Abstract
Cellulose, a major constituent of our natural environment and a structured biodegradable biopolymer, has been shown to exhibit shear piezoelectricity with potential applications in energy harvesters, biomedical sensors, electro-active displays and actuators. In this regard, a high-aspect ratio nanofiber geometry is particularly attractive as flexing or bending will likely produce a larger piezoelectric response as compared to axial deformation in this material. Here we report self-assembled cellulose nanofibers (SA-CNFs) fabricated using a template-wetting process, whereby parent cellulose nanocrystals (CNCs) introduced into a nanoporous template assemble to form rod-like cellulose clusters, which then assemble into SA-CNFs. Annealed SA-CNFs were found to exhibit an anisotropic shear piezoelectric response as directly measured using non-destructive piezo-response force microscopy (ND-PFM). We interpret these results in light of the distinct hierarchical structure in our template-grown SA-CNFs as revealed by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM).
Highlights
With the increasing global reliance on electronic devices, cheap and abundant electroactive materials are being actively sought for applications in sensors, transducers, actuators and energy harvesters
To fabricate self-assembled cellulose nanofibers (SA-CNFs), charged cellulose nanocrystals (CNCs) within an aqueous dispersion were drop-cast onto anodised aluminium oxide (AAO) templates facilitating self-assembly of CNCs within the nanoporous channels
We report for the first time the preparation of SA-CNFs, following a traditional, scalable AAO templatewetting method.[1,3,4,5,6]
Summary
With the increasing global reliance on electronic devices, cheap and abundant electroactive materials are being actively sought for applications in sensors, transducers, actuators and energy harvesters. In order to introduce flexibility in such devices, recent work has focussed largely on the use of piezoelectric polymers that can inter-convert mechanical and electrical energy, and which are commonly durable, light weight, and can be relatively manufactured.[1,2,3,4,5,6,7] Piezoelectric polymers such as PVDF ( polyvinylidene fluoride), and its co-variants,[1,3,5] odd-numbered Nylons (Nylon-11),[4,8] and poly-L-lactic acid (PLLA),[6] have been investigated for their energy harvesting properties by our group, where nanowires of these materials grown by template-wetting have been shown to exhibit superior piezoelectric properties as compared to bulk or thin films due to self-poling. There have been several other reports on polymer-based nanogenerators, including those involving biological and biocompatible polymers.[9,10,11,12,13,14,15,16,17,18,19] In this regard, cellulose belongs to the family of naturally occurring piezoelectric materials that has been the subject of continuous research.[9,10,11,12,13,14,16,20,21,22,23,24,25,26] the electromechanical properties of cellulose at the nanoscale have been scarcely studied, but could hold the key to unlocking the potential of this material in piezoelectric devices
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