By Will Soutter
An accidental discovery at MIT’s Research Laboratory of Electronics has led to the development of a technique to fabricate uniform spheres of size varying from nanoscale to pinhead from a range of materials. Traditional methods of microscopic spherical particle creation involve growing spheres from even tinier spheres.
Molten fiber undergoing Rlaeigh Instability to form spherical droplets. (Credit: Yan Liang/Fink Lab)
The approach limits the size of spheres produced. The new technique is an off shoot of the fabrication method of long, thin fibers from different materials perfected over the years by the team at MIT. The process for making spheres begins with the fabrication of thin fibers followed by heating of the fibers to produce a line of droplets much like a string of pearls. The control the process yields over the fabrication gives rise to complex, patterned spheres that could find application in many areas such as drug delivery, biomedical research, materials processing and electronics.
The technique involves the creation of a preform, which is a large polymer cylinder, with an inner cylindrical semiconductor core that is a scaled-up version of the ultimate fiber required. The preform is made soft enough to be pulled into fibers by heating. The inner polymer sheath remains intact. On further heating, the semiconductor core is liquefied and forms spherical droplets. The phenomenon is similar to the breaking of a shrinking stream of water from a faucet into water droplets. The new technique also overcomes a common problem of clumping in nanoparticle creation as the spheres freeze in place when the surrounding fiber solidifies. The polymer sheath keeps the droplets locked and are later dissolved away.
The research was jointly conducted by MIT and the University of Central Florida (UCF).