PVDF (polyvinylidene fluoride), is a long chain molecule formed by CFCH bonds, usually a semi-crystalline polymer. Refer to Figure 1 to its molecular structure diagram. Under different conditions, PVDF materials have different molecular structure up to five arrangements, named in α, β, γ, δ and ε types. Among them, the “β-type” has a piezoelectric effect, which, it has the ability to convert between electrical energy and mechanical energy. For the molecular structure of β-type PVDF, please refer to Figure 2.
The molecular chains of β-type PVDF are arranged in a planner-zigzag structure. The dipoles on the molecular chain are aligned in parallel to each other in the same direction, resulting in a spontaneously polarized polar structure, which gives it the piezoelectric properties. When the deformation is applied on β-type PVDF, the size of the dipole also changes, and therefore affect the total amount of charges in PVDF, inducing the surface charge difference and finally lead to voltage generation.
Typically, the β-type PVDF film material is made from the α-type PVDF by processes that inject polarities to the molecular structure. The method of making PVDF film is by mechanically stretching the material, and to go over poling process and gives the film piezoelectric properties.
PVDF film has the following characteristics:
- PVDF is the polymer with the strongest piezoelectricity. Compared with conventional piezoelectric materials, PVDF delivers wide frequency bandwidth and high sensitivity of power-to-electricity (and vice versa) conversion.
- The ease of matching the acoustic impedance
- Easy to process
- Excellent chemical resistance
- Based on the characteristics above, PVDF is chosen as the material for polymer piezoelectric films.
PVDF is the polymer with the strongest piezoelectricity. Compared with conventional piezoelectric materials, PVDF delivers wide frequency bandwidth and high sensitivity of power-to-electricity (and vice versa) conversion.
The main applications of PVDF piezoelectric film are the following:
- Acoustic use: microphone, speaker, hydrophone
- Medical use: Medical sensors such as blood pressure monitors, stethoscopes, heartbeat and pulse counters.
- Industrial use: accelerometer, non-destructive testing
- Civilian use: non-contact switch, wearable pedometer