The permittivities of PVDF/PMMA blends at hydrostatic pressure

Abstract

The complex permittivities of poly(viny1idene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperature T( 20 "-60 "C), frequency v ( 5 Hz-300 kHz), and hydrostatic pressure p (0-260 MPa). The values can be represented by a master curve with the shift factors &/A log (v/Hz) = -140 MPa at room temperature and A ( 1 /Z' ) /A log (v/Hz) = -2 -K-' at atmospheric pressure. The dependence of the activation energy AEA onpressurep is then given by AEA = (100 + 0.02 MPa-'p) kJ/mol. Furthermore, the results indicate that the @-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group.

The electric moment contribution to the piezoelectricity of PVDF

“…The overall permittivities, both their real and their imaginary parts, in dependence on hydrostatic pressure ( p = 0.1 to 260 MPa), temperature (2' = 20 to 60'C), and frequency (v = 5 Hz to 300 kHz) of isotropic [16] as well as the hydrostatic piezoelectric coefficients [9] of drawn and undrawn PVDF/PMMA blends at a frequency of 1 Hz and a t room temperature have been reported on earlier. Since only the E values and the compressibilities of isotropic samples are available, we can analyze here only the piezoelectricity of these materials where the melt-crystallized PVDF exhibits the crystalline amodification.…”

“…The permittivities of PVDF/PMMA blends a t 60'C and 1 Hz on which the following analysis is based are displayed in Figure 3. The values for p < 300 MPa have been measured [16]. Those at higher pressure have been calculated from the permittivities at other temperatures and frequencies by use of the composition independent empirical shift factors Ap/Alog(u) = -(140 =t 50) MPa at 20…”

“…at atmospheric pressure [16], with U in Hz. These shift factors have been derived from a corresponding analysis of the experimentally determined E values, and hold for the real as well as the loss parts, respectively, of the permittivities.…”

“…The permittivities E, and E, of the competing phases, assuming the volume fraction of the polarized phase to be U,, and that of the whole material E are related by [19,221 The overall permittivity E can therefore assumed to be a superposition of the contributions of the two phases as weighted by w , where the specific superposition rule depends on D,. This is easily seen when rearranging Equation (16) for the limiting cases of D, = 0 and D, = 1 By means of the superposition rule, calculation of the permittivity E , of the crystalline, polarized phase is possible from the overall values E for a given D, if it is assumed that 1. a t sufficiently high pressure all molecular relaxations are suppressed and only the optical polarizability contributes to E . Then, both the amorphous and the polarized phases have the same ~( p -+ w ,~ + w) = n2 = 2.02 (Figure 3), with n the refractive index;…”

“…Blending with PMMA, as already mentioned, additionally allows variation of the supermolecular structure to a wide extent. Finally, the hydrostatic pressure dependence of the dielectric permittivities already has been measured [16]. The task requires, to begin with, a suitable analysis of the moment term.…”