Mechanism of field-induced unwinding of Sm
                    <i>C</i>
                    * helix and bias field dependencies of dielectric permittivity and effective polarization

“…Since a helical structure is a periodic structure, the azimuthal angle of the average direction of molecules, defined in Fig. 1, in a deformed helical structure under the application of field can be written using the Fourier expansion as [17] ͑z͒ Ϸ qz + 0 sin qz + 1 sin͑2qz͒ +¯, ͑8͒…”

Section: B Single-biaxial-plate Approximationmentioning

confidence: 99%

Conoscopy of chiral smectic liquid crystal cells

2008

Self Cite

View full text Add to dashboard Cite

The conoscopic method for investigating the optical properties of a liquid crystal cell is studied with the aim of determining the effects of the approximations used in the calculation on the results. We confirm that the chiral liquid crystal cell forming a helical structure can be regarded as a single biaxial plate for analyzing the conoscopic image only if the helical pitch is less than several multiples of the wavelength of light. This approximation implies that the square of the refractive index along a direction is averaged over all the layers. An incorrectly chosen value for one of the principal refractive indices to be used in the analysis of the conoscopic data can lead to an incorrect conclusion, especially for the case when the wavelength dispersion of the refractive index is neglected. A thicker cell and a longer wavelength of the incident light can minimize these limitations of the conoscopic method. We propose a novel simulation method to find the molecular distribution in a liquid crystal cell based on the average-refractive-index approximation and the conoscopic data. This is shown to be a fast, more efficient, and useful method for estimating the director distributions.

show abstract

“…The helical unwinding process has shown more closeness to the fixed pitch theoretical model rather than the diverging model [8]. The winding process is found to be slower than the unwinding process as revealed by the studies of asymmetric square pulse [9].…”

Section: Introductionmentioning

confidence: 64%

Collective dielectric processes at the transition temperature of the Sm−C* and Sm−A* phase in a ferroelectric liquid crystal

et al. 2018

View full text Add to dashboard Cite

An anomalous dielectric relaxation process, called the partially unwound helical mode (p-UHM), is a collective dielectric process apart from the well known Goldstone and soft mode process; it is studied in the smectic C^{*} (Sm-C^{*}) phase and at the transition temperature of the Sm-C^{*}-Sm-A^{*} phase in the ferroelectric liquid crystal (FLC) material. To avoid the surface effect, a thick cell of 40 μm thickness was prepared with highly rubbed surfaces of the ITO substrates. It has been observed that the dielectric properties in Sm-C^{*} and at the T_{c} temperature are dominated by the p-UHM process which is dependent on an applied oscillating field in the Sm-C^{*} phase. The probing ac and dc bias field dependences of all these collective dielectric processes have been reported in the Sm-C^{*} and Sm-A^{*} phases of FLC materials.

show abstract

Mechanism of field-induced unwinding of Sm C * helix and bias field dependencies of dielectric permittivity and effective polarization

Cited by 10 publications

References 22 publications

Non-linear behaviour of phason mode with bias field in ferroelectric liquid crystals

Non-linear behaviour of phason mode with bias field in ferroelectric liquid crystals

Conoscopy of chiral smectic liquid crystal cells

Collective dielectric processes at the transition temperature of the Sm−C* and Sm−A* phase in a ferroelectric liquid crystal

Contact Info

Product

Resources

About