3-DIMENSIONAL MICROSTRUCTURE OF A POLYMER-DISPERSED LIQUID-CRYSTAL OBSERVED BY TRANSMISSION ELECTRON-MICROSCOPY

A film consisting of an amorphous photo-crosslinkable polymer matrix a nd a dispersion of microinclusions of a cholesteric polymer was invest igated by transmission electron microscopy (TEM). The polymerization p rocedure of the blend provides a composite with many small nodules of spherical or ellipsoidal shapes, with sizes between 0.4 and 6 mu m The cholesteric stratification is well evidenced in transmission electron microscopy by dark lines due to diffraction contrast. The 3D organiza tion was reconstructed by the observation of successive ultramicrotome d sections. Six types of nodules were distinguished according to the n umber of defects (foci or disclination lines), among which only three had already been observed and theoretically calculated. The confined g eometry inherent in the size of the nodules, close to the cholesteric pitch, is responsible of these unexpected structures. In these conditi ons, the surface forces are in tight competition with the cholesteric elastic forces.