Sodium (Na)-based batteries are being explored as a sustainable and cost-effective alternative to Lithium (Li)-ion batteries. In particular, an "anode-free" Na metal battery offers the possibility to match or even exceed the energy density of the incumbent Li-ion technology. Nevertheless, the present lifespan of these batteries is insufficient to render them suitable as an energy source for current electronic devices and grid systems. The main reason for this is the evolution and growth of Na metal dendrites during the charge-discharge process. In this study, we report a "nano-silica modified suspension electrolyte" that improves the average coulombic efficiency and cycling performance of anode-free Na metal batteries. The nano-silica additives increase the Na+ + diffusion coefficient in the electrolyte by 1000-fold, thereby decreasing the nucleation overpotential and inhibiting the formation of Na metal dendrites. We demonstrate that a Na|Cu half-cell with the suspension electrolyte can cycle stably for over 500 cycles at 1 mA cm- 2 current density and an aerial capacity of 2 mAh cm- 2 . When paired with an Na3V2(PO4)3 3 V 2 (PO 4 ) 3 (NVP) cathode, the anode-free NVP|Cu full-cell device with the nano-silica infused electrolyte drastically outperformed the conventional electrolyte in terms of specific capacity retention and coulombic efficiency.

Carbon Nanotubes (CNTs)-polymer composites are promising candidates for a myriad of applications. Ad-hoc CNTs-polymer composite fabrication techniques inherently pose roadblock to optimized processing resulting in microstructural defects i.e., void formation, poor interfacial adhesion, wettability, and agglomeration of CNTs inside the polymer matrix. Although improvement in the microstructures can be achieved via additional processing steps such as-mechanical methods and/or chemical functionalization, the resulting composites are somewhat limited in structural and functional performances. Here, we demonstrate that 3D printing technique like-direct ink writing offers improved processing of CNTs-polymer composites. The shear-induced flow of an engineered nanocomposite ink through the micronozzle offers some benefits including reducing the number of voids within the epoxy, improving CNTs dispersion and adhesion with epoxy, and partially aligns the CNTs. Such microstructural changes result in superior mechanical performance and heat transfer in the composites compared to their mold-casted counterparts. This work demonstrates the advantages of 3D printing over traditional fabrication methods, beyond the ability to rapidly fabricate complex architectures, to achieve improved processing dynamics for fabricating CNT-polymer nanocomposites with better structural and functional properties.

Epoxies are important thermoset materials with a broadrange ofapplications. They are nominally homogeneous, have high strength andstiffness, but are brittle. In this work, we develop heterogeneousepoxies via additive printing with the goal of improvingductility, without compromising the strength and stiffness. To thisend, we develop a reactive inkjet printing technology in which theresin and hardener components are printed successively using multinozzleprintheads and which provides control of the local stoichiometricratio. This allows creating epoxies with both in-plane and out-of-planelocal compositional and mechanical heterogeneity. We print and testheterogeneous materials with several microstructural designs and demonstratesignificant improvement of ductility, with retention of strength andstiffness. Furthermore, the properties of printed nominally homogeneoussamples are close to isotropic and identical to those of the castmaterial of the same composition. The technology developed makes useof commercially available inks (resin and hardener); it is fully automatedand provides sufficient flexibility and productivity to print complexmacroscopic samples with 50 & mu;m resolution of microstructuralcomposition control.

Despite decades of research, fatigue remains the primary culprit for catastrophic failure in carbon-fiber reinforced polymeric (CFRP) composites. Existing approaches to combat fatigue are usually based on nano-scale additives that slow the growth of cracks in the polymer. While this prolongs fatigue-life, it cannot avert eventual failure since crack growth is being slowed and not reversed. Other approaches have explored self-healing polymers that release a curing agent to repair local damage. However, this approach also fails to tackle fatigue, since once the curing agent is released, it gets consumed and cannot be re-used. To addresses the irreversibility of fatigue, we report here a vitrimeric system, for which reversal of fatigue damage can be achieved repeatedly, by heating the material to above its topology freezing transition temperature. This enables intermittent healing of fatigue-induced damage, as it accumulates in the vitrimer matrix. Using this approach, we show that fatigue failure in vitrimers and in carbon-fiber reinforced vitrimers (vCFRP) can be postponed indefinitely. Such vCFRPs could open the door to future materials, in which natural aging and fatigue processes can be periodically reversed, so as to guarantee safe and reliable long-term operation.

