Application of the temperature-ramped holographic relaxation spectroscopy in the investigation of physically cross-linked gels

Holographic relaxation spectroscopy (HRS), also known as forced Rayleigh scattering (FRS), can be used to study slow translational diffusion of probes inside a polymer gel. In this study, we demonstrated that, besides the translational diffusion coefficient, a combination of temperature ramp with HRS could lead to additional information on physically cross-linked gels, such as the gel content, the gel melting temperature, and the gel structure. Using a gelatin gel as an example, we correlated the temperature dependence of the intensity of the diffracted light to the formation of triple-stranded helixes (i.e., the renaturalization process). Such a correlation was supported by the optical rotation study. Our results showed that the renaturalization followed the first-order kinetics. The applications of such a combination of the temperature ramp with HRS have been envisioned.