Electrochemical and Microwave Characterisation of 'Microwave Smart Windows' Based on Poly(3,4- ethylenedioxythiophene) (PEDOT) Composites

摘要

Composite materials comprising the environmentally stable conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), a transition metal/metal salt redox couple in a solid polymer electrolyte matrix have been prepared and characterised. DC and microwave measurements on these materials have shown rapid and reversible changes in their impedances and microwave transmission. The composites may be switched from a high impedance state to a low impedance state for several hundred switching operations with no deterioration in performance when small DC or low frequency AC fields are applied across coaxial discs of the materials from the edges. When the fields are removed, the initial high impedance state is restored. The extent of the change is very dependent on the choice of redox pair and also on the composition of the polymer electrolyte phase. Copper has been shown to give the largest changes in microwave impedance from 185Ω (0V) to 11Ω (5V) at 300MHz. In this paper, we present a series of results for composites containing 26wt% by mass of PEDOT with several transition metal redox couples. The results of lithium tetrafluoroborate concentration in the polymer electrolyte phase on the microwave transmission loss of the PEDOT composite are discussed. The effect of copper metal concentration on the magnitude of the impedance change is also presented along with a proposed mechanism for the switching process.