Stretching of assembled nanoparticle helical springs.

Hybrid materials that possess high inorganic fractions of nanoscale particles can be advantageous for a wide range of functions, from optoelectronic or electronic devices to drug delivery. However, many current nanoparticle (NP) based materials lack the necessary combination of simple fabrication and robust mechanical properties that span across length scales greater than tens of microns. We have developed a facile, evaporative assembly method called flow coating to create NP based ribbons that can subsequently form helical structures. Here we analytically examine the stretching properties of these helical ribbons which are nanometers thick, microns wide, and arbitrarily long. We find that the force-extension behavior is well described by the elastic and surface energies, which can be used as a guideline for their design. In addition, we show that the properties may be tuned by changing the ribbon dimensions or material composition to yield a different stiffness. These macroscale mechanical properties, along with properties inherent to the nanometer length scale of the particles can provide tunable multifunctionality for a number of applications.