Battery electrodes comprise a mixture of active material particles, conductive carbon and binder additives deposited onto a current collector. Although this basic design has persisted for decades, the desired size scale of the active material particle is a matter of debate. Advances in nanotechnology have spurred interest in deploying nanoparticles as the active material. In this Perspective, we compare the features of nanoparticle and microparticle electrodes, and discuss why the battery industry is unlikely to replace microstructures with nanometre-sized analogues. We then address the question of whether there is a place for nanomaterials in battery design. We suggest that the way forward lies in microscale particles with built-in nanoscale features, such as microparticles assembled from nanoscale building blocks or patterned with engineered or natural nanopores. These multiscale particles offer exciting possibilities to develop battery electrodes that are quintessentially both micro and nano with respect to their performance attributes.

As rotorcrafts enter new generation of their design, they are expected to be subjected to more stringent performance requirement, Increased loads and operational frequency necessitates use of structural components with higher fatigue life. Carbon fiber reinforced polymer composites (CFRP) are popular as structural material due to their superior performance while being lightweight. However, fatigue originating in weaker polymer limits their fatigue life, moreover the fatigue damage introduced accumulated irreversibly resulting in catastrophic failure. The damage is irreversible due to permanent crosslinked nature of thermoset polymers used in CFRP. If the crosslinks are made dynamic i.e. reversibly crosslinked, the fatigue damage may be reversed imparting ultra-high fatigue life to the components. Vitrimers are such epoxy based networks which may be ideal candidate for this application as they possess ability to dynamic crosslinking at elevated characteristic temperature. Here we report a vitrimer based CFRP i..e., vCFRP which has properties comparable to conventional CFRP which has ability to retain its original properties in fatigue tests when they are subjected to periodic heating. The fractographic analysis suggests that periodic heating serves dual purpose of enabling dynamic crosslinking as well as repairing small scale fiber-matrix interface failure. Thus, rotorcraft components made with vCFRP may have very high fatigue life compared to conventional CFRP components.

Carbon fiber reinforced composites (CFRP) are frequently used in rotorcraft components due to their high strength to weight ratio. Carbon fibers are the principal load carriers whereas polymer matrix provides structural integrity to the CFRP components. Fatigue failure originating in the matrix pose a design constraint on CFRP components. The fatigue failure originates in form of small scale sub-critical cracks which eventually grow into macroscopic cracks/shear localization resulting in eventual failure. Research efforts have been directed at improving fracture and fatigue performance of polymeric matrix by arresting incipient cracks. Thermoset polymers are widely used as matrix material as they posses superior strength due to high crosslinking density. However, since no self-healing mechanism operates in thermosets, damage is irreversibly accumulated over the life cycle of components. A new class of materials called vitrimers provide a novel approach to develop fatigue resistant CFRP. Vitrimers are associative covalent adaptive networks (CAN) which have reversible crosslinking reactions which can be activated by external energy stimulus like heat. As the crosslinked network is reversible, the incipient damage can be 'healed' by application of heat. In this work we explore the self-healing properties of vitrimer fabricated by the reaction of adipic acid and epoxy resin. The vitrimer is initially tested in static tests to probe mechanical properties, followed by fatigue experiments. The vitrimer is then used to make a vitrimeric CFRP (vCFRP) composite and is tested for its static and fatigue performance.

We report a mesoscale toughening mechanism in polymer nanocomposites that is distinct from previously reported ones. Fractography analysis of epoxy composites with nano-silica additives reveals a stochastic dispersion of nanofiller clusters which creates mesoscale stiffness heterogeneity as confirmed by nanoindentation testing. To analyze the effect of heterogeneity, a finite element model where a crack grows through heterogeneous material was created. Simulations and experimental results indicate that inducing stiffness heterogeneity increases toughness by modification of the crack tip fields. Our results indicate that mesoscale toughening (induced by the nanoparticle additives) plays a significant role in influencing fracture toughness in nanocomposite materials.

