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Séminaires Chimie ED459 / ICGM

Multilayer polymer dielectric films for next generation film capacitors

Prof. Lei Zhu (Department of Macromolecular Science and Engineering and Center for Layered Polymeric Systems, Case Western Reserve University, Cleveland, OH, USA)

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Deux séminaires à l’ENSCM, amphithéâtre Chaptal :
– Le Mercredi 01 avril 2015 à 10h ;
– Le Jeudi 02 avril 2015 à 14h

1. Understanding relaxor ferroelectric structure and behavior in p(VDF-TrFE)-based copolymers

Mercredi 01 avril 2015 à 10h, ENSCM amphi Chaptal

Despite comprehensive understanding of novel ferroelectric [i.e., relaxor ferroelectric (RFE) and antiferroelectric (AFE)] behaviors for ceramics, RFE and double hysteresis loop (DHL) behaviors have just emerged for ferroelectric crystalline polymers since the past 15 years. A number of applications such as electrostriction, electric energy storage, and electrocaloric cooling have been realized by utilizing these novel ferroelectric properties. However, the fundamental understanding is still lacking. In this talk, we intend to achieve high k and low loss polymer dielectrics by unraveling the fundamental physics behind these novel ferroelectric behaviors. It is found that both crystal internal structure and nanoconfinement effects are important for achieving high k and low loss polymer dielectrics. For the crystal internal structure effect, friction-free dipole switching and nanodomain formation by pinning the polymer chains are essential, and they can be achieved via the mechanism of crystal repeating unit isomorphism. Physical pinning induces a reversible RFE↔FE phase transition and thus the DHL behavior, whereas chemical pinning results in the RFE behavior. The nanoconfinement effect is demonstrated in poly(vinylidene fluoride) (PVDF)-based multilayer films. These understandings will help us design new ferroelectric-based polymers with improved electrical properties and better applications.

2. Multilayer polymer dielectric films for next generation film capacitors

Jeudi 02 avril 2015 à 14h, ENSCM amphi Chaptal

Advanced dielectric film capacitors have become increasingly important in mobile power electronic systems such as those used in electric vehicles (EVs). Current state-of-the-art biaxially oriented polypropylene (BOPP) films start to face technical issues including low energy density and high conduction loss at temperatures above 85°C. At Case Western Reserve University, we have developed a novel multilayer film technology to meet the stringent requirements for next generation dielectric film capacitors in EVs and HEVs. By multilayering a high breakdown strength polymer such as polycarbonate (PC) with a high dielectric constant polymer such as poly(vinylidene fluoride) (PVDF), we have achieved high breakdown strength (>600 MV/m), high energy density at breakdown (16 J/cc), and relatively low dielectric dissipation factor (tanδ<0.006) and hysteresis loss (15% loop area). In this presentation, we will identify and discuss the fundamental issues for multilayer capacitor films. They include prevention of VDF dipole flipping, reducing migrational loss from impurity ions in PVDF, reducing DC conduction at high temperatures, and utilizing Maxwell-Wagner-Sillars interfacial polarization to achieve enhanced breakdown strength and lifetime.

Biographical sketch

Professor Lei Zhu received his B.S. degree in Materials Chemistry in 1993 and M.S. degree in Polymer Chemistry and Physics in 1996 from Fudan University, Shanghai. He received his Ph.D. degree in Polymer Science from University of Akron in 2000. After two-year post-doctoral experience at the Maurice Morton Institute, University of Akron, he joint Institute of Materials Science and Department of Chemical, Materials and Biomolecular Engineering at University of Connecticut, as an assistant professor. In 2007, he was promoted to associate professor with tenure. In 2009, he moved to Department of Macromolecular Science and Engineering at Case Western Reserve University as an Associate Professor. In 2013, he was promoted to full Professor. His research interests include high k polymer and organic-inorganic hybrid nanomaterials for high energy density capacitor applications, development of artificial antibody as nanomedicines, and supramolecular self-assembly of discotic liquid crystals. He is recipient of NSF Career Award, 3M Non-tenured Faculty Award, DuPont Young Professor Award, and Rogers Teaching Excellence Award. He is author and co-author of 121 refereed journal publications and 5 book chapters. He delivered 108 invited talks and 45 contributed presentations, and his total citation is over 4100 times with an H-index of 35 (Google Scholar).

Contact ICGM : Dr. Bruno Améduri, DR CNRS (équipe IAM)


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