Piezoelectric polymers poling

An SFM based lithography technique by means of mechanical interactions as applied to surfaces of polystyrene (PS) and polymethylmethacrylate (PMMA) is described in Sect. 6. Similarly, some results of SFM-based poling experiments performed on a piezoelectric polymer are elucidated in Sect. 7.6. 

Whiter, RA, Narayan, V, Kar-Narayan, S., 2014. A scalable nanogenerator based on self-poled piezoelectric polymer nanowhes with high energy conversion efficiency. Adv. Energy Mater. 4,1400519. 

Nilsson E, Lund A, Jonasson C, Johansson C, Hagstrom B. Poling and characterization of piezoelectric polymer fibers for use in textile sensors. Sensor Actual A- Phys 2013 201 477-86. 

Examples of polymers that have a piezoactive response are poled poly(vinylidene fluoride) (PVDF) (151) and its copolymers with trifluo-roethylene co(VDF-TrFE) (152), and the family of odd nylons (153) (see Piezoelectric Polymers). These are partially crystalline materials in which the crystalline regions have a permanent electric dipole moment. These polymers show ferroelectric switching behavior indicating that after poling they have a net... 

A molecular theory of the direct piezoelectric effect in poled amorphous piezoelectric polymers has been developed. An expression for the hydrostatic coefficient appears in the original paper (41). Later, this theory was extended, and an equation for dsi was obtained (44,45). By differentiating equation 14 and modifying it to account for dimensional effects such as stretching (44,46),... 

After the discovery of significant piezoelectricity in polymers in the late 60s, they were immediately considered for applications in the early 70s. Interest faded in the early 80s due to problems in producing reproducible devices. After solving these initial problems by developing efficient poling procedures and suitable electrical contacting methods, piezoelectric polymers became a commercial success in many niche applications. Science progresses in waves, and currently, we face a very active research phase where piezoelectric and relaxor ferroelectric polymers are employed... 

Piezoelectric polymer hydrophones have been proposed as probes (or mapping ultrasonic fields and determining acoustic field parameters in both water and biological media. Among the several PVDF hydrophones developed, the most widely used have been the original hoop membrane configuratioo (spot-poled membrane supported by means of a hoop) (40] and the needle-type probe (41]. While both can be used to assess ultrasonic field patterns in water, only the needle-type probe can be used for bioacoustic measurements, such as in vitro and in vivo evaluatkm of tissue properties. 

Although the mechanisms by which electrical activity influences peripheral nervous system regeneration are not understood, the results reported above indicale the possible helpful clinical use of piezoelectric polymers in the surgical repair of injured or severed peripheral nerves. The piezoelectric characteristics of poled PVDF tubes can obviate the need for external power sources and electrical connectioas. as requested in regenerating systems based on the application of electromagnetic fields or direct currents. 

The piezoelectric material itself may be a composite. For example, combinations of piezoelectric polymers and piezoelectric ceramics have been made. Spom and Schoenecker discuss ceramic fibers in a polymer matrix. First, PZT fibers with diameters <30 mm oriented uniaxially in a planar fiber architecture along with interdigital electrodes. Then the fiber/electrode architectures are embedded within glass fiber-reinforced polymers and the fibers are poled and become piezoelectric. 

It must in any case be noted that the piezoelectricity of polymer films due to charges is not an intrinsic property of polymers it varies from sample to sample and can be remarkably enhanced by drawing and/or poling, as will be described in following sections. 

Kawai (1) and (2) (1969) found that polar polymer films such as PVDF, poly (vinyl fluoride), PVC, nylon 11, and polycarbonate exhibit a strong piezoelectricity when they are drawn and then polarized under a high cLc. field Ep at a high temperature Tp and cooled keeping the d.c. field. The piezoelectricity thus obtained depends on Ep, Tp, and poling period. An improved poling technique was reported by Edelman, Grisham, Roth, and Cohen (1970). 

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