Stretchable Structures Research Articles

Highly stretchable and shape-controllable three-dimensional antenna fabricated by \u201cCut-Transfer-Release\u201d method

Recent progresses on the Kirigami-inspired method provide a new idea to assemble three-dimensional (3D) functional structures with conventional materials by releasing the prestrained elastomeric substrates. In this paper, highly stretchable serpentine-like antenna is fabricated by a simple and quick “Cut-Transfer-Release” method for assembling stretchable 3D functional structures on an elastomeric substrate with a controlled shape. The mechanical reliability of the serpentine-like 3D stretchable antenna is evaluated by the finite element method and experiments. The antenna shows consistent radio frequency performance with center frequency at 5.6 GHz during stretching up to 200%. The 3D structure is also able to eliminate the hand effect observed commonly in the conventional antenna. This work is expected to spur the applications of novel 3D structures in the stretchable electronics.

Stretchable Electronics: In‐Plane Deformation Mechanics for Highly Stretchable Electronics (Adv. Mater. 8/2017)

Scissoring/nonbuckling interconnects are proposed as a different route to stretchable structures, in which thick bar geometries replace thin ribbon layouts, to yield scissor-like/nonbuckling deformations instead of in or out of plane buckling, as discussed in article number 1604989 by Shuodao Wang, John A. Rogers, and co-authors. Metal and silicon structures with scissoring design can be stretched as much as 350% (previous maximum value 54%) and 90%, respectively, without fracture. Image designed by Zhenhai Li.

Needs and Enabling Technologies for Stretchable Electronics Commercialization

AbstractStretchable electronics represent an emerging class of devices that can be compressed, twisted and conform to very complicated shapes. The mechanical and electrical compliances of the technology promise to open up applications for healthcare, energy and entertainment purposes. However, advancement in the field has been hindered by material related constraints. Moreover, the current microfabrication facilities are optimized for rigid substrates such as silicon, which have significant different properties compared to elastomers. In this paper, four categories of enabling technologies for stretchable electronics commercialization are critically reviewed, namely: the novel design of stretchable structures, use of non-conventional materials, state-of-art printing techniques and also the patterning of electrodes or metal interconnects via conventional manufacturing techniques.

3D Stretchable Arch Ribbon Array Fabricated via Grayscale Lithography.

Microstructures with flexible and stretchable properties display tremendous potential applications including integrated systems, wearable devices and bio-sensor electronics. Hence, it is essential to develop an effective method for fabricating curvilinear and flexural microstructures. Despite significant advances in 2D stretchable inorganic structures, large scale fabrication of unique 3D microstructures at a low cost remains challenging. Here, we demonstrate that the 3D microstructures can be achieved by grayscale lithography to produce a curved photoresist (PR) template, where the PR acts as sacrificial layer to form wavelike arched structures. Using plasma-enhanced chemical vapor deposition (PECVD) process at low temperature, the curved PR topography can be transferred to the silicon dioxide layer. Subsequently, plasma etching can be used to fabricate the arched stripe arrays. The wavelike silicon dioxide arch microstructure exhibits Young modulus and fracture strength of 52 GPa and 300 MPa, respectively. The model of stress distribution inside the microstructure was also established, which compares well with the experimental results. This approach of fabricating a wavelike arch structure may become a promising route to produce a variety of stretchable sensors, actuators and circuits, thus providing unique opportunities for emerging classes of robust 3D integrated systems.

Highly Stretchable Anisotropic Structures for Flexible Micro/nano-electrode Applications.

The functionality of flexible metal electrodes relies on the stable performance of a metallic film. In this study, highly stretchable anisotropic structures are designed to investigate the behaviour of silver electrodes on polydimethylsiloxane. Treated using both the oxygen plasma and the surface chemical functionalization technology, the film resistivity was reduced to 5.856 × 10−9 Ω m after annealing at 150 °C for 30 min, which is equal to that of commercial silver films on glass. The maximum variation in the resistance was approximately 5.315 % with a strain of 50 % along the four directions, and the films also show remarkable tolerance to repetitive strain. These results prove the excellent anisotropy performance of these structures to minimize resistive strain sensitivity and thus enable durable flexible electronics.

Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene.

Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the 'Internet of Things' area.

Micro-wrinkling and delamination-induced buckling of stretchable electronic structures

This paper presents the results of experimental and theoretical/computational micro-wrinkles and buckling on the surfaces of stretchable poly-dimethylsiloxane (PDMS) coated with nano-scale Gold (Au) layers. The wrinkles and buckles are formed by the unloading of pre-stretched PDMS/Au structure after the evaporation of nano-scale Au layers. They are then characterized using atomic force microscopy and scanning electron microscopy. The critical stresses required for wrinkling and buckling are analyzed using analytical models. The possible interfacial cracking that can occur along with film buckling is also studied using finite element simulations of the interfacial crack growth. The implications of the results are discussed for potential applications of micro-wrinkles and micro-buckles in stretchable electronic structures and biomedical devices.

High-performance coils and yarns of polymeric piezoelectric nanofibers.

We report on highly stretchable piezoelectric structures of electrospun PVDF-TrFE nanofibers. We fabricated nanofibrous PVDF-TrFE yarns via twisting their electrospun ribbons. Our results show that the twisting process not only increases the failure strain but also increases overall strength and toughness. The nanofibrous yarns achieved a remarkable energy to failure of up to 98 J/g. Through overtwisting process, we fabricated polymeric coils out of twisted yarns that stretched up to ∼740% strain. This enhancement in mechanical properties is likely induced by increased interactions between nanofibers, contributed by friction and van der Waals interactions, as well as favorable surface charge (Columbic) interactions as a result of piezoelectric effect, for which we present a theoretical model. The fabricated yarns and coils show great promise for applications in high-performance lightweight structural materials and superstretchable piezoelectric devices and flexible energy harvesting applications.

Large-scale fabrication of flexible metallic nanostructure pairs using interference ablation

Paired one- and two-dimensional metallic nanostructures are created directly by exposing a thin gold film to the interference pattern between ultraviolet laser pulses, where the gold film is coated onto a soft substrate and is sandwiched by another soft slab. Metallic films in the bright fringes are melted and transformed into nanodroplets that are ejected onto the soft slab forming stretchable nanoisland structures. The pattern of the remaining films is coincident with the dark fringes. Thus, complementary metallic nanostructure pairs were fabricated using a single laser pulse. Fano resonance can be observed in the spectroscopic response of the fabricated nanostructures for TM and TE polarizations simultaneously. This nanofabrication technique may provide an annealing-free approach for the fabrication of flexible metallic nanostructures on a large scale and with low cost.

Physics of engineered protein hydrogels

AbstractArtificially engineered proteins and synthetic polypeptides have attracted widespread interest as building blocks for polymer hydrogels. The biophysical properties of the proteins, such as molecular recognition abilities, folded chain structures, and sequence‐dependent thermodynamic behavior, enable advances in functional, responsive, and tunable gels. This review discusses the design of polymer hydrogels that incorporate protein domains, highlighting new challenges in polymer physics that are presented by this emerging class of materials. Five types of engineered protein hydrogels are discussed: (a) physically associating protein polymer gels, (b) amorphous artificially engineered protein networks, (c) engineered proteins with crystalline domains, (d) stretchable protein tertiary structures in gels, and (e) protein gels with biological recognition properties. The physics of the protein component and the physical properties of the resulting hydrogels are summarized, illustrating how advances in understanding these systems are leading to exciting novel biofunctional hydrogels. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Stretchable and Strong Cellulose Nanopaper Structures Based on Polymer-Coated Nanofiber Networks: An Alternative to Nonwoven Porous Membranes from Electrospinning

