Polyorganosiloxane-microgels as probes for forced Rayleigh scattering

Abstract

We describe the synthesis of microgel spheres of 10 nm radius which are suitable as probes to study diffusion by forced Rayleigh scattering (FRS), a holographic grating technique. Those particles are obtained by a copolycondensation in microemulsion. The main advantage of organosiloxanes compared to purely organic monomers as styrene or methacrylate is the simple chemical functionalization of the particles. A rich choice of silane monomers which may be copolycondensated with the standard monomer trimethoxymethylsilane are commercially available. One of those, chlorobenzyltrimethoxysilane, is used as a coupling agent to attach the photoreactive dye orthonitrostilbene (ONS) to the microgel spheres. All samples are characterized by light scattering, GPC and electron microscopy. In addition, we determined the content of photoreactive dye chemically attached to the spherical particles by UV/visible absorption-spectroscopy. Our nano-particles are redispersible in organic solvents such as toluene or THF up to weight fractions as high as 50 wt%. To prove applicability of the particles as FRS probes we show some preliminary results obtained from FRS measurements of highly concentrated toluene solutions (particle concentration 45–50 wt%).