We actuate with light & magnets, we fold & unfold DNA, we cell-free express proteins, we play with drops, marbles & interfaces, we organize particles, we harness coffee rings.

Coffee rings are now photocontrolled and just published in Angewandte!

27 September 2014. Our manuscript "Dynamic photocontrol of the coffee-ring effect with optically-tunable particle stickiness" has just been accepted in Angewandte Chemie International Edition.

Abstract: When a colloidal drop dries on a surface, most of the particles accumulate at the drop periphery, yielding a characteristic ring-shaped pattern. This so-called coffee-ring effect (CRE) is observed in any pinned evaporating drop containing non-volatile solutes. Here, we show the first dynamic control of the CRE using light and demonstrate unprecedented reconfigurability of the deposit profile. This is achieved through a new mechanism where particle stickiness is optically tuned on-demand, thus offering reliable modulation of the deposition pattern. Our system consists of anionic nanoparticles and photosensitive cationic surfactants dispersed in water. We show that light-dependent modulation of surfactant-particle interaction dictates particle attraction and trapping at the liquid-gas interface, which allows us to direct particle deposition into a wide range of patterns from rings to homogeneous disks. Patterning from single drops is photoreversible upon changing the wavelength while spatial control in multiple drop arrays is achieved using a photomask (see picture below).


Dynamic photocontrol of the coffee-ring effect with optically-tunable particle stickiness
M. Anyfantakis, D. Baigl*
Angew. Chem. Int. Ed. 2014, in press
 - doi : 10.1002/anie.201406903