| Summary: | Most materials break through the extension of their most prominent crack, as Griffith predicted over a century ago. Despite the fact that the extension of a crack occurs in the nanometre-sized area located at the crack tip end, we still know little about the crucial role that forces play at this scale. With the advent of the Atomic Force Microscopy (AFM), we have been able to apply small calibrated forces at the nanoscale. Until now, AFM has been most successful at unveiling the mechanical properties of biological materials while pulling. Investigating the mechanics of materials while pushing, however, has been less successful. Until now, most indentation experiments were performed at a constant pushing velocity, which precluded measuring the detailed rupture kinetics of the material. In this vein, we have developed an AFM capable of applying a more complex indentation protocol, called force-clamp, which expands the time window of experimentation and allows mapping out the energy landscape of the rupture mechanism. Then, we have investigated the rupture kinetics of an Angstrom-scale simple 2D material – confined solvation layers. By applying force-clamp, we have discovered that the rupture (and reformation) of these solid-like layers occurs through the disruption of a single molecule, contrary to currently accepted mechanical contact models. Secondly, we have investigated the more complex mechanism of lipid membrane rupture, which involves the displacement of tens to hundreds of molecules. In this case, we have developed a pore nucleation model to fit the complex rupture kinetics, which is far from the currently used two-state model. Finally, we have indented whole live cells. As a result, we have measured that lipid membrane lateral interactions ultimately define cell membrane integrity. Altogether, these experiments point out the key role that intermolecular forces play to define the mechanical strength of materials from a fraction of nanometre to several micrometres.
|
|---|
