Holographic gratings in azobenzene side-chain polymethacrylates

Optical storage properties of thin unoriented liquid crystalline and amorphous side-chain azobenzene polymethacrylate films are examined by polarization holographic measurements. The investigated materials are free radical copolymers derived from two photochromic monomers, 6-(4-oxy-4'-cyanoazobenzene)hex-1-yl methacrylate and 8-(4-oxy-4'-cyanoazobenzene)oct-1-yl methacrylate, and a nonphotochromic optically active comonomer, (-)-menthyl methacrylate. The thermal behavior and phase transitions of the polymers have been investigated in detail through differential scanning calorimetry and polarizing optical microscopy. Atomic force microscopy investigations have been carried out on the polarization holographic gratings recorded in the polymethacrylate films. A surface relief grating has been found to appear in all films after irradiation. The copolymers with 50-75% dye content exhibit the largest surface relief. The stored information seems to be stable up to approximately 70 degrees C, except in the case of polymers with low dye content.