  Casimir forces between material surfaces at close proximity of less than 200
nm can lead to increased chaotic behavior of actuating devices depending on the
strength of the Casimir interaction. We investigate these phenomena for phase
change materials in torsional oscillators, where the amorphous to crystalline
phase transitions lead to transitions between high and low Casimir force and
torque states respectively, without material compositions. For a conservative
system bifurcation curve and Poincare maps analysis show the absence of chaotic
behavior but with the crystalline phase (high force/torque state) favoring more
unstable behavior and stiction. However, for a non-conservative system chaotic
behavior can occur introducing significant risk for stiction, which is again
more pronounced for the crystalline phase. The latter illustrates the more
general scenario that stronger Casimir forces and torques increase the
possibility for chaotic behavior. The latter is making impossible to predict
whether stiction or stable actuation will occur on a long term basis, and it is
setting limitations in the design of micro/nano devices operating at short
range nanoscale separations.
