The development of hydrogel-based underwater electronics has gained significant attention due to their flexibility and portability compared to conventional rigid devices. However, common hydrogels ...face challenges such as swelling and poor underwater adhesion, limiting their practicality in water environments. Here, a water-induced phase separation strategy to fabricate hydrogels with enhanced anti-swelling properties and underwater adhesion is presented. By leveraging the contrasting affinity of different polymer chains to water, a phase-separated structure with rich hydrophobic and dilute hydrophilic polymer phases is achieved. This dual-phase structure, meticulously characterized from the macroscopic to the nanoscale, confers the hydrogel network with augmented retractive elastic forces and facilitates efficient water drainage at the gel-substrate interface. As a result, the hydrogel exhibits remarkable swelling resistance and long-lasting adhesion to diverse substrates. Additionally, the integration of carboxylic multiwalled carbon nanotubes into the hydrogel system preserves its anti-swelling and adhesion properties while imparting superior conductivity. The conductive phase-separated hydrogel exhibited great potential in diverse underwater applications, including sensing, communication, and energy harvesting. This study elucidates a facile strategy for designing anti-swelling underwater adhesives by leveraging the ambient solvent effect, which is expected to offer some insights for the development of next-generation adhesive soft materials tailored for aqueous environments.
Swelling is ubiquitous for conventional hydrogels but is not favorable for many situations, especially underwater applications. In this study, an anti‐swelling and mechanically robust polyacrylic ...acid (PAAc)/gelatin composite hydrogel is reported with a rapid gelation process (101 s) under mild conditions via the synergy of MXene‐activated initiation and zirconium ion (Zr4+)‐induced cross‐linking, without the requirement of external energy input. The MXene is found efficient to activate the chain initiation, while the Zr4+ is prone indispensable for facilitating the cross‐linking of formed polymer chains. The resulting hydrogel exhibits integration of exceptional anti‐swelling properties and high mechanical performance at room temperature, thanks to the dense hydrogen bonds between PAAc and gelatin chains that enable an upper critical solution temperature above room temperature. Also, desirable electrical conductivity emerges in the hydrogel due to the simultaneous contribution of MXene and Zr4+, allowing stable electrical signal output of the gel upon deformation underwater. As a demonstration, an underwater communicator by harnessing the gel as a sensing module is assembled, which is capable of wirelessly delivering messages to the decoder on the ground via Morse codes. This study provides an exemplary way for the rapid gelation of tough and anti‐swelling hydrogels for durable underwater applications.
Rapid gelation of tough and anti‐swelling hydrogels under mild conditions is enabled by the synergistic effect of MXene and zirconium ions, without requiring external energy input. The MXene facilitates the chain initiation, while the zirconium ions cross‐link the formed polymer chains. The resulting hydrogels exhibit an upper critical solution temperature behavior to resist swelling at room temperature, promising their applications in underwater communication.
The rapid progress of information technology is accompanied by plenty of information embezzlement and forgery, but developing advanced encryption technologies to ensure information security remains ...challenging. Phase separation commonly leads to a dramatic change in the transmittance of hydrophilic polymer networks, which is a potential method for information security but is often neglected. Here, taking the polyacrylamide (PAAm) hydrogel system as a typical example, facilely adjustable information encryption and decryption via its regulable phase separation process in ethanol/water mixed solvent, are reported. By controlling the osmotic pressure of the external and internal environment, it is demonstrated that the diffusion coefficient during deswelling and reswelling, as well as the corresponding change of transmittance of the gel, can be well controlled. Relatively high osmotic pressure leads to rapid phase separation of the initial gel but slow phase remixing of the phase‐separated gel, opening the opportunity of applying the gel as a reversible information encryption device. As proof‐of‐concept demonstrations, several stable and reversible information encryption and decryption systems by making use of the phase separation process of the gels are designed, which are expected to inspire the development of next‐generation soft devices for information technology.
