Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Device

Anisotropy of the electro-optic Kerr effect in polymer-stabilized blue phases

“…When a field is applied parallel to the helical axis of a helical molecular arrangement, the liquid crystal molecules do not move until a threshold is reached, and reorient abruptly once the threshold is reached, in a manner similar to the Frederiks transition in nematic liquid crystals [25]. The threshold is related to the bend elastic constant K 33 , helical pitch p 0 , dielectric anisotropy a of the liquid crystal, and dielectric constant of vacuum 0 through the expression E c = 2π [9,23]. This threshold is significantly higher than the region where the ideal quadratic relationship between the induced birefringence and the applied field is observed in experiment; the contribution of this mode to the field-induced birefringence is, therefore, assumed to be zero in this analysis.…”

“…The two peaks yield lattice constants of 245 and 254 nm, according to the equation a = λ hkl √ h 2 + k 2 + l 2 /2n, where λ hkl is the Bragg wavelength and h,k,l are the miller indices of the lattice plane. n was assumed to be 1.584 and 1.623 for the (110)-and (200)-oriented samples, respectively, by referring to measured refractive index data of the host nematic liquid crystal [23]. Figure 3 shows the Kossel patterns of the two samples.…”

Bragg reflection band width and optical rotatory dispersion of cubic blue-phase liquid crystals

“…The most obvious feature of the phase transition is the discontinuous shift in the peak reflection wavelength (λ peak ) from approximately 540.2 to 479.4 nm. Using the refractive index of the host nematic LC available from literature [31] (Table I) and the relationship…”

“…Therefore, we also infer that the discontinuous shift in wavelength is due to a discrete change in the number of lattices existing in the cell. The reflection peak shift corresponds to a change in pitch from 240.6 to 246.7 nm using average refractive indices 1.5878 and 1.5862 at the two wavelengths, respectively [31]. Dividing the cell-gap (8.85 μm) by the pitch length yields approximately 26 and 25.5 as the number of periods (N ), implying that similar to the cholesteric helix, the BP I lattice also winds or unwinds in half-integer steps.…”