EX10521

Wouldn't it be nice to have cars with enhanced response to impact without the need to use more material on them?

By analyzing a simple mechanical problem, the deformation of a membrane forced to go through a ring, we found that the mechanical response of a thin membrane depends on how deformed it is (packing fraction) as well as on its frictional properties. We showed that a highly deformed membrane can be rationalized as one that is slightly deformed but thicker than the original one and that the basic deformations of it are conical deformations, as previously found for the case of weakly deformed elastic plates. Most strikingly, we showed that friction plays an important role once a highly deformed membrane touches itself; the larger the friction the larger the mechanical response. Our study suggests that the modification of frictional properties of a thin plate, say by changing its texture or by making it stickier, is a promising an inexpensive route to enhance the mechanical response of thin walled structures subject to extreme deformations.

LZ12356

The problem of how to pack objects into a confined space is something that is familiar to every economy-class flyer. Surprisingly, such problems find a broad range of scientific and industrial applications - these range from the mundane, as for example the most efficient way to pack Chinese egg rolls in cylindrical containers , to the high tech, such as molecular self assembly (the process by which molecules are deliberately guided into forming novel nano scale structures, which are at the heart of a number of next-generation technologies). An important problem of this type is finding the densest packing arrangement of equal sized hard spheres in a cylindrical tube . In this letter we demonstrate a surprising connection between this problem and the analogous problem of packing hard disks on the surface of the cylinder. The approach relies on ideas borrowed from phyllotaxis, a branch of biology that seeks to explain the emergence of floral patterns, e.g. the arrangement of florets on the head of a sunflower. This work will help researchers understand a wide range of columnar structures, encountered across the sciences, including wet foams, novel colloids, viruses and microtubules.


***

LU12663

Hand-Crafting Nanoparticles into Superstructures with Light

One of the Holy Grails of modern nanoscience is to assemble nanoparticles, tiny pieces of matter with diameters in the billionth of a yard range, into larger structures of any desired shape and form at will. Scientists have recently demonstrated a remarkably simple, elegant and cost effective way of achieving this goal via a process they term “Optically Directed Assembly” or ODA. ODA involves suspensions of gold and carbon nanoparticles in water. A small droplet of the suspension is placed on a glass slide and a low power laser is focused onto a small region within the droplet near its surface. Through a fascinating process involving optical trapping, heating, evaporation, convective fluid flow, and chemical interactions, the nanoparticles fuse near the laser focus and as the experimenter moves the laser focus around in the droplet a continuous filament of the fused material follows. These remarkable structures remain completely intact even after the fluid is drained off. In such a manner “hand-crafted” filaments of up to millimeter lengths and about 10-60 times wider than the original nanoparticles can be formed with arbitrary shape and design. These resulting hierarchical architectures could be useful for a variety of applications including biological sensing, electronics, optics and emerging energy technologies.