A multiple shape memory and self‐healing poly(acrylic acid)‐graphene oxide‐Fe3+ (PAA‐GO‐Fe3+) hydrogel with supertough strength is synthesized containing dual physically cross‐linked PAA network by GO and Fe3+. The first GO cross‐linked hydrogel can be reversibly reinforced by immersing in FeCl3/HCl and pure water and softened by immersing in HCl. The tensile strength is 2.5 MPa with the break strain of 700%. Multiple shape memory capability is found depending on this unique feature, the hydrogel can be fixed in four temporary shapes by adjusting the immersing time in FeCl3/HCl and pure water, and recovered in sequence by immersing in HCl. This hydrogel also exhibits perfect self‐healing behavior, the cut as‐prepared hydrogel is almost completely healed by immersing in FeCl3/HCl. Besides, the hydrogel shows enhanced electrical conductivity with the presence of GO and Fe3+. This supertough hydrogel provides a new way to design soft actuators.
A self‐healing polysaccharide hydrogel based on dynamic covalent enamine bonds has been prepared with a facile, cost‐effective, and eco‐friendly way. The polysaccharide hydrogel is obtained by mixing cellulose acetoacetate (CAA) aqueous solution with chitosan aqueous solution under room temperature. CAA is synthesized by reaction of cellulose with tert‐butyl acetoacetate (t‐BAA) in ionic liquid 1‐allyl‐3‐methylimidazolium chloride (AMIMCl). The structure and properties of CAA are characterized by FT‐IR, NMR, and solubility measurements. The results demonstrate that CAA possesses water solubility with a degree of substitution (DS) about 0.58–1.11. The hydrogel shows an excellent self‐healing behavior without other external stimuli and good stability under physiological conditions. Furthermore, the polysaccharide hydrogel exhibits pH responsive properties.
A self‐healable hydrogel with recoverable self‐healing and mechanical properties is reported. The hydrogel (coded as ACSH) crosslinked by Schiff base linkage contains two polysaccharides of acrylamide‐modified chitosan (AMCS) and oxidized alginate (ADA). Self‐healing and mechanical properties are heavily influenced by the crosslinking time. The hydrogel crosslinked for 2 h possesses better mechanical and self‐healing properties than hydrogel crosslinked for 24 h. Macroscopic test shows that hydrogel without self‐healing ability can recover the self‐repair and mechanical properties by adjusting the pHs. The recovery of self‐healing and mechanical properties relies on the pH sensitivity of the Schiff base linkage. Adjusting the pH to acid, the Schiff base linkage becomes unstable and breaks. Regulating the pH to neutral, reconstruction of Schiff base linkage leads to recovery of the self‐repair and mechanical properties. The recoverable self‐healing property can be cycled once breakage and reconstruction of the Schiff base linkage can be conducted. In addition, this study demonstrates that the hydrogel can be remodeled into different shapes based on self‐healing property of the hydrogel. It is anticipated that this self‐healable hydrogel with recoverable self‐healing and mechanical properties may open a new way to investigate self‐healing hydrogel and find potential applications in different biomedical fields. 相似文献
Development of hydrogels with excellent and tunable mechanical properties combining with multifunctions is an intriguing issue in material science and engineering. Herein, bioinspired tunable sacrificial bonds are introduced into the tetra‐poly(ethylene glycol) (PEG) based polyurethane (PU) (TP) network to afford a hydrogel with tunable mechanical properties, shape‐memory, and self‐healing functions. The mussel‐inspired compound of Lysine‐dopamine (LDA) is introduced into the network of TP hydrogel through polyurethane/polyurea chemistry to form LDA‐tetra‐PEG‐PU (LTP) hydrogel. As catechol groups in LDAs can intermolecularly interact with each other and can also coordinate with ferric ions with different coordination ratios, these physical interactions with different strengths in the afforded LTP hydrogel construct kinds of sequentially tuned sacrificial bonds. As a result, these sacrificial bonds preferentially rupture prior to the covalent network upon external loading, which dissipate the energy and endow the hydrogel with advanced and postadjustable mechanical properties. This mechanism is investigated in detail. Furthermore, the LTP hydrogel shows multifunctions such as shape‐memory and self‐healing abilities. In addition, the tetra‐PEG based hydrogel shows remarkable thermoresponsiveness that the hydrogel distinctly contracts with the increase of the temperature. The improved mechanical strength and multifunctions should enlarge the application areas of the tetra‐PEG based hydrogel in various fields. 相似文献
How to reasonably fabricate polymer network for high performance hydrogels is a critical issue but remains a challenge. This work reports an approach to high performance hydrogels by molecularly engineering fully flexible crosslinking (ffC) network. A model network cross‐linked by fully flexible crosslinking points of triblock copolymer micelles and ionic interactions is fabricated. Due to the unique structure, the resulting ffC hydrogels are mechanically robust, tough, and self‐recoverable. For as‐prepared ffC hydrogels, a tensile stress more than 3.5 MPa can be achieved and the energy dissipation can reach up to 6.61 MJ m−3 at the tensile strain of 125%. Moreover, ffC hydrogels fabricated under constant strain can achieve an energy dissipation ability up to 11.63 MJ m−3 at the tensile strain of 100% and a tensile stress of 17.57 MPa. Based on these results, a dynamic molecular mechanism in the ffC hydrogel network under tensile deformation is proposed. The high performances of the ffC hydrogels can be possibly attributed to the sequential breakage and energy dissipation of the flexible crosslinking points and the easily accessible polymer chain orientation during tensile deformation.
