Effects of Cross-Linking on the Morphology of Structured Latex Particles. 1. Theoretical Considerations

Cross-linking of the seed latex polymer introduces elastic forces into the thermodynamic analysis of the morphology of composite particles. By determining the elastic storage energy necessary to maintain a deformation within the seed latex particle (as in an occlusion of second-stage polymer), it can be combined with the interfacial energies internal to the particle and at its aqueous phase boundary to compute the total free energy of a specific particle morphology. At low levels of cross-linking it is found that the elastic and interfacial energies are of the same order of magnitude, with the final morphology determined by the balance between them. Elastic energies are dependent upon the state of deformation within the particle, and this makes the thermodynamic equilibrium morphology analysis dependent upon cross-link level, seed latex particle size, stage ratio (second polymer/seed polymer), and the interfacial tensions at the polymer/polymer and polymer/water interfaces. Computational results are presented which show the effects of each of these variables on the predicted morphology.