Self-Contained Underwater Adhesion and Informational Labeling Enabled by Arene-Functionalized Polymeric Ionogels

Adhesives and water exhibit a conflicting correlation as indicated by the failure of most synthetic adhesives in submerged and humid environments. Development of instant, strong, reversible, and long-lasting adhesives that can adhere to wet surfaces and function in underwater environments presents a formidable challenge, yet it is of paramount importance in biomedical and engineering applications. Herein, viscoelastic and moldable ionogels are developed based on synergistic engineering of aromatic substituents, fluorinated counterions, ionic building blocks, and 3D cross-linked networks. The molecular design and structural engineering result in a facile synthesis, two bonding methods (glue- and tape-type), and the combined mechanisms of enhanced adhesion and cohesion. The high underwater adhesion strength of over 8.9 MPa is among the best-performing tape-type underwater adhesives reported to date. A combination of excellent durability, reliability, deformation resistance, salt tolerance, water proof, antiswelling, and self-healing properties demonstrates the “self-contained” underwater adhesion. Furthermore, the extended π-conjugation of the aromatic pendant groups confers a new functionality to the ionogels – visible fluorescence, enabling intriguing applications such as underwater labeling, information encryption, and signal transmission. This study shines lights on the fabrication of ionogel-based adhesives and provides their future perspectives in underwater sealing, self-repair, crack diagnosis, and informational labeling.     

Wet‐Responsive,Reconfigurable, and Biocompatible Hydrogel Adhesive Films for Transfer Printing of Nanomembranes

This study presents a wet‐responsive and biocompatible smart hydrogel adhesive that exhibits switchable and controllable adhesions on demand for the simple and efficient transfer printing of nanomembranes. The prepared hydrogel adhesives show adhesion strength as high as ≈191 kPa with the aid of nano‐ or microstructure arrays on the surface in the dry state. When in contact with water, the nano/microscopic and macroscopic shape reconfigurations of the hydrogel adhesive occur, which turns off the adhesion (≈0.30 kPa) with an extremely high adhesion switching ratio (>640). The superior adhesion behaviors of the hydrogels are maintained over repeating cycles of hydration and dehydration, indicating their ability to be used repeatedly. The adhesives are made of a biocompatible hydrogel and their adhesion on/off can be controlled with water, making the adhesives compatible with various materials and surfaces, including biological substrates. Based on these smart adhesion capabilities, diverse metallic and semiconducting nanomembranes can be transferred from donor substrates to either rigid or flexible surfaces including biological tissues in a reproducible and robust fashion. Transfer printing of a nanoscale crack sensor onto a bovine eye further demonstrates the potential of the reconfigurable hydrogel adhesive for use as a stimuli‐responsive, smart, and versatile functional adhesive for nanotransfer printing.     

Novel Organic‐Dehydration Membranes Prepared from Zirconium Metal‐Organic Frameworks

Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well‐intergrown UiO‐66 metal‐organic framework membranes fabricated on prestructured yttria‐stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m^?2 h^?1 and excellent separation factor (>45 000) for separating water from i ‐butanol (next‐generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.     

Ionic Conductive Organohydrogels with Dynamic Pattern Behavior and Multi-Environmental Stability

Multi-environmental tolerant hydrogels have received significant attention and are promising for application as smart materials in multiple environments (e.g., water, oil, freezing, and dry). However, the macroscopic change and anti-swelling mechanisms of organohydrogels in different solvents and their corresponding applications have not been adequately harnessed. Herein, an ionic organohydrogel with excellent mechanical properties and unique behaviors (information identification and encryption) and mechanical sensing in multiple environments is prepared. The prepared organohydrogel shows an obvious transparent change in different solvents owing to the microphase separation in poor solvents and swelling in suitable solvents, and can be treated as a dynamic information memory device for recording and encrypting information. Furthermore, owing to the interaction between water and dimethylsulfoxide (DMSO), the organohydrogel demonstrates a prominent freezing resistance (−90 to 20 °C) and moisturizing retention properties (76% after 15 days). In addition, the ionic conductive hydrogel exhibits outstanding human motion detection and physiological signal response and displays a stable mechanical sensing performance in freezing, dry conditions, and oil or water environments. It is envisioned that the design strategies and mechanistic investigation of organohydrogels may be promising for application as bio-sensors and information-recognition platforms in harsh environments.     

