Mechanism of Hybrid Particle Formation

Based on the results of supplementary investigations (see Section 6.5.4) that were carried out to better understand the mechanism of hybrid particle formation and to determine particle morphology, the following observations can be made  

It is also interesting to note that during the feeding of the monomers, the zeta potential becomes less negative which indicates that the uniformity and stability of the whole system is diminishing. 

Investigations of swelling of DPUR particles with monomers indicate that although all monomer being fed into the system may theoretically enter DPUR particles, since the maximum degree of swelling is more than twice that of the monomer/ DPUR solids w/w ratio used commercially in synthesis of hybrid dispersions, in practice there will always be a natural tendency of the system to reach equilibrium between monomer droplets, non-swollen DPUR particles and swollen DPUR particles. Therefore, when hybrid dispersions are prepared according to method la, lb or 2 (see Section 6.3.2) the result will always be a mixture of particles of hybrid structure with DPUR and ASD particles, as has been explained in Section 6.3.2.1). 

This kind of structure is undoubtedly very interesting since it is a nanostructure where nanospheres of acrylic/styrene polymer are embedded in a polyurethane-urea matrix. Such a structure suggests that very specific properties of the film could be obtained if the components of the hybrid were especially selected. 

In this study, aqueous hybrid polyurethane-urea-acrylic/styrene polymer dispersions were obtained using four different methods. The dispersions are stable and their viscosity, and pH as well as average particle size and particle size distribution are similar to those observed for DPUR. Most of the hybrid dispersions formed transparent films of good mechanical properties, water resistance and organic solvent resistance. 

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The supplementary experiments, and especially investigations of the process of swelling of dispersion particles with monomers and film surface free energy determinations, allowed confirmation of the assumed mechanism of hybrid particle formation. 

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