MAGNETIC-FIELD ORIENTATION OF LIQUID-CRYSTALLINE EPOXY THERMOSETS

The effect of magnetic fields on the orientation and properties of 4,4 '-bis(2,3-epoxypropoxy)-alpha-methylstilbene cured with sulfanilamide has been studied. This epoxy system is initially isotropic and forms a smectic A phase upon curing. A magnetic field was applied during the cure reaction, resulting in alignment of the molecules along the direc tion of the applied field. Measurement of the orientation parameter of the fully cured material by wide-angle X-ray scattering (WAXS) showed that orientation improved with an increase in field strength. The ori entation parameters of the smectic layer normals calculated from the i nner reflection of the WAXS pattern attained a maximum level of approx imately 0.8 at a field strength of approximately 12 T. The orientation parameters calculated from the outer reflection of the WAXS pattern w ere considerably lower, possibly due to the presence of amorphous regi ons associated with domain boundaries or the loss of molecular alignme nt within the smectic layers due to topological restrictions of the cr oss-linking sites. Orientation resulted in an anisotropic linear therm al expansion coefficient after curing, although the overall volumetric expansion was constant. The elastic tensile modulus increased with th e square of the orientation parameter, attaining a maximum value of 8. 1 GPa, compared to 3.1 GPa for the unoriented material. The change in modulus with orientation could be fit with a simple model for the modu lus of anisotropic materials.