Moisture-tunable, ionic strength-controlled piezoelectric effect in cellulose nanocrystal films

Portable and flexible electronics, such as wearable devices and biosensors, require lightweight, sustainable, durable and low-cost piezoelectric materials with low toxicity. This imposes a challenge on commonly-employed mechanically-brittle ceramics and presents opportunities to explore inexpensive organic materials. Ferroelectric polymers such as polyvinylidene fluoride (PVDF) and its copolymers have been commercialized, however, a complex, expensive poling process is required to achieve adequate sensitivity. Bio-derived materials and polymers with inherent piezoelectric properties are a promising class of materials that can address these limitations, provided that a nuanced understanding of their electromechanical properties can be reached. We report a systematic study of piezoelectric charge response in a scope of cellulose nanocrystal (CNC) films to examine the effect of surface chemistry, particle morphology, ionic strength, and film microstructure on tuning the performance of bulk CNC. Our bottom-up, scalable method produced CNC films with stable piezoelectric response of |d33| ~ 29 pC.N−1 after 440 compressive cycles. Flexible and transparent CNC-polyethylene oxide nanocomposites displayed a comparable piezoelectric response of |d33| ~ 23 pC.N−1. Such materials are technologically significant opportunities for renewable CNCs in flexible organic field-effect transistors and multifunctional sensors.