Microlayer polymer structures via melt processing

Layered polymer microstructures have useful properties. Very regular, thin (<1 μm) microlayer structures are iridescent or mirror-like and can function as optical filters. Microlayer structures can also show enhanced mechanical properties. Even less regular and thicker layers can dramatically alter the permeability of the matrix polymer. We demonstrate that such layered structures arise naturally when 10-100 μm diameter drops of one polymer melt are sheared within another. This is due to the weak influence of interfacial tension compared to shear stress. A high second normal stress difference in the matrix can actually cause the drops to widen. Adding a block copolymer to the drops or grafting reactions across the interface greatly enhances area generation. Stretching microlayer structures in an extensional rheometer generates new interfacial area exponentially. Samples can be prepared by stacking alternating layers followed by compression in a heated press and also by multilayer coextrusion. Using 50 or more layers enhances interfacial effects permitting direct measurement of interfacial tension and grafting reactions. Interfacial tension is found to increase strongly with rate of area generation. Grafting reactions also increase interfacial effects rather than decrease as had been expected from some studies.