After seeing several talks on electrospinning of polymers, Saul Griffith and I decided to try electrospinning a nanoparticle colloid of metal to form very fine metal wires.  Electrospinning is technique in which a polymer solution is pumped through a capillary and exposed to an electric field.  The droplet at the end of the capillary deforms into a conical shape, known as a Taylor cone.  If the field exceeds the critical value to overcome surface tension, the apex of the cone ejects a  jet of material that, depending on viscosity either breaks into droplets (electrospraying) or forms a continuous stream.  Despite a plethora of patents on electrospinning, there is no work on metals, only polymers, biopolymers, and some conductive polymers.

Schematic of electrospinning

I believe this is an exciting project, not only because it is a new space, but because electrospinning of nanoparticles could be a commericially viable manufacturing technique to make lots of interesting materials - high surface area to volume catalysts, filters, textiles with very high conductivity, and the like.

This technique could easily transition to mass-production manufacture of nano-scale filaments.  A fabric woven of these filaments could display unsual and desirable properties due to the extremely small size of the filaments.  We hope to examine these and other potentially useful applications during our further studies.

Experimental apparatus

SEM image of gold wires on a silicon wafer

We chose a solution of gold nanoparticles in a heavy organic solvent and with a field of approximately 1 kV / cm were able to create the gold wires shown in the SEM images above and below.  Many of the wires produced are 1 um in diameter, and there remain quite a few unexplored parameters that could push that diameter even smaller, which is the focus of current work.

SEM image of gold wires on a glass slide

The Taylor cone at the end of the capillary is just visible in this image