Self-adhesive Properties Research Articles

Enhanced casein organohydrogel coating with the liquid metal catalyst for electric leather in human-machine interaction

Leather’s durability and multi-level structure make it an excellent substrate for electronics. Integrating leather with modern electronic technology to create electronic leather is becoming increasingly popular. However, significant challenges remain, such as adhering conductive media to leather, their penetration and dispersion, and the complexity of preparation. This study presents a new strategy for fabricating electronic leather by combining leather with a casein-based organic hydrogel using coating chemistry techniques. This hydrogel is simple to prepare and exhibits excellent biocompatibility and self-adhesive properties, offering a promising approach to overcome these challenges. Here, we designed casein-stabilized core-shell liquid metal-based catalysts and utilized acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPs), CNTs, and glycerol (Gly) to achieve in situ organohydrogel formation on leather under mild conditions (60 s, 25 °C). The resulting organohydrogel-coated material exhibits outstanding stretchability (tensile stress: 70.3 kPa, tensile strain: 1491.8 %), rapid response (423 ms), and high sensitivity (GF: 7.67) as a strain sensor. This substrate can be employed in designing flexible wearable electronic gloves, facilitating seamless information interaction between humans and devices. This innovation demonstrates significant potential in enhancing the functionality of leather as a wearable electronic device. Combining leather’s natural properties with cutting-edge organohydrogel technology is promising to revolutionize the wearable electronics industry, potentially creating highly versatile and multifunctional electronic skins.

Self-powered wearable remote control system based on self-adhesive, self-healing, and tough hydrogels

The advent of the fifth-generation mobile communication network era induces a great potential for the design and development of self-powered wearable electronic devices. Hydrogels, as a typical material for flexible electrodes, have been widely employed in self-powered wearable electronic devices. However, the hydrogel-based triboelectric nanogenerator (H-TENG) is usually compromised by the challenges in data collection, operational stability, and manufacturability due to the unstable combination between the friction layer and the electrode layer, the occurrence of hydrogel damage during prolonged operation, and also the difficulty of machining sticky hydrogel electrodes. In the present study, a composite hydrogel composed of acrylamide, crotonyl alcohol, and 4-carboxyphenylboronic acid was synthesized via ultraviolet crosslinking, which was specially developed for H-TENG and wearable wireless remote control interface, featuring with excellent stretchability and mechanical strength as well as self-healing and self-adhesive properties. The open-circuit voltage of the H-TENG prepared with the hydrogel reached up to 165 V, and the output voltage remained almost unchanged following 10,000 cycles of compression test. Additionally, a wearable wireless remote control system was designed that could accurately control the multiple appliances and adjust different working modes using the H-TENG. Consequently, the development of the H-TENG and wearable wireless remote control system has the potential to provide a new methodology for the application of next-generation wearable devices in various areas, such as smart homes, as a representative example.

Mechanically Robust and Electrically Conductive Hybrid Hydrogel Electrolyte Enabled by Simultaneous Dual In Situ Sol-Gel Technique and Free Radical Copolymerization.

Mechanically robust and ionically conductive hydrogels poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate-lithium)/TiO2/SiO2 (P(AM-co-AMPSLi)/TiO2/SiO2) with inorganic hybrid crosslinking are fabricated through dual in situ sol-gel reaction of vinyltriethoxysilane (VTES) and tetrabutyl titanate (TBOT), and in situ radical copolymerization of acrylamide (AM), 2-acrylamide-2-methylpropanesulfonate-lithium (AMPSLi), and vinyl-SiO2. Due to the introduction of the sulfonic acid groups and Li+ by the reaction of AMPS with Li2CO3, the conductivity of the ionic hydrogel can reach 0.19Sm-1. Vinyl-SiO2 and nano-TiO2 are used in this hybrid hydrogel as both multifunctional hybrid crosslinkers and fillers. The hybrid hydrogels demonstrate high tensile strength (0.11-0.33MPa) and elongation at break (98-1867%), ultrahigh compression strength (0.28-1.36MPa), certain fatigue resistance, self-healing, and self-adhesive properties, which are due to covalent bonds between TiO2 and SiO2, as well as P(AM-co-AMPSLi) chains and SiO2, and noncovalent bonds between TiO2 and P(AM-co-AMPSLi) chains, as well as the organic frameworks. Furthermore, the specific capacitance, energy density, and power density of the supercapacitors based on ionic hybrid hydrogel electrolytes are 2.88Fg-1, 0.09Whkg-1, and 3.07kWkg-1 at a current density of 0.05Ag-1, respectively. Consequently, the ionic hybrid hydrogels show great promise as flexible energy storage devices.

