Experimental investigation of equibiaxial extension and breakup of drops in a molten two-phase polymer blend

We experimentally investigate the breakup of an equibiaxially elongated polystyrene (PS) drop in a poly(methyl methacrylate) (PMMA) matrix during relaxation after melt elongation. In equibiaxial elongation, the initially spherical PS drop is deformed into an ellipsoidal disclike shape for our test parameters. Using a hotstage in combination with a light microscope, we observe the evolution of the drop shape during relaxation. In the initial stage of relaxation, fingers and holes are formed. The holes are located preferentially near the rim of the drop. The number and the size of the holes increase with time such that the elongated PS drop attains a complex shape during relaxation. The fingers form bulbous ends which separate from the fingers. We discuss the dynamics of this breakup process by taking into account the interfacial energy between PS and PMMA. Our analysis shows that a very large number of small PS droplets can be generated by the sequential breakup of the elongated PS drop.