LIGHT-SCATTERING IN THE COURSE OF A POLYMERIZATION-INDUCED PHASE-SEPARATION BY A NUCLEATION GROWTH-MECHANISM

Polymerization-induced phase separation was described using a phase tr ansformation diagram in conversion vs composition coordinates;, where metastable and unstable regions were located. Phase separation through a nucleation-growth (NG) mechanism, in the metastable region of the p hase diagram, was described with the usual constitutive equations. A d istribution of particle sizes was generated as a function of conversio n. Different possible composition profiles inside and outside the part icles were predicted, leading to refractive index profiles associated with individual particles. Representative sets of particles were prope rly located in the scattering volume, and the Light scattering pattern of the ensemble was generated. A maximum at a wave vector q not equal 0 was present in the following cases: (a) at low concentrations of di spersed-phase particles when a depletion layer surrounded the particle s and (b) at high concentrations of dispersed-phase particles due to t he correlation produced by the location of individual scatterers in a constrained space. Both effects generated a maximum in the scattered i ntensity at q not equal 0, even for broad particle-size distributions. The position of q(max) increased with the concentration of dispersed- phase particles. For systems that do not exhibit coarsening effects, t he light scattering peak will initially shift to the right and then gr ow in intensity at a constant value of the wave vector, when nucleatio n becomes negligible. Coarsening produces a shift of the scattering pe ak to the left, while increasing its intensity. Therefore, the presenc e of a maximum in the light scattering pattern should no longer be ind icated as the hallmark of Spinodal demixing, as is frequently stated i n the literature.