High stretchable and self-adhesive multifunctional hydrogel for wearable and flexible sensors

Ionic conductive hydrogel has recently garnered significant research attention due to its potential applications in the field of wearable and flexible electronics. Nonetheless, the integration of multifunctional and synergistic advantages, including reliable electronic properties, high swelling capacity, exceptional mechanical characteristics, and self-adhesive properties, presents an ongoing challenge. In this study, we have developed an ionic conductive hydrogel through the co-polymerization of 4-Acryloylmorpholine (ACMO) and sodium acrylate using UV curing technology. The hydrogel exhibits excellent mechanical properties, high conductivity, superior swelling capacity, and remarkable self-adhesive attributes. The hydrogel serves as a highly sensitive strain sensor, enabling precise monitoring of both substantial and subtle human motions. Furthermore, the hydrogel demonstrates the capability to adhere to human skin, functioning as a human-machine interface for the detection of physiological signals, including electromyogram (EMG) signals, with low interfacial impedance. This work is anticipated to yield a new class of stretchable and conductive materials with diverse potential applications, ranging from flexible sensors and wearable bio-electronics to contributions in the field of artificial intelligence.

Low-Temperature Rapid Polymerization of Intrinsic Conducting PAD/OC Hydrogels with a Self-Adhesive and Sensitive Sensor for Outdoor Damage Repair and Detection.

Intrinsic conducting hydrogels fabricated in situ at low temperatures with self-adhesive properties and excellent flexibility hold significant promise for energy applications and outdoor damage repair. However, challenges such as low polymerization rate and self adhesion, insufficient ionic conductivity, inflexibility, and poor stability under extreme cold conditions have hindered their utilization as high-performance sensors. In this study, we designed an intrinsic conducting hydrogel (PADOC) composed of acrylic acid, acryloyloxyethyltrimethylammonium chloride, N,N'-methylenebis(2-propenamide), self-fabricated oxidized curdlan (OC), and a water/glycerol binary solvent. The novel hydrogel exhibited rapid gelation (30 s) at 0 °C facilitated by the promotion of OC, without the need for external energy input. Our findings from FT-IR, NMR, XPS, XRD, EPR spectra, MS, and DSC analyses revealed that OC underwent selective oxidation via the evolved Fenton reaction at 30 °C, serving as bioaccelerators for PAD polymerization. Due to OC's reductive structure and increased solubility, the reaction activation energy of the PAD polymerization reaction significantly reduced from 103.2 to 54.4 kJ/mol. PADOC ionic hydrogels demonstrated an electrical conductivity of 1.00 S/m, 0.7% low hysteresis, 39.6 kPa self-adhesive strength, and 923% strain-at-break and kept even at -20 °C owing to dense hydrogen and ionic bonds between PAD and OC chains. Furthermore, PADOC ionic hydrogels exhibited antifatigue properties for 10 cycles (0-100%) due to electrostatic interactions and hydrogen bonding. Remarkably, using a self-designed device, the rapid polymerization of PADOC effectively repaired copper pipeline leakage under 86 kPa pressure and detected 1% strain variation as a strain sensor. This study opens a new avenue for the rapid gelation of self-adhesive and flexible intrinsic conducting hydrogels with robust sensor performance.