Environmental protection of inkjet-printed Ag conductors

Electrically conductive silver nanoparticle ink patterns were fabricated using the inkjet printing method. Two different polymer films were used as the substrate materials. The patterns were exposed to humidity and salt fog and the electrical performance (sheet resistance and RF performance) as well as mechanical endurance (adhesion) were measured before and after the environmental tests. The electrical properties of the printed structures remained good in all the measurable samples. The adhesion between the ink and a substrate material appeared to be a greater challenge in harsh environments. Protection capabilities of one dip coated and one hot laminated barrier materials were evaluated during the environmental tests. The results showed that there is a need for environmental protection in printed electronics. Especially the laminated barrier films can offer a potential solution for shielding printed electronics in harsh environments as they can provide good mechanical protection, and can easily be integrated in roll-to-roll process.     

TAPE: A Medical Adhesive Inspired by a Ubiquitous Compound in Plants

Adhesives play an important role in industrial fields such as electronics, architectures, energy plantation, and others. However, adhesives used for medical purpose are rather under‐developed compared with those used in industry and consumer products. One key property required for medical adhesives is to maintain their adhesiveness in the presence of body fluid. Here, an entirely new class of medical adhesives called TAPE is reported; this is produced by intermolecular hydrogen bonding between a well‐known polyphenol compound, tannic acid, and poly(ethylene glycol). The preparation method of TAPE is extremely easy, forming a few liters at once by just the simple mixing of the two compounds without any further chemical synthetic procedures. TAPE shows a 250% increase in adhesion strength compared with fibrin glue, and the adhesion is well maintained in aqueous environments. It is demonstrated that TAPE is an effective hemostatic material and a biodegradable patch for detecting gastroesophageal reflux disease in vivo. Widespread use of TAPE is anticipated in various medical and pharmaceutical applications such as muco‐adhesives, drug depots, and others, because of its scalability, adhesion, and facile preparation.     

Pressure Sensitive Adhesion of an Elastomeric Protein Complex Extracted From Squid Ring Teeth

The pressure sensitive adhesion characteristic of a protein complex extracted from squid ring teeth (SRT), which exhibits an unusual and reversible transition from a solid to a melt, is studied. The native SRT is an elastomeric protein complex that has standard amino acids, and it does not function as adhesives in nature. The SRT can be thermally shaped into any 3D geometry (e.g., thin films, ribbons, colloids), and it has a glass transition temperature of 32 °C in water. Underwater adhesion strength of the protein film is approximately 1.5–2.5 MPa. The thermoplastic protein film could potentially be used in an array of fields, including dental resins, bandages for wound healing, and surgical sutures in the body.     

Tough Adhesion of Nucleobase‐Tackifed Gels in Diverse Solvents

Adhesive gels have attracted increasing attention in biological medicine and industrial fields. However, it remains a huge challenge to achieve robust adhesion in various nonpolar and polar solvents. Herein, a tough nucleobase‐tackified adhesive gel is successfully fabricated and exhibits strong adhesion to various materials in diverse solvents, including hexane, chloroform, dimethyl sulfoxide, ethanol, and water (seawater, high salt, acid, and alkali aqueous solutions). The adhesive gels possess high toughness and excellent resist fatigue as well as impressive nonswelling behavior in water or oil. This tough gel‐based adhesive holds great promise for various applications, such as battery adhesives, soft robots, wound dressing, wearable devices, and 3D printing in various environments. It is anticipated that this strategy will provide a novel route for fabricating the next generation of adhesive soft materials.     

