Velocity of dissolution of polymers. Part I

Abstract

AbstractA short description is given of the apparatus for the solution of a macromolecular substance in a solvent and the mathematical treatment of the curves. A relation is obtained for the velocity of penetration ⋅ (cm./sec.) of the solvent into the polymer: where D is the integral, mutual diffusion coefficient and δ the thickness of the swollen layer on the surface of the polymer. The dependence of the process on the temperature is The swollen layer δ is investigated in detail. It consists first on the side of the solvent of a streaming layer (liquid layer) δ1. Below this is a rubberlike layer δ2. These layers are made visible by dispersed carbon black particles. The total layer δ increases with the temperature: The liquid, swollen polymer is removed from the surface and its polymer content measured. The mean content of polymer in the double layer δ1 + δ2 increases with the temperature. Viscosity measurements are made to draw final conclusions regarding the stability of δ. The mean viscosity in δ can be taken from these viscosity curves, as the content of polymer in δ is known. The stability (viscosity) increases with the temperature. The reason for it is the decrease of the solid, swollen layer below the rubberlike layer. The polymer content in the rubberlike layer increases to the same extent as the solid, swollen layer decreases. The total swollen layer δ is built up of four layers: a liquid layer δ1, a rubberlike layer δ2, the solid, swollen layer δ3, and an infiltration layer δ4. δ3 contains so few solvent molecules that its state at the temperature of solution is still solid and swollen. δ4 is a solid, glassy polymer, the holes and channels of which have only been filled with solvent molecules without swelling the structure. All four layers exist at temperatures of solution below the glass temperature of the polymer. δ3 and δ4 disappear at the glass temperature, and at the flow temperature the polymer and its layer are liquid. The variation of the concentration in δ is measured interferometrically. The concentration of solvent decreases sharply in δ3 + δ4 and linearly in δ1 + δ2 down to zero. The streaming of the solvent influences mostly δ1. The slope of the log ⋅ versus 1/T curves differs above and below the glass transition. The coefficient of diffusion can be calculated from the solution formula and, independently, from time lag measurements. Both values agree well.