Functional polymer nanocomposites : structural issues in relation to the piezoelectric response*

Poly(Vinylidene Fluoride) (PVDF) is a semi-crystalline polymer with complex polymorphism that has attracted considerable interest, owing to the electroactive properties displayed by its polar β and γ phases. Regarding PVDF-based nanocomposites, two strategies are considered in the following :
- The first one deals with the incorporation of piezoelectric inorganic nanofillers (BaTiO3), with primary issues related to nanoparticle dispersion and monitoring of interfacial cohesion, together with promoting the development of the highly polar β phase in the PVDF matrix. It is shown that the piezoelectric response may be modulated as a function of filler content, going through a zero value at some critical filler fraction.
- Alternatively, the introduction of carbon nanotubes in the PVDF matrix is achieved, with the result that the nanotubes induce the formation of the γ polar phase in their vicinity. The local structural organization of the α and γ phases in the PVDF nanocomposite is probed by atomic force microscopy and specific attention is paid to the local electroactive properties through the use of piezoelectric force microscopy (PFM).