Reliability and lifetime evaluation of different wire bonding technologies for high power IGBT modules

IGBT modules for power transmission, industrial and traction applications are operated under severe working conditions and in harsh environments. Therefore, a consequent design, focused on quality, performance and reliability is essential in order to satisfy the high customer requirements. One of the main failure mechanisms encountered in high power IGBT modules subjected to thermal cycles is wire bond lift-off, which is due to the large thermal expansion coefficient mismatch between the aluminum wires and the silicon chips. The paper describes various bonding technologies using different wire materials directly bonded onto chip metallisation as well as the ABB solution where the wire is bonded on a thin molybdenum strain buffer soldered onto the chip. We assess in the present paper the potential of these technologies to enhance module reliability and lifetime through a power cycling test. Failure analysis results are presented and the failure mechanisms related to each technology are explained in detail.     

压阻式金刚石微压力传感器

工业上的某些场合要求压力传感器能够在高温、高辐射以及恶劣的环境下正常工作。金刚石的某些特殊性质（如化学上的惰性、高的杨低模量）以及极大的压阻效应使其成为制作压阻型压力传感器的极佳材料。对利用多晶金刚石薄膜制造的新型高温、高灵敏度压阻型金刚石微压力传感器的原理、结构及其制造技术作了详细介绍。这种传感器适用于勘探、航空航天以及汽车工业。此外,还阐述了金刚石微压力传感器的研究现状,并进一步目前存在的问题。     

Injectable Self-Healing Natural Biopolymer-Based Hydrogel Adhesive with Thermoresponsive Reversible Adhesion for Minimally Invasive Surgery

Biocompatible hydrogel adhesives with multifunctional properties, including injectability, fast self-healing, and suitable on-demand detachment, are highly desired for minimally invasive procedures, but such materials are still lacking. Herein, an injectable self-healing biocompatible hydrogel adhesive with thermoresponsive reversible adhesion based on two extracellular matrix-derived biopolymers, gelatin and chondroitin sulfate, is developed to be used as a surgical adhesive for sealing or reconnecting ruptured tissues. The resulting hydrogels present good self-healing and can be conveniently injected through needles. The strong tissue adhesion at physiological temperatures originates from the Schiff base and hydrogen bonding interactions between the hydrogel and tissue that can be weakened at low temperatures, thereby easily detaching the hydrogel from the tissue in the gelation state. In vivo and ex vivo rat model show that the adhesives can effectively seal bleeding wounds and fluid leakages in the absence of sutures or staples. Specifically, a proof of concept experiment in a damaged rat liver model demonstrates the ability of the adhesives to act as a suitable laparoscopic sealant for laparoscopic surgery. Overall, the adhesive has several advantages, including low cost and ease of production and application that make it an exceptional multifunctional tissue adhesive/sealant, effective in minimally invasive surgical applications.     

Adaptive Ionogel Paint from Room-Temperature Autonomous Polymerization of α-Thioctic Acid for Stretchable and Healable Electronics

Development of a universal stretchable ionic conductor coating on insulating substrates, irrespective of surface chemistry and substrate shapes, is of immense interest for compliant and integrative large-area electronics but has proved to be extremely challenging. Existing methods relying either on the concurrent deposition of polymerizing precursors or on divided formulation and painting processes both suffer from several limitations in terms of adhesion, dehydration, processability, and surface pre-treatment. Here an ionogel paint that is readily prepared from the concentration-induced autonomous ring-opening polymerization of a natural small molecule—α-thioctic acid (TA) at ambient conditions is reported. The presence of ionic liquid prevents polyTA from further depolymerization via forming COOH···OS hydrogen bonds, resulting in ultra-stretchable ionogels with widely tunable mechanical and conductive properties, self-healability, as well as tissue-like strain adaptability. Moreover, owing to its universal adhesion and adjustable rheology, the ionogel paint can be directly coated on diverse substrates with arbitrary shapes (including porous materials, 3D printed frames, and elastic threads) to render them ionic conductivity. Applications of the ionogel-coated substrates as skin-like highly sensitive and durable large-strain sensors are further demonstrated, suggesting the ionogel paint's great potential in the emerging soft and stretchable electronics.     

