\”Science\” after recurrence \”AM\”: a new system of adhesive material – elastomer ion reversible low-voltage electrical junction adhesion!

Response to external stimuli, reversible conversion of adhesion has attracted widespread industry interest in bio-medicine, manufacturing and robotics applications. In the method developed to date, the electrical adhesion provides a simple and reversible electrostatic attractive force between the two surfaces is controlled by the electric field. Compared with other mechanisms, eiectroadhesive some advantages, such as precise control of the adhesive force, fast response speed, no residue, quiet operation and low power consumption. In particular, a tactile and robots have been increasingly used electrical adhesive, e.g., to make a soft grip, climbing robot, a touch screen and a touch virtual objects due to their dielectric stretchable, and has a small size and lightweight case under ability to function. However, adhesives based on electric current and the electron conductor insulating dielectric layer is generally limited by the need for applying a high voltage within the range of thousands of kV, not only a security risk, but also requires a dedicated circuit element compatible with a high pressure, one of the working voltage reduction strategy is to reduce the electrical thickness of the dielectric layer of adhesive, because the standard parallel plate capacitor model shows that the electrostatic force is inversely proportional to the electrical resistance. Dielectric electroluminescent adhesive previously impossible operate within a few volts, but instead of the dielectric layer, the charged macromolecules have been shown to reversibly adhered at a much lower potential of great promise. Polyanion and polycation complexed with an ion of opposite charge, response to external stimuli can provide adhesion mechanism of reversible conversion, widely used in many biological systems. Polyelectrolyte complexes between the oppositely charged solid support can be formed such that the adhesion of the shear stress of 1.5 MPa is achieved, followed by the addition of salt to make the two polyelectrolytes screened electrostatic interaction due disengaged. Later studies have shown that adhesion between the incoming ion concentration gradient by using the potential range of a few volts switching a polyanion and polycation hydrogels, but these examples are limited to operating in the water, so far only achieved attaching the two states (attached or separated). Electrical adhesion at a low voltage condition in the absence of liquid remains a huge challenge, and will extend this approach to new application areas have great potential.

\”Science\” implied an \”AM\”

2020 February 14, Professor Ryan C. Hayward University of Massachusetts and Harvard University Suo Zhigang Academy of Sciences to develop a double to correct use of ion and ion current is switched ion diode elastomerTubes, transistors. Team designed with two polyelectrolytes network cations and anions, respectively, which can be moved counter ions associated. The elastomeric backbone having counter ions to ionic bilayer construct (IDL), and it can be rectified without the electrochemical reactions occur \”on – off\” ion current. Ion movement occurs entropy associated driving loss generated ions heterojunction, which may be analogous meaning PN junction. Conventional PN junction can not be stretched, and the intrinsic ion stretchable elastomeric stretchable ion was heterojunction device basis. Papers related to \”Ionoelastomer junctions between polymer networks of fixed anions and cations\” in the title, published in \”Science\”. 《Science》之后再发《AM》:粘附材料新体系——离子弹性体结的低压可逆电粘附! Recently, Harvard University Professor and Professor Zhigang Suo University of Massachusetts Amherst Ryan C. Hayward teamed up again published an article in Advanced Materials, showing an ion-heterojunction new elastomer based at a potential of ≈1V electrical adhesive. By adjusting the control voltage across the IDL reversible adhesion between the two ions elastomer. 1A, in \”reverse bias\”, the flow of ions from the interface region drawn resulting from accumulation IDL fixed charge. These thin electric interface layer fixed charges in excess can cause the generated electrostatic adhesion between the two ions elastomer. In the \”forward bias\” (FIG. IB), moves into the cationic polycationic polyanionic domain from the domain, and vice versa. Thus, performance of the interface and resistive electrostatic adhesion force between two ions disappeared elastomer. 《Science》之后再发《AM》:粘附材料新体系——离子弹性体结的低压可逆电粘附! The present study used a poly (1-ethyl-3- methylimidazolium (3-sulfopropyl) acrylate) (ES) and poly (1- [2-acryloyloxyethyl] -3- imidazole bis (trifluoromethane) sulfonimide) (the AT) crosslinked network showing electric ion elastomer based adhesive. In the case where no voltage is applied, the use of highly crosslinked the AT and ES (containing 20 mol% of poly (ethylene glycol) diacrylate crosslinker) to reduce adhesion between the two ions elastomer, and to enhance the stability of both ions elastomer by adding fumed silica particles (2.5 wt%). In order to characterize the ion ES AT and elasticityElectrical adhesion between body used in this study has a cylindrical cross-geometry contact adhesive test (FIG. 2A). The Derjagui approximation, is equivalent to the cross-spherical geometry of the cylinder on a plane, it will produce a well-defined contact points, the air gap and minimize the influence of the electric adhesion. The applied load (P) and displacement ([delta]) measured values ​​(FIG. 2B) of the two perpendicularly intersecting the cylinder (radius r = 10 mm) together, to 0.05 mm s-1 at a constant speed ES generating layer between the contact and the aT, and remains fixed displacement charge 30 s ion elastomer, and then separated at the same speed 0.05 mm s-1 at a fixed voltage. The Johnson-Kendall-Roberts (JKR) model for contacting the adhesive between the elastic material calculations, the peak load can be separated (Ppeak is) converted into a critical strain energy release rate (Gc) Ppeak = (3/2) πrGc. 2C shows the various voltages applied to the three junctions ion elastomeric (i.e., ES / ES and AT / AT homojunction and ES / AT heterojunction) Ppeak and the value Gc. Contacting a schematic Adhesion Test A) using a cross cylindrical geometry:

