Piezoelectricity polymers and

Table II. Polarization data for some amorphous piezoelectric polymers and PVDF.

It should be kept in mind that materials development is considerably upstream from the development of new products. It is quite typical for new materials to find their way into commercial products about 20 years after their discovery. Examples include Kevlar , high-Tc ceramic superconductors, piezoelectric polymers, and gallium arsenide. It is also typical for the first applications to be quite different from those originally proposed and for their impact to be modest compared to that suggested during the initial excitement. A personal view of the status and prospects for biomimetic materials will be given at the end of this article. 

In this chapter a brief introduction on piezoelectric polymers and electrostrictive polymers is presented, and some representative polymers are given with their essential properties. The information should provide knowledge for readers to know the origin of modem research on piezoelectric and electrostrictive polymers and recent advances in this area. 

Bauer S, Bauer F (2008) Piezoelectric polymers and their applications. In Heywang W, Lubitz K, Wersing W (eds) Piezoelectricity evolution and future of a technology, vol 114, Springer series in materials science. Springer, Berlin/Heidelberg, pp 157-177... 

There are several different classes of biodegradable synthetic polymers used for peripheral nerve repair (eg, aliphatic polyesters, polyphosphoesters, polyurethanes, and piezoelectric polymers) and some of than are approved for clinical nse, such as PGA (Neurotube) and PLC (Nenrolac) (Li et al., 2015a Tan et al., 2012). 

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. 

Bauer, S. and F. Bauer, Piezoelectric polymers and their applications, piezoelectricity. Chap. 6, Springer Series in Materials Science, Vol. 114, Springer, Berlin, 2008. 

Piezocomposite transducers are an advancement of piezoelectric ceramics. Instead of the classic piezoceramic material, a compound of polymer and piezoceramic is used for the composite element to improve specific properties. The 1-3 structure, which is nowadays mostly used as transducer material, refers to parallel ceramic rods incorporated in an epoxy-resin matrix (see Fig. 1). 

The ramp of pressure to about 3 GPa observed in shock-loaded fused quartz has been used very effectively in acceleration-pulse loading studies of viscoelastic responses of polymers by Schuler and co-workers. The loading rates obtained at various thicknesses of fused quartz have been accurately characterized and data are summarized in Fig. 3.6. At higher peak pressures there are no precise standard materials to produce ramp loadings, but materials such as the ceramic pyroceram have been effectively employed. (See the description of the piezoelectric polymer in Chap. 5.)... 

For mechanical wave measurements, notice should be taken of the advances in technology. It is particularly notable that the major advances in materials description have not resulted so much from improved resolution in measurement of displacement and/or time, but in direct measurements of the derivative functions of acceleration, stress rate, and density rate as called for in the theory of structured wave propagation. Future developments, such as can be anticipated with piezoelectric polymers, in which direct measurements are made of rate-of-change of stress or particle velocity should lead to the observation of recognized mechanical effects in more detail, and perhaps the identification of new mechanical phenomena. 

In this chapter piezoelectric crystals and polymers ferroelectric and ferromagnetic solids resistance of metals shock-induced electrical polarization electrochemistry elastic-plastic physical properties. 

The science and technology of piezoelectric materials has long been dominated by the availability of specific materials with particular properties. Piezoelectric polymers are the most recent class of piezoelectrics developed. 

The most common piezoelectric polymers are PVDF, based on the monomer CH2 CF2 and copolymers of PVDF with C2F3H. Although there are many sources for materials that are nominally piezoelectric, sources for reproducible materials are limited. 

It is of interest to compare the observations with different physical mechanisms as shown in Fig. 5.19. Typically, the polarization values for polymers are weak and do not overlap those of piezoelectrics. What is observed is that there is over a 6 order-of-magnitude range in polarizations from the weakest signals (Teflon) to the strongest (PZT 95-5). The polarization signals from ionic crystals are stronger than those in polymers and overlap those of piezoelectrics, albeit at larger strains. 

Fig. 5.19. Shock-induced volume polarizations have been observed in a wide range of solids due to a number of different physical phenomena, including piezoelectricity and ferroelectricity. The signals observed from polymers and ionic crystals are not due to established phenomena, and are described as due to shock-induced polarization effects.

In this chapter studies of physical effects within the elastic deformation range were extended into stress regions where there are substantial contributions to physical processes from both elastic and inelastic deformation. Those studies include the piezoelectric responses of the piezoelectric crystals, quartz and lithium niobate, similar work on the piezoelectric polymer PVDF, ferroelectric solids, and ferromagnetic alloys which exhibit second- and first-order phase transformations. The resistance of metals has been investigated along with the distinctive shock phenomenon, shock-induced polarization. 

The piezoelectric polymer investigations give new physical insight into the nature of the physical process in this class of ferroelectric polymers. The strong nonlinearities in polarization with stress are apparently more a representation of nonlinear compressibility than nonlinear electrical effects. Piezoelectric polarization appears to be linear with stress to volume compressions of tens of percent. The combination of past work on PVDF and future work on copolymers, that have quite different physical features promises to provide an unusually detailed study of such polymers under very large compression. 

Theoretical estimations and experimental investigations tirmly established (J ) that large electron delocalization is a perequisite for large values of the nonlinear optical coefficients and this can be met with the ir-electrons in conjugated molecules and polymers where also charge asymmetry can be adequately introduced in order to obtain non-centrosymmetric structures. Since the electronic density distribution of these systems seems to be easily modified by their interaction with the molecular vibrations we anticipate that these materials may possess large piezoelectric, pyroelectric and photoacoustic coefficients. 

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

Fig. 4. Block diagram of the apparatus for measuring complex piezoelectric stress and strain constants of polymer films with varying frequency (Furukawa and...

Piezoelectric polymer film is usually partially crystalline and the crystallites are embedded in the amorphous phase, which exhibits mechanical relaxations. Therefore, the strain of each crystallite, S, may differ in both amplitude and phase from that of the film as a whole, S. In this case the complex piezoelectric constant of the film is written by putting S/S — K (complex quantity) in Eq. (62) as... 

Furukawa,T., Uematsu,Y., Asakawa,K., Wada,Y. Piezoelectricity, pyroelectricity, and thermoelectricity of polymer films. J. Appl. Polymer Sci. 12, 2675 (1968). 

Date,M., Fukada,E. An apparatus for measuring piezoelectric strain and stress constants in polymers. Rep. Progr. Polymer Phys. Japan 13, 375 (1970). 

Kitayama, T., Nakayama, H. Piezoelectricity of composite systems of polymer and powdered ferroelectric ceramics. 18 th Meeting on Appl. Phys. Japan (Apr. 1971) Tokyo. 

Spectrophotometry, 42 Absorbance, 42 Infrared, 44 Luminescence, 45 Raman, 48 Fiber Optics, 50 Refractive Index, 52 Piezoelectric Mass Sensors, 53 New Chemistry, 54 Immunochemistry, 54 Polymers and New Materials, 56 Recognition Chemistry, 57 Chromatography and Electrophoresis, 61 Flow Injection Analysis and Continuous Flow Analysis, 63 Robotics, 65 Chemometrics, 68 Communications, 70... 

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