Fabrication And Forming Mechanisms Of Wrinkles On Gold-PDMS Bilayer Structures

Micro wrinkles can be manufactured with low costs and at large scales, and they have become a very promising technology for micro/nano-scale patterning and fabrication. In this thesis, we have experimentally explored the conditions for the fabrication of a variety of wrinkle pat-terns using the gold-PDMS(polydimethylsiloxane) bilayer material model system. We have also studied the mechanical mechanisms behind wrinkle formation and the transition between different wrinkle modes. Our work lays the foundation for the ultimate goal of fabricating large area1-D and2-D periodic structures with well-controlled wrinkle patterns, periods and amplitudes, which are expected to have wide potential applications on stretchable electronics, tunable gratings, micro lenses, etc., and which would have significant commercial prospects.In the work reported in this thesis, a series of experiments were conducted. By changing experimental conditions like stress types, foundation thicknesses, foundation shapes and film thicknesses, we achieved wrinkles of different patterns and sizes. Some experimental results that we report have been achieved by other researchers in earlier work, which nevertheless is an essential part of our on-going research on wrinkle based photonic devices. Meanwhile, we have successfully demonstrated novel methods for the formation of new wrinkle patterns. We have also observed transition between wrinkle modes under conditions that have not been reported in literature.Mechanical stretching experiments were conducted to fabricate wrinkles perpendicular to the stretching direction. We conducted straight stretching and radial stretching experiments, then we achieved straight wrinkles and ring wrinkles respectively. The periods in the boundary regions are smaller than those in the center during both the straight stretching experiments and the radial stretching experiments, due to the thinner gold films near the boundaries. Cracks were found being distributed all over the gold films and perpendicular to the wrinkle strips, which are related to the materials’Poisson ratios. The light concentration ability of the ring wrinkle patterns has been demonstrated experimentally.Different foundation shapes brought various wrinkle patterns in thermal stress experiments. The one-dimension mode and the labyrinth mode formed on flat PDMS foundations, in the boundary areas and the center areas respectively. The herringbone mode formed on the inclined PDMS foundation. The svastiko mode formed on the striped PDMS foundation. Different patterns correspond to various energy states. Energy barriers between flat films and wrinkles have been experimentally studied. By impacting the flat films, the phenomenon of overcoming energy barriers has been experimentally observed.A spontaneous transition from the bubble mode to the labyrinth mode was observed in a thermal stress experiment. It conforms to the theoretical work by other researchers, which shows how the wrinkle patterns are dependent on the amount of strain and demonstrates that the degree of deformation determines the pattern of wrinkles. The bubble mode happens in the case of small deformation and the labyrinth mode happens in the case of large deformation. Moreover, a stable bubble mode was successfully obtained experimentally by changing the degree of deformations through the thicknesses of the PDMS foundations.In summary, we have partially realized our goal of controlling the wrinkle sizes and wrinkle patterns. The micro wrinkles got in our experiments have potential applications in areas like soft lens, light absorbing films and microfluidic sieves, which are the future work of us. The work reported in this thesis lays the foundation for these applications. Besides, in order to completely fulfill our goal, additional efforts are needed to build a closer relationship between the theoretical analysis and the practical experiments.