Carbon fiber reinforced polymer composites (CFRP) are extensively used as structural components in rotorcraft applications. Here, we report considerable improvement in the fatigue life of CFRP through the infiltration of nanoscale silica particles into the epoxy resin matrix (nanoCFRP). Fumed silica nanoparticles were initially added to the epoxy resin to prepare epoxy-silica nanocomposites, which were demonstrated to have superior fracture and fatigue properties. Fractographic analysis indicated presence of various key toughening mechanisms including crack deflection, plastic void growth as well as a hitherto unreported heterogeneity induced mesoscale toughening effect. The epoxy-silica nanocomposite resin was then used as the matrix material to fabricate nanoCFRP. Cyclic flexural bending tests indicate significant fatigue life enhancement for the nanoCFRP. The enhancement is especially pronounced in the high cycle fatigue regime. This enhancement in high cycle fatigue is indicative of transfer of small-scale toughening mechanisms from the silica-epoxy nanocomposite resin to the nanoCFRP system. Such nanoCFRP show promise to improve the fatigue life and reduce the operational/maintenance cost for next generation rotorcraft.

Carbon fiber reinforced polymer composites (CFRP) are ubiquitous in engineering applications where they are employed as structural components. Fatigue failure which originates in matrix of CFRP is a major design constraint in these composites. In this work we demonstrate considerable increase in fatigue life in nano modified carbon fiber reinforced polymer composite (nanoCFRP) through addition of nanoscale silica particles. Fumed silica particles are used as nanofillers which are incorporated in epoxy initially to explore their effect on fracture and fatigue performance. The results indicate improvement uniform improvement in the fatigue life with increasing silica loading fraction. Fractographic analysis performed indicated presence of various toughening mechanisms like crack deflection, void growth and heterogeneity induced toughening. The epoxy-silica nanocomposite was then used as the matrix material with carbon fibers to fabricate nanoCFRP with different silica loading fractions. nanoCFRP samples were initially tested statically in three point bending setup and the static strength was found to be uncorrelated with the loading fraction. The cyclic flexural tests, however, revealed significant improvement in fatigue life in nanoCFRP composites. The fatigue life improvement was pronounced in high cycle fatigue regime.

Carbon fiber reinforced polymer (CFRP) composites are increasingly the material of choice in a variety of high performance structural applications including the aerospace, defense, wind energy and automotive industries. A key limitation of these materials is their poor fatigue life induced by initiation and growth of small-scale cracks in the epoxy matrix. Here, we show that incorporation of nano-silica into the epoxy resin results in nano-modified CFRP (nanoCFRP) with 6–7 fold higher fatigue life in the high cycle fatigue regime. The mechanism for the observed performance improvement is the ability of the nano-silica to disrupt and prolong the propagation process of incipient cracks. This in turn postpones the eventual failure of the CFRP, leading to fatigue life increase. The ability to achieve such results with silica nanoparticles has strong practical implications, since nano-silica are easily accessible and economically inexpensive for large-scale industrial applications.

Rotorcraft components, which are often made with reinforced fiber composites, are subjected to severe fatigue loadings due to increased performance demands. Therefore, considerable research interest exists in improving fatigue life of conventional fiber reinforced composites. Nanocomposites are a new class of materials which seek to improve mechanical performance of materials by creating nanoscale crack-nanofiller interactions. In this study we demonstrate the fatigue life improvement of conventional composites by addition of SiO2 nanofillers. The epoxy resin was initially modified with nanofillers to test the static fracture toughness. Once the improvement in static facture toughness was confirmed, three phase modified fiber reinforced composites were made using the modified resin. Cyclic tests were performed at various stress level which demonstrate that three phase nanocomposites perform better than conventional fiber reinforced composites. Fractographic analysis suggests that nanofiller de-bonding from the matrix as well as crack deflection around nanofiller clusters contributes to the improved fracture toughness and fatigue life.