Light-scattering-mode optical switching and image storage in polymer/liquid crystal composite films by means of photochemical phase transition

Photochemical phase transition behavior triggered by photoisomerization of a guest azobenzene doped in nematic (N) liquid-crystalline (LC) domains was investigated in isotropic (I) acrylate polymers with alkyl side chains on their surfaces. These polymer/LC composite films were prepared by in situ thermal polymerization-induced phase separation method (thermal PIPS) from their starting mixtures containing a di- and a mono-functional acrylate monomer. Strong light-scattering states of the intrinsic composite films were transformed into complete transparent states by photochemical N-I phase transition of the LC domains within the polymer matrices that was induced by the trans-cis photoisomerization. Recovery process from the transparent state to the initial light-scattering state was strongly influenced by the alkyl side chains. While the composite film with short alkyl side chain acted as an all-optical switching material because the optical switching could be achieved reversibly and repeatedly between the two different optical states, the composite films with long alkyl side chain showed an ability of optical image storage with high contrast based on light-scattering mode. (C) 1999 Elsevier Science Ltd. All rights reserved.