Shape‐memory resists capable of high‐resolution curing into arbitrarily designed structures are increasingly demanded for soft robotics, optical sensors, microscale manufacturing, and biomedicine. Amorphous, shape‐memory thiol‐vinyl networks are printed using two‐photon polymerization (2PP) curing of a simple resin formulated with commercially available reagents. The ability to print high‐resolution feature sizes down to 200 nm is attributed to the use of radical‐mediated, thiol‐vinyl step‐growth polymerization that quickly cross‐links the resin, limiting diffusive transport. The thermomechanical behavior of the 2PP‐cured material analyzed in compression, tension, and three‐point bending is similar to the behavior of the UV‐polymerized samples. To demonstrate the ability to design, field, and test 4D responsive microstructures, an array of nine springs with coil diameters of 330 µm is printed. Following compressive shape‐fixing, printed arrays can release 11 µJ of stored elastic strain energy when reheated. Further, a new concept of dichroic‐memory of a metamaterial device is demonstrated by printing a twisted woodpile structure with circular dichroism as characterized by Mueller Matrix ellipsometry. The results of this study demonstrate how combining high‐resolution 2PP curing with stimuli‐responsive molecular architectures can further the engineering of responsive microstructures and metamaterials.
- NSF-PAR ID:
- 10275974
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 9
- Issue:
- 4
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 1164 to 1173
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Stimuli-responsive elastic metamaterials augment unique subwavelength features and wave manipulation capabilities with a degree of tunability, which enables them to cut across different time scales and frequency regimes. Here, we present an experimental framework for robust local resonance bandgap control enabled by enhanced magneto-mechanical coupling properties of a magnetorheological elastomer, serving as the resonating stiffness of a metamaterial cell. During the curing process, ferromagnetic particles in the elastomeric matrix are aligned under the effect of an external magnetic field. As a result, particle chains with preferred orientation form along the field direction. The resulting anisotropic behavior significantly boosts the sensitivity of the metamaterial’s elastic modulus to the imposed field during operation, which is then exploited to control the dispersive dynamics and experimentally shift the location and width of the resonance-based bandgap along the frequency axis. Finally, numerical simulations are used to project the performance of the magnetically-tunable metamaterial at stronger magnetic fields and increased levels of material anisotropy, as a blueprint for broader implementations of in situ tunable active metamaterials.
-
null (Ed.)Many engineering applications leverage metamaterials to achieve elastic wave control. To enhance the performance and expand the functionalities of elastic waveguides, the concepts of electronic transport in topological insulators have been applied to elastic metamaterials. Initial studies showed that topologically protected elastic wave transmission in mechanical metamaterials could be realized that is immune to backscattering and undesired localization in the presence of defects or disorder. Recent studies have developed tunable topological elastic metamaterials to maximize performance in the presence of varying external conditions, adapt to changing operating requirements, and enable new functionalities such as a programmable wave path. However, a challenge remains to achieve a tunable topological metamaterial that is comprehensively adaptable in both the frequency and spatial domains and is effective over a broad frequency bandwidth that includes a subwavelength regime. To advance the state of the art, this research presents a piezoelectric metamaterial with the capability to concurrently tailor the frequency, path, and mode shape of topological waves using resonant circuitry. In the research presented in this manuscript, the plane wave expansion method is used to detect a frequency tunable subwavelength Dirac point in the band structure of the periodic unit cell and discover an operating region over which topological wave propagation can exist. Dispersion analyses for a finite strip illuminate how circuit parameters can be utilized to adjust mode shapes corresponding to topological edge states. A further evaluation provides insight into how increased electromechanical coupling and lattice reconfiguration can be exploited to enhance the frequency range for topological wave propagation, increase achievable mode localization, and attain additional edge states. Topological guided wave propagation that is subwavelength in nature and adaptive in path, localization, and frequency is illustrated in numerical simulations of thin plate structures. Outcomes from the presented work indicate that the easily integrable and comprehensively tunable proposed metamaterial could be employed in applications requiring a multitude of functions over a broad frequency bandwidth.more » « less
-
more » « less
Abstract 2D metamaterials have immense potential in acoustics, optics, and electromagnetic applications due to their unique properties and ability to conform to curved substrates. Active metamaterials have attracted significant research attention because of their on‐demand tunable properties and performances through shape reconfigurations. 2D active metamaterials often achieve active properties through internal structural deformations, which lead to changes in overall dimensions. This demands corresponding alterations of the conforming substrate, or the metamaterial fails to provide complete area coverage, which can be a significant limitation for their practical applications. To date, achieving area‐preserving active 2D metamaterials with distinct shape reconfigurations remains a prominent challenge. In this paper, magneto‐mechanical bilayer metamaterials are presented that demonstrate area density tunability with area‐preserving capability. The bilayer metamaterials consist of two arrays of magnetic soft materials with distinct magnetization distributions. Under a magnetic field, each layer behaves differently, which allows the metamaterial to reconfigure its shape into multiple modes and to significantly tune its area density without changing its overall dimensions. The area‐preserving multimodal shape reconfigurations are further exploited as active acoustic wave regulators to tune bandgaps and wave propagations. The bilayer approach thus provides a new concept for the design of area‐preserving active metamaterials for broader applications.
-
more » « less
Abstract Maxwell lattices possess distinct topological states that feature mechanically polarized edge behaviors and asymmetric dynamic responses protected by the topology of their phonon bands. Until now, demonstrations of non‐trivial topological behaviors from Maxwell lattices have been limited to fixed configurations or have achieved reconfigurability using mechanical linkages. Here, a monolithic transformable topological mechanical metamaterial is introduced in the form of a generalized kagome lattice made from a shape memory polymer (SMP). It is capable of reversibly exploring topologically distinct phases of the non‐trivial phase space via a kinematic strategy that converts sparse mechanical inputs at free edge pairs into a biaxial, global transformation that switches its topological state. All configurations are stable in the absence of confinement or a continuous mechanical input. Its topologically‐protected, polarized mechanical edge stiffness is robust against broken hinges or conformational defects. More importantly, it shows that the phase transition of SMPs that modulate chain mobility, can effectively shield a dynamic metamaterial's topological response from its own kinematic stress history, referred to as “stress caching”. This work provides a blueprint for monolithic transformable mechanical metamaterials with topological mechanical behavior that is robust against defects and disorder while circumventing their vulnerability to stored elastic energy, which will find applications in switchable acoustic diodes and tunable vibration dampers or isolators.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0TC04999A
