Search results for "Thermotropic crystal"
showing 10 items of 51 documents
A thermotropic liquid crystal elastomer micro-actuator with integrated deformable micro-heater
2014
We present a liquid crystal elastomer (LCE) actuator with large stroke and fast reaction time. LCEs show a large macroscopic shape change when heated above the phase transition (≈120°C). Buried wafer-level fabricated micro-heaters offer optimal thermal reaction times and compact design of the actuators. A relative length change of λ = 1.28 was obtained with 320 mW power consumption. Heating the device from room temperature takes τrise = 19.7 s, cooling below the phase transition temperature from the fully contracted state needs τfall - 5.6s. We verify that the displacement may be accurately controlled by varying electrical input power.
Co-flow microfluidic synthesis of liquid crystalline actuating Janus particles
2016
A microfluidic synthesis of stimuli-responsive actuating Janus particles composed of a liquid crystalline elastomer (LCE) and a polymeric hydrogel is reported. , In this article the microfluidic synthesis and characterization of micrometer sized actuating Janus particles containing a liquid crystalline elastomer (LCE) is presented. On one side these Janus particles consist of a hydrophobic liquid crystalline part, featuring strong shape changes during the thermotropic phase transition, whereas the other side contains a hydrophilic polyacrylamide network. The synthesis is based upon the dispersion of two immiscible monomer mixtures in a continuously flowing silicone oil, using two glass capi…
Alkoxy substituted (E,E)-3,6-bis(styryl)pyridazine—a photosensitive mesogen for liquid crystals
2008
Abstract (E,E)-3,6-Bis(styryl)pyridazines (3a–t) bearing 2, 4 or 6 alkoxy chains were prepared by applying the Siegrist reaction of 3,6-dimethylpyridazine (13) and the corresponding azomethines 10a–t. The transversal dipole moment of these calamitic compounds effects an extremely high tendency for self-organization in thermotropic LC phases (N, SA, SB, SC, SE, SI/F, and Cub). The conjugated core structure represents moreover a chromophore with a high photosensitivity for (E,E)⇄(E,Z) isomerization reactions: this property makes the compounds interesting for optical imaging and switching techniques.
Thermotropic polyesters with mesogenic groups based on substituted hydroquinone units and highly flexible siloxan spacer in the main chain
1984
New thermotropic Polyesters having mesogenic groups based on substituted hydroquinone units and highly flexible oligosiloxan spacer in the main chain, are synthesized and characterized. The mesophase formed at low temperature are studied by differential scanning calorimetry (DSC) and polarized light microscopy. The liquid crystalline behaviour of these polyesters, particulary their transition temperatures and the mesophase width could be explained on the basis of their structural features.
Electric Field Effects and Miscibility in Cybotactic Micellar Nematic and Ordinary Nematic Polyesters
1984
Abstract Miscibility behavior and electro-optical instabilities are reported for two main chain thermotropic nematic polyesters formed by regularly alternating a disubstituted azoxy-benzene mesogen with a flexible spacer containing either 7 or 10 methylene units (HEPTA-9 and DDA-9, respectively). Polymer HEPTA-9 displays an ordinary nematic organization and polymer DDA-9 forms a cybotactic nematic phase. Both are totally miscible with each other, and with PAA, in the nematic phase. Williams domains and dynamic scattering modes are observed in both cases.
Electro-Hydrodynamic Instabilities in Main Chain Thermotropic Liquid Crystalline Polyesters
1984
Abstract We have investigated the response behavior of the thermotropic nematic polymer, DDA-9, in an electric field. DDA-9 is composed of regularly alternating moieties and flexible spacers. At a critical threshold voltage, dependent on molar mass, these polymers show the onset of instability. The appearance of a (non-fluctuating) striped pattern (Williams domains) is shown and the time of formation and relaxation of these patterns is investigated as a function of applied Voltage.
Monolayers of rod-shaped and disc-shaped liquid crystalline compounds at the air-water interface
2008
Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data a…
Characterization of blends of polypropylene with a semirigid liquid-crystal copolyester
1991
Abstract Blends with a liquid-crystal polymers (LCP) as one component show, in general, very interesting properties. Reduction of shear viscosity and improvement of mechanical properties are very remarkable. High melting temperatures and high costs of the LCP limit the use of these blends. A new class of thermotropic LCPs with flexible spaces, with relatively low melting temperatures, can overcome the first problem. In this work, rheological and mechanical properties of blends of polypropylene with low contents of this LCP are presented. Torque during extrusion and viscosity decrease with LCP content. Elastic modulus is remarkably increased when the LCP phase is oriented.
Photochemistry of 3,6-bis(styryl)pyridazines in solution and in neat liquid crystalline phase—optical switching and imaging techniques
2008
Abstract 3,6-Bis(styryl)pyridazines 1a – f with 2–6 alkoxy groups show on irradiation in solution a stereoisomerization which leads to a photostationary state of ( E , E )- and ( E , Z )-isomer. Sensitizing and quenching experiments reveal that the ( E , E )→( E , Z ) route is a pure triplet process, whereas the ( E , Z )→( E , E ) route can have a minor singlet by-reaction. Hexyloxy or dodecyloxy chains on the terminal benzene rings convey the ( E , E )-isomers of compounds 1a , b , d – f thermotropic liquid crystalline properties. In particular S A , S C , and S F/I phases were studied with regard to their photochemical behavior. Depending on the system, photodegradation of the smectic ph…
Thermotropic properties and molecular packing of discotic tristriazolotriazines with rigid substituents.
2014
Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstru…