Electron microscopic studies on planar texture and disclination of cholesteric mesophases in acyloyl chitosan/acrylic acid composite films

A novel amphiphilic chitosan derivative, acryloyl chitosan (AcCs), was synthesized by a homogeneous reaction of chitosan and acryloyl chloride using methanesulfonic acid as solvent and catalyst. The concentrated solutions of AcCs/acrylic acid were investigated by polarized optical microscopy (POM) and found demonstrate cholesteric mesophase above the critical concentration of 45 wt%. AcCs/polyacrylic acid (PAA) composite films were prepared via the photopolymerization of 52 wt% AcCs/acrylic acid solution, and subsequently the permanganic etching technique was employed to expose the textures and defects inside the composite films. The Grandjean planar textures were observed by POM, but a series of dark and bright striation lines, which were attributed to the periodic structure of the cholesteric helix, were detected by scanning electron microscopy (SEM). The disclination pairs, τ−λ+ and τ+λ−, were found, however λ+λ− and τ+τ− were absent. Effect of etching time on morphology of AcCs/PAA composite films was also investigated, comparing with 30 wt% free-acetyl chitosan (CS)/PAA composite films. The results showed that AcCs/PAA composite films had better anticorrosion ability than (CS)/PAA composite films, due to the crosslinking network between AcCs and PAA. FTIR confirmed that double bonds of AcCs involved in photo-solidification. Therefore the system studied takes the advantage of easy controlling for permanganic etching.