Versatile and recyclable double-network PVA/cellulose hydrogels for strain sensors and triboelectric nanogenerators under harsh conditions

Versatile and recyclable conductive hydrogels with long-term environmental adaptability and mechanical stability have attracted tremendous attention in wearable smart electronics. Here, double-network (DN) polyvinyl alcohol (PVA)/cellulose hydrogels were constructed after introducing a conductive rigid cellulose/Zn2+/Ca2+ network into a soft PVA/borax network. The resultant hydrogels possessed good mechanical and self-adhesive properties, along with transparency, recyclability, and remarkable resistance to freezing. They showed 30-day non-drying properties due to the presence of hygroscopic salts through a dynamic moisture adsorption and desorption process. Dehydrated hydrogels can return to their original states via self-regeneration under high relative humidity. Hydrogel-based strain sensors retained good sensitivity and a wide sensing range during the wide working temperature ranging from −40 °C to 50 °C and after recycling. Additionally, conductive hydrogels were integrated into triboelectric nanogenerators (TENGs) functioning as energy harvesters for powering electronics. TENGs retained stable electrical outputs even under harsh conditions and after recycling. Hydrogels were also assembled into flexible self-powered biomechanical sensors and tactile sensors. Thermally reversible interactions in composite hydrogels enabled their good recyclability, thereby reducing economic costs and environmental impacts caused by e-wastes. This work demonstrates the great potential of versatile and recyclable hydrogels with good environmental and mechanical stability in wearable smart electronics under harsh conditions.

3D Printing Self-Healing and Self-Adhesive Elastomers for Wearable Electronics in Amphibious Environments.

To meet the demands of challenging usage scenarios, there is an increasing need for flexible electronic skins that can operate properly not only in terrestrial environments but also extend to complex aquatic conditions. In this study, we develop an elastomer by incorporating dynamic urea bonds and hydrogen bonds into the polydimethylsiloxane backbone, which exhibits excellent autonomous self-healing and reversible adhesive performance in both dry and wet environments. A multifunctional flexible sensor with excellent sensing stability, amphibious self-healing capacity, and amphibious self-adhesive performance is fabricated through solvent-free 3D printing. The sensor has a high sensing sensitivity (GF = 45.1) and a low strain response threshold (0.25%) and can be used to detect small human movements and physiological activities, such as muscle movement, joint movement, respiration, and heartbeat. The wireless wearable sensing system assembled by coupling this device with a bluetooth transmission system is suitable for monitoring strenuous human movement in amphibious environments, such as playing basketball, cycling, running (terrestrial environments), and swimming (aquatic environments). The design strategy provides insights into enhancing the self-healing and self-adhesive properties of soft materials and promises a prospective avenue for fabricating flexible electronic skin that can work properly in amphibious environments.

Transparent, stretchable, self-healing, and self-adhesive ionogels for flexible multifunctional sensors and encryption systems

Conductive gels are promising soft ionic conductors for stretchable and flexible electronics. However, the integration of multiple functions into one gel remains a great challenge, as the tailoring of these properties is mutually exclusive. In this paper, a simple photopolymerization method is designed to prepare polyacrylic acid/ionic liquid /hydroxypropyl cellulose (PIH) ionogels, which have high transparency (89 %), and superior electrical conductivity (0.379 mS/cm). Owing to the dynamic and reversible nature between the polymer chains, the ionogel possesses good self-healing capability (79.6 %) and self-adhesive properties (242.32–742.76 kPa, typical substrate at room temperature). At the same time, the excellent chemical stability of ionic liquids ensures that PIH ionogels still have good temperature sensitivity (-30 ∼ 110 °C) in extremely harsh environments. Wearable strain sensors based on PIH ionogels can sensitively detect and distinguish body movements, such as limb bending, pronunciation, and pulse. When PIH ionogels are used as a temperature sensor, a cryptographic device with a temperature alarm and an externally stimulated UV switch is designed by using the excellent transparency and temperature response of PIH ionogels. It is believed that the designed ionogel will show great prospects in wearable devices and flexible encryption.

Self-healing and self-adhesive hydrogen gas sensing tape for robust applications

Chemochromic H2 gas sensing tape can be an ideal candidate for many robust applications because of its ease of use. The H2 gas sensing with self-healing and self-adhesive functionalities would add another degree of innovation. The current development is limited to noble metal-based and flexible sensors, while the self-healing and self-adhesive tape has not been explored widely. The objective of this paper is to develop a stretchable, self-healing and self-adhesive H2 gas sensing tape using Pd-WO3 chemochromic nanocomposites and PBS: Ecoflex hybrid polymer. The proposed development has been investigated using material and mechanical characterizations that ensure a high stretchability of 500 %, fast self-healing (in 30 s at room temperature), and excellent self-adhesive properties towards a variety of objects, including human skin, glass/plastic objects, stainless steel, gas cylinders, pipelines, and fittings. The optimized tape sensor is then tested in a real-application environment, where different concentrations of H2 were exposed to justify the chemochromic sensing performance. It is found that the sensor exhibits a rapid change in color from beige to blue with a maximum ΔE value of 40.28 in 10 s of H2 (100 %) exposure. The results are found very potential to be used in practical applications.

