Drying of a drop of polymer solution of PAN (polyacrylonitrile)-DMF (dimethylformamide) system.

Abstract

The drying behaviour of a drop of polymer solution of the polyacrylonitrile-dimethylformamide system was investigated in a wide range of drying air temperature (323-423 K), initial drop volume (2-8 μl), and initial concentration of solvent in a drop (5-18 kg DMF/kg PAN). The theoretical calculation of the drying history of a drop, based on the diffusion equation and the differential heat balance equation, using the experimental values of activity and apparent mutual diffusion coefficient, represented the experimental values satisfactorily. The changes of solvent content and temperature of a drop during drying were well correlated by the ratio (drying time)/(initial radius of a drop)2, eliminating the effect of drop size. The shift in controlling step of the drying rate from surface evaporation resistance controlling to internal diffusion resistance controlling is shown by means of changes in the concentrations at the center and the surface of a drop.