Browsing by Subject "Liquid Crystals"

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Open Access
Electrochemical investigations of ion transport in unconventional environments
(2018-07) Uzundal, Can Berk
Ion transport is a critical process that occurs routinely in all electrochemical devices. Especially the new generation batteries extensively utilized in portable devices, Li-Ion batteries, operate simply through Li+ transport. Although, a multitude of similar energy storage and conversion devices are prevalent in both the industry and the electrochemical literature, these devices are not the only technologies that ion transport is critical. Other technologies such as electrochromic devices, organic electronics and next generation display panels also involve electrochemical processes that are inherently dependent on or limited by ion transport. Conventional electrochemical methods enable interrogation of the various interfaces these devices possess however limited information on the behavior of the concentrated-like media investigated in this thesis compared to the well documented behavior of the dilute media, limits their applicability. In this thesis we not only offer investigations on possible esoteric materials that have unique ion transport properties that show emergent behavior in the systems they are employed at through fundamental electrochemical studies but also we outline the development of new electroanalytical tools to better interrogate ion transport in variety of electrochemical systems. The attempts at understanding and explaining the ion transport in various media and to leverage its benefits towards better devices is outlined. Electrochemical noise measurements for Li-Ion batteries is shown as a potential tool for ion transport interrogation, while the ion transport behavior of Liquid Crystals and Ionic Liquids are investigated. A new electroanalytical tool to separate counter ion diffusion from electron transfer is also shown. Finally, an electrochemical method to visualize corrosion that utilizes ion transport is outlined in this thesis.
Open Access
Light-induced pitch transitions in photosensitive cholesteric liquid crystals: Effects of anchoring energy
(American Physical Society, 2014) Orlova, T. N.; Iegorov, R. I.; Kiselev, A. D.
We experimentally study how the cholesteric pitch P depends on the equilibrium pitch P0 in planar liquid crystal (LC) cells with both strong and semistrong anchoring conditions. The cholesteric phase was induced by dissolution in the nematic LC of the right-handed chiral dopant 7-dehydrocholesterol (7-DHC, provitamin D3) which transforms to left-handed tachysterol under the action of uv irradiation at the wavelength of 254 nm. By using the model of photoreaction kinetics we obtain the dependencies of isomer concentrations and, therefore, of the equilibrium pitch on the uv irradiation dose. The cholesteric pitch was measured as a function of irradiation time using the polarimetry method. In this method, the pitch is estimated from the experimental data on the irradiation time dependence of the ellipticity of light transmitted through the LC cells. It is found that the resulting dependence of the twist parameter 2D/P (D is the cell thickness) on the free twisting number parameter 2D/P0 shows jumplike behavior and agrees well with the known theoretical results for the anchoring potential of Rapini-Papoular form. © 2014 American Physical Society.
Open Access
Molten-Salt-Asisted self-Assembly (MASA)-synthesis of mesoporous metal titanate-titania, metal sulfi de-titania, and metal selenide-titania thin films
(Wiley Online Library, 2013) Karakaya, C.; Turker, Y.; Dag, Ö.
New synthetic strategies are needed for the assembly of porous metal titanates and metal chalcogenite-titania thin films for various energy applications. Here, a new synthetic approach is introduced in which two solvents and two surfactants are used. Both surfactants are necessary to accommodate the desired amount of salt species in the hydrophilic domains of the mesophase. The process is called a molten-salt-assisted self-assembly (MASA) because the salt species are in the molten phase and act as a solvent to assemble the ingredients into a mesostructure and they react with titania to form mesoporous metal titanates during the annealing step. The mesoporous metal titanate (meso-Zn2TiO4 and meso-CdTiO3) thin films are reacted under H2S or H2Se gas at room temperature to yield high quality transparent mesoporous metal chalcogenides. The H2Se reaction produces rutile and brookite titania phases together with nanocrystalline metal selenides and H2S reaction of meso-CdTiO3 yields nanocrystalline anatase and CdS in the spatially confined pore walls. Two different metal salts (zinc nitrate hexahydrate and cadmium nitrate tetrahydrate) are tested to demonstrate the generality of the new assembly process. The meso-TiO2-CdSe film shows photoactivity under sunlight.
Open Access
A new, highly conductive, lithium salt/nonionic surfactant, lyotropic liquid-crystalline mesophase and its application
(Wiley-VCH Verlag, 2012) Albayrak, C.; Cihaner, A.; Dag, Ö.
Salty water! Lithium salts (LiCl, LiNO3, and LiClO4) at very high concentrations in water form lyotropic liquid crystalline (LLC) mesophases with a nonionic surfactant (10-lauryl ether) and display high ionic conductivities (10−2–10−4 S cm−1) over a broad temperature range (−10 to 80 °C) with excellent behavior as gel electrolytes in electrochemical applications.