Ultra-stretchable, fast self-healing, adhesive, and strain-sensitive wearable sensors based on ionic conductive hydrogels

A wearable hydrogel-based sensor has been developed by constructing various dynamic interactions to balance mechanical strength and conductivity as well as improve the self-healing and self-adhesive properties.

Ultrastretchable and adhesive MXene-based hydrogel for high-performance strain sensing and self-powered application

Conductive hydrogels have been extensively explored for human movement and health monitoring. However, the poor adhesion of hydrogels to the skin hinders their performance in real-time monitoring with minimal loss of signal transmission. In this work, hydrogels composed of acrylic acid (AA), acrylic acid–N-hydrosuccinimide ester (AA–NHS), sulfobetaine methacrylate (SBMA), and cellulose nanofibers (CNFs) in the presence of initiators were rapidly gelated (within a few minutes) after adding Ti3C2TX MXene as a versatile crosslinking agent. AA and SBMA copolymerized to form the main network structure of the hydrogel and the introduced CNF improved the tensile strain of the hydrogels from 1737 % to 2240 %. By virtue of the combined zwitterionic-adhesion mechanism and NHS-activated ester bonds, the hydrogels conformally adhered to porcine skin with an adhesive strength of 11.6 kPa. When assembled as strain sensors, the hydrogel sensors exhibited high sensitivity (gauge factor = 4.98) and a fast response (95 ms). Next, the hydrogel was assembled as the electrode in a triboelectric nanogenerator (TENG) for mechanical-energy harvesting and self-powered sensing. The TENG exhibited good electrical output properties and could charge commercial capacitors with the mechanical energy harvested from walking. This work promises the design of wearable hydrogel devices with mechanical extensibility and self-adhesive properties.

Next-generation self-adhesive dressings: Highly stretchable, antibacterial, and UV-shielding properties enabled by tannic acid-coated cellulose nanocrystals

Hydrogels with excellent high-water uptake and flexibility have great potential for wound dressing. However, pure hydrogels without fiber skeleton faced poor water retention, weak fatigue resistance, and mechanical strength to hinder the development of the dressing as next-generation functional dressings. We prepared an ultrafast gelation (6 s) Fe3+/TA-CNC hydrogel (CTFG hydrogel) based on a self-catalytic system and bilayer self-assembled composites. The CTFG hydrogel has excellent flexibility (800% of strain), fatigue resistance (support 60% compression cycles), antibacterial, and self-adhesive properties (no residue or allergy after peeling off the skin). CTFG@S bilayer composites were formed after electrospun silk fibroin (SF) membranes were prepared and adhesive with CTFG hydrogels. The CTFG@S bilayer composites had significant UV-shielding (99.95%), tensile strain (210.9 KPa), and sensitive humidity-sensing properties. Moreover, the integrated structure improved the mechanical properties of electrospun SF membranes. This study would provide a promising strategy for rapidly preparing multifunctional hydrogels for wound dressing.

A temperature and pressure dual-responsive, stretchable, healable, adhesive, and biocompatible carboxymethyl cellulose-based conductive hydrogels for flexible wearable strain sensor

