tailieunhanh - Electroactive Polymers for Robotic Applications - Kim & Tadokoro (Eds.) Part 7

Tham khảo tài liệu 'electroactive polymers for robotic applications - kim & tadokoro (eds.) part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Ferroelectric Polymers for Electromechanical Functionality 113 density. The smaller the number the higher the dipole density. The interrelationship between the number and the remnant polarization is tabulated in Table as reported by Mei . in 1993 82 . Table . Unit molecular weight dipole density and remnant polarization of odd-numbered nylons N-3 N-5 N-7 N-9 N-11 Molecular weight of repeat unit Dipole density D 100 Angstrom3 Remnant Polarization mC m2 180 125 86 68 56 Predicted Piezoelectricity of some representative odd-numbered nylons As with the piezoelectric properties of PVF2 the piezoelectric properties of odd-numbered nylons as semicrystalline polymers are determined by the remanent polarization in the materials and the mechanical properties. The remnant polarization primarily depends on the crystallinity or the content of polar crystals and the alignment of the polar crystal demains. Thermal annealing is the most popular method to increase crystallinity. However for odd-numbered nylons the melt-quench and cold-stretching process is critical for the parallel sheet structure formed by hydrogen bonds. Parallel-sheet-structured the odd-numbered nylons can generate typical ferroelectric property and therefore can result in expected piezoelectric properties after being poled. Three primary factors are important for poling the materials to achieve high remanent polarization poling temperature poling field and poling time. Generally a higher poling temperature higher than glass temperature higher poling field and longer poling time generate higher remnant polarization. Usually an optimization of the three primary factors is needed for the best poling effect. For instance a well-poled at room temperature melt-quenched and uniaxially stretched times at room temperature nylon 11 film usually can possess a remanent polarization Pr of 50 mC m2 and offer a piezoelectric strain coefficient d31 of N