ORIENTATION OF LIQUID-CRYSTALLINE EPOXIDES UNDER AC ELECTRIC-FIELDS

The curing of liquid crystalline (LC) epoxides containing phenyl benzo ate mesogens was studied under applied ac electric fields. When curing reactions began under a low-frequency electric field (similar to 1 V/ mu m), parallel molecular orientation slowly changed to perpendicular to the field, because a crossover (cutoff) frequency of molecular orie ntation shifted to much lower frequencies as the curing reaction took place. As a result, the cured networks possessed orientation perpendic ular to the applied ac electric fields regardless of the initial frequ ency. Due to electrohydrodynamic effects, curing reactions under a low -frequency electric field proceeded faster than those at high frequenc y. Electric fields also affected formation of the LC structure, in par ticular, in smectic networks. Curing of LC epoxides with twin mesogen architecture under an ac electric field produced a smectic-A like stru cture with a fan shape-like texture, whereas curing without an externa l field formed a disclination rich texture, The oriented smectic netwo rk possessed high orientation as well as high translational order. The mechanical properties of the oriented smectic-like network showed a n egative CTE as well as linear load-extension behavior in the rubbery r egime. These characteristics can be explained in terms of the smectic layer spacing and the lateral spacing between mesogenic groups as conf irmed by X-ray diffraction measurements.