Mechanically adaptive nanocomposites with cellulose nanocrystals: Strain-field mapping with digital image correlation

ZnO microrods sandwiched between layered CNF matrix: Fabrication, stress transfer, and mechanical properties

Functional metal oxide particles are often added to the polymers to prepare flexible functional polymer composites with adequate mechanical properties. ZnO and cellulose nanofibrils (CNF) outstand among these metal oxides and the polymer matrices respectively due to their various advantages. Herein, we in situ prepare ZnO microrods in the presence of CNF, which resultes in a layered composite structure. The ZnO microrods are sandwiched between the CNF layers and strongly bind to highly charged CNF, which provides a better stress transfer during mechanical activity. Digital image correction (DIC) and finite element analysis-based computational homogenization methods are used to investigate the relationship between mechanical properties and composite structure, and the stress transfer to the ZnO microrods. Full-field strain measurements in DIC reveal that the in situ ZnO microrods preparation leads to their homogenous distribution in the CNF matrix unlike other methods, which require external means such as ultrasonication. The computational homogenization technique provides a fairly good insight into the stress transfer between constituents in microstructure as well as a good prediction of macroscopic mechanical properties, which otherwise, would be challenging to be assessed by any ordinary mechanical testing in the layered composites. Finally, we also demonstrate that these composites could be used as physiological motion sensors for human health monitoring.

Temperature-Invariant Superelastic Multifunctional MXene Aerogels for High-Performance Photoresponsive Supercapacitors and Wearable Strain Sensors

Assembling MXene two-dimensional (2D) nanosheets solely into structurally robust three-dimensional (3D) multifunctional macroarchitectures with temperature-invariant elasticity is significant for widening their potential applications but has remained exceedingly challenging. To this end, a facile freeze-induced co-assembly was developed to allow the disparate integration of MXene 2D nanosheets into the directive heterogeneities to easily customize the controllable 3D architectures for geometry accessibility, structure integrity, and function adaptability. With functionalized cellulose nanocrystal serving as a structural modifier and cross-linking by polyurethane as well as manipulating the directionally ice templating process, multilevel nanostructured configurations with interconnected porous channels could be obtained for biomimetic aerogel electrodes across multiple length scales. Benefiting from the high ion pathway from the low-tortuosity topology, MXene aerogels showed outstanding electrochemical property (225 F/g), high-rate capacity, and temperature-invariant superelasticity (from 0 to 150 °C), which surpassed some of the best reported values. MXene quasi-solid-state supercapacitors presented superior electrochemistry (energy density: 38.5 μWh/cm²) and outstanding cycle ability (86.7% after 4000 cycles). Exhibiting excellent photoresponse capacity, they could be used as an integrated photodetector. More importantly, specially designed bio-mimicking structures with mechanically self-adaptive resilience could promote MXene 3D aerogels to apply in wearable electronic devices, monitoring various human motions. This work will shed light on MXene aerogels for smart and self-powered lightweight electronics.