Localized bonding processes for assembly and packaging of polymeric MEMS

Localized bonding schemes for the assembly and packaging of polymer-based microelectromechanical systems (MEMS) devices have been successfully demonstrated. These include three bonding systems of plastics-to-silicon, plastics-to-glass, and plastics-to-plastics combinations based on two bonding processes of localized resistive heating: 1) built-in resistive heaters and 2) reusable resistive heaters. In the prototype demonstrations, aluminum thin films are deposited and patterned as resistive heaters and plastic materials are locally melted and solidified for bonding. A typical contact pressure of 0.4 MPa is applied to assure intimate contact of the two bonding substrates and the localized bonding process is completed within less than 0.25 s of heating. It is estimated that the local temperature at the bonding interface can reach above 150/spl deg/C while the substrate temperature away from the heaters can be controlled to be under 40/spl deg/C during the bonding process. The approach of localized heating for bonding of plastic materials while maintaining low temperature globally enables direct sealing of polymer-based MEMS without dispensing additional adhesives or damaging preexisting, temperature-sensitive substances. Furthermore, water encapsulation by plastics-to-plastics bonding is successfully performed to demonstrate the capability of low temperature processing. As such, this technique can be applied broadly in plastic assembly, packaging, and liquid encapsulation for microsystems, including microfluidic devices.     

Zwitterionic Nanohydrogel Grafted PVDF Membranes with Comprehensive Antifouling Property and Superior Cycle Stability for Oil‐in‐Water Emulsion Separation

Fouling caused by oil and other pollutants is one of the most serious challenges for membranes used for oil/water separation. Aiming at improving the comprehensive antifouling property of membranes and thus achieving long‐term cyclic stability, it is reported in this work the design of a kind of zwitterionic nanosized hydrogels grafted poly(vinylidene fluoride) (PVDF) microfiltration membrane (ZNG‐g‐PVDF) with superior fouling‐tolerant property for oil‐in‐water emulsion separation. Sulfobetaine zwitterionic nanohydrogels with the diameter of ≈ 50 nm are synthesized by an inverse microemulsion polymerization process. They are then grafted onto the surface of PVDF microfiltration membrane, endowing the membrane a superhydrophilic and nearly zero oil adhesion property. This ZNG‐g‐PVDF membrane exhibits great tolerance and resistance to salts pH, especially an excellent antifouling property to oil‐in‐water emulsions containing various pollutants such as surfactants, proteins, and natural organic materials (e.g., humic acid). The comprehensive antifouling property of the membrane gives rise to the cyclic stability of the membrane greatly improved. A nearly 100% recovery ratio of permeating flux is achieved during several cycles of oil‐in‐water emulsion filtration. The ZNG‐g‐PVDF membrane shows great potential in treating practical oily wastewater containing complicated components in the effluent.     

Cucurbit[n]uril Supramolecular Hydrogel Networks as Tough and Healable Adhesives

Supramolecular noncovalent interactions are widely found in natural adhesion phenomena to control macroscopic adhesion and accomplish a variety of complex functions. Such supramolecular adhesives could impart the interfaces with intriguing properties, e.g., energy dissipation and self‐healing, on account of their dynamic nature. Here, we demonstrate that cucurbit[8]uril (CB[8])‐based supramolecular hydrogel networks can function as dynamic adhesives for diverse nonporous (e.g., glass, stainless steel, aluminum, copper, and titanium) and porous substrates (wood and bone). Without any surface prefunctionalization or introduction of curing agents, these CB[8] hydrogel networks can be readily applied by curing around the softening temperature, forming a tough and healable adhesive interlayer. The ability to fabricate a robust sandwich model consisting of substrate–CB[8] hydrogel network–substrate enables a number of applications including stretchable and wearable electronics, hybrid systems for biomedical devices or tissue/bone regeneration.     

