Highly Compressible, Anisotropic Aerogel with Aligned Cellulose Nanofibers.

Aerogels can be used in a broad range of applications such as bioscaffolds, energy storage devices, sensors, pollutant treatment, and thermal insulating materials due to their excellent properties including large surface area, low density, low thermal conductivity, and high porosity. Here we report a facile and effective top-down approach to fabricate an anisotropic wood aerogel directly from natural wood by a simple chemical treatment. The wood aerogel has a layered structure with anisotropic structural properties due to the destruction of cell walls by the removal of lignin and hemicellulose. The layered structure results in the anisotropic wood aerogel having good mechanical compressibility and fragility resistance, demonstrated by a high reversible compression of 60% and stress retention of ∼90% after 10 000 compression cycles. Moreover, the anisotropic structure of the wood aerogel with curved layers stacking layer-by-layer and aligned cellulose nanofibers inside each individual layer enables the wood aerogel to have an anisotropic thermal conductivity with an anisotropy factor of ∼4.3. An extremely low thermal conductivity of 0.028 W/m·K perpendicular to the cellulose alignment direction and a thermal conductivity of 0.12 W/m·K along the cellulose alignment direction can be achieved. The thermal conductivity is not only much lower than that of the natural wood material (by ∼3.6 times) but also lower than most of the commercial thermal insulation materials. The top-down approach is low-cost, scalable, simple, yet effective, representing a promising direction for the fabrication of high-quality aerogel materials.

Thermally Stable Cellulose Nanocrystals toward High-Performance 2D and 3D Nanostructures.

Cellulose nanomaterials have attracted much attention in a broad range of fields such as flexible electronics, tissue engineering, and 3D printing for their excellent mechanical strength and intriguing optical properties. Economic, sustainable, and eco-friendly production of cellulose nanomaterials with high thermal stability, however, remains a tremendous challenge. Here versatile cellulose nanocrystals (DM-OA-CNCs) are prepared through fully recyclable oxalic acid (OA) hydrolysis along with disk-milling (DM) pretreatment of bleached kraft eucalyptus pulp. Compared with the commonly used cellulose nanocrystals from sulfuric acid hydrolysis, DM-OA-CNCs show several advantages including large aspect ratio, carboxylated surface, and excellent thermal stability along with high yield. We also successfully demonstrate the fabrication of high-performance films and 3D-printed patterns using DM-OA-CNCs. The high-performance films with high transparency, ultralow haze, and excellent thermal stability have the great potential for applications in flexible electronic devices. The 3D-printed patterns with porous structures can be potentially applied in the field of tissue engineering as scaffolds.

Ultrafine Pitch Stencil Printing of Liquid Metal Alloys.

With high conductivity and stretchable for large cross-sections, liquid metals such as galinstan are promising for creating stretchable devices and interconnects. Creating high resolution features in parallel is challenging, with most techniques limited to a hundred micrometers or more. In this work, multilevel electroplated stencils are investigated for printing liquid metals, with galinstan features as small as ten micrometers printed on soft elastomers, a factor of 10 reduction over past liquid metal stencil printing. Capacitors and resistive strain sensors are also demonstrated, showing the potential for creating stretchable conductors and devices.

Magnetic elastomers for stretchable inductors.

In this work, silicone loaded with magnetic particles is investigated for creating a composite with higher permeability while still maintaining stretchability. Magnetic and mechanical properties are first characterized for composites based on both spherical and platelet particle geometries. The first magnetic-core stretchable inductors are then demonstrated using the resulting ferroelastomer. Solenoid inductors based on liquid metal galinstan are then demonstrated around a ferroelastomeric core and shown to survive uniaxial strains up to 100%. Soft elastomers loaded with magnetic particles were found to increase the core permeability and inductance density of stretchable inductors by nearly 200%.