Ferroelectric polymers based on poly(vinylidene fluoride) (PVDF) and its copolymers are good candidates for electric energy storage because of their relatively high permittivity (10-20) and high dc breakdown strength. However, the hysteresis loss for PVDF and its copolymers is too high due to their normal ferroelectricity. To realize low hysteresis for PVDF copolymers during electric polarization, either relaxor/paraelectric (single narrow loop) or antiferroelectric (double hysteresis loop) behaviors are highly desired. In this year, we continued the ferroelectric characterization of orientation and temperature dependent double hysteresis behavior in P(VDF-TrFE-CTFE)-g-PS graft copolymers. From the top panel of Fig. 1, linear dielectric behavior is observed for the nonoriented film. Double hysteresis loops gradually develop with increasing the crystal orientation. This is attributed to enhanced dipole switching in the crystals with increasing crystal orientation. From the bottom panel of Fig. 1, double hysteresis loops persist until 75 °C, above which electrical conduction and ion relaxation become so high that double hysteresis loops are replaced by large hysteresis loops. At room temperature, the double hysteresis loop behavior can persist more than 300 electric poling cycles.

Nanoconfined Polymer FerroelectricityLei Zhu, Case Western Reserve University, DMR 0907580

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Fig. 1. (top panel) D-E hysteresis loops for the P(VDF-TrFE-CTFE)-g-PS(14%) graft copolymer with different draw ratios; from A to D, 100%, 200%, 280%, and 450%, respectively. (bottom panel) D-E hysteresis loops for the P(VDF-TrFE-CTFE)-g-PS(14%) graft copolymer (A-G) under different temperatures and (H) continuous poling for 300 cycles at room temperature.

Nanoconfined Polymer FerroelectricityLei Zhu, Case Western Reserve University, DMR 0907580

Education at All Levels in 2010-2011

Graduate Research Ph.D. students: Lianyun Yang (3rd yr.) REU students: Andy Gong, University of Michigan Myela Paige, University of Maryland at Baltimore Visiting graduate student: Run Su, Sichuan University Visiting Scholar: Dr. Ruifang Guan, Jinan University (self- supported)

Undergraduate Research Mr. Yuan Yao (Macromol. Sci. & Eng.)

Fig. 2. 2012 summer group picture. (Figure 2A). Andy Gong (first from left in the last row), Myela Paige (first from left in the last third row), Dr. Ruifang Guan (first from left in the second front row)

In the lab (Figure 2B) , left: Yuan Yao, right: Lianyun Yang

Publications in 2011-2012:1. Pan, M., et al. Soft Matter 2011, 7, 11187-11193.2. Zhong, G., et al. Polymer 2011, 52, 5397-5402.3. Run, Su., et al. Polymer. 2012, 53, 728-739.4. Zhu, L., et all. Macromolecules. 2012, 45, 2937-29545. Run, Su, et all. J. Mater. Res. 2012, 27, 1389-1398