Orientational order in surface layers of gelatin films

The dependence of birefringence in gelatin films of different thicknesses on the angle of incidence of polarised light was studied, and the surface birefringence of the film determined. The intrinsic optical anisotropy (α1−α2) of the gelatin chains was determined to be +120×10−25 cm3 from photoelasticity measurements on swollen films. The comparison of the surface birefringence with the value of (α1−α2) enabled the orientation of the biopolymer with respect to the film surface to be elucidated. It was found that orientation parallel to the film surface was retained throughout the film, up to a film thickness of at least 0.5 mm.