Search results for "liquid crystal"
showing 10 items of 492 documents
Ordering and mobility of ferroelectric liquid crystal dimer as studied by FT-IR spectroscopy with 2D-IR correlation analysis
1997
Both a conservative rapid-scan FT-IR technique and a novel step-scan FT-IR technique with 2D correlation analysis were used to study the orientation and the mobility ofa ferroelectric liquid crystal dimer during switching under an electric field. The detailed mutual arrangements of different molecular segments (mesogen, poly(methylene) chain, polysiloxane chain) in a smectic C* phase were derived from the static spectra. It was shown that the long mesogen axis, the average poly(methylene) and the average polysiloxane chain axes do not coincide with each other. The hindered rotation of the carbonyl group is confirmed. Time-resolved FT-IR technique was used to follow the segmental motion with…
Manipulation of the ferroelectricity in LC polymers via photomechanical isomerization of azobenzene moieties
1996
We report the synthesis and characterization of a new ferroelectric liquid crystalline side chain copolymer containing photoisomerizable chromophores and non-photoisomerizable mesogenic units. On illumination with UV-light a suppression of the polar order is obtained as indicated by a substantial drop of the spontaneous polarization (Ps) compared to the dark state. We interpret this as the phase order being disrupted by the cis-isomer of the chromophore. After illumination with VIS-light only the major part of Ps is restored. The photochemical cis-trans back-isomerization (restoration of the phase) leads to a different stationary state than the dark state of the material. The thermal reisom…
Ferroelectric liquid crystalline polysiloxanes designed for high second-order nonlinear susceptibilities
1994
Ferroelectric liquid crystalline (FLC) copolysiloxanes containing suitable comonomers («NLO-chromophores») for second harmonic generation (SHG) have been prepared. Their important feature is a donor-acceptor x-system sited perpendicular to the long axis of the side-group moieties in order to adopt the polar ordering of the ferroelectric LC phase. The influcences of the mesogen structure and of the content of NLO-chromophores on the liquid crystalline and ferroelectric properties are studied. The desired chiral smectic C * phase is retained up to 30 mol-% of chromophore. Also, first measurements of second harmonic generation have been performed
Synthesis of PP-LCP graft copolymers and their compatibilizing activity for PP/LCP blends
1998
The aim of this work was the synthesis of new graft copolymers consisting of polypropylene (PP) backbones and liquid crystalline polymer (LCP) branches, to be used as compatibilizing agents for PP/LCP blends. The PP-g-LCP copolymers have been prepared by polycondensation of the monomers of a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2), that is, sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the mole ratio of 1 : 1 : 2, carried out in the presence of appropriate amounts of a commercial acrylic-acid-functionalized polypropylene (PPAA). The polycondensation products, referred to as COPP50 and COPP70, having a calculated PPAA concentration of 50 and…
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.
Time–temperature correspondence prediction of stress relaxation of polymeric materials from a minimum of data
2002
Abstract We have determined the stress relaxation of a longitudinal polymer liquid crystal (PLC), polypropylene and their blends containing 10 and 20% of the PLC at the constant strain of 0.5%. The results for nine temperature levels in the range between 20 and 100 °C were used to create master curves for T ref =20 ° C . The temperature shift factors aT were calculated using a general formula derived by one of us and based on free volume vf and the chain relaxation capability model. The predicted values agree with the experimental ones for all materials studied within limits of the experimental accuracy. Moreover, the relation between the shift factor aT and the reduced volume ṽ has been us…
Effect of the Orientation on the Properties of Compatibilized Polypropylene/Liquid Crystal Polymer Blends
1999
Abstract Blends of polypropylene and a semirigid liquid crystal polymer have been compatibilized with an acrylic acid modified polypropylene and with an ad-hoc synthesized graft copolymer made from polypropylene and from the monomers of the liquid crystal polymer. The two compatibilizers improve the adhesion and the mechanical properties of the two incompatible phases. The two compatibilizers give about the same results. The effect of the compatibilization improve also the orientation of the liquid crystalline polymer particles and the mechanical properties.
ChemInform Abstract: Monolayers and Langmuir-Blodgett Multilayers of Discotic Liquid Crystals?
1990
The field of monolayer and multilayer films of discotic LCs is at its very beginning. The scope and limitations of this preparation method have not yet been explored, and little is known about the structures obtainable. However, the potential access to extraordinary, ordered thin films is fascinating, and will stimulate research in the future.
Conformational Changes of a Single Semiflexible Macromolecule Near an Adsorbing Surface: A Monte Carlo Simulation
2009
The properties of a single semiflexible chain tethered to a planar surface with a long-ranged attractive potential are studied by means of Monte Carlo simulations. We employ the bond fluctuation lattice model and the Wang-Landau sampling technique. We present the diagram of states for semiflexible chains consisting of N = 64 and 128 monomer units as a function of temperature T and strength of the adsorption potential, epsilon(w), and also compare this with the diagram of states for flexible chains of these two lengths. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil, and quasi-two-dimensional solid globule with nematic bond ord…
Ferrochirality: a simple theoretical model of interacting, dynamically invertible, helical polymers, 2. Molecular field approach: supports and the de…
1995
Using a molecular field approach, the effect of interaction between reversibly invertible, helical polymers is investigated theoretically. The helices are modelled by nearest-neighbour statistical thermodynamics. If the interaction energy between two helices of common handedness is lower than that of oppositely handed ones, a critical temperature Tc exists, below which the system spontaneously must leave the racemic state, though there is no contact to any chiral centre or force. This is analogous to the second-order phase transition of ferromagnets. The critical point increases with molecular weight and optical persistence of the helices. At the critical point the system is highly sensitiv…