15 December 2014. Published in the 15 Dec issue of Angewandte Chemie, our paper on coffee rings is also illustrated in the inside cover page!
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).
Reference:
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).
Reference:
Dynamic photocontrol of the coffee-ring effect with optically-tunable particle stickiness
M. Anyfantakis, D. Baigl*
Angew. Chem. Int. Ed. 2014, 53, 14077–14081
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