Nitroxide radicals reduce shrinkage in acrylate-based holographic gratings

High resolution holographic polymer dispersed liquid crystal gratings are photo-induced periodic structures commonly affected by shrinkage. This phenomenon represents a problem in several application fields such as in high density optical storage. In this work we observed that, by directly monitoring the blue-shift of the reflection peak of the periodic structure, an evident shrinkage reduction occurs using the nitroxide radical Tinuvin770-N-yloxy [(bis(2,2,6,6-tetramethyl-piperidine-1-yloxy-4-yl)-sebacate] as inhibitor of polymerization. This compound is a stable hindered amine light stabilizer-derived free radical, which plays a significant role in the photo-polymerization dynamics.