Mass transport phenomena during lithographic polymerization of nematic monomers monitored with interferometry

Photopolymerization of liquid-crystalline diacrylates is a versatile tool to make optical films for liquid-crystal display (LCD) enhancement. The constant drive towards LCD's having an improved front-of-screen performance demands optical films with properties that can be adjusted on (sub) pixel level. Birefringent films made from liquid-crystalline diacrylates allow for the required adjustment of the optical property on (sub) pixel level. In this paper we report on the composition of the acrylate mixture that results in planarly aligned nematic films usable as optical retarder in transflective LCD's as well as the mass transport phenomena that take place during heating of a mask-exposed birefringent film of liquid-crystalline diacrylates. The mass transport phenomena are studied by interferometry as a function of temperature and time. Upon heating a pronounced surface corrugation arises from the latent image formed during the mask exposure. The surface profile largely depends on lateral feature sizes. For 1 × 1 - mm 2 areas the exposed areas rise compared to the nonexposed areas, whereas the opposite is observed for 100 × 100 - μ m 2 areas. Finally, the direction of the mass transport depends on the molecular orientation of the liquid-crystalline diacrylate. The protrusion formed by lengthwise diffusion is 1.7 times higher than that formed by sidewise diffusion.