Plastic damage of soft colloidal-based amorphous materials: a mesoscopic study*

Deformation mechanisms, notably fracture, of soft amorphous systems are not yet fully understood. Because of their complex, disordered nature, these materials break involving dissipative processes such as secondary cracking ahead of the main crack tip and local structural rearrangements. The aim of our work is to fabricate and fracture soft amorphous systems composed of large enough “atoms,” so that the above mentioned mechanisms can be observed optically.

We use classical microfluidics flow-focusing technique to synthesize concentrated emulsions, based on a difunctional acrylic monomer, as constitutive “atoms” of size ~50μm. Then, using in situ photopolymerization, the emulsions turn into soft colloidal particles that interact with each other to form soft colloidal-based gels. We vary the rheological properties of these emulsions by regulating conditions for photopolymerization. Using conventional optical microscopy, we also use a microfluidics-based test cell to hydraulically fracture these soft gels at controlled flow rates and examine both micro-cracking and plastic events, i.e. the local irreversible displacements around the crack tip.