《Science》之后再发《AM》:粘附材料新体系——离子弹性体结的低压可逆电粘附!
FIG. B) In the external bias, typically load ES / AT interchange – displacement curve, where red and blue data points represent the reverse and forward bias. C) Ppeak three values ​​of ion elastomeric connector.

Then, reversible ES / AT adhesive power Ppeak by multiple measurements at ± AC voltage of 1 V to the test. In repeated 30 cycles, \”on\” state (-1 V) and the observed \”off\” state (+1 V) was 41 ± 4 mN (FIG. 3A). Gc and turned off state corresponding values ​​were 2.3 and 0.9 J m-2. In addition, the article further measurements and ES AT shown in FIG. 3B illustration peeling Gc. Crack velocity at 0.2 mm s-1, the two ions elastomer easily peeled when +1 V, thereby producing Gc = 82 ± 6 J m-2. In contrast, at -1 V, measured Gc = 220 ± 3 J m-2 significantly higher. This paper compared with a contact pre-estimated adhesion test, mainly due to a larger value as the relative Gc in the T-peel test procedureThe impact of rapid crack propagation velocity. It is vital that the comparison between ES and Bakelite layer AT much stronger resistance to conventional electrical defect gum.

《Science》之后再发《AM》:粘附材料新体系——离子弹性体结的低压可逆电粘附!
FIG. 3: A) by contact adhesion test measurements ES / AT peak at a heterojunction ± AC voltage of 1 V. Blue dot reverse bias (-1 V), the red dot represents the forward bias (+1 V). B) ES / AT heterojunction T-peel test, the peel for the energy release rate (Gc).

Finally, elastomeric article demonstrates an ionic electrically adhesion paste, the paste may be subjected to +1 V at 5 kPa shear load, as shown in FIG. The pad consists of two parts: a power source connected to the AT and ES comprising, further comprising two elastomeric ion connected by wires. By this geometry, the second paste may be used without being connected to the weight holding power. In the illustration of FIG. 4A shows a circuit diagram of the system. When a voltage is -1 V is applied to the ion elastic body adhesive pad (adhesive pad contains per 1 cm2 and the ES AT) which can withstand the weight of 100 g, corresponding to a shear stress of 5 kPa. When the external voltage is switched to +1 V, loss of adhesion pad in a time range of approx. 1 s and separated from each other. These ions elastomeric adhesive for the design of the electrical junction soft micro robotic applications particularly attractive, because no large and heavy, or high voltage amplifier transistor and a high voltage logic operable element designed to be controlled. Ion elastic body adhesive present embodiment only in providing enhanced adhesion between the two opposite polarity particular material. Although such selectivity is complementary to the adhesive itself may be used (e.g., Velcro snaps, buttons and zippers), but using the low pressure plasma is bonded to the elastomer to achieve a more valuable also other surfaces.

《Science》之后再发《AM》:粘附材料新体系——离子弹性体结的低压可逆电粘附!
FIG. 4: ES / AT ion resilient electrical adhesive pad can withstand the shear load of 5 kPa is applied at a potential of -1 V. The pad consists of two parts: a power source connected to the layer comprising the AT and ES, AT ES and the other layer comprising a connecting wire.

Summary and Outlook:

In conclusion, this study has demonstrated plasma elastomer junction provides a novel electrical adhesive can be controlled by a low voltage (≈1V). In the reverse biasPressure, ionic double layer charging of the interface will provide an electrostatic force between two ions elastomers, in forward bias, mobile ions will be pushed into IDL and finally across the interface, so that breakdown electric field, thereby greatly reducing adhesion. Therefore, finding of this study is designed to provide a new electrical platform adhesives, the adhesive can be reversibly switched electrical adhesive force at low voltage, and more resistant to damage than the conventional dielectric electroluminescent adhesive. This approach will open new opportunities in many fields, such as including robotics, virtual reality hardware and response materials. The full text link: https: //onlinelibrary.wiley.com/doi/10.1002/adma.202000600

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