Fabrication of Model Colloidal Systems With Tunable Optical Properties for Self-Assembly Studies

We synthesize new types of micrometer-scale particles with engineered scattering properties. These particles are composed of small fluorescent polystyrene cores and large crosslinked poly(N-isopropylacrylamide) (polyNIPAM) shells. Immersed in water at ambient temperature, the shell of these particles is swollen and nearly index-matched to the surrounding fluid. In this state light scattering is dominated by the small polystyrene core, thereby eliminating multiple scattering from the suspension while still allowing the particles to be visualized under the optical microscope. Raising the temperature to similar to 35 degrees C leads to a decrease of the thermosensitive shell volume and an increase in scattering. We present some preliminary studies oil the self-assembly of these colloids as characterized by confocal microscopy. These index-matched, aqueous particles might be used as tracers in microrheology experiments or as model colloids for real-space studies of phase behavior.