Polarization-selective polymerization in a photo-crosslinking monomer film

The molecular order in a smectic monomer is utilized to create a photoreactive material that is highly polarization-selective during its photo-crosslinking polymerization. A dichroic photoinitiator adapts the molecular orientation of its aligned smectic B host monomer which reaches a degree of orientation larger than 0.9. This value correlates to a dichroic ratio, defined as the absorbance ratio of light with its polarization respectively parallel and perpendicular to the orientation axis, of 32. This is substantially higher than the dichroic ratio of similar dichroic initiators previously studied in nematic host monomers which considerably improves the polymerization contrast. The presence of an inhibitor, such as a hydroquinone, in the monomeric mixture enhances the polymerization contrast further. The effect of the inhibitor is due to the close to zero monomer to polymer conversion for the polarization perpendicular to the alignment in the initial stages of polymerization. It is argued that the high polarization-selectivity of the above-described system is potentially useful in nano and/or microstructuring techniques without the use of masks such as polarization holography.