Ferroelectric polymer

[5] Ferroelectric properties are derived from electrets, which are defined as a dielectric body that polarizes when an electric field and heat is applied.

Initially different blends and copolymers of PVDF were discovered, such as a polyvinylidene fluoride with poly(methyl methacrylate).

Subsequently, there has been tremendous growth during the past decade in exploring the materials science, physics, and technology of poly(vinylidenefluoride) and other fluorinated polymers.

PVDF molecules contain two hydrogen and two fluorine atoms per repeat unit, so they have a choice of multiple conformations.

However, rotational barriers are relatively high, the chains can be stabilized into favorable conformations other than that of lowest energy.

Ferroelectric polymers, such as polyvinylidene fluoride and poly[(vinylidenefluoride-co-trifluoroethylene], are very attractive for many applications because they exhibit good piezoelectric and pyroelectric responses and low acoustic impedance, which matches water and human skin.

A common approach for enhancing the dielectric constant is to disperse a high-dielectric-constant ceramic powder into the polymers.

This can be disadvantageous because lead can be potentially harmful and at high particulate loading, the polymers lose their flexibility and a low quality composite is obtained.

Current advances use a blending procedure to make composites that are based on the simple combination of PVDF and cheap metal powders.

Meyer predicted ferroelectricity in chiral smectic liquid crystals by pure symmetry conditions.

Shortly after, Clark and Lagerwall had done work on the fast electrooptic effect in a surface-stabilized ferroelectric liquid crystal (SSFLC) structure.

This opened up promising possibility of technical applications of ferroelectric liquid crystals in high-information display devices.

Through applied research, it was shown that SSFLC structure has faster switching times and bistability behavior in comparison with commonly used nematic liquid crystal displays.

The disadvantage is that these SCLCP's suffered from their slow switching times due to their high rotational viscosity.

[12] Thin Film Electronics successfully demonstrated roll-to-roll printed non-volatile memories based on ferroelectric polymers in 2009.

The device configuration is simple, it usually consists of a piece of ferroelectric film with an electrode on the top and bottom surfaces.

[17] When the device functions as a sensor, a mechanical or acoustic force applied to one of the surfaces causes a compression of the material.

In actuators, a voltage applied between the electrodes causes a strain on the film through the inverse piezoelectric effect.

Figure 1: Structure of poly(vinylidene fluoride)
Figure 2: Structure of polytrifluoroethylene
Figure 3: Brief timeline describing important events that have occurred in piezoelectricity and ferroelectric polymer history
Figure 7: Stress–strain curve showing the different regions. Light seen at fracture is known as triboluminescence and light emitted in the elastic regime is known as piezoluminescence.