Investigation of the Mechanism of Temperature-Responsiveness of Metal-Cholate Supramolecular Hydrogels

Abstract

Temperature-promoted hydrogel formation was investigated in a mixed solution of sodium cholate and metal ions. Transmission electron microscopy (TEM) was used to characterize the morphology of the microstructures of the hydrogels, and nanofibers were observed. The arrangement of the cholate and metal ions was proposed according to the X-ray diffraction (XRD) measurements. Rheological measurements revealed that the strength of the hydrogels increases with increasing temperature, while the fluorescence of the gels increased as well. Increasing the temperature also increased the gel formation rate. The critical micelle concentration of sodium cholate solution decreased slightly with increasing temperature. On the basis of the experimental results, we propose that the increased hydrophobicity of cholate ions with increasing temperature leads to stronger hydrogen bonding between cholate ions, which accounts for the unique heating-enhanced gelation behavior.