CTS-9805852 N. Balsara Polytechnic U. @ NY
A systematic experimental study of microstructure and internal interfaces in multicomponent polymer blends is proposed. In spite of several years of research on these systems, many fundamental issues remain unresolved. The proposed work is motivated by recent theoretical work [Schick, 1997, and Muthukumar, 1997] that indicate the presence a variety of complex phases in relatively simple mixtures of two homopolymers and a block copolymer. The predicted phases are similar to those found in oil/water/surfactant mixtures, and are characterized by a high density of internal interfaces. These theories make explicit and experimentally testable predictions of the parameters (molecular weight, temperature, etc.) that will lead to these structures.
Experiments will be conducted on polyolefin blends. Model materials, with molecular weights and compositions that are based on theoretical prescriptions, will be synthesized via anionic polymerization. The main characterization tools of microstructure will be neutron and light scattering. The curvature and other attributes such as interfacial thickness of the internal interfaces will be determined from static scattering experiments. Selective labeling and contrast matching will be used to focus on specific components in the multicomponent blends. In particular, the use of a labeled block copolymer, will enable a direct study of the interface, if the diblock is an active interfacial agent and coats the internal interfaces. Achieving equilibrium in polymer systems is not always possible, due to slow kinetics and the presence of metastable intermediate structures. Time-resolved scattering experiments will be conducted to study the evolution of structure when the blends are quenched from one region of the phase diagram to another. The main goal is to identify the conditions that lead to the formation of modulated phases [Bates, 1997]: multicomponent ordered phases that possess long range order, and microemulsions which are periodic structures that lack long-range order.
The absence of coherent strategies for designing interfaces in multicomponent polymer blends is well recognized. The fundamental knowledge that we propose to obtain will be a step toward developing such strategies. New materials may also emerge from our experimentation. In oil/water systems ordered phases have not received much attention due to their solid-like properties. Polymer-based ordered materials may he valuable in structural applications where solid-like properties are necessary. The thermodynamic stability of the internal interfaces will lead to better processing characteristics. Shear-induced phase transitions may lead to a new morphologies that were not accessible under quiescent conditions. ***