The study aimed to develop a novel temperature and pressure dual-responsive conductive hydrogel with self-healing, self-adhesive, biocompatible, and stretchable properties, for the development of multifunctional anti-counterfeiting and wearable flexible electronic materials. A conductive hydrogel based on carboxymethyl cellulose (CMC) was synthesized by simple “one pot” free radical polymerization of CMC, acrylamide (AAm) and acrylic acid (AAc). The hydrogel displayed temperature responsiveness and possessed an upper critical solution temperature (UCST) value. In addition, hydrogels also had surprising pressure responsiveness. The synthesized hydrogels were characterized by FTIR, TGA, DSC, and XRD analysis. Importantly, the obtained hydrogels exhibited exceptional mechanical properties (stress: 730 kPa, strain: 880%), fatigue resistance, stretchability, self-healing capability, self-adhesive properties, and conductivity. In addition, valuable insights were obtained into the synthesis and application of flexible anti-counterfeiting and camouflage materials by the temperature and pressure dual-responsive hydrogels. Moreover, the prepared hydrogel, with an electrically sensitive perception of external strain (GF = 2.61, response time: 80 ms), can be utilized for monitoring human movement, emotional changes, physiological signals, language, and more, rendering it suitable for novel flexible anti-counterfeiting materials and versatile wearable iontronics. Overall, this study provided novel insights into the simple and efficient synthesis and sustainable manufacturing of environmentally friendly multifunctional anti-counterfeiting materials and flexible electronic skin sensors.

The Effect of Pt-type Catalysts on Self-adhesive Properties of Silicone Pressure-sensitive Adhesives

AbstractUseful silicone pressure-sensitive adhesives (PSAs) have been prepared from a high solid silicone resin. Platinum catalysts and crosslinking compounds were used to obtain new self-adhesive tapes. The influence of catalysts and crosslinking compounds on the basic properties of self-adhesive tapes was tested, taking into account the compatibility of silicone composition. The obtained systems showed good self-adhesive properties, and high thermal resistance over 225 °C. The low viscosity of the compositions obtained relatively increases the application potential of self-adhesive tapes based on it. Moreover, the prepared compositions show the potential for further modifications, especially physical ones e.g. silicon powder. The obtained new tapes showed good self-adhesive properties and kept high thermal resistance over 225 °C. It is well known that silicone pressure-sensitive adhesives are a group of silicone adhesives for special applications. Due to their unique resistance to environmental conditions, temperature and chemical resistance, they are difficult to modify.

Nanographite/nanosilica-filled dopamine-containing polyacrylamide hydrogels of temperature-sensitive photothermal responses

Conductive hydrogels are of significant interest because of their important applications in flexible electronics, energy storage, and human-computer interaction. However, the deficiencies of weak electrical conductivity and mechanical properties seriously hinder the applications of conductive hydrogels in these frontier areas. In this research, conductive hydrogels with high electrical conductivity, excellent self-recovery properties and outstanding photothermal effects are prepared by synergistic interaction of dopamine, silica nanoparticles, graphite nano-powder (Grn) and polyacrylamide chains. The effects of Grn and temperature on the conductivity of the hydrogels are investigated in detail. The hydrogels feature highest conductivity (7.2 mS/cm) and even 9.1 mS/cm at 60 °C due to the excellent thermal and electrical conductivity of Grn, which also endows the hydrogels with excellent photothermal effect and stable energy storage properties. Notably, the catechol group of dopamine (DA) leads to excellent self-adhesive properties of the conductive hydrogels. The use of silicon dioxide nanoparticles (SNs) allows the conductive hydrogels to obtain favorable toughness as well as self-recovery properties. This provides a broad prospect for the applications of conductive hydrogels in practice.

An Ultrahighly Stretchable and Recyclable Starch-Based Gel with MultipleFunctions.

With the development of various gel-based flexible sensors, novel gels with multiple integrated and efficient properties, particularly recyclability, have been developed. Herein, a starch-based ADM (amylopectin (AP)-poly(3-[dimethyl-[2-(2-methylprop-2- enoyloxy)ethyl]azaniumyl]propane-1-sulfonate) (PDMAPS)-MXene) gel is prepared by a facile "cooking" strategy accompanying the gelatinization of AP and polymerization reaction of zwitterionic monomers. Reversible crosslinking in the gel occurs through hydrogen bonding and electrostatic interactions. The ADM gel exhibits high stretchability (≈2700%, after one month), swift self-healing performance, self-adhesive properties, favorable freezing resistance, and satisfactory moisturizing properties (≥30days). Interestingly, the ADM gel can be recycled and reused by a "kneading" method and "dissolution-dialysis" process, respectively. Furthermore, the ADM gel can be assembled as a strain sensor with a broad working strain range (≈800%) and quick response time (response time 211ms and recovery time 253ms, under 10% strain) to detect various macro- and micro-human-motions, even under harsh conditions such as pronunciation and handwriting. The ADM gel can also be used as a humidity sensor to investigate humidity and human respiratory status, suggesting its practical application in personal health management. This study provides a novel strategy for the preparation of high-performance recycled gels and flexible sensors.