Nonwoven membranes based on electrospun fibers are of great interest in applications such as biomedical, filtering, and protective clothing. The poor mechanical performance is a limitation, as is some of the electrospinning solvents. To address these problems, porous nonwoven membranes based on nanofibrillated cellulose (NFC) modified by a hydroxyethyl cellulose (HEC) polymer coating are prepared. NFC/HEC aqueous suspensions are subjected to simple vacuum filtration in a paper-making fashion, followed by supercritical CO(2) drying. These nonwoven nanocomposite membranes are truly nanostructured and exhibit a nanoporous network structure with high specific surface area, as analyzed by nitrogen adsorption and FE-SEM. Mechanical properties evaluated by tensile tests show high strength combined with remarkably high strain to failure of up to 55%. XRD analysis revealed significant fibril realignment during tensile stretching. After postdrawing of the random mats, the modulus and strength are strongly increased. The present preparation route uses components from renewable resources, is environmentally friendly, and results in permeable membranes of exceptional mechanical performance.

Adhesion and cyclic stretching of Au thin film on poly(dimethyl-siloxane) for stretchable electronics

This paper presents the results of an experimental study of the effects of cyclic damage and adhesion on nanoscale Au thin films deposited on a flexible poly(dimethyl-siloxane) substrate. The deformation and cracking mechanisms are elucidated as functions of film thickness. The implications of the results are also discussed for the design of stretchable electronic structures.

Stretchable diamond-like carbon microstructures for biomedical applications

Designing, fabricating, and evaluating stretchable electronics is a growing area of materials research. Electronic devices have traditionally been fabricated using rigid, inorganic substrates (e.g., silicon) with metallic components and interconnections. Conventional electronic devices may face limitations when placed in environments that are dominated by stretchable or three-dimensional structures, including those within the human body. This paper describes the use of pulsed laser deposition to create diamond-like carbon microstructures on polydimethylsiloxane. The viability of human epidermal keratinocyte cells on polydimethylsiloxane surfaces coated with arrays of diamond-like carbon islands was similar to that on unmodified polydimethylsiloxane surfaces, which are commonly used in medical devices. It is anticipated that stretchable electronic devices may be incorporated within novel medical devices and prostheses that interface with stretchable or three-dimensional structures in the human body.

Mechanics of stretchable inorganic electronic materials

Electronic systems that offer elastic mechanical responses to high strain deformation are of growing interest due to their ability to enable new applications whose requirements are impossible to satisfy with conventional wafer-based technologies. This article reviews the mechanics of stretchable inorganic materials on compliant substrates. Specifically, three forms of stretchable structures are reviewed. The first one is stretchable ribbon, which provides one-dimensional stretchability. The second is stretchable nanomembranes, which can be stretched in all directions. The last is a noncoplanar mesh design, which has the advantage of providing large stretchability up to and exceeding 100%. Mechanics models and their comparison to experiment are reviewed for these three cases. Such models provide design guidelines for stretchable electronics.

Ionic structures as intercalation compound host lattices. An ab initio perturbed ion study on lattice stretching

The effect of lattice expansion along one axis on lattice energy has been analyzed from a theoretical viewpoint. Thirteen ionic structures (LiF, NaF, NaCl, MgO, CsF, CsCl, TiO 2, ZrO 2 (m), ZrO 2 (t), ZrO 2 (c), CaF 2, SrTiO 3 and KMgF 3) have been considered due to their role as potential host lattices for intercalation compounds of the CsF·Br 2 type. Their structural parameters have been optimized and lattice energies evaluated by means of the ab initio perturbed ion method. Results indicate that the most easily stretchable structures based on energy requirements and therefore the best suited as host lattices in this kind of intercalation compound, are those with a rock salt or perovskite type of structure, particularly those formed by low charge ions.

Independent Statements about Finite Stretchable Structures

We consider several analogs of the theorem of Ehrenfeucht and Mostowski, in which the models generated by indiscernibles are finite; we show these analogs to be independent from strong axioms, ranging from Peano’s arithmetic to set theory with Mahlo cardinals.

Independent statements about finite stretchable structures

We consider several analogs of the theorem of Ehrenfeucht and Mostowski, in which the models generated by indiscernibles are finite; we show these analogs to be independent from strong axioms, ranging from Peano’s arithmetic to set theory with Mahlo cardinals.