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Flow visualization methods and their application in electronic systems
Published in Kaveh Azar, in Electronic Cooling, 2020
If surface maps of temperature are desired, the liquid crystal paint can be applied by brush, airbrush, roller, blade, silk-screen, or dipping. The surface should first be painted black to absorb the light transmitted through the liquid crystals, and thus make the colors visible. Several coats are often necessary, with dry layers of 30 to 50 μm producing good results. Liquid crystals have a usable life of 6 months to a year; exposure to ultraviolet light or abrupt spikes in heat flux can seriously damage their performance.
Inorganic Nanosheets as Soft Materials
Published in Kazuhiro Shikinaka, Functionalization of Molecular Architectures, 2018
Nobuyoshi Miyamoto, Shinya Anraku, Morio Shintate
Before addressing nanosheet LCs, let us begin with general introduction of LCs. Liquid crystals are the materials that possess both the fluidity like liquids and the structure like crystals. An LC is an important member of a soft materials and they have intriguing optical properties arising from the regulated anisotropic structures. The property is switchable by external stimuli such as electric field. Utilizing these features, liquid crystal displays (LCDs) and other optical devices have been produced and have won huge success in industries. LCs are also applicable to produce materials with superior mechanical properties due to alignment of the molecular components: Tough and heat-resistant liquid crystalline polymers such as poly(paraphenyleneterephthalamide), commercially available as Kevlar, are used for bullet-proof jackets and rescue-suits.
Applications
Published in Raj P. Chhabra, CRC Handbook of Thermal Engineering Second Edition, 2017
Joshua D. Ramsey, Ken Bell, Ramesh K. Shah, Bengt Sundén, Zan Wu, Clement Kleinstreuer, Zelin Xu, D. Ian Wilson, Graham T. Polley, John A. Pearce, Kenneth R. Diller, Jonathan W. Valvano, David W. Yarbrough, Moncef Krarti, John Zhai, Jan Kośny, Christian K. Bach, Ian H. Bell, Craig R. Bradshaw, Eckhard A. Groll, Abhinav Krishna, Orkan Kurtulus, Margaret M. Mathison, Bryce Shaffer, Bin Yang, Xinye Zhang, Davide Ziviani, Robert F. Boehm, Anthony F. Mills, Santanu Bandyopadhyay, Shankar Narasimhan, Donald L. Fenton, Raj M. Manglik, Sameer Khandekar, Mario F. Trujillo, Rolf D. Reitz, Milind A. Jog, Prabhat Kumar, K.P. Sandeep, Sanjiv Sinha, Krishna Valavala, Jun Ma, Pradeep Lall, Harold R. Jacobs, Mangesh Chaudhari, Amit Agrawal, Robert J. Moffat, Tadhg O’Donovan, Jungho Kim, S.A. Sherif, Alan T. McDonald, Arturo Pacheco-Vega, Gerardo Diaz, Mihir Sen, K.T. Yang, Martine Rueff, Evelyne Mauret, Pawel Wawrzyniak, Ireneusz Zbicinski, Mariia Sobulska, P.S. Ghoshdastidar, Naveen Tiwari, Rajappa Tadepalli, Raj Ganesh S. Pala, Desh Bandhu Singh, G. N. Tiwari
Liquid crystals can be divided into three groups, depending on their molecular arrangements: (1) smectic, (2) nematic, and (3) cholesteric. Most of the temperature-sensitive liquid crystals now in use are cholesteric: made from esters of cholesterol. Their molecules are arranged in planar layers of molecules with their long axes parallel and in the plane of the layer. The molecules in each layer are rotated with respect to those in its neighboring layers by about 15 min of arc in a continuous, helical pattern along an axis normal to the layers.
New multi-fluorinated benzofuran liquid crystals with large dielectric anisotropy and improved solubility
Published in Liquid Crystals, 2022
Jian Li, Lingchao Mo, Zhaoyi Che, Juanli Li, Minggang Hu, Danyang Wan, Zhongwei An
Liquid crystals have been successfully used in various display devices. Generally, liquid crystal molecules in display devices are composed of benzene ring and cyclohexane, and their structure and properties are well known [1–3]. In developing new high-performance materials, heterocyclic and fused heterocyclic liquid crystals have become a research hotspot because of their variable structures and excellent performances [4–10]. Heterocyclic and fused heterocyclic liquid crystals have also been found in applications beyond display, such as organic light-emitting diodes, field-effect transistors and OPV [11–13]. Compared with the common core unit such as benzene ring or cyclohexane ring, heterocyclic compounds usually have larger polarity, which leads to an increase of dipole moment, dielectric anisotropy and birefringence. Heterocyclic structures such as tetrahydropyran-based liquid crystals with large dielectric anisotropy and low viscosity have been successfully used in display panels [14–17]. Recently, liquid crystals based on benzoxazole and benzimidazole were synthesised, and their mesogenic properties were investigated [18,19–22].
Thermal and optical properties of amphitropic liquid crystals derived from cholesterol and cinnamic acid
Published in Liquid Crystals, 2021
Yi-Hua Hung, Chun-Yen Liu, Wei-Chieh Chen, Jui-Hsiang Liu
Liquid crystals have become ubiquitous in everyday applications ranging from cellphones to high-definition flat-panel displays. The use of liquid crystal displays is widespread in information devices, such as computer monitors, televisions, and mobile displays. This is due to the advantageous thin structure, high image quality, energy-saving ability and integrated manufacturing infrastructure of liquid crystal displays. Among the liquid crystal systems, cholesteric liquid crystals (CLCs) possess many unique optical properties because of their periodic helical structure. This structure serves as a spontaneously formed one-dimensional photonic crystal. Hence, there has been considerable attention paid to the use of CLCs for photonic devices such as dye lasers. One of the advantages of using CLCs for laser devices is the tunability of the liquid crystals. Many types of tunable lasers have been proposed that utilise external influences such as temperature [1–6], electric field [7–9], mechanical strain [10], light irradiation [11–13], and so on.
Investigation of the viscoelastic properties of 4-propoxy-biphenyl-4-carbonitrile
Published in Liquid Crystals, 2019
Pınar Özden, Atilla Eren Mamuk, Nejmettin Avcı
Liquid crystals are of great interest for material science as well as for applied aspects [1–5]. Liquid crystals constitute molecules that organise into an intermediate state of matter between the liquid and the solid crystal during their phase transitions. Liquid crystal compounds show different mesophases, which are classified on the basis of the degree of molecular ordering. The simplest one is the nematic phase. On average, the orientation of individual molecules is parallel (or antiparallel) to a preferred direction (). Nematic liquid crystals are characterised by long-range orientational order and the combination of their fluidity, optical anisotropy and sensitive to electric and/or magnetic fields [1–5]. The nematic liquid crystal materials are applied in various types of optical devices relying upon several properties for instance the elastic constants, optical birefringence, rotational viscosity, dielectric constant, orientational order parameter etc. [1–3].