Controlling Dispersion Forces Between Small Particles with Artificially Created Random Light Fields

Article: published in Nature Communications by Juan José Sáenz, IFIMAC researcher.

Dispersion forces between molecules arise from electromagnetic fields generated by natural quantum and thermal fluctuations. In an article appearing in Nature Communications the groups of Prof. Scheffold in Fribourg (Switzerland) and Prof. Sáenz in Madrid and Donostia-San Sebastian (Spain) show that dispersion forces can be induced, controlled and tuned by random laser fields.

Emulating Spiderman: adhesion forces activated by laser light clouds

van der Waals forces are ubiquitous in nature and responsible of uncountable natural processes like adhesion or surface tension and play a key role in the behaviour observed in biological fluids (proteins, blood cells, …), paints, inks or foodstuffs. A team of researchers from the Donostia International Physics Center (DIPC), Condensed Matter Physics Center (IFIMAC) from Universidad Autónoma de Madrid and Fribourg University show for the first time in Nature Communications that it is possible to induce and control this type of dispersion forces at the nanoscale with external random laser fields.

The origin of van der Waals forces, also known as “dispersion forces”, can be found in naturally present, extremely fast fluctuating electric and magnetic fields. Compared to ordinary chemical bonds, such fluctuations induce a relatively weak interaction between molecules and small objects. However, by combining the van der Waals forces of millions of small hairs, geckos and some spiders (including Spiderman) can adhere to a surface being able to climb vertical smooth walls without any adhesive.

To mimic the natural field fluctuations (of both quantum and thermal origin), the researchers generated a laser light cloud with properties similar to the light you see when the sun shines through mist on a foggy day, albeit with a much higher intensity. In the experiment two tiny plastic beads are held in place and embedded in the light cloud (picture). The interaction force between the beads can be measured by studying precisely the relative position of the two particles with a microscope.
The higher the light intensity in the cloud, the more the two particles attract each other. Like in nature, the forces only depend on the relative distance between the particles, but not their actual position within the cloud. The strength and properties of the forces present can also be controlled by the appropriate selection of the intensity and the colour of the light in the cloud.

The results suggest that it should be possible to completely control interactions between small bodies in two or three dimensions. This approach could facilitate the design of colloidal suspensions and nanostructured materials with tailored properties “à la carte”. [Full article]