Gold squeezed into micro-Velcro

The research is published today in Science and Technology of Advanced Materials.

Velcro consists of one surface with loops, and another with hooks that latch onto the loops, joining opposing surfaces strongly. A miniaturised version of Velcro could be used in micro- and nanotechnology, but to form the surfaces, microwires are needed with properties that provide strength and durability.

Several different approaches have been used to construct 'micro-Velcro', but the most promising are those that use self-assembling or self-organising techniques, where microwires are 'squeezed' from a composite material by compression. Researchers at Ruhr University Bochum, Germany, have used this technique to produce gold microwires that have suitable properties for micro-Velcro.

The scientists created thin films of composite materials containing gold and tungsten metal. These were then heated to very high temperatures, causing the tungsten to react with oxygen and form tungsten oxide. This increased the volume of the tungsten and caused compression within the composite, 'squeezing' the softer gold out as 'whiskers'.

Different ratios of gold to tungsten were tried in the original composite, and these were heated to different temperatures and for different times to find the optimal conditions. The best result produced gold microwires approximately 35 micrometres long -- similar to the width of a human hair -- and 2 micrometres in diameter.

The resulting gold microwires have larger diameters than indium metal microwires that had previously been made using a similar technique, making them more suitable for micro Velcro. The results demonstrate that this new approach is a feasible one for producing the microwires that could be used to make micro-Velcro.

This research was published in the journal, Science and Technology of Advanced Materials.