Probing stresses at the nanoscale

ended

Summary: I will exploit novel molecules whose fluorescence properties depend strongly on the environment, notably on their spatial confinement, to study local stresses in complex materials down to the nanometer length scale and with unprecedented temporal resolution. Based on successful preliminary tests, I will develop this innovative methodology to tackle the fundamental scientific challenge of quantifying the long-range and very non-linear elasto-plastic stresses that govern the dynamics of friction, the glass transition and rheology. Friction is an immense global source of energy loss; the glass transition is perhaps the most important unsolved problem in condensed matter physics; and rheology in complex fluids is at the same time ubiquitous and poorly understood. The common denominator of these three open challenges is that in each, the material’s macroscopic mechanical behavior results from a complex interplay between microscopic stresses that remain ill characterized. This presents a scientific bottleneck as well as a major obstacle in the engineering of many important materials and tools such as ball bearings, plastics and foodstuffs. The fluorescent environmentally sensitive probes will allow me to achieve breakthrough results in three areas at once: (1) Locally measuring stresses in a frictional contact; (2) Probing the glass transition by local stress and viscosity measurements; (3) Visualizing and quantifying stress transmission in flowing complex fluids to explain non-Newtonian and non-local viscosity effects microscopically. I have a track record in providing new insights in long-standing problems, spurring renewed scientific interest, and in combining fundamental research with potential for technological innovation. By probing local stresses in much more detail than was possible before, this project will break open some of the toughest research areas in non-linear physics and (statistical) mechanics with far-reaching engineering consequences.