  Colloidal particles, amphiphiles, and functionalized nanoparticles are
examples of systems that frequently exhibit short-range attractions coupled
with long-range repulsions. In this work, we observe striking differences in
the dynamics of self-assembled clusters that form in a simple isotropic model
of such systems when the strength of attraction is varied. We find that while
attraction-dominated particles self-assemble into compact clusters with
properties similar to micelles formed by amphiphilic molecules,
repulsion-dominated particles self-assemble into open clusters which have much
shorter life-times. There is also a significantly different dependence of the
solution osmotic pressure versus composition: formation of compact clusters
causes a decrease in the pressure vs. density slope, while formation of open
clusters does not effect the pressure. This thermodynamic quantity turns out to
be much more sensitive in picking out different clustering characteristics than
the overall aggregation curves or cluster shapes. Our results have significant
implications in developing design principles for stable cluster self-assembly
and detection in both laboratory settings and in computer simulations.
