9. K.Tahiro et al., Phase Trans, Vol. 18,217(1989)
Conformation of PVDF from a-b plane
10. Process of PVDF
Form I β Form III γ
Form II α
Form IIp δ
MeltSolution
high-temperature
annealing
high-pressure
quenching
casting from
DMA
slow cooling
slow cooling
drawing
casting from
HMPTA casting from
acetone
poling
poling
high-temperature annealing
drawing
Fig. Interconversion between crystal modifications
K.Tahiro et al., Phase Trans, Vol. 18,217(1989)
11. Phase diagram for
VDF/TrFE ratio
copolymer(○:melting
point;●:crystallization
point, Δ:Curie point on
heating; ▲:Curie point on
cooling; □:ferroelectric-to-
anti-ferroelectric transition
point)
T. Furukawa .Advances in Colloid and
Interface Science.71-72.183-208(1997)
Copolymer P(VDF/TrFE)
13. TT IR Spectra
100
60
40
20
0
80
1400 1200 1000 800 600 400
Wavenumber/cm-1
Transmission/%
Fig. infrared spectra of PVDF forms I and III
1280
840
510
445
K.Tahiro et al., Phase Trans, Vol. 18,217(1989)
14. TGTG- in IR Spectra
100
60
40
20
0
80
1400 1200 1000 800 600 400
Wavenumber/cm-1
Transmission/%
Fig. infrared spectra of PVDF forms II and III
796
776 610 532
K.Tahiro et al., Phase Trans, Vol. 18,217(1989)
15. T3G+T3G- IR Spectra
100
60
40
20
0
80
1400 1200 1000 800 600 400
Wavenumber/cm-1
Transmission/%
Fig. infrared spectra of PVDF forms cast III and III
1134
1115
811
K.Tahiro et al., Phase Trans, Vol. 18,217(1989)
α phase is one of the first discovered phases in polymer. Because of its lowest Gibbs free energy, it is the most stable and common phase in polymer in the room temperature. This phase is a non-polar one, but it can turn into β phase through stretching.it with annealing. Typical α phase can be obtained by melt crystallization or solution crystallized. For those films cast from appropriate solutions, the α phase predominates if evaporation occur at temperautre close to 110℃. Temperatures between 70℃ and 110℃ result in a mixure of α and β phase. α phase has a TGTG-1 conformation, with two chains of anti-parrallel dipole components which counteract each other.
This phse is usually obrained by giving high excitation voltage(120MV/m) to α phase under room temperature. In the α phase, the adjecent chains are anti-parallel, while in the δ phase they become parallel. That's why this phase shows some polarization. Because of this, the phase is also called the polaized II. Its conformation is generally the same as the α phase except for the parallel chains. So the counteract in α phase is gone and this δ shows polarization. If this phase was given a even higher excitation voltage, it could transfer to β phase.
β phase has a crystal symmetry of m2m in point group, which means its symmetrical in a axis(the longest axis after stretching) and c axis, and that leads to non-polar in these two directions. But it has a polar direction in b axis and makes it possible to polarize. β phase pvdf has the longest chain, as we know, it can be obtained by stretching. When stretched, all of its fluorine atoms come to one side of the chain and all the hydrogen come to the other. This makes it the all-trans comformation and gives it the largest polarization. Most of the dipoles are aligned in the same direction normal to the chain axis, the b axis. If we take CH2 group as the head and CF2 group as the tail, β phase is a head-tail chain. And to eliminate the over-crowded CF2 groups, they may be deflected 7°to the left and right of the plane, suggested by hasegawa. This will result in a planar zig zag structure. However, the β phase is not always achievable during the processing because there is chances of head to head or tail to tail configurations. So β phase is commonly achieved by methods which require high pressure or epitaxial techniques, or by mechanical deformation or electrical poling.
