Search results for "liquid crystal"

Passive and active light scattering obstacles

2005

Simulation of vision pathologies and adverse viewing conditions in laboratory conditions requires optical phantoms with different level of light scattering. Such obstacles are designed as passive or active elements applying several technologies. We used for studies two kinds of solid state smart materials with electrically controllable light scattering - electrooptic PLZT ceramics, polymer dispersed liquid crystals PDLC and obstacles with fixed light scattering - composite of polymer methylmethaacrilat PMM together with grinded glass microparticles. Report analyzes optical characteristics of such obstacles - attenuation, scattering, depolarization of different wavelength light at various sc…

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

2018

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as wel…

Reversible Physical Network Stabilized Ferroelectric Liquid Crystals

2001

Effective interactions of colloids on nematic films.

2008

The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied theoretically for large separations $d$. The elastic interaction is repulsive and of quadrupolar type, varying as $d^{-5}$. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to $d^{-5}$ as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying capillary attractions. However, their strength turns out to be too small to be of importanc…

Modes of Structure Formation in Doped Discotic Polymers and Low Molar Mass Model Systems

1991

By doping low molar mass or polymeric liquid crystals containing flat disc-like units with electron acceptors one achieves a stabilization of columnar phases, the induction of a columnar phases in otherwise discotic nematic or even in amorphous systems. Theoretical models based on the assumption of strong electron donator-acceptor (EDA) complex formation are able to account for the structure formation on a molecular level and the thermodynamic properties of the mixtures and the model of diffusion limited aggregation (DLA) for the structure formation on a supermolecular structure.

Transient photoconductivity in a discotic liquid crystal

1993

Using a time-of-flight technique, different transport mechanisms, deep trapping, multiple shallow trapping, and ideal itrinsic transport, can be observed in the different temperature and phase regions of the liquid-crystalline photoconductor hexapentyloxytriphenylene. The temperature and field dependences of carrier mobilities up to 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{2}$/V s have been determined; this value exceeds considerably the mobilities of the most commonly used organic photoconductors. The experiments reflect a variety of transport phenomena which are novel in the field of liquid-crystalline systems.

Interfacial tension of the isotropic-nematic interface in suspensions of soft spherocylinders.

2005

The isotropic to nematic transition in a system of soft spherocylinders is studied by means of grand canonical Monte Carlo simulations. The probability distribution of the particle density is used to determine the coexistence density of the isotropic and the nematic phases. The distributions are also used to compute the interfacial tension of the isotropic--nematic interface, including an analysis of finite size effects. Our results confirm that the Onsager limit is not recovered until for very large elongation, exceeding at least L/D=40, with L the spherocylinder length and D the diameter. For smaller elongation, we find that the interfacial tension increases with increasing L/D, in agreem…

Isotropic-nematic interface and wetting in suspensions of colloidal platelets.

2006

We study interfacial phenomena in a colloidal dispersion of sterically stabilized gibbsite platelets, exhibiting coexisting isotropic and nematic phases separated by a sharp horizontal interface. The nematic phase wets a vertical glass wall and polarized light micrographs reveal homeotropic surface anchoring both at the free isotropic-nematic interface and at the wall. On the basis of complete wetting of the wall by the nematic phase, as found in our density functional calculations and computer simulations, we analyze the balance between Frank elasticity and surface anchoring near the contact line. Because of weak surface anchoring, the director field in the capillary rise region is uniform…

Direct observation of smectic layers in side chain liquid crystal polymer films

1987

Abstract By applying stringent conditions to the imaging process it has been possible to produce electron micrographs of the smectic planes in a highly beam sensitive polymethcrylate side chain liquid crystal polymer. These planes show a high degree of internal perfection, while, at the same time, showing clear evidence of curvature. The director orientation was determined over a fairly large region.

Induced roughness in thin films of smectic-C* elastomers

2002

The surface topography of a thin homeotropically oriented film of ferroelectric smectic-C* elastomer is studied by atomic force microscopy. We find that when the film is mechanically stretched, its surface becomes increasingly rough, in proportion to the applied strain. The effect depends strongly on the nature of crosslinks forming the elastomer network. The r.m.s. roughness correlations show a consistent trend [h(x) − h(0)]21/2 ~ (x/ξ)0.5. We introduce a theoretical model assuming that random disorder in the smectic tilt angle is induced by deformations via the coupling of mesogens to the elastic network. The model describes the observed power law and gives a prediction for the correlatio…