Friday, March 25, 2011 3:00 pm – 4:00 pm
Room 610, M&M Building
Dr. John Y. Fu
Department of Mechanical and Aerospace Engineering
State University of New York
Historically, the study of flexoelectricity is closely related to that of piezoelectricity though the physicalmechanisms behind these phenomena are completely different . In solid dielectrics, bothpiezoelectricity and flexoelectricity can be derived from the energy coupling in crystalline structures,which are based on equilibrium thermodynamics. However, those phenomena in polymers and liquidcrystals are more complicated due to their complex molecular chains and conformations. Recently, agiant flexoelectric phenomenon has been observed in bent-core nematic liquid crystal elastomers(BCLCEs) , which attracts much scientific attention since the nematic phase cannot be regarded asthe ferroelectric phase in most mesomorphic materials. It was believed that the giant flexoelectric effectmight only be observed in certain mesomorphic materials with the chiral smectic C* phase, a ferroelectricphase predicted by Meyer in the 1970s for liquid crystals . Inspired by this study, we investigatedcertain polyvinylidene fluoride (PVDF) polymer films. A giant flexoelectric effect in a PVDF polymer filmwith mixed α- and β-phases has been observed in our group , which contradicts the previoustheoretical estimation that the flexoelectric coupling is small, on the order of 10 pC/m. In this seminar, Iwill re-visit the definitions of both piezoelectricity and flexoelectricity in solid dielectrics, and then comparethem with their counterparts in liquid crystals and polymers. Some peculiar physical phenomena relatedto both piezoelectricity and flexoelectricity in polymers will also be discussed. Finally, I will demonstratethat such a giant flexoelectric effect can be exploited to fabricate soft flexoelectric piezoelectriccomposites and devices by using non-piezoelectric soft materials.
References:  P. G. de Gennes, Physics of Liquid Crystals (Oxford University Press, London, 1974).  J. Hardenet al., Appl. Phys. Lett. 96, 102907 (2010).  R. B. Meyer, L. Liebert, L. Strzelecki, P. Keller, J. Phys. Lett. (Paris)36, 69 (1975).  J. Y. Fu et al., “Giant flexoelectricity in a polyvinylidene fluoride film”, submitted to Applied PhysicsLetters.
Dr. John Y. Fu is an assistant professor of mechanical engineering. He came to Buffalo and joined theMAE Department in August 2008. Between 2005 and 2008, Dr. Fu worked as a postdoctoral scholar in a navysponsored materials research laboratory. He completed his college education in China, and received his Ph.D.degree in electrical engineering from the Pennsylvania State University at University Park in December 2004. Dr.Fu holds one American patent and four American and international pending patents. His current research interestsfocus on polymer physics, dielectric polymers, ferroelectric polymers, liquid crystal polymers, flexoelectricpiezoelectric polymer composites and devices, and flexoelectric and flexoviscous phenomena in polymers andbiomaterials.