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Deformation, Fracture and Adhesion of Soft Materials

Costantino Creton, Dominique Hourdet, Tetsuharu Narita, Matteo Ciccotti,

One of the important aspects of the research done in our group is the relationship between molecular structure (at the 50 nm length scale), mesostructure (at the micron scale) and macroscopic mechanical properties. Around this rather general definition, we focus more specifically on the design of soft polymer networks of varying complexity ranging from conventional rubbers, to softer self-adhesive materials all the way to very soft swollen hydrogels.

In all cases we are interested in relating the structure of the material to its deformability : in the elastic regime of course but more importantly in its large strain regime where the dissipative mechanisms, important for fracture are active. From a practical standpoint, we are particularly interested in controlling independently stiffness (the modulus) and resistance to fracture (fracture toughness) through an appropriate molecular design of the network. Because the materials we study are soft, they deform significantly before fracturing and we show some examples on the figures below.

Debonding of soft adhesive
SEM image courtesy of Ken Lewtas

In this example a soft and sticky pressure-sensitive adhesive is observed in the scanning electron microscope. Note the fibrillar structure formed as the adhesive is detached. This deformation is responsible for the stickiness.

Fracture d’un hydrogel

In this second example the gel pictured here contains 90% of water. Yet it is difficult to break because it contains loose Silica nanoparticles which can dissipate energy when they detach from the polymer structure as the material is deformed.

The key to achieving new and interesting properties is the precise control of the heterogeneities in the material. Tough materials are not so much defect free but resistant to the growth of a small defect into a macroscopic crack. Very homogeneous materials are generally not tougher than randomly heterogeneous materials. The optimum often results from the controlled design of heterogeneities at a mesoscopic length scale (50 nm to 50 µm), obtained through synthesis or through formulation.

Améliorer la ténacité
Hydrogel modifé hydrophobe

In our current research projects we apply this general strategy to a variety of problems :

- Adhesive properties of soft pressure-sensitive-adhesives made from supramolecular assemblies
- Modeling of adhesion and fracture of soft materials
- Fracture mechanisms of filled and unfilled rubbers
- Adhesion of hydrogels under water
- Mechanical properties and fracture of hybrid hydrogels

Selected Publications

Ducrot, E. Chen, Y. Bulters, M., Sijbesma, R.P., Creton, C.
"Toughening Elastomers with Sacrificial Bonds and Watching Them Break"
Science 11 April 2014 : 186-189.

Tanguy, F., M. Nicoli, A. Lindner and C. Creton (2014). "Quantitative analysis of the debonding structure of soft adhesives" The European Physical Journal E 37(1) : 1-12.

Sudre, G., L. Olanier, Y. Tran, D. Hourdet and C. Creton (2012). "Reversible adhesion between a hydrogel and a polymer brush". Soft Matter 8(31) : 8184 - 8193.

Mzabi, S., D. Berghezan, S. Roux, F. Hild and C. Creton (2011). "A critical local energy release rate criterion for fatigue fracture of elastomers." Journal of Polymer Science : Polymer Physics 49 : 1518-1524.