Assembly of conductive Au films on poly(urethane urea) elastomers using a solution-based approach

Conductive Au films were successfully assembled on poly(urethane urea) (PUU) films using a solution-based approach. This method does not require prior surface functionalization before the Au attachment. Immersion of the PUU film in a colloidal Au solution immobilizes the Au particles on the surface, and the growth increases with time. This attachment occurs via strong interactions of Au with the amine and amide groups in the polymer. Three different PUUs with hard segment contents of 20%, 30%, and 35% were studied. Growth of the films was monitored using UV-vis spectroscopy and scanning electron microscopy. Immersion in the gold solution for long times, or for shorter times with subsequent seeding, forms very conductive films. The resistivity of the films was (7 +/- 1) x 10(-5) Omega(.)cm. Using this approach, PUUs can be used as adhesives for the attachment of gold to different surfaces. Since the PUUs are highly elastic materials, the effect of strain on the resistance was also studied. It was seen that the resistance increased as a function of the strain. This change in resistance was reversible and was recovered when the material was relaxed. Higher strains of > 50% cause the conductive film to become completely insulating. However, it becomes conducting again as the film is relaxed. Such a switching behavior in the resistance has potential applications in sensors and electromechanical switches.