Self‐Healing Graphene Oxide Based Functional Architectures Triggered by Moisture

Self‐healing materials are capable of spontaneously repairing themselves at damaging sites without additional adhesives. They are important functional materials with wide applications in actuators, shape memorizing materials, smart coatings, and medical treatments, etc. Herein, this study reports the self‐healing of graphene oxide (GO) functional architectures and devices with the assistance of moisture. These GO architectures can completely restore their mechanical‐performance (e.g., compressibility, flexibility, and strength) after healing their broken sites using a little amount of water moisture. On the basis of this effective moisture‐triggered self‐healing process, this study develops GO smart actuators (e.g., bendable actuator, biomimetic walker, rotatable fiber motor) and sensors with self‐healing ability. This work provides a new pathway for the development of self‐healing materials for their applications in multidimensional spaces and functional devices.     

Superior Low-Temperature Reversible Adhesion Based on Bio-Inspired Microfibrillar Adhesives Fabricated by Phenyl Containing Polydimethylsiloxane Elastomers

Gecko-inspired microfibrillar adhesives have achieved great progress in microstructure design and adhesion improvement over the past two decades. Space applications nowadays show great interest in this material for the characteristics of reversible adhesion and universal van der Waals interactions. However, the impact of harsh environment of space on the performance of microfibrillar adhesives, especially the extreme low temperature, is rarely addressed. Herein, microfibrillar adhesives fabricated by phenyl containing polydimethylsiloxane (p-PDMS) elastomers with superior low-temperature reversible adhesion is proposed. p-PDMS elastomers are synthesized through one-pot anionic ring-opening copolymerization, and the resulting elastomers become non-crystallizable with excellent low-temperature elasticity. Low-temperature adhesion tests demonstrate that the adhesion strength of microfibrillar adhesives fabricated by p-PDMS elastomers can be well maintained to as low as −120 °C. In contrast, the adhesion strength of pure PDMS microfibrillar adhesive reduces more than 50% below its crystallization temperature. The low-temperature cyclic adhesion tests further demonstrate that p-PDMS microfibrillar adhesives exhibit superior reversible adhesion compared to that of PDMS microfibrillar adhesives, owing to the sustainable conformal contact and even distribution of loads over repeated cycles. This study provides a new fabrication strategy for microfibrillar adhesives, and is beneficial for the practical application of microfibrillar adhesives.     

Effect of Gold Stud Bump Topology on Reliability of Flip Chip on Flex Interconnects

The flip chip technique using conductive adhesives have emerged as a good alternative to solder flip chip methods. Different approaches of the interconnection mechanism using conductive adhesives have been developed. In this paper, test chips with gold stud bumps are flip-chipped with conductive adhesives onto a flexible substrate. An experimental study to characterize the bonding process parameters is reported. Initial results from the environmental studies show that thermal shock test causes negligible failure. On the other hand, high humidity test causes considerable failure in flip chip on flex assemblies. Improvements in the reliability of the assembly are achieved by modifying the shape of the gold stud bumps.     

各向异性导电胶互连技术的研究进展

随着微电子封装技术的发展,各向异性导电胶作为一种绿色的连接材料,广泛应用于电子产品中。文中主要介绍各向异性导电胶互连器件的粘接原理和影响其可靠性的各种因素,如粘接工艺参数、外界环境的干扰、各向异性导电胶的物理特性等。     

The contact resistance and reliability of anisotropicallyconductive film (ACF)

The effect of bonding pressure on the electrical and mechanical properties of anisotropic conductive film (ACF) joint using nickel particles and metal-coated polymer ball-filled ACFs was investigated. The contact resistance decreases as the bonding pressure increases. Contact resistance of ACF is determined by the contact area change between particles and contact substrates. Electrical conduction through the pressure engaged contact area between conductive particles and conductor substrates is the main conduction mechanism in ACF interconnection. In addition, environmental effects on contact resistance and adhesion strength such as thermal aging, high temperature/humidity aging and temperature cycling were also investigated. Interestingly, the contact resistances of the excessively bonded samples deteriorated more than those of optimally bonded ones. Increasing contact resistance and decreasing adhesion strength after harsh environmental tests were mainly due to the loss of contact by thermal stress effect and moisture absorption, and also partially due to the formation of metal oxide on the conductive particles