A Comprehensive Study of Piezoelectricity in Chitosan Films

Chitosan films have attracted interest as flexible and biocompatible materials in health monitoring technologies due to their intrinsic piezoelectricity. This work studies, for the first time, the piezoelectric performances of solution-cast chitosan films in relation to their fabrication process and crystalline content. We investigate how processing parameters, such as solvent type, NaOH treatment duration, and thermal annealing, affect the crystalline content of chitosan films and its correlation with the overall piezoelectric behavior through comprehensive physico-chemical characterizations. Special care is devoted to a reliable determination of converse piezoelectricity, using constant-excitation frequency-modulation piezoresponse force microscopy (CE-FM-PFM), a scanning probe method specifically suited to suppress measurement artifacts that affect conventional PFM in the investigation of soft materials such as semicrystalline polymers. Our findings reveal that a post-processing strategy combining NaOH treatment and thermal annealing significantly enhances the piezoelectric response of chitosan, with a piezoelectric coefficient d ₃₃ reaching 27 pm V^-1, nearly twice as high as those previously reported in the literature. These results pave a promising path for the development of eco-friendly and functional piezoelectric materials for biomedical applications.