References
IUPAC name	poly-1,1-difluoroethene
Other names	polyvinylidene difluoride, KYNAR, HYLAR, SOLEF, SYGEF
Identifiers
CAS number	24937-79-9 Y
Properties
Molecular formula	-(C2H2F2)n-
Appearance	whitish or translucent solid
Solubility in water	not soluble in water
Structure
Crystal structure	mm2(Kawai, 1969)
Dipole moment	2.1 D(Zhang, 2002)
Related compounds
Related compounds	PVC, PTFE, P(VDF-TrFE)
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Polyvinylidene Fluoride, or PVDF is a highly non-reactive and pure thermoplastic fluoropolymer.

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 of around 177°C.

It has a 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 injected, molded or 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 or HYLAR 5000 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.

PVDF membranes are used for western blots for immobilization of proteins, due to its non-specific affinity for amino acids.

Contents 1 Properties 2 Processing 3 Copolymers 4 Usage 5 See also 6 References 7 External links

[edit] Properties

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.

PVDF has a glass transition temperature (Tg) of about -35°C 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 in several forms: alpha (TGTG'), beta (TTTT), and gamma (TTTGTTTG') phases, depending on the chain conformations as trans (T) or gauche (G) linkages. 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.

Unlike other popular piezoelectric materials, such as PZT, PVDF has a negative d₃₃ value. Physically, this means that PVDF will compress instead of expand or vice versa when exposed to the same electric field.

[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. In aqueous emulsion polymerization, the fluorosurfactant perfluorononanoic acid is used in anion form as a processing aid by solubilizing monomers.^[1] For characterization of the molecular weight via gel permeation chromatography (also called SEC), solvents such as DMSO or THF may be used.

Processed materials are typically in the non-piezoelectric alpha phase. The material must either be stretched or annealed to obtain the piezoelectric beta phase. The exception to this is for PVDF thin films (thickness in the order of micrometres). Residual stresses between thin films and the substrates on which they are processed are great enough to cause the Beta phase to form.^{[verification needed]}

In order to obtain a piezoelectric response, the material must first be poled in a large electric field. Poling of the material typically requires an external field of >=30 MV/m. Thick films (typically >100 µm) must be heated during the poling process in order to achieve a large piezoelectric response. Thick films are usually heated to 70-100 °C during the poling process.

A quantitative defluorination process was described by mechanochemistry (Zhang , 2001), for safe eco-friendly PVDF waste processing.

[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.

While the copolymers' unit structures are less polar than that of pure PVDF, the copolymers typically have a much higher crystallinity. This results in a larger piezoelectric response. d₃₃ values for P(VDF-TrFE) have been recorded to be as high as -38 pC/N⁷ versus -33 pC/N in pure PVDF⁵.

[edit] Usage

PVDF is used for specialty fishing lines sold as fluorocarbon as replacement for nylon filament where it has several advantages. Optical density is lower which makes the line less easily discernable. The surface is harder so it is more resistant to sharp fish teeth and wear. Furthermore PVDF doesn't take up water and it is resistant to UV-light. It is also more dense than nylon, which makes it sink faster as it will not float on the water surface. ^[2]

PVDF is also commonly used as insulation on some kinds of electrical wires, thanks to its combination of flexibility, light weight, and good resistance to chemicals, heat and fire. In this use the wire is generally referred to as "Kynar wire", from the trade name. Most of the narrow 30-gauge wire used in wire wrap circuit assembly is PVDF-insulated.

In the biomedical sciences PVDF is used in immunobloting as a membrane (usually 0.22 or 0.45 micron thick) on which proteins are transferred using electricity. (see western blotting). PVDF is resistant to solvents and therefore these membranes can be easily stripped and reprobed to look at other proteins making it very convenient.

Piezoelectric panels made of PVDF are used on Venetia Burney Student Dust Counter, a scientific instrument of the New Horizons space probe that measures dust density in outer solar system.

[edit] See also

• Piezoelectricity
• Plastic
• Polymer
• Ferroelectric polymers

[edit] References

1. Kawai, H., (1969). Jpn. J. Appl. Phys, 8, p975.
2. 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.
3. Vinogradov, A., Schwartz, M. (Ed.), (2002). "Piezoelectricity in Polymers", Encyclopedia of Smart Materials, Volumes 1-2, John Wiley & Sons, 780-792.
4. Tasaka, S., Miyata, S., (1981). Ferroelectrics, 32 (1), 17-23.
5. E. L. Nix and I. M. Ward, (1986) Ferroelectrics 67, 137.
6. K. Tashiro, M. Kobayashi, H. Tadokoro, and E. Fukada, (1980). Macromolecules 13, 691
7. Kenji, O., Hiroji, O., Keiko, K., (1996). J. Appl. Phys. 81, 2760.
8. Zhang, QW., Lu, J.F, Saito, F., Baron, M., (2001). J. Appl. Polym. Sci. 81 (9), 2249-2252.

1. ^ Prevedouros K, Cousins IT, Buck RC, Korzeniowski SH (January 2006). "Sources, fate and transport of perfluorocarboxylates". Environ Sci Technol. 40 (1): 32–44. doi:10.1021/es0512475. PMID 16433330. 
2. ^ http://www.seaguar.com/About_SEA.html

[edit] External links