Cellulose nanocrystals (CNCs) are renewable nanomaterials obtained by strong acid hydrolysis of biomass. CNC surface charge and properties can be manipulated and controlled during the hydrolysis process, whereby a tunable measure of surface charge and active moieties can be engineered. The electric dipole moment of CNCs has been measured using transient electric birefringence, with a reported 4400 ± 400 D magnitude permanent dipole along the CNC long axis. Many natural materials, including wood, show piezoelectric properties by virtue of the non-centrosymmetric orientation of their molecular components. However, we will show how CNCs – unlike other natural materials – have unique, tunable and long-lasting piezoelectric response, whether alone or in combination with other polymeric materials. We discovered that the piezoelectric response of CNC films strongly depended on the surface properties of CNCs and the ionic strength of the CNC dispersion. An increase in |d33| from 0.4 to 5.5 pC N-1 was observed by converting CNCs from Na-form to H-form, and this value was further improved to 82.6 pC N-1 by controlling the ionic strength of the CNC suspensions before evaporation-induced self-assembly (EISA). This d33 value was higher than that typically observed for PVDF, the most widely used piezoelectric polymer material, as well as PZT-polymer composites, and some piezoelectric ceramics, e.g., BiFeO3. The paper will detail the mechanisms responsible for these unique responses governed by controllably manipulating CNC surface characteristics, and how this knowledge can be applied to develop sustainable, cost-effective organic electronic materials for a variety of end-use engineering and biomedical applications.

Piezoelectric properties of cellulose nanocrystals

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ACS Fall 2022

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