The hydrostatic piezoelectric coefficient of PVDF/PMMA blends

Crystallization-induced composition inhomogeneities in PVDF/PMMA blends

“…Earlier investigations revealed that PVDF crystallizes only negligibly and with rather low rate if the PMMA content exceeds 50 wt %. 16 This value can immediately be linked to that of 52 wt %, for which crystallization and diffusional displacement rates are in equilibrium, and which is reached after about 4 h. The change of the composition at the spherulite surface from 40 to 52 wt %, i.e., of about 25% rel., accounts for the remarkable decrease of the growth rate of more than one order of magnitude [ Fig. 4(a)].…”

Microscopic origin of the high-strain mechanical response of poled and non-poled poly(vinylidene fluoride) in the β-phase

“…On the other hand, the electromechanical coupling in the direction perpendicular to the chains in weak and mediated by the amorphous phase. The coupling is small and can even change sign under different loading conditions [24]. As the effect of poling is larger along the longitudinal direction, in the following we will mainly concentrate in the difference between poled and non-poled samples just along the longitudinal direction and use the perpendicular non-poled sample for comparison, whenever considered relevant.…”

The electric moment contribution to the piezoelectricity of PVDF

“…Blending with PM-MA, however, allows preparation of piezoelectric samples with a degree of crystallinity adjustable between zero and 60%. With such samples it was found that, surprisingly, Po decreases by orders of magnitude when the crystallinity decreases only slightly ( Figure 1) [8,9].…”

“…Nevertheless, small contributions to the nonlinearity could originate also in the competing term. In contrast, both terms rule the nonlinearity of hydrostatic piezoelectricity as could be deduced from the pressure dependence of the compressibility [9]. The discussion and the separation of contributions of the two terms require careful definition and determination of the sign of the piezoelectricity.…”

“…It is the aim of the present paper to investigate, by this means, the contribution of the dielectric properties to the hydrostatic piezoelectricity of PVDF/PMMA blends. This material is advantageous for this purpose since the hydrostatic piezoelectric coefficients d p of PVDF/PMMA mixtures have already been determined, and have been shown to depend strongly on pressure [9,15]. Blending with PMMA, as already mentioned, additionally allows variation of the supermolecular structure to a wide extent.…”