Spherical and rod-like colloids with polymer-brush surfaces

Abstract

In this paper, we describe a strategy to overcome incompatibility of colloidal particles and polymer coils as well as immiscibility of spherical and rod-shaped nanoparticles. Two new types of model colloids are presented, colloidal nanospheres with hairy surfaces (spherical brushes) and polymacromonomers to represent cylindrical brushes. The spherical brushes are synthesized from polyorganosiloxane-μ-gels of diameter 20 nm by grafting onto anionically prepared polystyrene macromonomers of molecular weight M w=5000 g/mol. On average, each sphere has a surface layer of 200 polymer chains. Compatibility of spherical nanoparticles with polymer coils was probed by turbidity of as-cast films as well as electron microscopy and atomic force microscopy. In contrast to their precursors without hairy surfaces, the spherical brushes are compatible with polymer coils of low molecular weight (M=4000 g/mol) upto very high concentrations. The cylindrical brushes are synthesized by radical polymerization of polystyrene-methylmethacrylate macromonomers of molecular weight M w=4000 g/mol. The product shows a high polydispersity in length of the PMMA-backbone. By applying continuous polymer fractionation (CPF) we were able to reduce length polydispersity of the cylindrical particles from above 4.0 to smaller than 1.5. Analogous to spherical brushes, these cylinders are also compatible with low molecular weight polymer coils. Further, we have prepared transparent films containing mixtures of spherical and cylindrical brushes in a matrix of low molecular weight polystyrene upto high particle concentrations.