Origami and Kirigami Nanocomposites.

The arts of origami and kirigami inspired numerous examples of macroscale hierarchical structures with high degree of reconfigurability and multiple functionalities. Extension of kirigami and origami patterning to micro-, meso-, and nanoscales enabled production of nanocomposites with unusual combination of properties, transitioning these art forms to the toolbox of materials design. Various subtractive and additive fabrication techniques applicable to nanocomposites and out-of-plane deformation of patterns enable a technological framework to negotiate often contradictory structural requirements for materials properties. Additionally, the long-searched possibility of patterned composites/parts with highly predictable set of properties/functions emerged. In this review, we discuss foldable/stretchable composites with designed mechanical properties, as exemplified by the negative Poisson's ratio, as well as optical and electrical properties, as exemplified by the sheet conductance, photovoltage generation, and light diffraction. Reconfiguration achieved by extrinsic forces and/or intrinsic stresses enables a wide spectrum of technological applications including miniaturized biomedical tools, soft robotics, adaptive optics, and energy systems, extending the limits of both materials engineering concepts and technological innovation.

Kirigami Nanocomposites as Wide-Angle Diffraction Gratings.

Beam steering devices represent an essential part of an advanced optics toolbox and are needed in a spectrum of technologies ranging from astronomy and agriculture to biosensing and networked vehicles. Diffraction gratings with strain-tunable periodicity simplify beam steering and can serve as a foundation for light/laser radar (LIDAR/LADAR) components of robotic systems. However, the mechanical properties of traditional materials severely limit the beam steering angle and cycle life. The large strain applied to gratings can severely impair the device performance both in respect of longevity and diffraction pattern fidelity. Here, we show that this problem can be resolved using micromanufactured kirigami patterns from thin film nanocomposites based on high-performance stiff plastics, metals, and carbon nanotubes, etc. The kirigami pattern of microscale slits reduces the stochastic concentration of strain in stiff nanocomposites including those made by layer-by-layer assembly (LBL). The slit patterning affords reduction of strain by 2 orders of magnitude for stretching deformation and consequently enables reconfigurable optical gratings with over a 100% range of period tunability. Elasticity of the stiff nanocomposites and plastics makes possible cyclic reconfigurability of the grating with variable time constant that can also be referred to as 4D kirigami. High-contrast, sophisticated diffraction patterns with as high as fifth diffraction order can be obtained. The angular range of beam steering can be as large as 6.5° for a 635 nm laser beam compared to ∼1° in surface-grooved elastomer gratings and ∼0.02° in MEMS gratings. The versatility of the kirigami patterns, the diversity of the available nanocomposite materials, and their advantageous mechanical properties of the foundational materials open the path for engineering of reconfigurable optical elements in LIDARs essential for autonomous vehicles and other optical devices with spectral range determined by the kirigami periodicity.

A kirigami approach to engineering elasticity in nanocomposites through patterned defects.

Efforts to impart elasticity and multifunctionality in nanocomposites focus mainly on integrating polymeric and nanoscale components. Yet owing to the stochastic emergence and distribution of strain-concentrating defects and to the stiffening of nanoscale components at high strains, such composites often possess unpredictable strain-property relationships. Here, by taking inspiration from kirigami­the Japanese art of paper cutting­we show that a network of notches made in rigid nanocomposite and other composite sheets by top-down patterning techniques prevents unpredictable local failure and increases the ultimate strain of the sheets from 4 to 370%. We also show that the sheets' tensile behaviour can be accurately predicted through finite-element modelling. Moreover, in marked contrast to other stretchable conductors, the electrical conductance of the stretchable kirigami sheets is maintained over the entire strain regime, and we demonstrate their use to tune plasma-discharge phenomena. The unique properties of kirigami nanocomposites as plasma electrodes open up a wide range of novel technological solutions for stretchable electronics and optoelectronic devices, among other application possibilities.