  We simulate structural phase behavior of polymer-grafted colloidal particles
by molecular Monte Carlo technique. Interparticle potential, which has a finite
repulsive square-step outside a rigid core of the colloid, was previously
confirmed via numerical self-consistent field calculation. This model potential
is purely repulsive. We simulate these model colloids in the canonical ensemble
in 2 dimensions and find that these particles containing no interparticle
attraction self-assemble and align in a string-like assembly, at low
temperature and high density. This string-like colloidal assembly is related to
percolation phenomena. Analyzing the cluster size distribution and the average
string length, we build phase diagrams and discover that the average string
length diverges around the region where the melting transition line and the
percolation transition line cross. This result is similar to Ising spin
systems, in which the percolation transition line and the order-disorder line
meet at a critical point.
