Steve Granick, University of Illinois, USA, and co-workers have developed latex spheres, called Janus spheres, which have a hydrophobic and a hydrophilic side. The dual nature gives the spheres an ability to form unusual structures.

At low concentrations of salt, clusters of only a few spheres form. At higher levels, larger clusters form, eventually self-assembling into chains with a helical structure. Small, kinetically favored isomers fuse, before they equilibrate, into fibrillar triple helices with at most six nearest neighbors per particle.

The team hopes to explore the colloid properties further with a view toward engineering more unnatural structures. Janus particles of differing sizes or shapes could open the door to building other supermolecules and to greater control over their formation.

• Supracolloidal Reaction Kinetics of Janus Spheres
  Q. Chen, J. K. Whitmer, S. Jiang, S. C. Bae, E. Luijten, S. Granick,
  Science 2011, 331(6014), 199-202.
  DOI: 10.1126/science.1197451