Domains, cigar-shaped

T he behavior of liquid crystals in applied electric fields has been the object of several recent studies (1, 3, 4)- The materials primarily used here were those in which the dipole moment of the molecule was not in the same direction as the molecular axis. When an electric field is applied to such a system by transparent electrodes, the characteristic cigar-shaped domains shown in Figure 1 for p-azoxyanisole are readily observed, using relatively low magnification with or without polarized light. The optical behavior of such domains between crossed polarizers indicates that their optic axis is essentially parallel to the electrode surface and essentially perpendicular to the direction of the applied field. 

Observations between crossed polarizers of the effects of electric fields on the optical properties of butyl p-anisylidene-pf-amino-cinnamate (BA AC) have demonstrated the existence of a domain pattern which, in contrast to the cigar-shaped patterns of p-azoxyanisole, is circular. These circular domains have their optic axis parallel to the applied field, while in p-azoxyanisole the optic axis is essentially perpendicular to the field. Measurement of the polarization as a function of applied field in nematic BAAC has yielded hysteresis loops similar to those found in ferroelectric crystals. This evidence for a spontaneous polarization indicates that in a material such as BAAC with a dipole moment essentially along the molecular axis the molecules are predominantly oriented in one direction within the domains. 

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