Search results for "Mesophase"

Mesophase behaviour of 2,5-dibenzoyloxy-p-benzoquinone derivatives and tetrahydrobenzene tetraesters

1991

Abstract The synthesis of 2,5-dibenzoyloxy-p-benzoquinone derivatives, their products after reduction and tetraesters from tetrahydroxybenzene prepared from those products is described. Their phase behaviour was investigated by differential scanning calorimetry and polarizing microscopy and is discussed in terms of their detailed structure.

Tris(5-aryl-1,3,4-oxadiazolyl)benzotrithiophenes : discotic liquid crystals with enormous mesophase ranges

2021

Synthesis and Characterization of a New Class of Fully Aromatic Liquid Crystal Polymers

1999

Abstract A new fully aromatic LCP, obtained by polycondensation of N-(4-carboxyphenyl) trimellitimide and tert-butyl hydroquinone (FAPT), was previously described. The polymer shows very interesting physical and mechanical properties but a very high glass transition temperature which does not allow a good processability. In order to overcome this problem, a new class of LCPs, obtained by partial substitution of the dicarboxylic moiety with isophthalic acid, is described. The new thermoplastic materials were characterized from the physicochemical and mechanical point of view. All the polymers obtained with an isophthalic acid (FA-IA) content varying from 10 to 40% of the substituted moiety s…

Free-standing smectic LC elastomer films

2001

ABSTRACTWe probe the mesophase transitions and layer structures in thin ordered smectic liquid crystalline elastomer films by means of x-ray diffraction and optical microscopy. Oriented elastomer films of submicrometer thickness are produced by crosslinking freely suspended smectic polymer films. After crosslinking, the mesomorphism is similar to that of the precursor polymer. Smectic layers align parallel to the film plane. The layer spacing increases with temperature in the SmC* phase while it decays above the SmC*-SmA transition.

Synthesis of New Functionalized Discotic Liquid Crystals for Photoconducting Aplications

1996

Abstract The columnar structure of discotic liquid crystals has been shown to be well suited for electronic transport parallel to the columnar axis. To tailor the processibility and mesophase behavior of such materials, several hydroxytriphenylene derivatives were synthesized. These hydroxytriphenylenes can be converted into oligomers, networks or polymers. Further, they can be reduced to arenes which posses reactive sites for classical aromatic substitutions. A number of mixed tail triphenylene derivatives and fluorescent, low symmetry triphenylene discotic liquid crystals were synthesized and characterized.

Structural variations of liquid crystalline polymers with phasmidic-type mesogens

1989

Abstract The fixation of phasmidic-type mesogens through spacer groups to polysiloxane backbones provided a method of obtaining liquid crystalline polymers with phasmidic mesogens as side groups. The polymer 6b showed a bilayer structure in the mesophase range. The tendency to form liquid-crystalline phase depends on the number and the length of alkoxy substituents.

Synthesis and thermal behavior of Janus dendrimers, part 2

2010

Abstract The thermal properties of twelve Janus-type dendrimers up to the second generation were evaluated by termogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-bis-dodecyloxybenzoic acid, 3,5-bis-dodecyloxybenzoic acid or 3,4,5-tris-dodecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The thermal stability of the compounds was evaluated by TGA, displaying onset decomposition temperatures ( T d ) at around 250 °C. DSC measurements upon heating and cooling confirmed that OH terminated Janus dendrimers featuring large polarity difference in opposite …

Phase identification of triphenylene-based discotic monomer and its main chain polymers

1998

Abstract A monomer, 2,3,6,7,10,11-hexakispentyloxy triphenylene (HPT) possesses a triphenylene core as a discotic mesogen. Polymers containing this discotic mesogen have been studied using wide-angle X-ray and electron diffraction. HPT is known to show a discotic liquid crystal phase, noted as Dho (h for hexagonal bidimensional lattice, o for ordered molecular spacing in each column). In this paper, however, HPT liquid crystalline phases, heated up from the crystalline state and cooled down from the isotropic state, were characterized in the diameter dimensions. In addition. the diameters of the columns are close to a parameter of two separate crystals. A core orientation was, therefore, pr…

Rheological behavior of a semirigid liquid crystal polymer

1993

The rheological behavior of liquid crystal polymers is still far from completely clarified from both experimental and theoretical points of view. In this paper, the shear flow and the non-isothermal elongation flow behavior of a semi-rigid liquid crystal copolyester is discussed. The viscosity strongly decreases when the test temperature is increased above the crystal-nematic transition temperature; below this temperature the viscosity is very high. The thermal history strongly affects the shear viscosity. The elongational flow behavior depends also on temperature. Above the crystal-nematic transition temperature and the mesophase is easily spinnable, whereas below this temperature, the spi…

Preparation of Soft Microactuators in a Continuous Flow Synthesis Using a Liquid-Crystalline Polymer Crosslinker

2012

We present the synthesis of a polymeric liquid crystalline (LC) crosslinker and its usage in the preparation of soft microactuators. The microactuators, composed of thermoresponsive liquid crystalline elastomers (LCE), are fabricated in a microfl uidic device in a continuous “on the fl y” process. The LC polymer crosslinker is miscible with the LC monomer and provides for a rapid polymerization and crosslinking. Most importantly, it promotes an enantiotropic mesophase of the mobile monomer phase, which is not provided by conventional nonmesogenic crosslinkers. This allows an isothermal handling inside the microfl uidic setup. Temperature-driven shape changes up to 65% could be achieved by j…