Orientational order in surface layers of gelatin films

The dependence of birefringence in gelatin films of different thicknesses o n the angle of incidence of polarised light was studied, and the surface bi refringence of the film determined. The intrinsic optical anisotropy (alpha (1) - alpha (2)) of the gelatin chains was determined to be +120 x 10(-25) cm(3) from photoelasticity measurements on swollen films. The comparison o f the surface birefringence with the value of (alpha (i) - alpha (2)) enabl ed 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. ( C) 2000 Elsevier Science Ltd. All rights reserved.