The morphology of ternary polystyrene/styrene-butadiene rubber/polyethylene (PS/SBR/PE) blends has been investigated in the limits of a constant content of the major component (PS; 75 wt%) while changing the weight ratio of the two minor constitutive polymers. A core-shell structure for the dispersed phase has been predicted from the spreading coefficients and observed by transmission electron microscopy. Actually, upon increasing the relative content of PE with respect to SBR, the structure of the dispersed phase changes from a multicore structure to a PE/SBR core-shell morphology. The size of the PE subphase in the mixed dispersed phase increases sharply at a PE content that corresponds to phase inversion in the parent SBR/PE binary blends. The ultimate mechanical properties of these blends are sensitive to the strength of the SBR interphase between PS and PE. Some synergism has been observed in the PE/SBR composition dependence of the tensile strengths at yield and break.

Droplet deformation and the development of the final morphology after solvent evaporation were studied in two-phase ternary polymer/polymer/solvent mixtures in an electric field. The polymer mixtures used included polystyrene (PS) with such other polymers as poly(vinyl acetate) (PVA), poly-(methyl methacrylate) (PMMA), or polybutadiene (PB) in toluene as a solvent. In a dc field, the dispersed phases were distorted into ellipsoids with their major axes either parallel (prolate ellipsoids) or perpendicular (oblate ellipsoids) to the field direction, and/or they aligned in the field direction to form pearl chains. Droplets of the dispersed phases sometimes coalesced to form columns either parallel or perpendicular to the electric field direction. Sometimes the droplets or columns broke up into smaller droplets in the dc field. The final morphology usually contained spheres or prolate or oblate ellipsoids either randomly distributed in the matrix or in the form of pearl chains or columns. It was found that the conductivity ratio between the dispersed and continuous phases is extremely important in structure formation in these nonconducting systems.