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Advanced Materials That Respond to Light
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
LCE films with azo molecules represent a viable candidate for developing sophisticated micromachines because these materials are capable of producing relatively strong and efficient mechanical actuation that is directly powered by light energy without the need for electrical wires or external batteries. The photo-induced deformations such as expansion/contraction and bending can be used to produce mechanical work and motion with appropriate rotational and linear translational machine components. One of the first examples was demonstrated by Ikeda and his coworkers (Yamada et al. 2008a,b) who translated the photo-induced deformations of a cross-linked azo LCE film into rotational motion by joining two ends of an LCE film to create a continuous moving ring (Mahimwalla et al. 2012). The azo mesogens in this light actuated motor were aligned in the circular direction of the ring. Note that a mesogen is any compound that can exist as a mesophase and is the part of the molecule of a liquid crystal that is responsible for its properties.
Polycondensation Polymers (Step-Reaction Polymerization)
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
The mesogens form the ordered structures necessary to give the overall material anisotropic behavior. A number of different mesogen groupings have been identified. Chains arranged so that the mesogen portions are aligned in one preferred direction with the ordering occurring in a three-dimensional layered fashion compose one group of arrangements called smectic arrangements. Here, the lateral forces between the mesogen portions are relatively higher than the lateral forces between the nonmesogen portions, allowing a combination of segments that permit “flowing” (the passage of nonmesogen portions) and segments that retain contact (mesogen portions) as the material flows imparting a “memory”-type behavior of the material. A number of different “packings” of the mesogens have been identified. The most ordered of the mesogenic groupings is called “smectic B,” which is a hexagonally close-packed structure present in a three-dimensional arrangement. A much less ordered grouping is called the “Smectic A” phase. Here, there is a somewhat random distribution of the mesogens between the layers.
Lipid Nanoparticles Based on Liquid Crystalline Phases
Published in Vladimir Torchilin, Mansoor M Amiji, Handbook of Materials for Nanomedicine, 2011
Liquid crystalline phases represent a very special state of matter. For the first time, they were described in 1888 by Reinitzer who studied the melting behavior of cholesteryl benzoate and noticed that the cholesterol ester first turned into a turbid liquid before it melted into an isotropic liquid upon further heating.1 The term “fließende Kristalle” (“liquid crystals”) was introduced for such materials by Lehmann in 1889.2 As the concept implies, liquid crystals possess properties that are common for isotropic liquids (fluidity on the molecular level, e.g. lack of positional short range order) and those of crystals (orientational long range order). Examples for the structures of well known liquid crystalline phases are presented in Fig. 10.1. As the liquid crystalline state is in between the crystalline and the liquid state, the terms mesogen and mesophases are used for a liquid crystal forming molecule and liquid crystalline phases, respectively.
Imidazole and benzoimidazole derived new ionic liquid crystal compounds: synthesis, characterisation, mesomorphic properties and DFT computations
Published in Liquid Crystals, 2021
AbdulKarim-Talaq Mohammad, Omar S. Khalefa, H. T. Srinivasa, Wissam Ahmed Ameen
In recent years, the interest in the ionic liquid crystals (ILCs) has been increased significantly due to their potential applications [1–4]. ICLs belongs to a class of material that usually referred to as the ionic liquid matters, which exhibits a crystal-like state (Cr) and is referred as ‘mesophase’ or mesomorphic’ state. The materials that exhibit liquid crystalline-like characteristics are referred as ‘mesogens’. In terms of order of the molecules, the state of material which is neither fully aligned state nor exhibits any degree of the order is referred to as ‘liquid crystalline’ [5]. One of the main features of ILCs, that it combines the properties of ionic liquids and liquid crystals where both cations and anions co-exist. The ILCs have a set of interesting characteristics such as significant low vapour pressure. Moreover, it is stable in terms of thermal and chemical standards. In addition to the lack of flammability, ILCs show a significant conductivity value [6,7]. These properties enable ILCs to be a candidate to play the role of solvent in the synthesis and separation within the electrochemistry process [8–10].
Liquid crystal elastomers: an introduction and review of emerging technologies
Published in Liquid Crystals Reviews, 2018
Sabina W. Ula, Nicholas A. Traugutt, Ross H. Volpe, Ravi R. Patel, Kai Yu, Christopher M. Yakacki
Liquid crystals are a class of materials that demonstrate both the order of solid crystals and the fluidity of liquids [22]. While typical liquids, such as water, are a collection of randomly oriented molecules, liquid crystals possess a degree of long-range order. As a result, they possess anisotropic optical, electrical, magnetic, and mechanical properties. Liquid crystals are comprised of rigid molecules called mesogens that have an affinity for self-organization. This tendency toward self-organization is what gives liquid crystals their ability to be ordered while in a fluid-like state. Mesogens have distinct properties that lead them towards liquid crystallinity. For example, mesogens tend to have an anisotropic, elongated shape, which encourages organization. They also have a rigid backbone core with an average of two to three aromatic rings linked together and double bonds along their long axis. Additionally, mesogens have strong dipoles that are easily polarizable [22]. Flexible ends also contribute to liquid crystallinity by allowing mesogens to reorient themselves easily while flowing [23]. The structure of the aromatic rings in the mesogen core strongly influences its temperature, birefringence, and dielectric properties [24].
Effect of alkyloxy substituents on mesomorphic and photophysical properties of star-shaped tristriazolotriazines
Published in Liquid Crystals, 2023
N. V. Zharnikova, O. B. Akopova, A. V. Kazak, K. S. Nikitin, S. D. Usoltsev, N. A. Pigolkina, N. I. Giricheva, A. I. Smirnova, V. A. Kulev, I. V. Kholodkov, Yu. S. Marfin, N. V. Usol’tseva
In recent decades, there has been a rapidly growing interest in materials based on mesogens with a complex molecular structure. Among them are star-shaped organic polyconjugated structures [1–4]. These are promising as materials for electronic, optical, nonlinear optical, and other devices [1,4–11]. A number of star-shaped heterocyclic compounds containing various central fragments with high symmetry, which depending on their molecular structure, can exhibit mesomorphic and fluorescent properties, or in some cases – combination of both [1,6,9,12], have been studied.