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Some strategies for hydrogel toughening, from polymer adsorption onto NPs to responsive toughening by phase-separation
Based on gel’s remarkable features of absorption, storage or release of water (or solvent), gels have become essential in engineering applications like superabsorbent, soilless agriculture or tissue engineering and regeneration. Gels could also be key players for the design of flexible actuators, valves or sensors. However, their generally weak mechanical performances combined with the inherent difficulties of manufacturing and assembling them still limit applications. By using concepts of polymer physics, here we present some strategies we have explored to design tough “hybrid” networks that combine covalent (permanent) cross-links and physical (reversible) interactions. Polymer adsorption onto silica nanoparticles [1-4] can be a remarkably simple and efficient means for the mechanical toughening (in bulk or adhesion) of gels. More recently, a novel mode of fracture toughening by crack bifurcation has been highlighted in phase-separated hydrogels, by exploring the coil-to-globule transition [5]. Usually, the phase transition of covalently cross-linked gels entails a drastic volume-change that makes it difficult to reveal the role of phase transition on the mechanical toughening independently of the polymer concentration effect. To clear up this ambiguity, we designed original gel topologies that phase-separate at constant macroscopic volume and quite high level of hydration, independently of the phase-separation process. Polymer network combines a conventional network with thermo-responsive domains which act as reinforcing fibers operating at a targeted temperature : purely organic responsive nanocomposite gels. Beyond the achieved high values of fracture energy ( kJ m-2) for relatively high hydration level, the fracture patterns have highlighted an unreported toughening mechanism for gels demonstrating a systematic crack bifurcation.
References
1. Carlsson, Rose, Hourdet, Marcellan, Soft Matter (2010)
2. Rose, Dizeux, Narita, Hourdet, Marcellan, Macromolecules (2013)
3. Gennisson, Marcellan, Dizeux, Tanter, IEEE Trans. Ultrasonics Ferroelec. & Freq. Control (2014)
4. Rose, Prevoteau, Elziere, Hourdet, Marcellan, Leibler, Nature (2014)
5. Guo, Sanson, Hourdet, Marcellan, Advanced Materials (2016)