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International audienceA remarkable self-healing property has been achieved recently with rubbers formed by a supramolecular network of oligomers. Here we explore this property through a tack-like experiment where two parts of supramolecular rubber are simply brought into contact and then taken apart. These experiments reveal that the self-adhesive strength of rubber surfaces is significantly enhanced by fracture or other damaging processes. The mechanical energy required to separate two fracture surfaces that were brought back into contact is about one order of magnitude larger than that for surfaces close to thermodynamic equilibrium. Moreover, we find that fracture faces stored apart at room temperature still self-heal after 12 h but that this self-healing can be fully deactivated within a couple of hours by annealing around 90 °C. More generally, these results provide useful quantitative data to investigate the intensity and kinetics of self-healing in these soft rubbers

Dispersing particles within a semicrystalline polymer can result in remarkable impact strength improvement and opens promising routes toward super-tough materials. Although the technique is extensively employed to modify polymer properties, predicting which dispersions yield toughness remains a challenging issue. By comparing the characteristic lengths and deformation processes involved in toughening, we explain why a minimum matrix confinement or ligament thickness is required to induce ductility. Our model was used to interpret experimental data and show how this critical confinement length depends on material properties, temperature, and processing history. Most importantly, it reveals an unexpected particle size effect. The predictions provide fresh insight into the design of toughened materials. The model also provides guidance to understanding the fracture mechanics of other complex systems such as composites or biological matter.

Attaching hydrogels to soft internal tissues is a key to the development of a number of biomedical devices. Nevertheless, the wet nature of hydrogels and tissues renders this adhesion most difficult to achieve and control. Here, we show that the transport of fluids across hydrogel−tissue interfaces plays a central role in adhesion. Using ex vivo peeling experiments on porcine liver, we characterized the adhesion between model hydrogel membranes and the liver capsule and parenchyma. By varying the contact time, the tissue hydration, and the swelling ratio of the hydrogel membrane, a transition between two peeling regimes is found: a lubricated regime where a liquid layer wets the interface, yielding low adhesion energies (0.1 J/m2 to 1 J/m2), and an adhesive regime with a solid binding between hydrogel and tissues and higher adhesion energies (1 J/m2 to 10 J/m2). We show that this transition corresponds to a draining of the interface inducing a local dehydration of the tissues, which become intrinsically adhesive. A simple model taking into account the microanatomy of tissues captures the transition for both the liver capsule and parenchyma. In vivo experiments demonstrate that this effect still holds on actively hydrated tissues like the liver capsule and show that adhesion can be strongly enhanced when using superabsorbent hydrogel meshes. These results shed light on the design of predictive bioadhesion tests as well as on the development of improved bioadhesive strategies exploiting interfacial fluid transport.

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Equilibrium morphologies in molten ABC triblock terpolymers are much more difficult to attain than in AB diblocks. Here, we show that even the simplest lamellar structures exhibit high sensitivity to preparation conditions and that strongly trapped structural defects inherent to ABC triblock architecture cannot be removed by long annealing. Poly(styrene)-block-poly(butadiene)-block-poly(methyl methacrylate) (SBM) triblock terpolymers with nearly symmetric composition and low molar mass are studied by combining transmission electron microscopy with dynamical mechanical analysis and smallangle X-ray scattering. We find that annealing can induce a transition from a lamellar structure in which S and M end blocks are mixed together to a lamellar structure where all three components S, B, and M are segregated. The presence of B "loops" and B "bridges" is at the origin of characteristic defects which are difficult to eliminate. In a blend of SBM triblock terpolymer with a poly(styrene)-block-poly(butadiene) (SB) diblock having the same block length, diblock chains are completely incorporated in the lamellar structure obtained after solvent evaporation. However, annealing induces a macroscopic phase separation of SB and SBM chains. We propose a scenario for the separation mechanisms based on highly confined diffusion of SB chains within the SBM ordered structures.

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