Extensional flows are much more efficient for dispersive mixing in comparison with shear flows. Extensional Mixing Elements (EMEs) were developed to impart extension dominated flow in twin screw extruders (TSE) through stationary hyperbolic contraction channels. New EME prototypes have been built and optimized for both twin- and single-screw extruders. Previously, EMEs for TSE were mild in the sense that they had only horizontal contracting channel. The improved mixing elements are made more aggressive by incorporating a vertical hyperbolic contraction as well, thus imparting extensional stresses in both horizontal and vertical directions. This new EME concept has also been extended to single-screw extruder (SSE) operations. A novel modular metering zone single-screw design was developed to have both dispersive (EME) and distributive (Pineapple) mixing elements simultaneously. The efficacy of this solution is tested experimentally for two types of systems: (a) Immiscible polymer blends, i.e., fluid-fluid systems, and (b) Nanocomposites, i.e., fluid/solid systems; the resulting morphologies are compared and the results show a significant improvement in mixing with only a small penalty in throughput.