Search results for "Liquid Crystal"
showing 10 items of 492 documents
Microfluidic Synthesis of Actuating Microparticles from a Thiol-Ene Based Main-Chain Liquid Crystalline Elastomer.
2016
In this article the microfluidic synthesis of strongly actuating particles on the basis of a liquid crystalline main-chain elastomer is presented. The synthesis is carried out in a capillary-based co-flow microreactor by photo-initiated thiol-ene click chemistry of a liquid crystalline monomer mixture. These microparticles exhibit a deformation from a spherical to a rod-like shape during the thermal-initiated phase transition of the liquid crystalline elastomer (LCE) at which the particles’ aspect ratio is almost doubled. Repeated contraction cycles confirm the complete reversibility of the particles’ actuation properties. The transition temperature of the LCE, the temperature range of the …
Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric Fields.
2010
ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low T(g)-matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly …
Dimesogenic ferroelectric polysiloxanes
1994
Dimesogenic polysiloxane [Si(Me) 2 O] m [Si(Me)(R)O] n (R= (CH 2 ) 3 CH(COO[CH 2 ] 11 OPhPhOCOPh(NO 2 )OC * H(Me)C 6 H 13 ) 2 are synthesized by hydrosilylation. The phase transition temperaturs are determined and the ferroelectric properties are investigated
Monodomain Liquid Crystal Main Chain Elastomers by Photocrosslinking
2007
A new synthetic strategy for the preparation of macroscopically oriented smectic main chain liquid crystal elastomers (MC-LCE) by the photocrosslinking of laterally functionalized polyesters is presented. X-ray measurements proved the formation of the monodomain and allowed a quantitative determination of the order parameter. The thermo-actuation of our material at the phase transition from the liquid-crystalline to the isotropic phase was demonstrated by temperature dependent measurements of the sample length, showing a fully reversible shape change of � 40%. Mechanical measurements showed that the sample can be stretched by up to 60% along the smectic layer normal without any reorientatio…
Nanosized shape-changing colloids from liquid crystalline elastomers.
2010
A method to prepare shape-changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main-chain polyester and subsequently crosslinked into a nanometer-sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature-dependent transmission electron microscopy. The phase transition-induced shape change leads to strongly shape anisotropic nanosized elastomer particles.
Microactuators from a main-chain liquid crystalline elastomer via thiol–ene “click” chemistry
2013
Recently it has been described that liquid crystalline elastomer (LCE) particles of the side-chain type can be prepared in microfluidic devices. Here we present the preparation of micrometer-sized LCE particles of the main-chain type by thiol–ene chemistry. The LCE particles are UV-crosslinked via thiol–ene click chemistry of the nematic monomer, carrying terminal thiol and ene groups, and non-mesogenic tetrathiol and tetraene crosslinkers. The preparation of the LCE particles with a microfluidic device by a continuous “on the fly” technique allows their fast processing with an irradiation time of less than 2 seconds. The resulting particles undergo a temperature-driven volume change up to …
Molecular dynamics in liquid crystalline N-acylated oligoethylenimines as studied by broadband dielectric spectroscopy
1996
The molecular dynamics and the charge transport in six liquid crystalline N-acylated oligoethylenimines were investigated by dielectric spectroscopy. The dielectric spectra in the temperature range from 125 K up to 400 K and in the frequency range between 10 -2 Hz and 10 7 Hz could be described by a conductivity contribution and three relaxation processes. The molecular assignment of the α-process is a relaxation of the rigid benzamide unit. Its mean relaxation time is influenced by the length of the alkoxy side chains, the spacer length (ethylene or propylene groups) and the neighboring repeating units. In the columnar mesophase this process is cooperative due to sterical hindrance. A norm…
Spin crossover in metallomesogens
2009
Abstract In this review article are illustrated the strategies developed in order to achieve interplay/synergy between spin transition and liquid crystal transition. The synthesised Fe(II) metallomesogens exhibit different types of interplay between both phase transitions. A classification according to the analysis of the magnetic and structural data has led to the separation of three types of interplay, namely: type i systems with coupled phase transitions, subdivided into three groups a , b and c (in a the structural changes associated with the Cr ↔ LC drive the spin transition while in b these structural changes influence the spin state of the metallic centers but they are not the drivin…
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.
Extended liquid-crystalline oligofluorenes with photo- and electroluminescence
2010
In this paper we report the synthesis and characterization of a series of low-molecular weight light-emitting molecules based on short oligofluorene cores, from one to three 9,9-dioctylfluorene units, elongated at the 2- and 7-positions by means of promesogenic units. The effect of this structural modification on the mesomorphic properties, as well as on the optical and electrochemical properties, is studied. The possibility of using these molecules as emitters in light-emitting diodes (LEDs) and polarized photoluminescent layers has been explored.