Dynamics of blue-phase selective reflections in an electric field

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Abstract
Electric fields can cause structural changes of the blue phases (BP) that appears in chiral liquid crystals. In BP I and BP II, electrostrictive effects cause a shift of the Bragg reflection wavelengths with little intensity change. In BP III, for systems with negative dielectric anisotropy, there is a strong increase in the selective reflection intensity in addition to electrostriction. We have measured the time response of these effects to on-off modulated electric fields for a material with negative dielectric anisotropy. We observe that the response times for BP I and BP II electrostriction are ∼10 s, while the response times for BP III peak intensification are ∼10 ms. We discuss the results in terms of models for these mechanisms and the as yet unknown structure of BP III.