The effects of electric fields on the molecular alignment in the liquid crystal p-(anisa1amino)-phenyl acetate are discussed. The behavior of this material is similar to that of p-azoxyanisole in that the ordering which is normally observed shows an alignment with the molecular axis preferring a direction parallel to the field at low audio frequencies, and perpendicular to the field for frequencies of a few hundred kHz. Results comparing the effectiveness of electric and magnetic fields for producing molecular alignment are presented which support a theory presented earlier to explain the ordering in p-azoxyanisole at audio frequencies. This theory involves the anisotropy associated with the electrical conductivity. Results are also presented which show that the effectiveness of dc electric fields is comparable to that for low audio frequencies. A few comments are made concerning recent work employing electric fields to produce ordering in liquid crystals for NMR studies.
This work involves the alignment of molecules in the anisotropic liquid phase of p-azoxyanisole due to externally applied dc and ac electric fields and walls of the sample holder. Microwave techniques involving dielectric measurements are used to provide a measure of the alignment. Results are discussed which suggest that for very pure samples an alignment should be produced with the long axes of the molecules perpendicular to the externally applied electric field. The alignment with the long axes parallel to the external field which is often observed appears to be due to an extremely small amount of impurity. This alignment appears to be associated with the conductivity, with an alignment produced such that the conductivity is a maximum in the direction of the field. Results are also discussed which suggest that small amounts of impurity are effective in producing an alignment of the molecules parallel to the walls of the sample holder.
The real and imaginary parts of the complex dielectric constant of the normal liquid phase of anisaldazine were measured at a temperature of 185°C for a frequency range from 900 Mc to 24 kMc. A plot of the complex dielectric constant in the complex plane satisfies the requirements for the Cole—Cole representation reasonably well. The temperature dependence of the dielectric loss at frequencies 6, 15, and 24 kMc indicates that any changes in the dielectric loss for a random orientation are very small as anisaldazine passes from its anisotropic to normal liquid phase. This implies that a plot of the complex dielectric constant in the complex plane for the anisotropic phase would probably satisfy the requirements for a Cole—Cole plot. Measurements of the dielectric loss in the presence of an external electrostatic field show that an ordering exists with the long axes of the molecules parallel to the external electric field.
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