Collaborative Research: Dynamics of Ionomer Melts

University Of Akron, Akron OH

Investigators

Abstract

1066517 Weiss Ionomers are chain molecules with strong attractive intermolecular forces that exhibit complex flow phenomena due to strong physical associations of the ionic dipoles attached to the chains. The strength of the interactions and the relaxation times of the associations are dependent on the nature of the fixed ion and the mobile counterion, the concentration of such charges and the time, temperature and amplitude of the deformation of the fluid. The details of the relationship between the physical intermolecular associations and the melt flow of ionomers is poorly understood, and this has hampered, in many cases, their commercial application. Previous research on the rheology of ionomers has been hindered by the inability to separate effects from the dipolar interactions and chain entanglements. This research focuses on characterizing the rheological behavior of a model ionomer system, lightly sulfonated polystyrene ionomers, with molecular weight below that where chain entanglements occur. The unsulfonated polystyrene is a Rouse chain, and only the influence of the dipolar interactions will affect the rheological properties of the ionomer melts. The specific objectives of the research are: 1) to develop an understanding of how the nature of the mobile counterion affects the rheology, specifically the relaxation times of the chain and the ionic associations; 2) to determine how elasticity is developed in these unentangled systems, 3) to resolve the origin of shear-thickening that has been observed in ionomer melts, and 4) to understand how low molecular weight additives can be used to engineer the melt rheology. The project will include the synthesis and characterization of the ionomers, steady state, dynamic shear and relaxation measurements of tionomer melts, and real-time, small angle neutron scattering evaluation of the ionomer chain structure in the melt during shear deformation. Graduate students will be trained in the field of complex fluids and polymer rheology, skills that are increasingly in demand by the U.S. polymer industry. High school, undergraduate and graduate students will participate in the research. The PI is part of a demonstration program between the University of Akron and a local high school in the city of Akron, OH, that provides opportunities for students, grades 10-12 to carry out inquiry-based research in the PI's laboratory. Graduate and undergraduate students will be recruited from academic programs and by targeted recruiting of students from underrepresented groups. The PI and students working on this research will also cooperate with the Akron Global Polymer Academy to develop teaching and demonstration aids on complex fluids. Ionomers are used in a variety of commercial applications, including commodity thermoplastics, thermoplastic elastomers, membranes (e.g., for fuel cells, reverse osmosis, humidification and batteries), compatibilizers for polymer blends, adhesives, hydrocarbon solution viscosifiers, drilling muds and organogels. An understanding of the rheological behavior of ionomers and how to control the rheology by composition, external variables such as temperature and stress, and with additives is important with regard to those applications, as well as for processing films and shaped articles from these polymers. A detailed understanding of how to engineer the processing behavior of ionomer melts while still achieving the desirable physical and mechanical properties of these materials could result in new technologies, such as the extrusion of functional thin films and roll-to-roll processing, technologies that are currently dominated by solution casting and batch processes.