Electrochemical Cloud Point Temperature from Thermoamperometry: Real-Time Analysis for Phase Transition of Thermoresponsive Polymers.

Cloud point temperature ( T cp ) is a thermal index used to define the phase transition of thermoresponsive polymers. In this study, we used electrochemical techniques to obtain an electrochemical cloud point temperature ( T ecp ) that exhibits the more accurate phase transition temperature and can replace T cp . Thermoamperometry on an ultramicroelectrode was conducted with a poly(arylene ether sulfone) (PES 10 ) as a model system to obtain a current-temperature ( i - T ) curve in real time; the T ecp of the PES 10 was determined from the i - T curve. The i - T curve shows an unprecedented current decrease in the PES 10 solution despite increasing temperature; on the other hand, the current increased linearly with increasing temperature in the solution without PES 10 . This phenomenon was analyzed by considering the characteristics of PES 10 during phase transition, such as dynamic viscosity, temperature of the solution, and electrode impedance. It was confirmed that the current drops shown in the i - T curves were mainly due to the decrease of real electrode area. The comparison of T ecp and T cp showed that both depended similarly on the concentrations of the thermoresponsive polymer and the supporting electrolyte. The results reveal that by adjusting the concentration of polymer and electrolyte in an organic solution, T ecp , as a new analytical method, can be used in electric circuit-based energy storage appliances such as Li-ion batteries and supercapacitors.