Janus Colloids
Alejandro Wolosiuk, Postdoctoral Fellow (2002-2006)
(Ms. Science (Chemistry) University of Buenos Aires, Argentina (1997)
PhD in Chemistry University of Buenos Aires, Argentina (2002).
Previous work on the self assembly of high symmetry objects such as spheres has shown the formation of simple crystal like structures as hexagonal or cubic closed packing. Therefore, creating building blocks with broken symmetry such as "Janus particles"1 or even with a surface pattern can induce novel superstructures. For instance, the possibility of introducing functional groups with an sp3 valence on the surface of a nanosphere will result in tetravalent colloids. Moreover, these particles can be reacted to form a tetravalent colloidal crystal with a diamond lattice structure which is predicted to have a large photonic band gap.
Pattern templating or selective chemical modification of big flat surfaces it is well known. On the other hand, it is evident that to scale the same processes to the surface of a small particle new approaches must be taken into account. In particular the use of ordered media (e.g. liquid crystal and nanoreactors) and partition between interfaces (e.g. emulsions and dispersions) are relevant to the controlled deposition of molecules and macromolecules on small curved surfaces.
My research is focused on the selective spatial decoration of colloids with smaller nanoparticles or molecules. Controlling the pattern imprinted on the colloids allows to manipulate the interaction between particles and therefore, to direct the self assembly process. Besides, this results in the formation of micron sized objects with connectivity similar to those found for molecules. In this context, we are investigating different driving forces like diffusion and electric fields in ordered media for accomplishing the colloid modification.
1. in Roman religion, god of beginnings. Janus was usually represented with two bearded heads placed back to back so that he might look in two directions at the same time.
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Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign