  Strongly nonlinear phononic crystals were assembled from a chain of
Parylene-C coated steel spheres in a polytetrafluoroethylene (PTFE) holder.
This system exhibits strongly nonlinear properties and extends the range of
materials supporting "sonic vacuum" type behavior. The combination of a high
density core and a soft (low elastic modulus) coating ensures a relatively low
velocity of wave propagation. The beads contact interaction caused by the
deformation of the Parylene coating can be described as classical nonlinear
Hertz theory despite the viscoelastic nature of the polymer and the high strain
rate deformation of the contact area. Strongly nonlinear solitary waves excited
by impacts were investigated experimentally and compared to chains composed of
uniform steel beads. Fracture of the polumer coating was detected under
relatively large pulse amplitude.
