네이처 컨텐츠

Editorials

p.252

doi: 10.1038/462252a

전문

News

p.256

doi: 10.1038/462256a

전문

p.258

doi: 10.1038/462258b

전문

p.263

doi: 10.1038/462263a

전문

p.264

doi: 10.1038/462264a

전문

p.265

doi: 10.1038/462265a

전문

News Features

p.266

doi: 10.1038/462266a

전문

p.270

doi: 10.1038/462270a

전문

p.272

doi: 10.1038/462272a

전문

News & Views

p.291

doi: 10.1038/462291a

전문

p.292

doi: 10.1038/462292a

전문

p.294

doi: 10.1038/462294a

전문

p.295

doi: 10.1038/462295a

전문

p.296

doi: 10.1038/462296a

전문

Guiding light p.297

version="1.0"?> ]>

Nature 462 7271 20091119 2972971 0028-0836 1476-4687 2009Nature Publishing Group 10.1038/462297a Chemical physicsGuiding light AndrewMitchinsonA

With microfluidic devices gaining prominence for many applications in chemistry and biology, the hunt is on to find ways of accurately controlling the motion of liquid droplets. In Angewandte Chemie, Antoine Diguet et al. describe a method for using light to trap and move oil droplets floating on an aqueous solution (A. Diguet et al. Angew. Chem. Int. Edn doi:10.1002/anie.200904868; 2009).

This isn't the first time that light has been used to push droplets around. But Diguet and colleagues take a new approach based on the chromocapillary effect, in which light generates a tension gradient at a liquid–liquid interface. This gradient can induce an interfacial flow between droplets and bulk liquids, which propels the droplet in the opposite direction to the gradient.

The authors' technique depends on the compound dissolved in the bulk liquid. Diguet et al. used a surfactant that isomerizes in response to different wavelengths of light — it adopts a polar isomeric form when illuminated with ultraviolet light, and a less polar form when lit with visible light. The light-induced changes in polarity modulate the surface tension between the surfactant solution and oil droplets floating on its surface. So, when the authors partially illuminated such a droplet with ultraviolet light, the tension gradient caused the droplet to move away from the lit area. If they then partially irradiated the droplet with visible light, the droplet moved towards the lit area.

By combining ultraviolet and visible light, Diguet et al. made a chromocapillary trap that captured oil droplets cast onto the surface of the surfactant solution. The authors could then drag the droplets across the surface of the solution, at speeds of about 300 micrometres per second, simply by moving the trap around. The image above is a montage of superimposed frames from a movie, and shows a droplet (gold colour) being directed by a trap (cyan halo) along a heart-shaped path; the Petri dish is 5.1 centimetres in diameter.

Chromocapillary traps should work for various combinations of immiscible liquids, and could thus be useful for controlling droplets in micro- or millifluidic devices. The authors' system could also be used to safely handle dangerous liquids, or in light-responsive materials.

doi: 10.1038/462297a

전문

p.298

doi: 10.1038/462298a

전문

Articles

Letters

Review Articles