The application of traditional chemically crosslinked hydrogels is often limited by poor mechanical properties because of their own inhomogeneous network and irreversible crosslinking bonds. Herein, physical interactions are applied to crosslink the interpenetrating network hydrogel, i.e., hydrogen bonding and crystalline domain for polyvinyl alcohol network, and hydrophobic interaction inside micelle for poly (acrylamide‐co‐stearyl methyl acrylate) [P(AAm‐co‐SMA)] network. In this gel network system, reversible energy dissipation mechanism is realized by dissociation and reassociation of weak interactions including hydrogen bonding and hydrophobic interaction inside the micelle. Strong crystalline domains serve as permanent crosslinking interactions to maintain network integrity under large extension. As a result, the synergy of weak and strong interactions leads to tough, antifatigue, fast recovery, and self‐healing properties of the hydrogel. This proposed strategy of achieving versatile hydrogels can broaden the use of hydrogels into load‐bearing applications. 相似文献
2D graphene with high quality holds great promise in improving the performance of the hydrogels owing to its exceptional electronic, thermal, and mechanical properties. However, the structure defects existed in graphene restrict its further applications. Herein, a simple and green method of fabricating defect‐free graphene nanosheets with the assistance of supercritical carbon dioxide (SC CO2) is designed. The graphene nanosheets directly assemble with acrylic acid monomer and clay, and a flexible semitransparent hydrogel is fabricated. Benefiting from the excellent properties of the defect‐free graphene, the hydrogel exhibits the high mechanical performance, superfast self‐healing capability, excellent conductivity, and super photothermal conversion efficiency. According to the advantages above, the graphene/poly(acrylic acid)/clay hydrogels can be used for intelligent sensors for disease diagnosis, artificial electronic skin, and military stealth materials in the near future. 相似文献
In this paper, highly transparent, robust, and superhydrophilic polyethylene glycol tert‐octylphenyl ether nonionic surfactant/epoxy (Triton X‐100/epoxy, TXE) composite coatings are successfully prepared with a facile, one‐step drop‐casting method by mixing Triton X‐100 with an epoxy resin and an amine curing agent. The hydrogen bond reaction between the hydroxyl group of Triton X‐100 and the ether group of the epoxy resin improves the compatibility and reduces the glass transition temperature (Tg) of the TXE composite coatings. The free Triton X‐100 surfactant easily accumulates on the surface of the TXE composite coatings, which improves the hydrophilicity of the TXE composite coatings. The TXE composite coatings are self‐healable because of their low Tg and the migration of Triton X‐100 small molecule surfactant. Any damage arising from denting, cutting, or wiping by tetrahydrofuran can be healed, and the composite coating can regain its superhydrophilic properties through a heating process. The TXE composite coatings demonstrate excellent acid, alkali, salt, high temperature, and ultrasonic‐resistant properties. This facile preparation technique has the potential to be applied in the scalable fabrication of multifunctional coatings in anti‐fogging, oil–water separation, and optical–electric devices. 相似文献
Self‐healing paints would have the potential benefit of protecting the underlying substrate and extending the coating's service life. As a step toward those types of coatings, this work examines layer‐by‐layer films of branched poly(ethylene imine)/poly(acrylic acid) with the inclusion of various types of latex particles with different Tg and different compositions. Due to high mobility of the polyelectrolyte chains when plasticized with water, water enabled self‐healing of these films is demonstrated, as well as steam enabled self‐healing. The films with various latex particles show different swelling ratios, surface hydrophilicity, as well as varying ability to self‐heal scratches. This self‐healing property is studied as a function of temperature. Also, the mechanical properties such as hardness and modulus of the films are measured. 相似文献
It remains a challenge to develop tough hydrogels with recoverable or healable properties after damage. Herein, a new nanocomposite double‐network hydrogel (NC‐DN) consisting of first agar network and a homogeneous vinyl‐functionalized silica nanoparticles (VSNPs) macro‐crosslinked polyacrylamide (PAM) second network is reported. VSNPs are prepared via sol‐gel process using vinyltriethoxysilane as a silicon source. Then, Agar/PAM‐SiO2 NC‐DN hydrogels are fabricated by dual physically hydrogen bonds and VSNPs macro‐crosslinking. Under deformation, the reversible hydrogen bonds in agar network and PAM nanocomposite network successively break to dissipate energy and then recombine to recover the network, while VSNPs in the second network could effectively transfer stress to the network chains grafted on their surfaces and maintain the gel network. As a result, the optimal NC‐DN hydrogels exhibit ultrastretchable (fracture strain 7822%), super tough (fracture toughness 18.22 MJ m‐3, tensile strength 431 kPa), rapidly recoverable (≈92% toughness recovery after 5 min resting at room temperature), and self‐healable (can be stretched to 1331% after healing) properties. The newly designed Agar/PAM‐SiO2 NC‐DN hydrogels with tunable network structure and mechanical properties by multi‐bond crosslinking provide a new avenue to better understand the fundamental structure‐property relationship of DN hydrogels and broaden the current hydrogel research and applications. 相似文献
