NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES

This work focuses on interfacial structure and dynamics of structured polymers in thin films and in solutions using neutron techniques accompanied by atomic force microscopy. We probed polymers with a common theme that were highly segregated either because of presence of ionic groups or topological constraints. In these polymers the interfacial regions often define their function in different applications such as clean energy, printing adhesions and drug delivery systems. Thin film studies include systems of polystyrene/sulfonated polystyrene, a rigid sulfonated polyphenylene and polystyrene three-arm stars/linear polystyrene. The first two systems include ionic components and the last exhibits topological constraints. Polystyrene is often used as a model polymer because of the ease of exercising synthetic control over its molecular weight. Interdiffusion at the polymer-polymer interface was followed as well as diffusion of guest molecules. We found that the interfacial diffusion at the interfaces of ionic-nonionic polymers is strongly impacted by the presence of ions. The presence of ionic groups results in surface aggregation which in turn impacts the interfacial diffusion. The rigidity of the polymer also plays an important role as it results in significant interstitial spaces that dominate diffusion. The interfaces formed by these polymers are often inhomogeneous and contain both ionic and nonionic species that impact the onset of dynamics. In parallel, we studied the interfacial segregation of three-arm star polymers in a matrix of polystyrene. The contact point between the three-arms forms topological constraints that impact the segregation. The interfacial compositions were found to be balanced between entropic forces that drove polymer chain ends to the interfaces and the effects of topological constraints that hindered the motion of polymers. Interfacial segregation effects are seen not only in thin films but also strongly affect the assembly of polymers in solution. Here we studied a penta-block copolymer that consists of an ionic center block in hydrophobic solution. We found that very stable aggregates are formed where these shapes and stability are attributed to the ionic block. Finally the synthesis of structured alternating copolymers and their optical characteristics are introduced