Phase separation of a PVDF–HFP film on an ice substrate to achieve self-polarisation alignment

Flexible self-polarised poly(vinylidene fluoride) (PVDF) piezoelectric films that have a high electroactive phase content and can be easily prepared are applied in force–electricity conversion, particularly as self-power supplies for small devices and the detection of body signals. Filler addition, phase separation and polarisation by a substrate are the most used methods to fabricate self-polarised PVDF films. However, the alignment of films is hard to realise using these self-polarising techniques, thus making it difficult to increase piezoelectric generation. In this study, phase separation on an ice substrate was used to prepare a self-polarised poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) film. Strong polarisation via hydrogen bonding between PVDF–HFP and a flat ice substrate contributes toward a high β-phase content of 86.5% and good film alignment. Moreover, the low preparation temperature provided by ice has considerable impact on self-polarisation, with excellent alignment observed because of the reduced disturbance by solvent flow and the Brownian motion of the PVDF–HFP solution at low temperature having less impact on self-polarisation via hydrogen bonding. The phase separation on ice of the PVDF–HFP film was confirmed to be an efficient self-polarisation method to considerably improve its β-phase content, alignment and piezoelectric generation performance.