How to Design Both Mechanically Strong and Self-Healable Hydrogels?
Several strategies have been developed in the past decade for the fabrication of self-healing or self-recovery hydrogels. Because self-healing and mechanical strength are two antagonistic features, this chapter tries to answer the question “How to design
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How to Design Both Mechanically Strong and Self-Healable Hydrogels? Oguz Okay
Contents 1 Introduction 2 H-Bonding Interactions 3 Hydrophobic Interactions 3.1 Hydrophobically Modified Associative Hydrogels 3.2 Mechanically Strong Hydrophobically Modified Hydrogels 4 Conclusions and Outlook References
Abstract Several strategies have been developed in the past decade for the fabrication of self-healing or self-recovery hydrogels. Because self-healing and mechanical strength are two antagonistic features, this chapter tries to answer the question “How to design both mechanically strong and self-healable hydrogels?”. Here, I show that although autonomic self-healing could not be achieved in high-strength hydrogels, a significant reversible hard-to-soft or first-order transition in cross-link domains induced by an external trigger creates self-healing function in such hydrogels. I mainly focus on the physical hydrogels prepared via hydrogen-bonding and hydrophobic interactions. High-strength H-bonded hydrogels prepared via selfcomplementary dual or multiple H-binding interactions between hydrophilic polymer chains having hydrophobic moieties exhibit self-healing capability at elevated temperatures. Hydrophobic interactions between hydrophobically modified hydrophilic polymers lead to physical hydrogels containing hydrophobic associations and crystalline domains acting as weak and strong cross-links, respectively. Semicrystalline self-healing hydrogels exhibit the highest mechanical strength reported so far and a high self-healing efficiency induced by heating above the melting temperature of the alkyl crystals. Research in the field of self-healing hydrogels provided several O. Okay (*) Department of Chemistry, Istanbul Technical University, Istanbul, Turkey e-mail: [email protected]
O. Okay
important findings not only in the field of self-healing but also in other applications, such as injectable gels and smart inks for 3D or 4D printing. Keywords Hydrogels · Hydrogen-bonding interactions · Hydrophobic associations · Mechanical properties · Self-healing · Semicrystalline hydrogels
Abbreviations βo ηo ε εf ε_ λ λbiax,max λmax νedry ξH σf σ nom ω AAc AAm AMPS BAAm C12M C17.3M C18A C22A CNFs Co CTAB DAT DMAA DMSO DNA E EtBr fν G0 G00 GO MAAc NAGA
CTAB/AAc molar ratio in the gelation solution Zero-shear viscosity Strain Fracture strain Strain rate Deformation ratio Maximum biaxial extension ratio Maximum deformation ratio Cross-link density Hydrodynamic correlation length Fracture stress Nominal stress Frequency Acrylic acid Acrylamide 2-Acrylamido-2-methyl-1-propanesulfonic acid N,N0 -Methylenebis(acrylamide) Dodecyl methacrylate Stearyl methacrylate N-Octadecyl acrylate Docosyl acrylate Cellulose nanofibrils Initial monomer concentration Cetyltrimethylammonium bromide Diaminotriazine N,N-Dimethylacrylamide Dimethyl sulfoxide Deoxyribonucleic acid Young’s modulus Ethidium bromide Fraction of associations broken during the loading Storage modulus Loss modulus Graphene oxide Methacrylic acid N-Acryloyl glycinamide
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