| It is well known that densely cross-linked, brittle epoxy materials may be toughened with elastomeric or thermoplastic modifiers. In an effort to gain a deeper understanding of how the modifier concentration and the curing temperature affect resultant morphologies, differential scanning calorimetry, time-resolved small-angle light scattering, and optical microscopy have been employed to investigate the polymerization-induced phase separation dynamics of diglycidyl ether of bisphenol-A (DGEBA)/polyetherimide (PEI) mixtures cured with 4,4'-diaminodiphenyl sulfone (DDS). PEI concentration may alter the mechanism by which phase separation occurs explained by the temporal evolution of the phase diagram with epoxy-amine conversion. In addition, the relatively high glass transition temperature of PEI played an important role in the observed reaction kinetics and phase separation rates.; In a variation of this technique, unusual phase separation dynamics characterized by phase separation, dissolution, and secondary segregation have been witnessed in a system where both the epoxy and the modifier are reactive to promote interfacial adhesion between the phases. To elucidate the underlying physics of this phenomenon, reaction-diffusion equations coupled with a total free energy functional have been numerically solved in two dimensions. The observed behavior is described as a competition between the tendency towards separation as the entropy of mixing decreases with increasing polymerizations and the cross-reaction between the two species, which drives the mixture towards homogeneity.; Similar equations have been computationally solved in three dimensions to gain information regarding the formation of holographic polymer-dispersed liquid crystalline materials (H-PDLC's), where geometrically arranged beams of light selectively polymerize a mixture containing photo-sensitive monomer and inert nematic liquid crystal through destructive and constructive interference. This modeling technique has revealed information concerning optimal LC concentration and beam intensity, as well as the realization that elastic polymers over traditionally utilized acrylates may afford crystal structures with less point defects.; Lastly, observations of phase-inversions in polymer solutions where the minority constituent forms the continuous phase during separation have been theoretically investigated through the application of a two-fluid model incorporating viscoelastic contributions. The observance of transient network-like structures has been attributed to the dynamic asymmetry in properties between the polymer and solvent. |
