Polymer latices as model colloids

Influence of the Counterion Nature on the Stability Sequence of Hydrophobic Latex Particles

The aggregation kinetics of negatively charged polystyrene latex particles in the presence of monovalent electrolytes have been investigated. The inferred coagulation critical concentrations were compared to establish the stability sequence. With the same representative co-ions, this sequence is reversed when using kosmotrope sodium and chaotrope potassium cations. The results have been ascribed to a variable competition of the co-ions toward the hydrophobic surface depending on the lyotropic nature of the associated counterion. They provide new insights into the implication of ionic specificity in the stability behavior of aqueous dispersions of charged colloids.

Colloidal crystal assembly on topologically patterned templates

A variety of methods have been successfully used to produce crystals of colloidal particles made of polymeric (or silica) microspheres. Achieving highly accurate growth and control of the packing symmetry, packing efficiency and packing quality of these crystals is of paramount importance for many applications, for example in photonics. If colloidal crystals are formed in self-assembly processes, it is usually the most densely packed (111) set of planes that terminates the crystal-air interface. However, often exposure of (given) different packing facets is required at the crystal surface. In addition, there is ( in photonics) need for crystals exhibiting lower than the tightest packing, and possessing also lower degrees of packing symmetry. These requirements demand development of various engineering approaches for controlled particle assembly in regular structures. The synthesis of polymer colloidal particles with different sizes, shapes and surface charge density is first briefly outlined. The various interactions and forces that control growth for a broad range of colloidal crystals are subsequently discussed. In the main section of this review we give an account of various template-assisted, graphoepitaxial assembly approaches to produce colloidal crystals with tailored packing structures and controlled crystal orientation with respect to the topologically patterned substrates used to direct the assembly process. In the outlook we also describe various selected emerging approaches, which have the potential to produce crystals with low degree of packing symmetries, for example using direct one-to-one colloidal particle assembly.

The cleaning of polymer colloids

The current state of knowledge of the cleaning of polymer colloids is reviewed with regard to a wide range of cleaning and characterisation techniques. The type, level and quantity of impurities involved with different polymer latex formulations varies widely. Even for similar formulations, differences in the nature and number of functional groups reported are often a consequence of sometimes subtle differences in the cleaning procedures employed. Not only may surface functionality be affected but also monomer and oligomer extraction procedures may lead to morphological changes in the particles. No single technique alone is likely to be able to remove all impurities. Care is needed to avoid the introduction of new impurities from the equipment, materials and water used as well as possible contamination from atmospheric carbon dioxide, bacteria and fungi. These factors also need to be considered in the storage of latex particle standards.

A new method to isolate polyalkylcyanoacrylate nanoparticle preparations

A simple method for the separation of polyalkylcyanoacrylate nanoparticles was developed using polyisohexylcyanoacrylate (PIHCA) as a model. Fluorescein isothiocyanate dextran 70 was used to label the nanoparticles. Ultracentrifugation onto a performed sucrose gradient allowed the easy elimination of the dextran and of the free molecules remaining in the upper phase. After such treatment, the physicochemical characteristics of the PIHCA nanoparticles were not modified. This method could be usefully extended to other types of nanoparticles.