We present the crystallization kinetics for two polydisperse hard-sphere particle stocks with differing particle size distributions. One of the latexes had a relatively symmetrical distribution, the other had a more polydisperse distribution, which was highly skewed to smaller sizes. The emerging Bragg reflections from the crystallizing samples were measured using a technique that provides improved statistical averaging over our previous methods. It was observed that, for the more polydisperse particles, the onset of nucleation was delayed by up to an order of magnitude in reduced time, and displayed qualitatively different growth behavior compared to the particles with the more symmetric size distribution. Based on these measurements and time lapse photographs, we propose a growth mechanism whereby crystallization occurs in conjunction with a local fractionation process near the crystal-fluid interface, which significantly alters the kinetics of crystallite nucleation and growth. This fractionation effect becomes more significant as polydispersity or skewness increases.

By combining optical tweezers with polarization microscopy, the hydrodynamic coupling between position and orientation fluctuations in a pair of colloidal spheres has been measured. Imaging of birefringent particles under crossed polarizers allows for the simultaneous determination of the positions and orientations of both particles. The temporal cross-correlation function between random displacements of one particle and orientation fluctuations of its neighbor allows for the quantification of the hydrodynamic rotation-translation coupling between the spheres. Our results are in good agreement with predictions for the hydrodynamic mobility tensors calculated in the creeping-flow limit of the Navier-Stokes equation.

We have developed a method to convert 10 different LC acrylate monomers into colloids by dispersion polymerization. This yields nine different types of anisotropic colloids with nematic and different smectic phases. The diameter of these colloids mostly varied between 0.5 and 3.5 µm; it can be adjusted by variation of the solvent mixture and it can be systematically increased by seed polymerization. The polydispersity of the anisotropic colloids is thereby often below 10%. Polarizing microscopy shows that colloids of a size between about 2 to 4 µm appear to have a bipolar director configuration. Smaller colloids appear uniaxially oriented, the resolution does, however, not allow a more refined investigation of the director pattern. These anisotropic spheres (diameter between 0.7 and 3.7 µm) can be trapped with an optical tweezers. Circularly polarized light transfers a torque to the particles, enabling one to rotate them clockwise and anticlockwise, which makes these spheres attractive as actuators. The size dependence of their rotational frequency makes it additionally possible to determine changes of the director configuration with size. For a nematic colloid (P 6), it could be shown that the anisotropy stays constant from 1.6 to 3.4 µm.

We demonstrate a simple method for the accurate characterization of the particle size distributions of colloidal particles with small polydispersities using a combination of dynamic light scattering and static light scattering. This method takes advantage of the variation in apparent radius observed using dynamic light scattering, as the scattering angle is increased through minima in the intensity form factor. Two-colour dynamic light scattering is used to ensure there are no contributions from multiple scattering. We demonstrate that the polymethylmethacrylate based particles used here have negatively skewed particle size distributions, and in many cases can be characterized by a two parameter Weibull distribution. The importance of the accurate characterization of the particle size distribution for studies of crystallization in hard sphere colloidal suspensions is discussed.

In this paper we present measurements of the crystallization kinetics of binary mixtures of two different sized hard sphere particles. The growth of the Bragg reflections over time were analyzed to yield the crystallite scattering vector, the total amount of crystal, and the average linear crystal size. It was observed that a particle size distribution skewed to higher sized particles has a less detrimental effect on the crystal structure than a skew to smaller sized particles. In the latter case we observe that initial crystallite growth occurs at only a small number of sites, with further crystallization sites developing at later times. Based on these measurements we elaborate further on the previously proposed growth mechanism whereby crystallization occurs in conjunction with a local fractionation process in the fluid, which significantly affects the kinetic growth of crystallites in polydisperse systems.