Polystyrene beads represent one of the most used polymer colloids (latex) and several studies have been performed to control the bead size and monodispersity since the thirties of the previous century. The water—styrene emulsion has been extensively studied over the past 30 years for various ap¬plications in material science, chemistry, and biology [1-8]. New methodologies for synthesizing polystyrene beads are stili relevant because they provide accessible chemical meth¬ods to obtain micrometer-sized particles with a given shape and size and a monodispersity even less than 2%. Indeed, the spherical shape allows the self-assembly of such beads into crystalline arrays, with lattice periodicities comparable to their diameters [1,9,10]. Such arrays also function as re-movable templates for the fabrication of three-dimensionally ordered porous materials and find fascinating applications in the field of photonic band gap materials  as found in the abundant literature in this area. Surface bead modification (e.g., dye doping) or lattice infiltration with active dopant have been used  to control the photonic band gap by combining the bead lattice periodicity with dye properties (e.g., wavelength-sensitive refractive index).
The early procedures adopted for the reaction involved the addition of a surfactant that helps the “compartmental-ization” of styrene in water. However, since the surfactants
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could contaminate the surface of the bead, a soapless reac-tion was proposed in 1965.
Several different mechanisms have been proposed for such emulsion polymerization in water without the use of a surface-active agent. These studies [2-6,13-15] are con-cerned primarily with particle formation and growth. Three basic mechanisms have been suggested: (i) homogeneous nucleation, (ii) homogeneous—coagulative mechanisms, and (iii) in situ micellization. These proposed mechanisms for bead synthesis essentially consider three reaction stages [3¬6,13-15]. The first step concerns charged oligomer forma-tion from initiator decomposition and subsequent “precursor nucleus” formation depending on the degree of polymeriza¬tion. The colloidal suspension of such precursor nuclei is unstable and the nuclei coagulate into a stable suspension of “mature nuclei.” The second stage of the reaction involves growth by polymerization of monomer on each monomer¬swelled mature nucleus [2,13-15]. The third stage is the termination of the reaction associated with the depletion of monomer. The studies reported in the literature have mainly concerned nucleus formation and growth. The observed de¬pendency of the nucleus size, and hence the nucleus concen¬tration, on synthesis parameters is described in the literature [2-6], but there are no simple models for the prediction and control of bead size and concentration in latex suspension. In this communication we propose a generai model, indepen¬dent of any polymerization mechanism, to predict the bead diameter and to provide experimental parameters to control the concentration of latex particles. This model is supported by experimental data.
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