Fine structure and optical properties of cholesteric films prepared from cellulose 4-methylphenyl urethane/ N-vinyl pyrrolidinone solutions

Solutions of 4-methylphenylurethane of cellulose in N-vinyl pyrrolidinone have been investigated, and a cholesteric mesophase was found above a concentration of 35 wt % of polymer. The selective reflection of light from the cholesteric solutions lies in the visible region of the spectrum and moves from blue toward red with increasing temperature. After photopolymerization of these solutions, solid opalescent films, which conserve the cholesteric order of the lyotropic phase, can be prepared. The fine structure of these colored films has been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In the fractured surfaces of the films, a periodic lamellar structure, which may arise from the helically twisted structure of the cholesteric mesophase, is observed. The periodicity of the lamellar structure is in good agreement with the calculated value of half a pitch of the cholesteric helix.