[minaabbasi]

Hi,

I have some questions regarding Polyvinylidene fluoride. It would be great if anyone could heمp and answer them.

1- I know this material is used in lighters because of its piezoelectricity property. I want to know if this property is stable or like batteries it has a life span?

2- about this property, what really changes in the structure of Polyvinylidene fluoride when it is stretched? If you can even provide me a reference to show what happens when it is stretched, it would be so helpful.

3- is there any other material that has this property and is not toxic with long lasting?

Thank you very much.

[gianegizelle]

1. http://en.wikipedia.org/wiki/Piezoelectricity

2. http://www.sciencedirect.com/science/article/pii/S092150930701458X

3.wikipedia

[Enthalpy]

In lighters, it converts mechanical into electrical energy. This doesn't consume the Pvdf, nor does it alter significantly - within engineering limits.

Pvdf is not strictly piezoelectric. It's ferroelectric - but after having been formed mechanically and electrically, it behaves like a piezoelectric material, and is much more efficient in that use than normal piezo materials like BaTiO₃, PZT and others.  You may also consider copolymers and terpolymers of Pvdf. Ceramics are less attractive: brittle, expensive, heavy metals...

The copolymer poly(vinylidenefluoride-trifluoroethylene) is often written as P(VDF-TrFE).

After stretching, a Pvdf chain has "all" (simplified!) fluorine on one side and all hydrogen on the other side, so negatively charged fluorine give the chain a side polarization. Mechanical deformation pushes these charges, resulting in high voltage and, for a short time, current - good for a spark.

I had vaguely hoped that polyvinyl dichloride would be ferroelectric as well, for similarity with Pvdf, and cheaper - but the bulky chlorine atoms must prevent straight chains. Stretching and trying wouldn't be difficult. I suppose it fails, because PVC also would be ferroelectric, but I never noticed that on electric cables, while it's easily observed with Pvdf insulation.

Better alternatives? I doubt! Pvdf is already tough and rather cheap. It makes a simple lighter.

[Enthalpy]

A few candidates as ferroelectric polymers, without expensive fluorine?

• I had hoped -(CH2-O)- known as POM-H or polyoxymethylene might, but the conformation looks unfavourable.
• Polypropylene glycol? Usually understood as the liquid oligomer, but the high polymer is solid.
• Polyvinyl oxide doesn't seem to exist.
• Polyvinyl alcohol? It needs protection against humidity.

In every case, this needs precise control of the tacticity of the polymer, possibly followed by a mechanical treatment (stretch, elongate...) and electrical forming. Credible candidates shall have nearly straight chains, which I couldn't check quickly, but explain the choice of small oxygen instead of chlorine.

The attached conformations estimated by AM1 (log in to see the picture) are NOT reliable! Angles cumulate over the polymer, and long-distance order is needed here.

Such an undertaking must exceed what you're willing to invest to develop a lighter.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Carbonates make liquids with a big permittivity, suggesting polycarbonates as ferroelectric polymers, but a least the usual polycarbonate in its usual state
-[CO-O-pPh-C(CH3)2-pPh-O]n
is not known for this property.

Some very strong polymers have stiff straight chains; grafting polarizing functions at one side only looks interesting.