Pulse NMR study of structural characteristics of temperature-sensitive hydrogel

The proton relaxation behavior of a temperature-sensitive gel, observed through using a pulse NMR technique, was related to the structural characteristics of the gel. As the temperature increased, the pore size of the gel decreased gradually while the relaxation time constants, T₁ and T₂, showed different patterns of change. It is believed that the proton relaxation was affected by a direct temperature effect and an indirect, temperature-related structural effect. The response of the protons to these effects varied depending on where the protons resided. A sudden increase in several NMR parameter values occurred at around 30°C, the lower critical solution temperature (LCST). This may be related to a transition state of the gel undergoing dramatic local non-uniform changes around the LCST.