27 research outputs found
The quadratic electro-optical effect in ferroelectric liquid crystal helical nanostructures: role of the driving voltage shape
No full textRecently it was shown that in deformed helix ferroelectric (DHF) structure, the electrically controlled birefringence of chiral smectic C* phase with subwavelength helix pitch ( is known to be proportional to the square of the electric field E) depends on the cell thickness and on the frequency of applied voltage, given as a Step function of the time. The purpose of the present work is to investigate whether this quadratic effect depends also on the voltage function shape, comparing the electrically controlled birefringence and the Kerr constant in DHF cells with different thickness, driven by STAIR and Step voltage functions
Development of ferroelectric liquid crystals with low birefringence
No full textWe propose an approach for development of ferroelectric liquid crystals (FLC) with low birefringence Δn. Two basic principles have been used to get lowering of Δn: selection of molecules with short chains of conjugation as components for achiral matrix and averaging of local refractive indices by FLC helical structure. FLC mixtures with low birefringence (0.07 < Δn < 0.10 at wavelength 589.3 nm of sodium line) were elaborated and investigated. They consist of an achiral matrix including both nematic and smectic liquid crystal components and of phenylpyrimidine derivatives as chiral dopants. The materials developed can be used for all basic electro-optical FLC modes such as surface stabilised FLC (SSFLC), deformed helix ferroelectrics (DHF) and electrically suppressed helix (ESH). The mixtures developed allow to reduce the FLC cells chromatic retardance variation due to the weaker birefringence dispersion as compared with the known FLC materials to date
The quadratic electro-optical effect in ferroelectric liquid crystal helical nanostructures: role of cell thickness and voltage frequency
No full textIt was reliably proved in recent years both theoretically and experimentally that the electrically controlled birefringence ΔnE of chiral smectic C* phase with subwavelength helix pitch is proportional to the square of the electric field E. The goal of the present work is to investigate the restrictions of the quadratic effect imposed by the thickness of the smectic C* layer between two solid substrates, and by the frequency of applied voltage. It is shown that these restrictions are mainly associated with the dielectric dispersion of the Goldstone mode under various boundary conditions
X-ray investigation of new isomeric oxadiazoles
No full textAn x-ray investigation has been performed on five new 2,5- disubstituted 1,2,4-oxadiazoles with reversed structures containing 4-amylbiphenyl-, trans-4-amylcyclohexylphenyl- and 2-halophenyl- as substituents. The aim was to confirm the data about the phase sequence, obtained via polarizing microscopy and differential scanning calorimetry, and to measure the structural parameters. Through x-ray diffraction technique, all substances showed only the nematic mesophase. Moreover, it was proved that some enthalphy variations previously attributed to crystal-crystal transitions are in fact due either to the rearrangement of the lattice or to the coalescence of the grains. However, for some substances, a second crystalline from c' appeared at the melting point, on cooling from the isotropic phase. C' turned out to be different from the starting form C1 of the sample, which had no thermal cycle before
Phase modulation and ellipticity of the light transmitted through a smectic C* layer with short helix pitch
No full textDevelopment of personal biodosimeter of UV radiation based on vitamin D photosynthesis in nematic liquid crystal matrix
No full textA new approach to the problem of personal UV biodosimeter is described. Nematic liquid crystal (LC-805) is converted into induced cholesteric phase using photosensitive chiral dopant of steroid biomolecules (7-dehydrocholesterol (provitamin D3) or 7-DHC-benzoate). Significant changes in optical characteristics of the LC films depending on the duration of UV exposure are observed as a result of UV initiated photoisomerizations that change helical twisting power of dopant molecules.We would like to express our gratitude to Dr. Sofia Torgova (SSC of Russian Federation «NIOPIK») for helpful advice and generous gift of LC-805, and to Dr. Wolfgang Reischl (University of Vienna) for his help with synthesis of 7-dehydrocholesterol-Benzoate
Development of personal biodosimeter of UV radiation based on vitamin D photosynthesis in nematic liquid crystal matrix
No full textA new approach to the problem of personal UV biodosimeter is described. Nematic liquid crystal (LC-805) is converted into induced cholesteric phase using photosensitive chiral dopant of steroid biomolecules (7-dehydrocholesterol (provitamin D3) or 7-DHC-benzoate). Significant changes in optical characteristics of the LC films depending on the duration of UV exposure are observed as a result of UV initiated photoisomerizations that change helical twisting power of dopant molecules.We would like to express our gratitude to Dr. Sofia Torgova (SSC of Russian Federation «NIOPIK») for helpful advice and generous gift of LC-805, and to Dr. Wolfgang Reischl (University of Vienna) for his help with synthesis of 7-dehydrocholesterol-Benzoate
Development of personal biodosimeter of UV radiation based on vitamin D photosynthesis in nematic liquid crystal matrix
No full textA new approach to the problem of personal UV biodosimeter is described. Nematic liquid crystal (LC-805) is converted into induced cholesteric phase using photosensitive chiral dopant of steroid biomolecules (7-dehydrocholesterol (provitamin D3) or 7-DHC-benzoate). Significant changes in optical characteristics of the LC films depending on the duration of UV exposure are observed as a result of UV initiated photoisomerizations that change helical twisting power of dopant molecules.We would like to express our gratitude to Dr. Sofia Torgova (SSC of Russian Federation «NIOPIK») for helpful advice and generous gift of LC-805, and to Dr. Wolfgang Reischl (University of Vienna) for his help with synthesis of 7-dehydrocholesterol-Benzoate