The homogeneous phase of polyacrylamide hydrogels progressively separates into polymer‐rich and polymer‐dilute phases with contrasting network chain densities in good/poor mixed solvents, leading to a transparent–opaque transition. Such a phase separation behavior is reversible and can be well regulated by the internal and external solvent strength of the gel, promising its application in adjustable information encryption.
Common hydrogels containing abundant water are insulating materials and lose stretchability easily below the freezing point of water, holding limited potential in emerging applications such as ...wearable soft devices. The introduction of compatible biomass-derived materials into hydrogel systems could be a potential solution that simultaneously enables anti-freezing ability, mechanical enhancement, and antibacterial properties. Based on such a hypothesis, here we report the facile development of biocompatible hydrogels that are capable of maintaining satisfying mechanical properties and electrical conductivity well below zero degrees centigrade. The strategy is to reinforce neat polyacrylamide (PAAm) hydrogels with biomass-derived cellulose nanocrystal (CNC) and phytic acid (PA), transforming the originally weak, insulating hydrogels into tough, highly conductive ones. Anti-freezing and antibacterial properties also emerge in the reinforced hydrogels, enabling them to work as efficient wearable sensors below zero degrees centigrade. Considering that numerous polymer hydrogel systems are compatible with CNC and PA, we believe that this simple biomass-based strategy can work universally to enhance and functionalize various weak and insulating hydrogels that are traditionally susceptible to frost and bacteria.
Solar steam generation is a promising method for clean water production. However, existing evaporation systems are limited by either expensive and complex equipment, or inadequate solar evaporation ...performance. In this paper, we prepared a biomass hybrid hydrogel (BHH) with hierarchical porous structure for efficient solar evaporation, in which starch and chitosan were used as hydrophilic substrates and PDA-Fe NPs was used as absorber. This specific microstructure plays an important role in improving light absorption, photothermal conversion and water transportation. The kerosene lamp structure evaporator endows centralized heat management and less heat loss. Therefore, our BHH evaporator performs high evaporation rate (3.9 kg m-2 h-1) and solar evaporation efficiency (103.2%). In addition, the evaporator shows favorable salt-resistant, durability and self-cleaning capacity, ensuring long-term and stable seawater evaporation. This study paves a new way for the development of low-cost, sustainable, efficient and salt-resistant evaporators for solar evaporation and desalination.
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•A sustainable and efficient evaporator was prepared by using starch and chitosan.•The biomass hybrid hydrogel forms specific hierarchical porous structure.•The hydrogel evaporator performs favorable evaporation and desalination behaviors.
•MPCM shows remarkable low-temperature phase change energy storage properties.•The phase change aerogel retains an excellent melting enthalpy of 104 J/g.•The composite aerogel shows low density and ...reshaping capabilities through heating.•The phase change aerogel exhibits exceptional mechanical properties.
Cryogenic transportation and storage confront significant challenges from harsh weather conditions, heightened energy consumption, and epidemic situations, compelling the need for the creation of exceptionally efficient thermal insulation materials. To address this demand, a composite phase change aerogel was designed in this study through incorporating low-temperature microencapsulated phase change microcapsules (MPCM) into a cellulose nanofiber/polyvinyl alcohol (CNF/PVA) system. The MPCM, consisting of a polyurethane-acrylate (PUA) shell and an n-tetradecane core, exhibited excellent encapsulation performance with leak-proof capability. Remarkable low-temperature phase change energy storage properties were observed, including a phase change temperature of approximately 6 °C and an impressive phase change enthalpy of 112 J/g. The MPCM also demonstrated stability during successive heating–cooling repetitions, maintaining its heat storage capacity and morphology for at least 300 cycles. These exceptional thermal characteristics endowed the resulting aerogel with effective thermal insulation and temperature retardation abilities. Meanwhile, the integration of CNF/PVA as the matrix in the composite aerogel led to minimal degradation of thermal storage performance compared to pure MPCM. Moreover, the addition of MPCM significantly enhanced the compressive strength, reaching 5.6 times that of the neat CNF/PVA aerogel. The composite aerogel showed a notably low density of 0.165 g/cm3 and could be reshaped through heating. This work provides a simple yet effective idea for designing bulk materials with low-temperature phase change capabilities, offering promising prospects in the field of thermal insulation.
