Towards a 'smart window' for microwave applications

Discs of poly(aniline)-silver-polymer electrolyte particulate composites exhibit rapid and reversible changes in their microwave impedance when small electric fields are applied across them in a coaxial line test set in a resonant condition. The effect of composition on the cyclic voltammetry and microwave characteristics of the composites is described. The experimental data show that changes in the gradients of the cyclic voltammograms coincide with large changes in microwave resonant null depth consistent with increasing conductivity of the composite when the fields are applied during electrochemical cycling. The reverse change occurs when the field is removed. An equivalent network model comprising a parallel resistor and capacitor has been fitted to the measured data. Scanning electron microscopy studies on both the cycled and uncycled composites are presented and suggest that, during cycling, the silver metal dissolves and is then re-precipitated.