic surface with unevenness.