Simultaneous Monte Carlo Determination of Particle Size Distribution and Pair-Correlation Function of Spherical Colloids from a Diffraction Experiment

A new simulation method was developed in which both positions and radii of the particles are treated as variables in a reverse Monte Carlo-like procedure. The new method can be used in the evaluation of diffraction data on one-component spherical colloids, where the polydisperse feature of the particles cannot be neglected. It reproduces the target function the measured scattered intensities well, without the a priori knowledge of the parameters of a supposed Schulz distribution of the particle size. The method is successful at a wide range of densities, but it fails at very dense systems and at broad distribution of particle size. Small-angle neutron and light-scattering data on spherical polystyrene colloids were evaluated by the new method and compared to data evaluated using the monodisperse assumption, where contact pairs were observed. A good reproduction of experimental data was achieved and no contact pairs were found in agreement with theoretical and other experimental results.