Phase separation in ternary polymer solutions induced by solvent loss

Laser scanning confocal microscopy and image analysis have been used to study the phase separation behavior of ternary solutions of dextran, poly(ethylene glycol), and water during drying. The morphology development is strongly affected by the inhomogeneous nature of the solvent quench and by gravitational sedimentation, A range of transient structures is seen in which the morphology varies with depth into the sample. The origin and development of these structures are explained using simple models. For mixtures where the overall volume fraction of the dextran-rich phase, phi(s), is 0.1 or 0.34 a droplet morphology is observed whose development is analyzed in detail. The mean radius of the largest droplets is found to increase linearly with time, For mixtures with phi(s) = 0.5, a bicontinuous morphology is seen in which the characteristic length scale decreases with depth into the sample as a result of the inhomogeneous distribution of water in the drying film.