Dr. Wei Lei (Nanyang Assistant Professor, School of Electrical & Electronic Engineering) and his collaborators have developed a way to break fibres or sheets into many tiny, almost perfectly uniform segments or strips. The method can work on plastics, metals, glasses, and even natural materials such as silk, hair, and ice, producing sectioned particles ranging in size from nanoscale particles to ones that can be handled and easily seen with the naked eye. The new findings are published in the journal Nature in 2016 (doi:10.1038/nature17980).
The underlying technology, a process called “Cold-drawing”, has been used for almost a century in the production of synthetic fibres such as polyester and nylon, and has become a rather mature technique for producing fibres of high tensile strength and flexibility. Dr. Wei Lei and his collaborators, however, have found that under the right conditions, some materials embedded within synthetic polymer fibres naturally break apart into pieces of uniform length. The cause of this surprising phenomenon is a kind of wave that sweeps along the polymer fibre during the drawing process. This wave is known as a “neck,” since it propagates in the form of a depression with moving “shoulders” that continuously extend in opposite directions until they span the whole fibre length. As the shoulders propagate down the fibre, they pinch off any brittle threads embedded in the fibre, which break apart into short, uniformly sized segments, as shown in Figure 1. The result can be a bundle of short rods kept in place within the polymer fibre, or the polymer can be dissolved away to leave a collection of separated rods of precisely matched size and shape, which can be of a nanoscale size that would be difficult to manufacture by other methods. This represents a novel, scalable route to production of nano- and micro-particles of almost arbitrary cross-section. Remarkably, the cold-drawing process is highly robust and can even be done - literally - by hand!
One potential application of this work is controlling the optical properties of macroscopic composite structures through dynamical and thermoreversible nano-scale mechanical processes. Another application which should be realisable in the near future is scalable fabrication of micro- and nanoparticles with arbitrary cross sections - at a level far beyond what is achievable with current chemical synthesis methods. Indeed, the work rests at the cross-section of many disciplines ranging from polymer mechanics to optics to nanotechnology, leading to an important path to scale up the production of larger quantities of nanoparticles, nanorods, and nanowires of a very wide variety of compositions.
Published on: 06-Oct-2016