This study presents a novel, green, and efficient way of preparing crosslinked aerogels from cellulose nanofibers (CNFs) and alginate using non-covalent chemistry. This new process can ultimately facilitate the fast, continuous, and large-scale production of porous, light-weight materials as it does not require freeze-drying, supercritical CO2 drying, or any environmentally harmful crosslinking chemistries. The reported preparation procedure relies solely on the successive freezing, solvent-exchange, and ambient drying of composite CNF-alginate gels. The presented findings suggest that a highly-porous structure can be preserved throughout the process by simply controlling the ionic strength of the gel. Aerogels with tunable densities (23-38 kg m(-3)) and compressive moduli (97-275 kPa) can be prepared by using different CNF concentrations. These low-density networks have a unique combination of formability (using molding or 3D-printing) and wet-stability (when ion exchanged to calcium ions). To demonstrate their use in advanced wet applications, the printed aerogels are functionalized with very high loadings of conducting poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:TOS) polymer by using a novel in situ polymerization approach. In-depth material characterization reveals that these aerogels have the potential to be used in not only energy storage applications (specific capacitance of 78 F g(-1)), but also as mechanical-strain and humidity sensors.

Spinning filaments from nature's own high-performance building block, cellulose nanofibrils (CNFs), requires additional considerations compared to conventional manmade fibers commonly made from polymer solutions or melts. We herein utilize the colloidal properties of the highly anisotropic CNFs and demonstrate the preparation of core-shell filaments using a coaxial nozzle. The nanofibril dispersion is passed through the core channel, and the sheath flow consists of a functionalizing solution. The flow rates of the suspensions/solutions are carefully controlled to create an extensional flow at the exit of the nozzle, allowing orientation of the nanofibers into continuous filaments that are then extruded into a fixation bath before drying. The self-assembly mechanism relies on the control of the colloidal stability of carboxymethylated CNFs altered by pH or ionic strength changes. In the simplest approach, HCl is used in the sheath flow to assemble the accelerated CNFs in the core flow, leading to an irreversible association of the nanofibers into an oriented filament. The filaments are continuous and homogeneous, with a dry diameter of approximately 20 mu m. The orientation of the CNFs in the spun filament was investigated by wide-angle X-ray scattering, and an orientation index of 0.79 is achieved. The tensile strength of the filaments is 431 +/- 89 MPa, the Young's modulus is 19.2 +/- 3.4 GPa, and the strain at break is 7.4 +/- 1.3%. Core-shell structures are also prepared by incorporating active materials such as carbon nanotubes in the sheath flow. The resulting filaments show a thin shell of a conductive nanotube network covering a core of cellulose nanofibrils, and the conductivity of such structures reaches 1000 S cm(-1), opening up opportunities for composites and interactive materials.

Chemically cross-linked highly porous nano cellulose aerogels with complex shapes have been prepared using a freeze-linking procedure that avoids common post activation of cross-linking reactions and freeze-drying. The aerogel shapes ranged from simple geometrical three-dimensional bodies to swirls and solenoids. This was achieved by molding or extruding a periodate oxidized cellulose nanofibril (CNF) dispersion prior to chemical cross-linking in a regular freezer or by reshaping an already prepared aerogel by plasticizing the structure in water followed by reshaping and locking the aerogel into its new shape. The new shapes were most likely retained by new cross-links formed between CNFs brought into contact by the deformation during reshaping. This self-healing ability to form new bonds after plasticization and redrying also contributed to the mechanical resilience of the aerogels, allowing them to be cyclically deformed in the dry state, reswollen with water, and redried with good retention of mechanical integrity. Furthermore, by exploiting the shapeability and available inner structure of the aerogels, a solenoid-shaped aerogel with all surfaces coated with a thin film of conducting polypyrrole was able to produce a magnetic field inside the solenoid, demonstrating electromagnetic properties. Furthermore, by biomimicking the porous interior and stiff exterior of the beak of a toucan bird, a functionalized aerogel was created by applying a 300 mu m thick stiff wax coating on its molded external surfaces. This composite material displayed a 10-times higher elastic modulus compared to that of the plain aerogel without drastically increasing the density. These examples show that it is possible to combine advanced shaping with functionalization of both the inner structure and the surface of the aerogels, radically extending the possible use of CNF aerogels.

