Diffusion of acetone into cellulose nitrate films and study of the accompanying orientation

Studies have been made of sorption and desorption of acetone by films of cellulose nitrate (11 and 12% N) at 30°C. by following the weight of vapor takeup or loss as a function of time. The takeup‐time curves show marked inflections and plots of takeup versus {article}{empty}{document}√ t{document} are initially nonlinear for both sorption and desorption, indicating that Fick's law with the usual boundary conditions is not obeyed. The rate of vapor takeup is also considerably more rapid and different in character for films cast on glass than for films cast on mercury. A striking result is that for successive sorption‐desorption cycles the rate of sorption decreases markedly, e.g. , by a factor of 16 for five cycles. Studies of the optical anisotropy of the films show that the orientation of the polymer molecules normal to the plane of the film is increased by the diffusion process and it is concluded that this accounts for the decreased rate for successive sorption‐desorption cycles and provides an explanation for the diffusion anomalies. A possible cause of this orientation is the observed anisotropic swelling combined with slow movement of the polymer segments.