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a) Stress-strain behavior of Sylgard 184/Ecofl ex 00-30 blend with different mixing ratio. Shown are the arithmetic means of the stressstrain data of four individual samples (blue symbols) of each elastomer blend (20 wt% steps), the ±1σ confi dence intervals (blue shaded areas) and the respective Gent fi ts (blue dashed lines). b) Young's moduli of the blends: experimental values and theoretical modelling using the Halpin-Tsai composite model, together with experimental and theoretical values for the extreme confi gurations of purely serial and purely parallel alignment. c) The increasing stiffness of the Sylgard 184/Ecofl ex 00-30 blends visualized by gravitational bending. d,e) Combination samples for serial and parallel alignment of the elastomers.
Source publication
Toy bricks are an ideal platform for the cost-effective rapid prototyping of a
tabletop tensile tester with measurement accuracy on par with expensive,
commercially available laboratory equipment. Here, a tester is presented that
is not only a versatile demonstration device in mechanics, electronics, and
physics education and an eye-catcher on exhi...
Contexts in source publication
Context 1
... detailed fabrication process is given in the Experimental Section. We fi tted the stress-strain data of four samples per mixing ratio ( Figure 2 a) with the Gent hyperelastic model (Equation ( 1) ) using the Young's Modulus Y , the limiting parameter J m , the rotational invariant I 1 (Equation ( 2) ) and an assumed Poisson- Ratio of ν = 0.5 ...
Context 2
... arithmetic means of the stress-strain data, the ±1σ confi - dence interval and the Gent fi ts are plotted in Figure 2 a. The high reproducibility of the results demonstrates that this elas- tomer blend can be engineered with consistent mechanical properties. ...
Context 3
... a combination of randomly distributed serial and parallel connections between the fi ller and reinforcement elastomer domains determines the Young's modulus. To visualize the theoretical extremes of purely serial (Figure 2 d) and purely parallel alignments (Figure 2 e) of the two elastomers, these cases were also tested and the effec- tive Young's moduli ( Y PAR and Y SER ) of the combinations mod- eled with a linear stress-strain behavior (Equations ( 4) and ( 5) , respectively); these are also the limits of Equation ( 3) for ζ → ∞ and ζ = 0, respectively ...
Context 4
... a combination of randomly distributed serial and parallel connections between the fi ller and reinforcement elastomer domains determines the Young's modulus. To visualize the theoretical extremes of purely serial (Figure 2 d) and purely parallel alignments (Figure 2 e) of the two elastomers, these cases were also tested and the effec- tive Young's moduli ( Y PAR and Y SER ) of the combinations mod- eled with a linear stress-strain behavior (Equations ( 4) and ( 5) , respectively); these are also the limits of Equation ( 3) for ζ → ∞ and ζ = 0, respectively ...
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Toy bricks are an ideal platform for the cost-effective rapid prototyping of a tabletop tensile tester with measurement accuracy on par with expensive, commercially available laboratory equipment. Here, a tester is presented that is not only a versatile demonstration device in mechanics, electronics, and physics education and an eye-catcher on exhi...
Citations
... GSA fabrication and target moduli were achieved in accordance with previous work 55 . All modulus characterizations were measured using ISO527-2-type5b standards 55,56 . ...
... GSA fabrication and target moduli were achieved in accordance with previous work 55 . All modulus characterizations were measured using ISO527-2-type5b standards 55,56 . Stress-strain measurements were conducted with an Instron 5942 universal tensile tester (Norwood, MA, USA) set at a velocity of 200 µm s −1 . ...
Gecko adhesive performance increases as relative humidity increases. Two primary mechanisms can explain this result: capillary adhesion and increased contact area via material softening. Both hypotheses consider variable relative humidity, but neither fully explains the interactive effects of temperature and relative humidity on live gecko adhesion. In this study, we used live tokay geckos (Gekko gecko) and a gecko-inspired synthetic adhesive to investigate the roles of capillary adhesion and material softening on gecko adhesive performance. The results of our study suggest that both capillary adhesion and material softening contribute to overall gecko adhesion, but the relative contribution of each depends on the environmental context. Specifically, capillary adhesion dominates on hydrophilic substrates, and material softening dominates on hydrophobic substrates. At low temperature (12 °C), both capillary adhesion and material softening likely produce high adhesion across a range of relative humidity values. At high temperature (32 °C), material softening plays a dominant role in adhesive performance at an intermediate relative humidity (i.e., 70% RH).
