Effect of counterion species on colloidal crystal

Synthesis and characterization of novel functional electrosterically stabilized colloidal particles prepared by emulsion polymerization using a strongly ionized amphiphilic diblock copolymer

Amphiphilic diblock copolymers such as poly(styrene)-block-poly(styrene sulfonate) (PS-b-PSS) (Matsuoka, H.; Maeda, S.; Kaewsaiha, P.; Matsumoto, K. Langmuir 2004, 20, 7412), belong to a class of new polymeric surfactants that ionize strongly in aqueous media. We investigated their self-assembly behavior in aqueous solutions and used them as an emulsifier to prepare electrosterically stabilized colloidal particles of different diameters between 70 to 400 nm. We determined the size, size polydispersity, effective charge, total dissociable charge, structural ordering, and phase behavior using light scattering, transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and potentiometric titration. These experiments clearly demonstrated that all of the synthesized particles were nearly monodisperse (polydispersity index<or=6%). The results of DLS and TEM clearly suggested the existence of hairy particles. The form factors obtained by SANS were well described by a polydisperse sphere model. The estimated total number of dissociable charges per particle was found to be larger than 10(4)e, whereas the effective charges per particle were found to be around 1000e. This significant difference suggested the confinement of charges inside the corona regions of the polyelectrolyte brush shell. Finally, these monodisperse particles were found to self-assemble into 3D ordered colloidal crystalline arrays at a low volume fraction (=0.00074) that diffract light in the visible region.

Rupture and regeneration of colloidal crystals as studied by two-dimensional ultra-small-angle X-ray scattering

The structure of colloidal crystals of silica particles in water was studied by using the two-dimensional (2D) ultra-small-angle X-ray scattering (USAXS) technique. By violent shaking of the dispersion, large (body-centered cubic, bcc) crystals were broken into microcrystals while the lattice structure and lattice constant were preserved. The 2D-USAXS profiles revealed that the [111] direction of bcc microcrystals was parallel to the capillary axis and their orientational distribution with respect to the capillary axis was random. While a prepeak was observed in the one-dimensional USAXS measurements, no such peak was detected by the 2D-USAXS technique. The prepeak was concluded to be due to {110} being rotated by 54.7 degrees (the angle between [001] and [111]) from the capillary axis. The diffraction from the plane was out of the horizontal plane and was observed at a lower angle as a prepeak by detector scanning in the horizontal direction.

Synthesis and characterization of charged polystyrene-acrylic acid latex particles

Novel, monodisperse charged colloidal particles of polystyrene cross linked with divinylbenzene and surface-grafted with acrylic acid were synthesized by emulsion polymerization and were characterized by estimating the dissociable surface charge by conductivity titration, the particle effective charge by conductivity verses particle concentration, and the particle size by dynamic light scattering and atomic force microscopy. The structural ordering and dynamics were investigated as a function of the volume fraction of the particles using static and dynamic light scattering, respectively. Furthermore, from the electrophoresis measurements, these particles are found to have a high salt tolerance due to increases in charge as a function of salt concentration.