Visualization and characterization of the switching process in dye-doped dual-frequency nematic mixtures

In the intriguing field of active plasmonics, liquid crystals are considered a well-suited materials to be used as an active medium[1]. Recently, dual-frequency nematic liquid crystals (DFNLCs) pave the way for the so-called liquid-crystals plasmonics as a modulators since the material enables the tuning of plasmonic properties and behaves as an active control of the localized surface plasmon modes[1]. One of the most important parameters in DFNLCs, from the application point of view, is the cross-over frequency[2-4] because, at this frequency, the dielectric anisotropy changes sign; which results in a dynamic control of LC switching. In this work, fluorescence confocal polarizing microscopy (FCPM) is employed for mapping the switching as well as analyzing the molecular behavior at the cross-over frequency on respectively two different DFNLCs doped with a dichroic dye. The performed confocal measurements represent a convenient tool for studying the DFNLCs dielectric relaxation process. In detail, two different mixtures have been considered (1832B and 1909C, both doped with the 2679 dye), showing different textures, as well as intensity of the light emission at the fc which in turn agrees with the low cross-over value (respectively, 10 kHz and 15 kHz).