Mesomorphic Ceramic Film Fabricated via Blade Coating of a Lyotropic Nematic Liquid Crystal for High-Power Lasers

Mesomorphic ceramic films are fabricated over large areas by blade coating of a lyotropic nematic sol of zinc oxide nanorods. Upon calcination to remove organics, continuous monodomain films with a uniform thickness result as transparent ceramics, exhibiting uniform birefringence over centimeter dimensions. At low blade-coating velocities, the dry film thickness varies inversely with the coating velocity, whereas at high coating velocities, it increases with increasing velocity as prescribed by the Landau-Levich theory. The thickness-velocity scaling in the Landau-Levich regime depends on the shear-thinning behavior of the lyotropic nematic sol. The optimization of the coating process for the minimization of optical defects leads to transparent monodomain films that exhibit a uniform in-plane birefringence of 0.032 +/- 0.002 from 580 to 1690 nm. After calcination, the resulting mesomorphic ceramic films span large areas (3.5 cm x 2.5 cm), are optically transparent with uniform thickness (0.60 +/- 0.03 mu m), and exhibit smooth surface finish with an average surface roughness of 20 nm. The alignment of zinc oxide crystallites along the coating direction within mesomorphic ceramics is confirmed by X-ray diffraction texture analysis and scanning electron microscopy imaging. As explained by the effective medium theory, the measured in-plane birefringence of 0.118 +/- 0.003 is primarily contributed by form birefringence over intrinsic birefringence of zinc oxide in mesomorphic ceramics. The reported approach to highly ordered mesomorphic ceramics directly from lyotropic nematic sols, avoiding the gel state, could be generally applicable to other mineral liquid crystals, thereby benefiting the manufacture of optics for high-power lasers.