Aggregate formation of PEG-150 pentaerythrityl tetrastearate.

PEG-150 pentaerythrityl tetrastearate (PEG-150PETS) is an amphiphilic molecule with a tetrameric structure comprising four ethylene oxide blocks bound to a central carbon atom and terminal stearic chains. This starshaped tetrameric molecule can be classified as a nonionic oligomeric surfactant. Generally, PEG-150PETS is used as a cosurfactant by mixing it in small amounts with aqueous solutions of other surfactants to increase the viscosity of the solution. In this study, we investigated aggregate formation and surface properties of PEG-150PETS in an aqueous solution. Pyrene probing and light scattering methods revealed that PEG-150PETS formed aggregates at concentrations above 0.015 mmol L-1. The size of the aggregates was an average of 500-700 nm by dynamic light scattering measurements. Transmission electron microscopy revealed that the aggregates formed giant micelle, which is composed of a mesh-like framework. By contrast, the surface tension of the aqueous solution of PEG-150PETS was reduced to 51 mN m-1, but the surface activity was not as high as that of general surfactants. Tetrameric surfactants, which have large molecular structures, are more favorable than surface activity for the formation of aggregates.