Electrical and microstructural changes of ß-PVDF under different processing conditions by scanning force microscopy

Poly vinylidene fluoride (PVDF) has been widely investigated due to its important pyroand piezoelectric properties. These properties have found various applications, especially as sensor and actuators. The existence and optimization of these properties is intimately related with the fraction of the polymer in the crystalline phase, its structure, microstructure and orientation. All of these in turn heavily depend on the processing conditions. PVDF is a semi-crystalline polymer which shows polymorphism and is commonly crystallized in non-polar crystalline α-phase. The piezo- and pyroelectric properties mainly depend on the ß-phase, so that increasing ß-phase content has always been of great concern in this field. ß-phase can be obtained by mechanical stretching of a-phase films at a given temperature or directly from solution. Conversion of a into ß-phase takes place at stretching temperatures below 100°C, at a stretch ratio of about 3-5. Nevertheless the achieved amount of ß-phase in the crystalline fraction of the material is never 100%. In the films obtained from solution, 100% beta phase films can be achieved in either a porous or non-porous form. The degree of crystallinity is also larger for the samples obtained from solution. This work is mainly devoted to the study of the variations in the topological morphology and piezoelectric domain response of PVDF prepared by the aforementioned methods by scanning force microscopy in a piezo-response mode.