Experimental studies of low-density fluid phases in tunable dipolar colloids

Experiments of low-density colloidal fluid phases in the presence of an external electric field are presented. We obtain angular order parameters as a function of the applied electric field. When plotted against a dimensionless dipolar strength parameter, the order parameters for different particle sizes fall on a single curve, suggesting that colloids in a fluid phase in the presence of electric fields do indeed interact by an effective point dipolar interaction. We then explore the statistics of particle packings at low-density and extract the experimental compressibilities and equation of state for these dipolar colloids.