Electroclinic effect in the chiral lamellar α phase of a lyotropic liquid crystal

In thermotropic chiral $\mathrm{Sm}\text{\ensuremath{-}}{A}^{*}$ phases, an electric field along the smectic layers breaks the ${D}_{\ensuremath{\infty}}$ symmetry of the $\mathrm{Sm}\text{\ensuremath{-}}{A}^{*}$ phase and induces a tilt of the liquid crystal director. This so-called electroclinic effect (ECE) was first reported by Garoff and Meyer in 1977 and attracted substantial scientific and technological interest due to its linear and submicrosecond electro-optic response [S. Garoff and R. B. Meyer, Phys. Rev. A 19, 338 (1979)]. We now report the observation of an ECE in the pretransitional regime from a lyotropic chiral lamellar ${L}_{\ensuremath{\alpha}}^{*}$ phase into a lyo-$\mathrm{Sm}\text{\ensuremath{-}}{C}^{*}$ phase, the lyotropic analog to the thermotropic $\mathrm{Sm}\text{\ensuremath{-}}{C}^{*}$ phase which was recently discovered by Bruckner et al. [Angew. Chem. Int. Ed. 52, 8934 (2013)]. We further show that the observed ECE has all signatures of its thermotropic counterpart, namely (i) the effect is chiral in nature and vanishes in the racemic ${L}_{\ensuremath{\alpha}}$ phase, (ii) the effect is essentially linear in the sign and magnitude of the electric field, and (iii) the magnitude of the effect diverges hyperbolically as the temperature approaches the critical temperature of the second order tilting transition. Specific deviations between the ECEs in chiral lamellar and chiral smectic phases are related to the internal field screening effect of electric double layers formed by inevitable ionic impurities in lyotropic phases.