Membranes with controllable separation properties play a vital role in advanced energy and environmental applications. Underlying mechanisms and structure-property relationships that promote permselectivity have been explored in great detail for polymer membranes that separate gas molecules, but for polymers that contain attached ionic groups and absorb water, such as fuel cell membranes, the underlying molecular concepts of why selectivity exists in these systems and how selectivity can be enhanced through rational molecular design are not clear. The fundamental difference between gas separation membranes and water-absorbing membranes is that the transport processes in gas separation membranes are dominated by the polymer dynamics where the water-absorbing membrane transport properties are dominated by the motion of water within the relatively stationary polymer matrix. Therefore, this project will focus on the critical role of water-polymer interactions and water binding and diffusion within the chemical and physical framework of the polymer. Intellectual Merit: The central theme of the proposed research is to study a system of end-linked polymers that contain sulfonate groups and to determine the critical molecular parameters for designing fuel cell and nanofiltration membranes with tunable selectivity for water, ions, and small molecules. The tailored materials with well-controlled structural variation will advance our fundamental understanding of the different routes to increasing selectivity in sulfonated polymers. The characterization tasks will be intimately integrated with the synthetic efforts to probe how the molecular characteristics of the membrane influence binding and diffusion of water, and in turn how the water properties influence the transport of ions and small molecules. An in-depth study of membrane and transport properties on the molecular, multi-nanometer, and membrane length scales will be performed using a combination of spectroscopy, morphological analysis, and transport measurements, with special attention paid to the chemical and physical framework and the water binding within the membrane. By combining both fundamental insights and performance-specific transport measurements, a complete picture of molecular structure-transport properties can be formed for these important materials.
Broader Impacts: The success of this project will open a completely new direction in the development of ion-containing membranes and has profound implications for rational design of nanostructured membranes with new architectures and superior selectivity and transport properties. Future scientists capable of working in the interdisciplinary field of polymer membranes and fuel cells will be trained and educated within this program. Undergraduates and minorities will be integrally involved in the research program. The "Materials + Creativity + Community = Energy" modules including lecture materials, handouts, slides, and hand-on experimental demonstrations will be created and deployed in campus open houses, during student group activities on and off campus (seminars, student club gatherings, high school visits), and during two new summer residential camps including Penn State Science Workshop for grades 9-12 teachers and ASM Materials Camp for high school students.
Normal 0 false false false EN-US ZH-CN X-NONE Membranes with controllable separation properties play a vital role in advanced energy and environmental applications. For instance, proton/methanol selectivity is a critical aspect in the design of new polymer electrolyte membranes (PEMs) for direct methanol fuel cells (DMFCs). One of the main barriers to fully realizing the potential of DMFCs is the methanol permeability of the PEMs. The central themes of the project are to develop new membrane structures that have the potential to perform low-energy aqueous separations with high selectivity. Membrane synthesis and fabrication motifs with low methanol permeability/high proton conductivity have been sought in tailored materials to improve our fundamental understanding of transport mechanism of methanol, ions, and water in PEMs. An in-depth study of membrane and transport properties on the molecular, multi-nanometer, and membrane length scales have been performed using a combination of spectroscopy, morphological analysis, and transport measurements, with special attention paid to the chemical and physical framework and the water binding within the membrane. Specially, we have designed and synthesized several series of new membrane materials including Nafion-based composite membranes, fluoropolymer membranes and ionic liquid-containing membranes. The prepared polymers have been carefully characterized by a library of analytic methods. The morphology of the membranes has been investigated by using electron microscopy and small-angle X-ray diffraction. We have investigated the morphological structure, ion-exchange capacity, water uptake, proton conductivity and methanol permeability of the prepared membranes as functions of the chemical structures, composition, temperature and relative humidity. We have studied the state of the absorbed water within the membranes and its correlation with transport properties of methanol and protons. Overall, the grant has led to one review article, twenty journal publications, five undergraduate theses, one MS theses, and three PhD theses. Undergraduate students, women, and under-represented minorities have been integrally involved in the research activities. Eight undergraduate students from NSF REU, Woman in Science and Engineering Research and Minority Undergraduate Research Experience programs have participated in this project. The graduate students who worked on this project have given six oral presentations in the ACS and MRS national meetings. The PIs organized a symposium entitled "Functional Polymer Nanocomposites for Energy Harvesting and Conversion" at 2009 ACS National Meeting in Salt Lake City, UT. One session in the symposium focused on functional polymer based membranes for fuel cell and battery applications. The PIs organized a symposium entitled "Polymer Membranes and Thin Films for Energy Applications" at the 2010 ACS National Meeting in San Francisco, CA with sessions devoted to fuel cells, capacitors, and organic photovoltaics. The PIs have co-edited an ACS symposium book entitled "Functional Polymers for Energy Harvesting and Conversion". The PIs has given more than 20 invited talks in the ACS and MRS national meetings and universities. The PIs have also attended annual openhouses and outreach events to promote participation of minority students and high school kids in science learning and career.
