Chemical Engineering Seminar

Acid- and ion-containing polymers have specific interactions that produce complex and hierarchical morphologies that impart remarkable ranges of tunable properties.  Renewed interest in these materials arises from various applications including as single-ion conductors in battery applications, selective membranes for water treatment, and self-healing materials.  Most of these polymers are copolymers and often random copolymers wherein the separation between the functional groups on the polymers is non-uniform and individual copolymers have distinct compositions.  This inherent structural diversity confounds the longstanding efforts to establish robust structure-property relationships.  In contrast, precise acid copolymers and their ionomers are synthesized by acyclic diene metathesis (ADMET) from macromonomers, such that the functional groups are evenly spaced along linear polyethylene.  These unique model materials provide molecular precision that imparts unprecedented morphological uniformity and control and we have identified numerous new morphologies.  Our primary experimental tool is X-ray scattering to probe the nano-scale morphology a room temperature, elevated temperature and during mechanical deformation.  At elevated temperatures, we find outstanding agreement with course grain and atomistic molecular dynamics simulations that provide new insights about acid and ionic aggregation in these materials.  In particular, the experiments and simulations suggest the presence of highly branched, stringy aggregates that can be percolative structures.  Most recently, we are using quasi-elastic neutron scattering measurements to investigate polymer dynamics and the impact of aggregate structure.  The relationships between the chemical structures of precise copolymers, their hierarchical aggregate structures and the effect on polymer dynamics will be discussed.