Crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order .2. Anisotropic swelling behaviour in water

Hydroxypropyl cellulose solid films crosslinked with two kinds of dialdehyde (glyoxal and glutaraldehyde), retaining cholesteric liquid crystalline order, were prepared by casting the liquid crystalline solution in methanol. Effects of crosslinking agent concentration and type, and heat treatment on the swelling behaviour of the crosslinked films in water were determined. The change in cholesteric pitch of crosslinked films during swelling was also determined by means of circular dichroism (c.d.) study. The swelling behaviour and the change in the peak wavelength of the c.d. spectrum were compared, and the anisotropic swelling behaviour of crosslinked films was discussed. The swelling ratio (B) in the film thickness direction was greater than that in width or length direction. B decreased with crosslinking agent concentration and heat treatment. B for the films crosslinked with glyoxal was greater than that for the films crosslinked with glutaraldehyde. The swelling behaviour and the shift in the peak wavelength of the c.d. spectrum as a function of soaking time were almost the same. The shift depended similarly on the concentration and type of the crosslinking agent as the swelling behaviour did. The similarity of the shift in the peak wavelength of the c.d. spectrum and the swelling behaviour clarified that the swelling in the film thickness direction is correlated to the change in the cholesteric pitch of the crosslinked films. Copyright (C) 1996 Elsevier Science Ltd.