... The simplest stretchable electronic systems devisable with the materials mentioned above feature a highly deformable substrate, a printed conductive ink such as the ones mentioned above, and surface-mounted devices (SMDs), such as rigid passive components, integrated circuits (ICs), batteries, or connectors. The presence of the rigid components on top of a deformable substrate plays a crucial role in the electromechanical behaviour of these systems, and often there is the need to minimize the dimensions of these 'rigid islands' in order to reduce strain concentration happening upon deformation of the system [28][29][30][31][32][33] . Recent application of this type of strategy, for example, feature the combination of multiple phenomena, such as prestretching the substrate to induce microbuckling or serpentine structures, together with the use of microislands with specific shapes to enhance the system electrical behaviour under cyclic loading 34,35 . ...
Stretchable electronics promise to extend the application range of conventional electronics by enabling them to keep their electrical functionalities under system deformation. Within this framework, development of printable silver-polymer composite inks is making possible to realize several of the expected applications for stretchable electronics, which range from seamless sensors for human body measurement (e.g. health patches) to conformable injection moulded structural electronics. However, small rigid electric components are often incorporated in these devices to ensure functionality. Under mechanical loading, these rigid elements cause strain concentrations and a general deterioration of the system’s electrical performance. This work focuses on different strategies to improve electromechanical performance by investigating the deformation behaviour of soft electronic systems comprising rigid devices through Finite Element analyses. Based on the deformation behaviour of a simple stretchable device under tensile loading, three general strategies were proposed: local component encapsulation, direct component shielding, and strain dispersion. The FE behaviour achieved using these strategies was then compared with the experimental results obtained for each design, highlighting the reasons for their different resistance build-up. Furthermore, crack formation in the conductive tracks was analysed under loading to highlight its link with the evolution of the system electrical performance.
... Generally, hydrogel strain sensors usually require high mechanical strength, toughness, and stretchability for transducing mechanical deformation into electrical/chemical/optical signals. [52][53][54][55] Specifically, in vivo injectable hydrogel strain sensors must be biodegradable and biocompatible, and their degraded products also need to be biocompatible with minimal inflammatory responses. ...
Development and fabrication of stimuli-responsive polymers into hydrogel strain sensors with high sensitivity and specificity to subtle changes in environmental stimuli have open the door for exploring the opportunities from fundamental materials design principles to emerging applications of electronic skins, health monitors, and human-machine interfaces. This review mainly summarizes recent progress, particularly over the past 5 years, on hydrogel strain sensors from different aspects, including materials designs, gelation/fabrication methods, stimuli-responsive principles, sensing performance, and some typical or interesting examples of these hydrogel sensors. Finally, current challenges and future perspectives of hydrogen strain sensors are also discussed to stimulate the more and better research in this emerging field.
... Details of the fabrication process are described in the Experimental Section. Because Ecoflex (50 kPa) 55 has a relatively low elastic modulus compared to PDMS (1910 kPa), 55 Ecoflex is strained to a large magnitude in comparison to PDMS. Figure 4b,c shows finite element simulation images of the local strain of the PDMS island array in Ecoflex under an overall strain of 50%. Figure 4d is the resulting strain profile across the midsection of the PDMS islands along the direction of strain (see dashed line). As seen in Figure 4c,d, strain between the PDMS islands was 101.8% (Ecoflex region) and on the PDMS islands was 5.8%. ...
... Details of the fabrication process are described in the Experimental Section. Because Ecoflex (50 kPa) 55 has a relatively low elastic modulus compared to PDMS (1910 kPa), 55 Ecoflex is strained to a large magnitude in comparison to PDMS. Figure 4b,c shows finite element simulation images of the local strain of the PDMS island array in Ecoflex under an overall strain of 50%. Figure 4d is the resulting strain profile across the midsection of the PDMS islands along the direction of strain (see dashed line). As seen in Figure 4c,d, strain between the PDMS islands was 101.8% (Ecoflex region) and on the PDMS islands was 5.8%. ...
... The PDMS islands were assumed to be a linear elastic material with a modulus of elasticity of 1910 kPa, Poisson's ratio of 0.49, and density of 970 kg/m 3 , and Ecoflex was assumed to be a linear elastic material with a Young's modulus of 50 kPa, Poisson's ratio of 0.49, and density of 1040 kg/m 3 . 55 A constant displacement was applied to the edge of the model so that the total strain was 50%. The resulting deformation distribution was represented by the strain in the direction of elongation caused by the stress in that direction. ...
An ultra-high sensitive capacitive pressure sensor based on porous pyramid dielectric layer (PPDL) is reported. Compared to that of the conventional pyramid dielectric layer, the sensitivity was drastically increased to 44.5 kPa-1 in the pressure range <100 Pa, an unprecedented sensitivity for capacitive pressure sensors. The enhanced sensitivity is attributed to lowered compressive modulus and larger change in effective dielectric constant under pressure. By placing the pressure sensors on islands of hard elastomer embedded in soft elastomer substrate, the sensors exhibited insensitivity to strain. The pressure sensors were also non-responsive to temperature. Finally, a contact resistance-based pressure sensor is also demonstrated by chemically grafting PPDL with a conductive polymer, which also showed drastically enhanced sensitivity.
