Thermal Analysis Reveals the Morphology of Complex-Nanoparticle Mixtures

Date: Tuesday, December 09, 2014
Time: 11:00 AM - 12:30 PM EST (GMT-5:00).


The performance of new materials and devices depend heavily on morphological considerations: degree of crystallinity, conformation of amorphous species, and relative organization of one species with respect to another, characteristics which can be determined by thermal analysis. These considerations are important for functional materials such as photovoltaics and MEMS devices, as well as bulk materials that derive their performance characteristics from specific local morphologies. One such example is a polymer-based solar cell. The mixture discussed here is an organized, phase-separated, mixture of polymer and nanoparticle. The desired morphology has circa 10 nm square rods of phase separated nanoparticles (the electron acceptor) aligned vertically with 10 nm square rods of the polymer (the primary light absorber which is the electron donor and hole conductor) within a 250 nm thick film. From the top the film would look like a checkerboard and from the side vertical stripes of the two materials. These target dimensions are dictated by material optical and electronic transport properties but are difficult to manufacture and verify. We have used thermal analysis to determine the degree of polymer crystallinity within the film which is crucial to optimal performance. Surprisingly, this thin film polymer is only 30% crystalline, much less than in the bulk form. In addition, modulated differential scanning calorimetry (MDSC) reveals the morphology within the 70% amorphous part which constitutes a mixture of polymer and nanoparticles called the mobile amorphous phase (MAP) and, we believe, another part called the rigid amorphous fraction (RAF) which is pure polymer. The make-up of the MAP and the amount of RAF is difficult to determine but can be if thermal analysis data is used in combination with neutron scattering results. The underlying experimental techniques necessary to characterize these two phases and hypotheses about their effect on performance will be discussed.

Michael E. Mackay, Ph.D.

Michael E. Mackay, Ph.D., received his undergraduate degree in chemical engineering with distinction from the University of Delaware then worked for Proctor and Gamble prior to attending graduate school at the University of Illinois (Urbana) where he received M.S. and Ph.D. degrees in chemical engineering. He subsequently became a postdoctoral fellow at the University of Melbourne (Australia) and then has had positions at the University of Queensland (Australia), Stevens Institute of Technology, Michigan State University and is presently the Distinguished Professor of Materials Science and Engineering at the University of Delaware in the Materials Science and Engineering Department. He is a nationally known leader in nanotechnology specializing in how nanoparticles improve polymer performance and their use in making novel devices and materials. Recently, he has focused his research efforts to make polymer-based solar cells that can be made cheaply on any surface.

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