Field induced orientation

Firouzi, A Schaefer, DH Tolbert, SH Stucky, GD Chmelka, BE, Magnetic-Field-Induced Orientational Ordering of Alkane Lyotropic Silicate-Surfactant Liquid Crystals, Journal of the American Chemical Society 119, 9466, 1997. 

Electric field induced orientation of polar groups in these polymers occurs via the mechanism of large scale motion, common for rigid polymers. However, the incorporation of a spacer within a macromolecule (polymer 5, Table 16) changes sharply the mode of intramolecular aggregation and the mechanism of orientation in an electric field. 

Boker A et al (2006) The influence of incompatibility and dielectric contrast on the electric field-induced orientation of lamellar block copolymers. Polymer 47(3) 849-857... 

There have also been reports on the preparation of polar materials by a photo-electro-poling technique that combines the optically induced quadrupolar depletion of chromophores in the direction of the light electric vector with an additional field-induced orientation of dipolar chro-mophores. The latter allows the preparation of cold electrets, which are interesting for nonlinear optical applications, such as optical harmonic generation, wave mixing, etc. ... 

The electric field-induced orientational order in a nematic liquid crystal is given by Equation (4.7). The liquid crystal has the parameter fi = 03. Numerically calculate the order parameter 5 as a function of the normalized temperature t in the region from -0.1 to 0.1 under various normalized electric fields e = 0.0, 030 121), 0121),... 

Electric-Field-Induced Orientation. Despite the fact that electric field orientation of liquid crystals is an important technology used, for example, in liquid crystal displays, there has been almost no work on the electric field alignment of LCTs. This may be because electric fields are effective only for thin films the high field strengths required, on the order of 10 V/cm or greater, can lead to dielectric breakdown in thick samples. Nevertheless, although bulk orientation cannot be obtained via electric fields, use of electric fields does provide a complement to the surface-induced techniques described above. 

Magnetic-Field-Induced Orientation. Liquid crystals may be oriented in magnetic fields, even though they are diamagnetic, due to the anisotropy in their diamagnetic susceptibility. The advantage of magnetic fields over surface-induced orientation or electric fields is that samples are not confined to thin films. 

Electric Field-Induced Orientation and Relaxation of Liquid-Crystalline Systems... 

Figure 2-7. Electric field-induced orientation of a liquid crystal, (a) Construction of the measurement cell, (b) Homogeneous alignment of the LC between the anisotropic electrode surfaces before application of the electric field.

Figure 2-12. Slack-plot of spectra measured during the electric field-induced orientation and during part of the relaxation of the 6CPB molecules (41 C .

The concept of mechanical field induced orientation can easily be transferred to nematic elastomers with oblate chain conformation, i.e., side chain end-on elastomers with an even number of spacer atoms. In order to achieve a monodomain structure, a globally oblate chain conformation has to be established. This can be achieved by uniaxial compression or biaxial stretching of the polydomain elastomer which induces a uniform homeotropic alignment of the nematic director perpendicular to the film plane. Up to now, this orientaticMi technique has only been realized experimentally for chiral nematic elastomers [72]. 

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