Critical voltages and blocking stresses in nematic gels : dynamics of director rotation for nematic elastomers under electro-mechanical loads.

We present a model of the dynamics of director rotation in nematic gels under combined electro-mechanical loading. Focusing on a model specimen, we describe the critical voltages that must be exceeded to achieve director reorientation, and the blocking stresses that prevent alignment of the nematic director with the applied electric field. The corresponding phase diagram shows that the dynamic thresholds defined above are different from those predicted on the sole basis of energetics. Multistep loading programs are used to explore the energy landscape of our model specimen, showing the existence of multiple local minima under the same voltage and applied stress. This leads us to conclude that hysteresis should be expected in the electro-mechanical response of nematic gels.