Layer-by-layer (LbL) assembly is a versatile tool for fabricating multilayers with tailorable nanostructures. LbL, however, generally relies on polyelectrolytes, which are mostly insulating and induce large interlayer distances. We demonstrate a method in which we replace polyelectrolytes with the smallest unit capable of LbL self-assembly: a molecule with multiple positive charges, tris(3-aminopropyl)amine (TAPA), to fabricate LbL films with negatively charged single-walled carbon nanotubes (CNTs). TAPA introduces less defects during the LbL build-up and results in more efficient assembly of films with denser micromorphology. Twenty bilayers of TAPA/CNT showed a low sheet resistance of 11 k Omega, a high transparency of 91% at 500 nm, and a high electronic conductivity of 1100 S/m on planar substrates. We also fabricated LbL films on porous foams with a conductivity of 69 mS/m and used them as electrodes for supercapacitors with a high specific capacitance of 43 F/g at a discharging current density of 1 A/g.

The Layer-by-Layer (LbL) deposition technique was used to treat fibres before papermaking on a pilot scale. Following a laboratory pre-study performed earlier to determine the adsorption isotherms and the kinetics of formation of multilayers of polyamideamine epichlorydrine (PAE) and carboxymethylated cellulose (CMC) on unbeaten, bleached softwood fibres, online LbL treatment of the furnish was carried out on the EuroFEX pilot paper machine. Papers from fibres coated with up to four layers of polyelectrolytes were produced. Two different LbL systems were investigated, with anionic CMC in combination with either PAE or cationic starch (CS). The results showed that the mechanical strength of the paper significantly increased when the fibres were LbL-treated online. A comparison with conventional beating of the fibres revealed that the LbL treatment was a potential substitute to beating treatment, as the density of the LbL-treated papers remained constant while the mechanical properties were significantly improved. At the same time, the press solids content was significantly higher (2%) when using LbL-treated fibres than with beaten fibres.

The adhesive characteristics of poly(allylamine hydrochloride) (PAH)/hyaluronic acid (HA) self-assemblies were investigated using contact adhesion testing. Poly(dimethylsiloxane) spheres and silicon wafers were coated with layer-by-layer (LbL) assemblies of PAH/HA. NO increase in adhesion was observed when surfaces covered With dried LbL films were placed in contact. However, bringing the coated surfaces in contact while wet and separating them after drying resulted in an increase by a factor of 100 in the work of adhesion (from one to three bilayers). Herein we discuss the adhesion in PAH/HA and PAH/poly(acrylic acid) assemblies. PAH/HA assemblies have potential application as strong biomedical adhesives.

Traditional thin-film energy-storage devices consist of stacked layers of active films on two-dimensional substrates and do not exploit the third dimension. Fully three-dimensional thin-film devices would allow energy storage in bulk materials with arbitrary form factors and with mechanical properties unique to bulk materials such as compressibility. Here we show three-dimensional energy-storage devices based on layer-by-layer self-assembly of interdigitated thin films on the surface of an open-cell aerogel substrate. We demonstrate a reversibly compressible three-dimensional supercapacitor with carbon nanotube electrodes and a three-dimensional hybrid battery with a copper hexacyanoferrate ion intercalating cathode and a carbon nanotube anode. The three-dimensional supercapacitor shows stable operation over 400 cycles with a capacitance of 25â €‰Fâ €‰g â '1 and is fully functional even at compressions up to 75%. Our results demonstrate that layer-by-layer self-assembly inside aerogels is a rapid, precise and scalable route for building high-surface-area 3D thin-film devices.