Particle/polymer stoichiometry

Since this process depends on the stoichiometry of the reactants, sufficient amounts of EDA must be present to produce fully solidified polymer particles. Incomplete reactions yielded a polyurethane shell, which on the removal of unreacted liquid in the core by evaporation resulted in hollow particles (68). It would appear that the solid encapsulating polymer inhibits the diffusion of EDA into the rest of the original droplet. 

Figure 7. Solution diagrams for spheres with adsorbed polymer. Left for oxide particles In water the triangular region marked gel" Is a single phase which separates from the solvent (upper part of the flocculation region, above the o.f.c.) or from a dispersion of excess spheres (below the o.f.c.). The boundary between stabilization and flocculation corresponds to the saturation of the surfaces with polymer. Right for surfactant micelles, all these boundaries are replaced by a stoichiometry which divides a region containing necklaces only from a region containing necklaces plus excess micelles (no phase separation).

Thereafter as the particles increase in size, their stoichiometry more closely approaches that for a sphere, as postulated. Thus above a degree of polymerization of 500 (particle size as anhydrous SiO, of 3.5 nm), the composition of the polymer is very close to that calculated for a spherical particle. 

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