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 t hermal polymerization-induced phase separation method (thermal PIPS) from t heir starting mixtures containing a di- and a mono-functional acrylate mono mer. Strong light-scattering states of the intrinsic composite films were t ransformed into complete transparent states by photochemical N-I phase tran sition of the LC domains within the polymer matrices that was induced by th e 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 a chieved reversibly and repeatedly between the two different optical states, the composite films with long alkyl side chain showed an ability of optica l image storage with high contrast based on light-scattering mode. (C) 1999 Elsevier Science Ltd. All rights reserved.