Phase behavior and crystallization kinetics of PHSA-coated PMMA colloids

Polymethylmethacrylate (PMMA) colloids sterically stabilized by a layer of chemically grafted poly-12-hydroxystearic (PHSA) are widely used in experiments as model hard spheres. However, due to the coating, the interaction between particles is slightly soft. Here we report a numerical study of the effect of the PHSA coating on the phase behavior and crystallization kinetics of PMMA colloids based on parameters determined from surface-force measurements on PHSA-PMMA-coated mica surfaces [B. A. de L. Costello and P. F. Luckham, J. Colloid Interface Sci. 156, 72 (1993); B. A. de L. Costello et al., Langmuir 8, 464 (1992)]. We find that the core volume fraction of particles at freezing measured by Pusey and van Megen [Nature 320, 340 (1986)] can only be reproduced by using a thickness of the PHSA layer that is considerably larger than literature values. This may indicate that the particles are in fact slightly charged. Compared to perfect hard spheres, the crystallization rate in these slightly soft particles was found to be increased by about two orders of magnitudes.