Characterization and compatibilization of cocontinuous polymer blends

Polymer blends offer an important route to new materials with combinations of properties not available in a single polymer. In many cases, the polymers are immiscible, leading to phase separation at equilibrium. However, a number of useful non-equilibrium blend morphologies can be created by intense mixing during processing. Among these are cocontinuous morphologies which are distinguished by the mutual interpenetration of the components. Cocontinuous blends have numerous applications including blends with enhanced mechanical properties, packaging for static-sensitive materials, or packaging for moisture-sensitive materials. However, cocontinuous blends are not well understood.; This research has focused on developing reliable methods for detecting cocontinuity and improving the stability of cocontinuous blends. The methods used for detecting cocontinuity include scanning electron microscopy (SEM) with image analysis, solvent extraction, electrical conductivity measurements, and rheological measurements. A new image analysis technique was developed to directly measure the amount of interface in polymer blends from SEM images. The amount of interface in polymer blends was shown to reach local maxima at compositions corresponding to the boundaries of the region of cocontinuity. Solvent extraction experiments were used to determine the connectivity of the phases. A new model that accounts for surface effects improves the reliability of solvent extraction experiments. Electrical conductivity measurements modeled using percolation theory were also shown to be useful for detecting the onset of cocontinuity. Rheological measurements on polymer blends revealed that the elastic modulus at low frequency reached local maxima at compositions corresponding to the boundaries of the region of cocontinuity.; The effect of pre-made block copolymer on the stability of cocontinuous polymer blends was investigated. It was shown that an intermediate molecular weight block copolymer reduced the size scale of the blend morphology and slowed phase coarsening more effectively than high or low molecular weight block copolymers.; Two new devices for mixing polymer blends and making rheological measurements were tested. A double wall couette was shown to mix polymer blends, but was not able to create cocontinuous blends. An asymmetric minimixer was able to create cocontinuous morphologies, but its mixing was non-uniform. It was shown to be useful for rheological measurements.