The dark circles are micro-pillars formed by an electrohydrodynamic instability in a thin polymer film. A liquid polymer is coated onto an electrode to be used in a parallel plate capacitor. When a voltage is applied across the two capacitor electrodes, the pillars grow in the liquid polymer. This is a result of electrohydrodynamic instabilities at the interface between the polymer and air in the gap between the two electrodes.  The pillars are 10x smaller than the width of a human hair. The finger like patterns are formed when a less viscous fluid (here the air) displaces another of higher viscosity (the polymer).The colours in the image are the result of thin film interference where light interacts with very thin layers of material. The resulting patterned surfaces are used for optics and tissue culture applications.
Claire Trease, Kingston University
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>