DSC studies on the transitions in poly(vinylidenefluoride) and some related copolymers

Léonard, Céline; Halary, Jean Louis; Monnerie, L.; Micheron, F.

doi:10.1007/bf00258030

Cited by 50 publications

(43 citation statements)

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“…Indeed, there is one more endothermic transition at ($ 708C besides the melting peak in PVDF samples with a-modification prepared by nonisothermal crystallization by quenching from the melt. This mechanism disappears at annealing [56][57][58] (or after repeated heating cycle 57 ). The authors 56,58 consider it as an indication for the existence of upper glass transition point (T g U ), where RAP relaxation occurs.…”

Section: Resultsmentioning

confidence: 93%

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Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Kochervinskiĭ

Malyshkina

Markin

et al. 2007

J of Applied Polymer Sci

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The molecular mobility in copolymers of vinylidene fluoride-hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10 À1 -10 7 Hz), differential scanning calorimetry DSC (À100 to 1508C), and of wide angle X-ray diffraction WAXS. Four relaxation processes and one ferroelectric-paraelectric phase transition have been detected. The process of the local mobility b-(at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (a a -relaxation) depend on the ratio of comonomer with lower kinetic flexibility. a c -relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of a-(a p -) phase. Diffuse order-disorder relaxor type ferroelectric transition connected with the destruction of the domains in low-perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (a-process) was observed for both copolymers in high-temperature region. DSC data shows that it falls on the broad temperature region of aphase crystals melting. It is considered to be connected with the space charge relaxation.

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Section: Resultsmentioning

confidence: 93%

“…This mechanism disappears at annealing [56][57][58] (or after repeated heating cycle 57 ). The authors 56,58 consider it as an indication for the existence of upper glass transition point (T g U ), where RAP relaxation occurs. 12,[43][44][45] The authors 57 do not agree with this.…”

Section: Resultsmentioning

confidence: 93%

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Kochervinskiĭ

Malyshkina

Markin

et al. 2007

J of Applied Polymer Sci

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“…Fig. 3 shows the infrared spectra in the range 4000 to 400 cm-~ for as-drawn films of PVF 2/PMMA 100/0, The nature of PVF2 crystalline bands has been previously shown to depend on the PVF2/PMMA blend composition [4,11]. The infrared spectra also indicate the existence of three crystalline forms, i.e.…”

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Effect of PMMA on the morphology andα → β phase transition of oriented PVF2/PMMA blends

Yang

Thomas

1987

J Mater Sci Lett

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“…[5] Also, small endothermic peaks were observed in the range of 45-60C (Figure 2a) for samples quenched at TQ <20C, which disappeared for samples quenched at higher temperatures (TQ>40C). These peaks are attributed to the upper glass transition, [29] reorganisation within conformationally disordered α-crystals, [30] or melting of paracrystalline domains within the PVDF films. [31] Field Code Changed…”

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Exclusive self-aligned β-phase PVDF films with abnormal piezoelectric coefficient prepared via phase inversion

et al. 2015

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Keywords: PVDF, piezoelectric effect, self-alignment, β-phase, Piezo Force Microscopy Poly(vinylidene fluoride), (PVDF), is one of the most attractive polymers owing to its remarkable pyro-, piezo-and ferro-electroactive properties. [1][2][3][4] These properties stem from its unique polymorphism which also gives rise to its extraordinary mechanical properties, high chemical resistance, good thermal stability and biocompatibility. [5] PVDF shows four significant crystalline phases α, β, δ and γ; [2,6] with the electroactive β-phase being utilized most frequently for the development of sensors, actuators [7,8] and microgenerators. [4,9,10] Owing to its importance, the formation of electroactive β crystalline phase has been intensively investigated through various routes, including melt casting, [15] solution deposition, [11] spin coating [12] and phase inversion. [13,14] While, the films or membranes formed by 2 melting/crystallisation are dominated by α-phase, [15] those obtained by spin-coating and further dried at temperature between 30-60 ºC are largely dominated by β-phase crystals. [12] For the phase inversion technique, PVDF films are formed by quenching the casting films into a nonsolvent bath to induce a series of liquid-solid and liquid-liquid phase separation events. [5,13,14] The microstructure and crystalline phase of the polymer films in phase-inversion can be controlled by adjusting paramteres like composition, [5,12] type of solvent, [16,17] quenching temperature etc. [18,19] Although PVDF films formed by this technique can have high β-phase contents, they are mostly porous and not suitable for electroactive applications. Moreover, the β-phase crystals are randomly oriented in these PVDF films and show no specific directional preference. Polarization under high electric field, [6,20] by Corona poling, [12] or by mechanical stretching [3,6,15] is subsequently carried out to obtain electroactive PVDF films. These operations need to be done at elevated temperatures (>80 o C), requiring high voltage equipment and films with dense structure and high β-phase content. Spontaneous formation of electroactive -phase in PVDF nanofibers formed by drawing was reported to have piezoelectric coefficient up to d33=58.5 pm/V. [25] Similarly, PVDF mesoscale rod arrays, without any poling process, too were also reported to possess good piezoelectric properties due to their high β content. [24] In both these cases, mechanical stretching and stress during the template guiding are believed to be responsible for the piezoelectric effect. Self-polarization of oriented β-phase crystals has also been observed in ultrathin (~20 nm) PVDF copolymer films by spin-coating or by Langmuir-Blodgett (LB) method, and is attributed to the built-in electric field, in-film stress and the strong interaction of PVDF molecules with polar water. [21,22,23] Generally speaking, PVDF films or membrane formed by melt casting, solution deposition, spin coating and phase inversion etc. do not exhibit aligned β-phase crystals without additional t...

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DSC studies on the transitions in poly(vinylidenefluoride) and some related copolymers

Cited by 50 publications

References 3 publications

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

Effect of PMMA on the morphology andα → β phase transition of oriented PVF2/PMMA blends

Exclusive self-aligned β-phase PVDF films with abnormal piezoelectric coefficient prepared via phase inversion

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