Dynamic diagnosis of metamaterials through laser-induced vibrational signatures.

Mechanical metamaterials at the microscale exhibit exotic static properties owing to their engineered building blocks1-4, but their dynamic properties have remained substantially less explored. Their design principles can target frequency-dependent properties5-7 and resilience under high-strain-rate deformation8,9, making them versatile materials for applications in lightweight impact resistance10-12, acoustic waveguiding7,13 or vibration damping14,15. However, accessing dynamic properties at small scales has remained a challenge owing to low-throughput and destructive characterization8,16,17 or lack of existing testing protocols. Here we demonstrate a high-throughput, non-contact framework that uses MHz-wave-propagation signatures within a metamaterial to non-destructively extract dynamic linear properties, omnidirectional elastic information, damping properties and defect quantification. Using rod-like tessellations of microscopic metamaterials, we report up to 94% direction-dependent and rate-dependent dynamic stiffening at strain rates approaching 102 s-1, as well as damping properties three times higher than their constituent materials. We also show that frequency shifts in the vibrational response allow for characterization of invisible defects within the metamaterials and that selective probing allows for the construction of experimental elastic surfaces, which were previously only possible computationally. Our work provides a route for accelerated data-driven discovery of materials and microdevices for dynamic applications such as protective structures, medical ultrasound or vibration isolation.

Tunable Mechanical Response of Self-Assembled Nanoparticle Superlattices.

Self-assembled nanoparticle superlattices (NPSLs) are an emergent class of self-architected nanocomposite materials that possess promising properties arising from precise nanoparticle ordering. Their multiple coupled properties make them desirable as functional components in devices where mechanical robustness is critical. However, questions remain about NPSL mechanical properties and how shaping them affects their mechanical response. Here, we perform in situ nanomechanical experiments that evidence up to an 11-fold increase in stiffness (∼1.49 to 16.9 GPa) and a 5-fold increase in strength (∼88 to 426 MPa) because of surface stiffening/strengthening from shaping these nanomaterials via focused-ion-beam milling. To predict the mechanical properties of shaped NPSLs, we present discrete element method (DEM) simulations and an analytical core-shell model that capture the FIB-induced stiffening response. This work presents a route for tunable mechanical responses of self-architected NPSLs and provides two frameworks to predict their mechanical response and guide the design of future NPSL-containing devices.

Phase Change Dispersion Made by Condensation-Emulsification.

Cooling processes require heat transfer fluids with high specific heat capacity. For cooling processes below 0 °C, water has to be diluted with organic liquids to prevent freezing, with the undesired effect of reduced specific heat capacity. Phase change dispersions, PCDs, consist of a phase change material, PCM, being dispersed in a continuous phase. This allows for using the PCD as heat transfer fluid with a very high apparent specific heat capacity within a specified, limited temperature range. So far, the PCMs being reported in the literature are paraffins, fatty acids, or esters and are used for isothermal cooling applications between +4 and +50 °C. They are manufactured by high shear equipment like rotor-stator systems. A recently published method to produce emulsions by the direct condensation of the dispersed phase into the emulsifier-containing continuous phase is applied on this PCD. n-Decane is used as PCM, and the melting temperature is -30 °C. The achieved apparent specific heat capacity lies above 15 kJ/kg·K, more than 3 times the value of water. This paper presents experimental methods and data, formulation details, and thermophysical and rheological properties of such new PCD. Food conservation or isothermal cooling of lithium-ion batteries is a potential application for the presented method. The properties of the developed PCD were determined, and the successful application of such a PCD at -30 °C has been demonstrated.

Enhancing the Injectability of High Concentration Drug Formulations Using Core Annular Flows.

Highly concentrated biological drug formulations would offer tremendous benefits to global health, yet they cannot be manually injected using commercial syringes and needles due to their high viscosities. Current approaches to address this problem face several challenges such as crosscontamination, high cost, needle clogging, and protein inactivation. This work reports a simple method to enhance formulation injectability using a core annular flow, where the transport of highly viscous fluids through a needle is enabled by coaxial lubrication by a less viscous fluid. A phase diagram to ensure optimally lubricated flow while minimizing the volume fraction of lubricant injected is established. The technique presented here allows for up to a 7x reduction in injection force for the highest viscosity ratio tested. The role of buoyancy-driven eccentricity in governing nominal pressure reduction is also examined. Finally, the findings are implemented into the development of a double barreled syringe that significantly expands the range of injectable concentrations of several biologic formulations.