Janus and Multiblock Colloids

This talk surveys emerging areas opened up by the directional interactions presented by the specially-designed spheres known as Janus. The ``diblock'' motif, mutually attractive on one domain and repulsive on another, makes this a prototypical system for elucidating, on a mechanistic level, how concepts of chemical reaction kinetics explain the development of stable and highly ordered nonequilibrium structures. With the ``triblock'' motif, spheres that attract one another on two polar regions but repel at the middle band, we go beyond this to demonstrate the self-assembly of a useful low-density lattice of spheres, the colloidal Kagome lattice, and visualize its aqueous assembly dynamics on the single-particle level. A newer area of opportunity is ``dynamic self-assembly,'' in which energy fed into the system as a control variable generates big surprises. The generalization of these design rules will be discussed.