Copolymers
Copolymers of PVDF are also used in piezoelectric and electrostrictive applications. One of the most commonly used copolymers is P(VDF-trifluoroethylene), 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-tetrafluoroethylene). 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/N versus −33 pC/N in pure PVDF.
Read more about this topic: Polyvinylidene Fluoride