Note on «new electromechanical effect in chiral smectic C liquid crystals»

We show how the recent experimental results concerning an electromechanical coupling in smectic C * can be obtained from the macroscopic dynamic equations derived by the authors. We point out that the coupling observed is a reversible dynamic cross coupling between the change in the polarization inside the layers and velocity gradients. This type of reversible cross coupling is unique to systems which possess a pseudoscalar quantity (e.g. a helix) and does not exist in nonchiral smectic C Le couplage electromecanique observe est un couplage dynamique reversible entre les variations de polarisation dans les couches et les gradients de vitesse