Rheological properties of wormlike micellar gels formed by novel bio-based isosorbide surfactants

Abstract

Utilization of renewable resources is gaining significance. Isosorbide, which is derived from corn, has been attracting attention as a basic component in various industrial applications. Isosorbide surfactants having an isosorbide group as a building block are called bio-based surfactants. In this study, we report wormlike micelle formation with a mixed surfactant solution of sodium 5-O-dodecyl isosorbide sulfate (SDSS) and 2-O- or 5-O-dodecyl isosorbide (2-DS or 5-DS, respectively). We studied the viscosity behavior of the 3wt%NaCl aq./SDSS system with 2-DS or 5-DS at a constant surfactant concentration (5wt%). The maximum viscosity was achieved at the same surfactant mixing composition for both systems but was higher in the 5-DS system. We also studied the dynamic rheological behavior. Oscillatory-shear (frequency sweep) measurements were performed on the viscoelastic samples that were formed around the viscosity maximum composition. Liquid-like behavior (G′<G′′) was observed in the low-frequency region, whereas solid-like behavior (G′>G′′) was observed in the high-frequency region. The Maxwell-type oscillatory rheological behavior of viscous micellar solutions can be related to the transient network formed by the entanglement of wormlike micelles. The Maxwell model was also fitted to the data, indicating wormlike micelle formation. The mesh size for the 2-DS system (58nm) was larger than that for the 5-DS system (47nm) around the maximum viscosity. This suggests that the 2-DS system forms shorter wormlike micelles with SDSS than does the 5-DS system, because of the possible larger head group area of 2-DS in the SDSS-2-DS mixed layer. Therefore a higher maximum η0 was observed in the 5-DS system.