Unraveling the control of reversibility for actuators based on cellulose nanofibers
Abstract
n this work, we have prepared cellulose-based actuators taking advantage of the pH-sensitive solubility of
chitosan (CH) and the mechanical strength of CNFs. Bilayer films were prepared by vacuum filtration inspired by
plant structures that exhibit reversible deformation under pH changes. The presence of CH in one of the layers
led to asymmetric swelling at low pH, thanks to the electrostatic repulsion between charged amino groups of CH,
and the subsequent twisting with the CH layer on the outside. Reversibility was achieved by substituting pristine
CNFs with carboxymethylated CNFs (CMCNFs), that are charged at high pH and thus competed with the effects
of amino groups. Swelling and mechanical properties of layers under pH changes were studied by gravimetry and
dynamic mechanical analysis (DMA) to quantify the contribution of chitosan and the modified CNFs on the
reversibility control. This work evidenced the key role of surface charge and layer stiffness to achieve revers-
ibility. Bending was triggered by the different water uptake of each layer, and shape recovery was achieved when
the shrunk layer shower higher rigidity than the swollen layer.
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