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.