USOFT · Ultrasound-based techniques for soft jammed materials

Soft materials are involved in most parts of our everyday life. In spite of a tremendous industrial importance, their properties still confront the physicists with challenging questions. Indeed, the constituents of soft materials are often stuck into a disordered structure, as for oil droplets in a concentrated emulsion like mayonnaise and for attractive particles in a colloidal gel. This phenomenon is known as ""jamming"" and leads to solid-like properties at rest that slowly evolve in time as the system ""ages"" under spontaneous rearrangements. When a jammed material is submitted to some external stress, a ""yielding"" transition from solid to liquid behaviour is commonly observed. Besides the fundamental issues raised by such out-of-equilibrium, glassy features, the design of soft materials that can strongly respond to a well-controlled excitation is of great interest for practical applications.This project aims at developing original tools for both physical investigation and design of soft jammed materials, based on the use of ultrasound. We will first set up ultrafast ultrasonic imaging techniques in the single and multiple scattering regimes in an attempt to overcome some limitations of current optical methods and to elucidate jamming, aging and yielding processes in a wide variety of model and real materials. High-intensity ultrasound will then be used to mechanically stress jammed materials and trigger local rearrangements or even large-scale structuration, leading to new insights into the physics of jamming and to innovations in the field of material design.""