... 32 To make this technology more "user-friendly," we sought a more instructive colorimetric response. Sylgard 184 was cast around the partially cured SP-PDMS, in a manner similar to that previously published for Ecoflex 42 and patterned here in the shape of the word "STOP" (Figure 3), and then, the entire device is fully cured. Devices cast around partially cured STOP patterns survived to significantly higher strains than those cast around fully cured patterns. ...
... Composite elastomers of Sylgard 184 and Dragon Skin 30 were made in a manner similar to the previous composites in the literature. 42 The SP-PDMS prepolymer was cast onto a polyester surface within a 3/ 64″ thick mold cut from polycarbonate. To ensure an even surface of uniform height, a polyester film was placed on top of the sample, followed by an aluminum block. ...
Soft and stretchable electronics are promising for a variety of applications such as wearable electronics, human-machine interfaces, and soft robotics. These devices, which are often encased in elastomeric materials, maintain or adjust their functionality during deformation, but can fail catastrophically if extended too far. Here, we report new functional composites in which stretchable electronic properties are coupled to molecular mechanochromic function, enabling at-a-glace visual cues that inform user control. These properties are realized by covalently incorporating a spiropyran mechanophore within poly(dimethylsiloxane) to indicate with a visible color change that a strain threshold has been reached. The resulting colorimetric elastomers can be molded and patterned so that, for example, the word "stop" appears when a critical strain is reached, indicating to the user that further strain risks device failure. We also show that the strain at color onset can be controlled by layering silicones with different moduli into a composite. As a demonstration, we show how color onset can be tailored to indicate a when a specified frequency of a stretchable liquid metal antenna has been reached. The multi-scale combination of mechanochromism and soft electronics offers a new avenue to empower user control of strain dependent properties for future stretchable devices.
Nanogenerators have emerged recently as a new technology for harvesting energy from renewable and clean energy sources. Water in nature carries high amounts of kinetic and electrostatic energy; it is ubiquitous and widely accessible in different forms: i.e. as droplets, flows or waves. Either piezoelectric or triboelectric nanogenerators (PENGs, TENGs) have been shown to be effective for harvesting energy from liquids and ocean but the integration of both transduction mechanisms in a single hybrid device allows to exploit several operating conditions and to optimize performances, overcoming the limits of single components. Current piezo-tribo hybrid devices are mostly based on scarcely durable polymers or thick lead-based ceramic materials. Additionally, they are often limited to a specific application or environment due to their architecture and employed materials. In this work, a multifunctional, flexible and conformal hybrid nanogenerator (HNG) has been developed with a sub-100µm thickness and with a novel combination of biocompatible thin-film piezo-ceramic and soft polymeric materials, for harvesting energy of different water sources, i.e. impacts, raindrops and buoying waves. The PENG component is based on a double-sided metallized AlN thin film, sputtered on polyimide. The TENG component is made of a metallized porous patch made of a mixture of PDMS and platinum-catalyzed silicone (EcoflexTM), encapsulated by a friction film of Parylene C surface-treated with UV/ozone. As a result, the HNG exhibits non-algebraic enhanced performances: the resulting power densities under tapping are ~6.5 mW/m² for PENG, 65 mW/m² for TENG, ~230 mW/m² for HNG. Multifunctionality is demonstrated by harvesting energy from different water-conveyed sources (i.e. impacts/breakwaters, raindrops, buoying waves). In particular, the device shows optimal and reliable energy harvesting performance under strong impulsive impacts (~0.8W/m²) and raindrops impacts (~9 mW/m²). A custom buoyant device, called piezo-JellyFish (pJF), is proposed to exploit the HNGs for harvesting wave energy, based on a connection of three HNGs acting as oral arms: this system yields ~3.2 mW/m², with 3 cm-amplitude standing waves. Finally, the HNG exhibits optimal adhesion on the skin and can be also used for monitoring human motions, revealing its multifunctionality also as a wearable conformal sensor.
Introducing methods for instant tough bonding between hydrogels and antagonistic materials—from soft to hard—allows us to demonstrate elastic yet tough biomimetic devices and machines with a high level of complexity. Tough hydrogels strongly attach, within seconds, to plastics, elastomers, leather, bone, and metals, reaching unprecedented interfacial toughness exceeding 2000 J/m2. Healing of severed ionic hydrogel conductors becomes feasible and restores function instantly. Soft, transparent multilayered hybrids of elastomers and ionic hydrogels endure biaxial strain with more than 2000% increase in area, facilitating soft transducers, generators, and adaptive lenses. We demonstrate soft electronic devices, from stretchable batteries, self-powered compliant circuits, and autonomous electronic skin for triggered drug delivery. Our approach is applicable in rapid prototyping and in delicate environments inaccessible for extended curing and cross-linking.
