  Microgels are soft colloidal particles that, when dispersed in a solvent,
swell and deswell in response to changes in environmental conditions, such as
temperature, concentration, and $p$H. Using Monte Carlo simulation, we model
bulk suspensions of microgels that interact via Hertzian elastic interparticle
forces and can expand or contract via trial moves that allow particles to
change size in accordance with the Flory-Rehner free energy of cross-linked
polymer gels. We monitor the influence of particle compressibility, size
fluctuations, and concentration on bulk structural and thermal properties by
computing particle swelling ratios, radial distribution functions, static
structure factors, osmotic pressures, and freezing densities. For microgels in
the nanoscale size range, particle compressibility and associated size
fluctuations suppress crystallization, shifting the freezing transition to a
higher density than for the hard-sphere fluid. As densities increase beyond
close packing, microgels progressively deswell, while their intrinsic size
distribution grows increasingly polydisperse.