In this study, hydroxyapatite (HAp) nanorods were prepared by a simple hydrothermal method and hydrophobically modified with lauric acid (LA). Modified HAp and magnetic triiron tetraoxide (Fe3O4) ...nanoparticles as emulsifiers were loaded on polycaprolactone (PCL) microspheres by Pickering emulsion template method. The structure, composition and morphology of prepared HAp and m-RHAp-PCL microspheres were characterized by IR, XRD, SEM and TGA. Furthermore, the adsorption capacity of pure HAp and m-RHAp-PCL microspheres was investigated by malachite green (MG) as a model dye. The results showed that the adsorption processes of pure HAp and m-RHAp-PCL microspheres correlated better with the Langmuir isothermal adsorption curve. The maximum adsorption capacity of m-RHAp-PCL microspheres was 609 mg/g, and the relative adsorption capacity of HAp on microspheres was higher than that of pure HAp, indicating its greater adsorption potential for MG. The values of RL and 1/n indicated that the adsorption process was spontaneous. The adsorption kinetic data of samples was in good agreement with the pseudo-second-order kinetic model. In addition, the adsorbent could be easily recovered under magnetic fields. The removal ability of MG was retained after four cycles, which demonstrated the excellent reusability and stability of m-RHAp-PCL microspheres for MG adsorption from aqueous as a potential adsorbent candidate material.
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•Magnetic hollow microspheres with dye adsorption function were prepared in one step.•The microsphere preparation process does not require polymerization, which is simple and requires no post-treatment.•The hollow structure of the microspheres reduces the polymer ratio and increases the adsorbent percentage and magnetic responsiveness.
Salt ions are multifunctional in living beings, in contrast to their limited efficiency in abiotic materials. Achieving the versatility of salt ions in synthetic materials is promising yet demanding. ...Here, we report that multivalent metallic ions can act multiple crucial roles in a polyacrylamide/sodium alginate (PAAm/SA) composite hydrogel system, inducing a quadruple effect that toughens and functionalizes the originally weak gel. Fixation of anisotropic structures (effect I), mechanical enhancement (effect II), conductivity improvement (effect III), as well as antifreezing and moisture retention properties (effect IV) simultaneously emerge in the gel, all of which are enabled by the ion effect. The resulting tough hydrogels exhibit excellent comprehensive properties that rival existing state-of-the-art hydrogels, promising a wide range of potential applications. As proof-of-concept demonstrations, extremely durable hydrogel-based soft electronic devices are developed, which operate stably even in harsh environments. We also prove that the ion effect can be induced by other multivalent metallic ions. This work highlights the versatility of salt ions in nonliving materials, providing a simple but enlightening idea for the development of all-around soft materials.
Abstract Mineralized bio‐tissues achieve exceptional mechanical properties through the assembly of rigid inorganic minerals and soft organic matrices, providing abundant inspiration for synthetic ...materials. Hydrogels, serving as an ideal candidate to mimic the organic matrix in bio‐tissues, can be strengthened by the direct introduction of minerals. However, this enhancement often comes at the expense of toughness due to interfacial mismatch. This study reveals that extreme toughening of hydrogels can be realized through simultaneous in situ mineralization and salting‐out, without the need for special chemical modification or additional reinforcements. The key to this strategy lies in harnessing the kosmotropic and precipitation behavior of specific anions as they penetrate a hydrogel system containing both anion‐sensitive polymers and multivalent cations. The resulting mineralized hydrogels demonstrate significant improvements in fracture stress, fracture energy, and fatigue threshold due to a multiscale energy dissipation mechanism, with optimal values reaching 12 MPa, 49 kJ m −2 , and 2.98 kJ m −2 . This simple strategy also proves to be generalizable to other anions, resulting in tough hydrogels with osteoconductivity for promoting in vitro mineralization of human adipose‐derived mesenchymal stem cells. This work introduces a universal route to toughen hydrogels without compromising other parameters, holding promise for biological applications demanding integrated mechanical properties.
