Wrinkling of Stiff Films on Stretched Compliant Films: Experimental and Theoretical Studies

Wrinkling of stiff film on semi-infinite compliant substrates has attracted attentions recently due to its important applications in stretchable electronics and micro-pattern metrology. However, wrinkling of a stiff film on a compliant thin film substrate has not been well understood. The composite bilayer comprised with a stiff film and a stretched film has a critical application in developing advanced thin film solar cells for long duration stratosphere balloons.

The presented thesis focuses on wrinkling of stiff films with finite widths on stretched compliant thin sheet via experimental and theoretical approach. Polyester films and low density polyethylene films have been utilized as the surface films and substrate films, respectively. Flexible polyvinyl chloride films have also been employed to serve as the surface layer for better understanding the physics behind the phenomena. The experiments reveal wrinkling phenomena of the film on the stretched thin sheet are very similar to that of a stiff film on a semi-infinite elastic foundation. A theoretical model considering finite width effect is formulated based on the concept of effective elastic foundation observed from the experiments via variational approach and principle of minimum potential energy. The result predicted by the theoretical model is validated via experiments and the finite width effect is also investigated and discussed.

In summary, the presented study shows the stretched film plays the role as a virtual semi-infinite elastic foundation for the surface film. The experimental ob- servations and theoretical prediction of the phenomena has been achieved. It may provide a physics-based foundation for technology adventures in thin-film solar cell powered scientific balloon.