Optical Anisotropy of Carbon Nitride Thin Films and Photografted Polystyrene Brushes

Abstract Polymer brushes on surfaces enable advanced material design. In the present contribution, transparent and flat photoactive polymeric carbon nitride (pCN) thin films are employed as a photoactive substrate and primer layer to grow polystyrene (PS) brushes. These films are then characterized by ellipsometry. For the first time herein is reported on the optical anisotropy of pCN thin films revealing a high positive birefringence up to 0.71 with an in‐plane n _D of 2.54 making this material of high interest for photonic devices. Furthermore and rather surprising, the photografted polystyrene brushes exhibit an unusual high negative birefringence, too. This negative birefringence can be attributed to a practically complete stretching of the polymer chains throughout growth in the radical chain process. As the stretched PS brushes grafted from the pCN surfaces also provide unusual surface properties, the overall system can be of great interest for photonics, but also as mechanical coating and membranes for gas separation.