Radial Dependence of Film Formation During the Spin-coating of an Immiscible Polymer Blend

The mixing of polymer blends is thermodynamically unfavourable and phase separation can often be observed in the morphology of spin-coated polymer blend films. Little work has been undertaken in determining the radial dependence of the spin coating process. In situ light scattering experiments before and method has been extended to explore how the effect varies radially at 0, 4, 8, and 12 mm from the centre of the film for solutions of 2% and 4% polymer concentration by mass for spin-coating at 1000 and 2000 rpm. It is shown that there is a significant radial dependence to the film formation. Inertial forces initially govern spin-coating until solvent evaporation becomes dominant. The turbulent forces change with radius and thus vary the evaporation rate with radius, resulting in a radial variance. These results are discussed in terms of applicable models.