Liquid Crystals :Experimental Study of Physical Properties and Phase Transitions

Kumar, Satyendra

doi:10.3390/61201055

Cited by 115 publications

(129 citation statements)

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“…This conclusion was also supported by the experimentally observed correlation between the measured conductivity of liquid crystals and the concentration of free inorganic ions, in line with the expression Equation (1) [8]. It should be noted that some liquid crystals can become chemically unstable, and the probability of this process is higher under harsh conditions such as elevated temperatures, high electric fields, and an exposure to the strong UV light [2,11,81,82]. All these factors create additional sources of ions of organic origin [82].…”

Section: Classical Methods Of Liquid Crystal Purificationsupporting

confidence: 69%

“…It should be noted that some liquid crystals can become chemically unstable, and the probability of this process is higher under harsh conditions such as elevated temperatures, high electric fields, and an exposure to the strong UV light [2,11,81,82]. All these factors create additional sources of ions of organic origin [82]. However, recent advances in the chemical synthesis of novel liquid crystal materials exhibiting improved chemical stability reduced the probability of such events significantly [83][84][85][86].…”

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

“…Liquid crystals can get contaminated with ionic impurities during the process of chemical synthesis. The level of this contamination can be reduced by working with highly purified reagents at the stage of chemical synthesis, and by using classical methods such as multiple recrystallization, extraction, vacuum distillation, vacuum sublimation, zone refining, chromatography, ion exchange and other chemical techniques [82,87,88]. Physical-chemical methods used to purify liquid crystals can be applied multiple times to reach a certain level of the chemical purity.…”

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

“…Physical-chemical methods used to purify liquid crystals can be applied multiple times to reach a certain level of the chemical purity. The chemical purity of synthesized liquid crystal materials can be checked with the help of high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and electronic paramagnetic resonance (EPR), and differential scanning calorimetry (DSC), to name a few [82,[89][90][91]. However, if not specifically tailored, these methods do not provide information on the ionic content of liquid crystals [82].…”

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

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Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

2015

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Abstract:The presence of ions in liquid crystals is one of the grand challenges that hinder the application of liquid crystals in various devices, which include advanced 3-D and flexible displays, tunable lenses, etc. Not only do they compromise the overall performance of liquid crystal devices, ions are also responsible for slow response, image sticking, and image flickering, as well as many other negative effects. Even highly purified liquid crystal materials can get contaminated during the manufacturing process. Moreover, liquid crystals can degrade over time and generate ions. All of these factors raise the bar for their quality control, and increase the manufacturing cost of liquid crystal products. A decade of dedicated research has paved the way to the solution of the issues mentioned above through merging liquid crystals and nanotechnology. Nano-objects (guests) that are embedded in the liquid crystals (hosts) can trap ions, which decreases the ion concentration and electrical conductivity, and improves the electro-optical response of the host. In this paper, we (i) review recently published works reporting the effects of nanoscale dopants on the electrical properties of liquid crystals; and (ii) identify the most promising inorganic and organic nanomaterials suitable to capture ions in liquid crystals.

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Section: Classical Methods Of Liquid Crystal Purificationsupporting

confidence: 69%

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

Section: Classical Methods Of Liquid Crystal Purificationmentioning

confidence: 99%

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Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

2015

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“…In order to understand the phase transitions and molecular orientational order in liquid crystals, various types of study, including nuclear magnetic resonance (NMR) and electrical field effect, have been conducted. Thermotropic liquid crystals can have nematic, smectic and cholesteric phases at different temperatures [1][2][3][4]. In contrast to the nematic phase that possesses orientational order without any positional order, the smectic phase possesses both minimal and orientational orders.…”

Section: Introductionmentioning

confidence: 99%

¹H Nuclear Magnetic Resonance of a Ferroelectric Liquid Crystalline System

K.¹,

Lee²,

Oh³

et al. 2010

Journal of Magnetics

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We used 1 H nuclear magnetic resonance (NMR) to study the phase transitions and molecular dynamics in a characteristic ferroelectric liquid crystal with a carbon number n = 7, S-2-methylbutyl 4-n-heptyloxybiphenyl-4'-carboxylate (C7). The results were compared with those of our recent work on S-2-methylbutyl 4-n-octanoyloxybiphenyl-4'-carboxylate (C8), with a carbon number n = 8. While the recrystallization and isotropic phase transitions exhibited a first-order nature in the 1 H NMR spin-lattice and spin-spin relaxation measurements, a second-order nature was shown at the Sm-A -Sm-C * liquid crystalline phase transition. A soft-mode anomaly arising from the tilt angle amplitude fluctuation of the director, of which only a hint had been noticed in the C8 system, was manifested in the C7 system at this transition.

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NMRSpectroscopy in Liquid Crystalline and Ordered Phases

Dong

2012

Encyclopedia of Analytical Chemistry

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Applications of nuclear magnetic resonance (NMR) spectroscopy as an analytical tool in liquid crystals (LCs) are surveyed. Proton, deuteron, carbon‐13, and nitrogen‐14 are commonly used as probes in solid‐state NMR of condensed phases. Their usages in LCs are discussed in some details. Complex mathematical expressions needed to interpret NMR observables (both equilibrium and dynamic properties) are kept to a minimum, and the reader can refer to original articles and books for details. As it is impossible to provide an exhaustive coverage of the literature, selective examples are chosen to highlight areas of recent interests in the study of liquid‐crystal materials, particularly thermotropics, in terms of their physics and chemistry. Orientational/positional order parameters are readily obtained in ordered liquid‐crystal phases by means of NMR. They can serve as characteristic signatures of the studied mesophases. Liquid‐crystal ordering depends on intermolecular potentials among neighboring molecules. Solutes dissolved in LC solvents are good candidates to reveal different ordering mechanisms. Nonzero spin interactions are used to determine molecular structure of large and small molecules, and/or their conformation statistics. Nuclear spin relaxation times are readily measured by means of different NMR pulse techniques and can be powerful for revealing dynamic properties of mesogens with increasing structural complexity.

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Liquid Crystals :Experimental Study of Physical Properties and Phase Transitions

Abstract: n/

Cited by 115 publications

References 0 publications

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

¹H Nuclear Magnetic Resonance of a Ferroelectric Liquid Crystalline System

NMRSpectroscopy in Liquid Crystalline and Ordered Phases

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Liquid Crystals :Experimental Study of Physical Properties and Phase Transitions

Abstract: n/

Cited by 115 publications

References 0 publications

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

1H Nuclear Magnetic Resonance of a Ferroelectric Liquid Crystalline System

NMRSpectroscopy in Liquid Crystalline and Ordered Phases

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¹H Nuclear Magnetic Resonance of a Ferroelectric Liquid Crystalline System