Harmonic strain-optical response revealed in the isotropic (liquid) phase of liquid crystals

P Kahl (1) , P Baroni (1) , Laurence Noirez (1)

1 LLB - UMR 12 - Laboratoire Léon Brillouin

A strong optical birefringence is observed when applying a small amplitude oscillatory strain to the liquid phase of a liquid crystal. This unpredicted birefringence is found to oscillate at the same frequency as the driving frequency, with frequencies down to 0.01 Hz. This birefringence is visible up to 15 C above the liquid crystal transition. This opto-dynamic property is interpreted as a result of a coupling of the orientational pretransitional fluctuations existing in the isotropic phase and long range elastic interactions recently identified in liquids. The conversion of the mechanical wave in an optical response is shapeable. Two examples of synchronized periodic signals are shown: the sine and the square waves. The optimization of the signal is analyzed using a Heaviside-step shear test. This optical property is immediately exploitable to design low energy on/off switching materials

Domaines: Matière Molle [cond-mat.soft]

P Kahl, P Baroni, Laurence Noirez. Harmonic strain-optical response revealed in the isotropic (liquid) phase of liquid crystals. Applied Physics Letters, 2015, ⟨10.1063/1.4929321⟩. ⟨hal-01353743⟩