Influence of diatomite and its base modifications on the self-adhesive properties of silicone pressure-sensitive adhesives

The study examined how diatomite and its modifications affected the self-adhesive ability of silicone pressure-sensitive adhesives. To create adhesive composition for testing, fillers were added to a commercial silicone resin, which were then used to create new modified pressure-sensitive tapes. The resulting tapes were tested to determine their adhesion, tack, cohesion at room and elevated temperature, SAFT test (Shear Adhesive Failure Temperature), pot-life (viscosity) and shrinkage. The results obtained were compared with those of the unmodified tapes. The tests resulted in higher thermal resistance (225 °C) and lower shrinkage (0.1%). As a result, we can conclude that materials with thermal resistance with a slight decrease in other parameters were obtained.

A hydrophobic eutectogel with excellent underwater Self-adhesion, Self-healing, Transparency, Stretchability, ionic Conductivity, and fully recyclability

As an emerging soft material, eutectogels have attracted widespread interest for their excellent optical, mechanical, ion-conductive, self-adhesive, and self-healing properties. However, these properties of eutectogels are usually heavily affected by water molecules, leading to functionality failure in wet or underwater environments. Here, a novel hydrophobic eutectogel (HEG) is rapidly prepared with the help of photopolymerization by simultaneously introducing soft and hard acrylate monomers in a hydrophobic benzyltriethylammonium chloride/thymol deep eutectic solvent. Due to the abundant non-covalent and hydrophobic interactions within the polymer network, the synthesized HEG addresses the shortcomings of conventional eutectogels that are sensitive to water, while enabling good self-healing and self-adhesive properties both in air and underwater. Typical HEGs also exhibit high transparency, tunable mechanical properties, and ionic conductivities. The combination of these advantages makes HEG very suitable for the use of underwater adhesives and sensors with stable performance. In addition, it can be also used to prepare fully self-healing, recyclable and flexible electroluminescent devices. The design and applications based on HEGs show great promise for wearable sensors, self-healing flexible devices, and iontronics.

Research Progress of Polydopamine Hydrogel in the Prevention and Treatment of Oral Diseases.

Oral diseases represent one of the most prevalent diseases globally and are associated with serious health and economic burdens, greatly altering the quality of life of affected individuals. Various biomaterials play important roles in the treatment of oral diseases. To some extent, the development of biomaterials has promoted progress in clinically available oral medicines. Hydrogels have unique tunable advantages that make them useful in the next generation of regenerative strategies and have been widely applied in both oral soft and hard tissues repair. However, most hydrogels lack self-adhesive properties, which may result in low repair efficacy. Polydopamine (PDA), the primary adhesive component, has attracted increasing attention in recent years. PDA-modified hydrogels exhibit reliable and suitable adherence to tissues and easily integrate into tissues to promote repair efficiency. This paper reviews the latest research progress on PDA hydrogels and elaborates on the mechanism of the reaction between PDA functional groups and hydrogels, and summarizes the biological properties and the applications of PDA hydrogels in the prevention and treatment of the field of oral diseases. It is also proposed that in future research we should simulate the complex microenvironment of the oral cavity as much as possible, coordinate and plan various biological events rationally, and realize the translation from scientific research to clinical practice.

Influence of Illite and Its Amine Modifications on the Self-Adhesive Properties of Silicone Pressure-Sensitive Adhesives.

Obtaining new silicone self-adhesive in the presence of modified illite has been described. The filler was modified with N,N,4-trimethylaniline. The effect of illite content and modification on functional properties (adhesion, cohesion, stickiness, and shrinkage) was determined. Additionally, the thermal resistance (the SAFT test) of obtained silicone pressure-sensitive adhesives was evaluated. For all the systems tested, an increase in thermal resistance and shrinkage decrease were noted. Moreover, only a slight adhesion and tack decrease was revealed. Such self-adhesives could be applied for joining elements operating at increased temperatures, e.g., in heavy industry.