Synthesis of non-aqueous fluorescent hard-sphere polymer colloids

We describe the synthesis of fluorescent colloidal polymer spheres which when suspended in non-aqueous solvents behave as classical hard spheres. Monodisperse poly(methyl methacrylate) particles with sizes varying between 200 and 600 nm have been prepared by dispersion copolymerisation of methyl methylacrylate, methacrylic acid and the fluorescent monomer, 7-nitrobenzo-2-oxa-1,3-diazole-methyl methacrylate. Increasing the concentration of dyed particles in suspension resulted in the rapid nucleation and growth of colloidal crystals. Measurement of the equilibrium phase behaviour confirmed that the potential between dyed particles was close to hard-sphere. The resulting polymer colloids provide an ideal model system for the study of colloidal phenomena using fluorescent confocal microscopy.