Brownian Motion Used To Power Molecular Motor

New research, cited in Nature Materials and announced at the BA Festival of Science, could have far reaching implications in the fields of nano-scale science and engineering. Chemist David Leigh and colleagues from Edinburgh University have achieved a breakthrough in harnessing the natural random movement of molecules known as Brownian motion. Brownian motion is familiar to most high school chemistry students as the random movement of molecules caused by collisions with molecules around them. The new research involves controlling (or ‘biasing’) Brownian motion so that molecule movements are no longer completely random.

The team demonstrated the technique by using light to stimulate man-made molecules to propel small droplets of liquid, not only across flat surfaces, but also up 12 degree slopes. While this doesn’t sound tremendously exciting, the work done by the specially engineered molecules is prodigious, analogous to tiny movements in a conventional machine raising objects to over twice the height of the world’s tallest building. The researchers say this is the first time ever that man-made molecules have been used to move larger than atom sized objects.

Leigh’s team, as well as scientists from Italy and the Netherlands, developed a way of covering a gold surface with specially engineered molecules. When stimulated by ultra-violet light, the components of these molecules change position (a chemical reaction takes place in one part of the molecule that causes it to repel another part). These changes in position dramatically alter the surface tension of a droplet of liquid placed on the gold surface and in this way produce enough energy to move the droplet a distance of up to a millimeter. While a millimeter isn’t far on the human scale, it’s an immense distance on the nano-scale.

It’s possible that the team’s findings could eventually lead to the development of artificial muscles that use molecular nano-machines with biased Brownian motion as their motive power to help perform physical tasks. “Nature uses molecules as motors and machines in all kinds of biological and chemical processes. Although man’s understanding of how to build and control molecular machines is still at an early stage, nano-scale science and engineering could have a life-enhancing impact on human society,” said Leigh.

Source: Media release – BA Festival of Science

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