We show that homogeneous polymer blend microparticles can be prepared in si
tu from droplets of dilute solution of codissolved polymers. Provided that
the droplet of solution is small enough (<10 mu m), solvent evaporation is
rapid enough to inhibit phase separation. Thus the polymers that are being
mixed need not be miscible, which greatly enhances the applicability of the
technique. From analysis of two-dimensional Fraunhofer diffraction (angula
r scattering) patterns, we show that both the real and the imaginary parts
of the refractive index can be tuned by adjustment of the relative weight f
ractions of polymers in solution. (C) 1999 Optical Society of America.