Polyvinylidene fluoride
From Wikipedia, the free encyclopedia
| Polyvinylidene difluoride | |
|---|---|
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| General | |
| Systematic name | poly-1,1-difluoroethene |
| Other names | polyvinylidene difluoride |
| Molecular formula | -(CH2CF2)n- |
| SMILES | ? |
| Appearance | whitish or translucent solid |
| CAS number | [] |
| Properties | |
| Density and phase1,2 | 1.76 g/cm3 (110 lb/ft3), solid |
| Solubility in water | not soluble in water |
| Melting point4 | 134–169 °C (273–336 °F, 407-442 K) |
| Thermal conductivity4 | 0.18 W m-1 K-1 |
| Coefficient of expansion4 | 0.18×10-6 K-1 (0.10×10-6 °F-1) |
| Yield strength4 | 15–35 MPa (2.2–5.0 kpsi) |
| Elongation at rupture4 | 200%–750% |
| Modulus of elasticity | 350–1100 MPa (50–160 kpsi)4 E1= 2.56GPa, E2= 2.6GPa (Vinogradov, 2002) |
| Poisson ratio | ν21~0.1, ν31~0.8 (Tasaka, 1981) |
| Volume resistivity4 | ≥ 1x1012 Ω·m |
| Piezoelectric constants | d33=20 pC/N, d31= -5 to -16 pC/N, d32= -3 to -5 pC/N |
| Structure | |
| Crystal structure | mm2 (Kawaii, 1969) |
| Dipole moment | 2.1 D (Zhang, 2002) |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | ? |
| NFPA 704 | |
| Flash point | ? °C |
| R/S statement | R: ? S: ? |
| RTECS number | ? |
| Supplementary data page | |
| Structure and properties |
n = ?, εr = 9 to 11. 3 |
| Related compounds | |
| Related compounds | PVC, PTFE, P(VDF-TrFE) |
| References | |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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Polyvinylidene Difluoride, or PVDF is a highly non-reactive and pure thermoplastic fluoropolymer. It is also known as KYNAR®.
PVDF is a specialty plastic material in the fluoropolymer family; it is used generally in applications requiring the highest purity, strength, and resistance to solvents, acids, bases and heat and low smoke generation during a fire event. Compared to other fluoropolymers, it has an easier melt process because of its relatively low melting point. It has a relatively low density (1.78) and low cost compared to the other fluoropolymers. It is available as piping products, sheet, tubing, films, plate and an insulator for premium wire. It can be injection molded and welded and is commonly used in the chemical, semiconductor, medical and defense industries, as well as in lithium ion batteries. A fine powder grade, KYNAR 500 PVDF, is also used as the principal ingredient of high-end paints for metals. These PVDF paints have extremely good gloss and color retention, and they are in use on many prominent buildings around the world, e.g. the Petronas Towers in Malaysia and Taipei 101 in Taiwan, as well as on commercial and residential metal roofing. PPG Industries, Inc. is a well-known supplier of such PVDF-containing coatings.
When poled, PVDF is a ferroelectric polymer, exhibiting efficient piezoelectric and pyroelectric properties. These characteristics make it useful in sensor and battery applications. Thin films of PVDF are used in some newer thermal camera sensors.
PVDF has a glass transition temperature (Tg) of about -35oC and is typically 50-60% crystalline. To give the material its piezoelectric properties, it is mechanically stretched to orient the molecular chains and then poled under tension. PVDF exists several forms: alpha (TGTG'), beta (TTTT), and gamma (TTTGTTTG') phases, depending on the chain conformations as trans (T) or gauche (G) linkages.
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[edit] Processing
PVDF may be synthesized from the gaseous VDF monomer via a free radical (or controlled radical) polymerization process. This may be followed by processes such as melt casting, or processing from a solution (e.g. solution casting, spin coating, and film casting). Langmuir-Blodgett (LB) films have also been made. In the case of solution-based processing, typical solvents used include DMF as well as the more volatile MEK. For characterization of the molecular weight via GPC (also called SEC), solvents such as DMSO or THF may be used.
[edit] Copolymers
Copolymers of PVDF are also used in piezoelectric and electrostrictive applications. One of the most commonly-used copolymers is P(VDF-TrFE), usually available in ratios of about 50-50 wt% and 65-35 wt% (equivalent to about 56-44 mol% and 70-30 mol%). Another one is P(VDF-TFE). They improve the piezoelectric response by improving the crystallinity of the material.
Another material is a composite of PVDF and PZT.
[edit] History
In 1969, the strong piezoelectricity of PVDF was observed by Kawai et al. The piezoelectric coefficient of poled thin films of the material were reported to be as large as 6-7 pCN-1, 10 times larger than that observed in any other polymer.
[edit] See also
[edit] References
- Kawai, H., (1969). Jpn. J. Appl. Phys, 8, p975.
- Zhang, Q. M., Bharti, V., Kavarnos, G., Schwartz, M. (Ed.), (2002). "Poly (Vinylidene Fluoride) (PVDF) and its Copolymers", Encyclopedia of Smart Materials, Volumes 1-2, John Wiley & Sons, 807-825.
- Vinogradov, A., Schwartz, M. (Ed.), (2002). "Piezoelectricity in Polymers", Encyclopedia of Smart Materials, Volumes 1-2, John Wiley & Sons, 780-792.
- Tasaka, S., Miyata, S., (1981). Ferroelectrics, 32 (1), 17-23.
