In this paper, we report a chemical way to resolve longer motions units in the glass-rubber transition region of poly (ethyl acrylate) (PEA), so called internal plasticization. The ethyl acrylate (EA) monomers were copolymerized with little amount of isoprene (IP) monomers. We propose that the single bonds adjunct to double bonds would have better flexible activity than usual single bonds, so the motion units located between two adjunct double bonds would be enhanced. The dynamic mechanical spectra of internally plasticized PEA (IPPEA) and PEA show that the tan δ of IPPEA is asymmetric, while the tan δ of PEA is symmetric. Furthermore, the results of 2D-DMAS show that the LSM, SRM and RM of IPPEA are located at 7 °C, 12 °C and 36 °C. The shoulder peak of tan δ of IPPEA at higher temperature side was confirmed that it contains sub-rouse mode (SRM) and rouse mode (RM). Thus, internal plasticization is an effective way to resolve modes above T g .
Weiqian Song,Yangxi Yan,Maolin Zhang,Dongyan Zhang,Li Jin,Zhimin Li
In this study, Co-doped 0.49 Pb(Ni 1/3 Nb 2/3 )O 3 -0.51 Pb(Hf 0.3 Ti 0.7 )O 3 ceramics with high piezoelectric constants, electromechanical coupling coefficients, and low dielectric losses were prepared by conventional solid-phase reaction method for use as piezoelectric energy harvesters in both resonant and non-resonant working states. XRD results showed the dissolution of Co ions in the crystal lattice , thereby replacing B-sites and transforming the crystal phase into tetragonal phase. Valence states of Co obtained from fitted XPS data confirmed the existence of Co as Co 2+ in the lattice. The introduction of Co 2+ effectively increased grain size, improved ferroelectric properties , reduced leakage current density, and enhanced electromechanical coupling coefficient k p . Impacts of Co-doping on properties of the as-obtained ceramics were discussed. The optimal performances were obtained at x = 1.25, with piezoelectric constant d 33 ~780 pC/N, electromechanical coupling coefficient k p ~0.62, and dielectric loss tan δ = 0.78%. In sum, the excellent piezoelectric properties of Co-doped PNN-PHT ceramics look promising for use as piezoelectric energy harvesters.
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