Composite micro- and nanoscale particles were precipitated from rapidly expanding, multiple-component supercritical solutions. A monomer-monomer system consisting of 2,5-distyrylpyrazine (DSP) and diethyl p-phenylenediacrylate (EPA) and a monomer-polymer system consisting of DSP and a fluorinated polyacrylate (FAA) were precipitated from supercritical chlorodifluoromethane (F22). The product morphology was investigated at several different operating conditions (concentration, nozzle temperature and pressure). Single-component (binary system) phase behavior measurements were performed and compared to that of the monomer-monomer-solvent and monomer-polymer-solvent ternary systems. The resulting particle morphology was investigated using atomic force microscope (AFM), scanning electron microscope (SEM) and optical microscopy. It was determined that the microstructure of the composite precipitates depends strongly on the processing conditions and can range from segregated materials to encapsulated particles. (c) 2005 Elsevier B.V. All rights reserved.