Percolating Behavior of Solid Bimodal (Polymethylmethacrylate + Inert) Particle Packings during Polymerization
A percolation-based thermodynamical model was able to predict the break-down of bimodal PMMA + I solid particle packings (P-MMA, polymethylmethacrylate; I, solid phase inert to MMA polymerization) due to the polymerization process of the MMA monomers. By slip casting of biphasic PMMA + I aqueous suspensions, homogeneous samples of polymethylmethacrylate and various inert solid aggregates (I = Ca3(PO4)2, ZrO2, Si3N4, and Al2O3) were prepared and embedded in liquid methylmethacrylate to start the kinetics of the network formation. For any I component, breakdown of samples did not occur in well defined PMMA mass concentration ranges, which were strongly related to the signs of PMMA and I surface charges (i.e., isoelectric points) of the aqueous solid monodispersed systems. As application of percolation theory in composite materials suggest, when the samples resisted the polymerization kinetics the occurrence of a percolative behavior was expected. Accordingly, the model was performed by dealing thermodynamically with the physicochemical features of the starting aqueous suspensions (e.g., adsorption from solution at the solid/liquid interface and solid agglomeration) at the percolation threshold in bicontinuous PMMA + I systems during the progress in the polymerization reaction. Thresholds have been regarded as percolation of cubic units and related to the sign of the solid PMMA and I surface charge in aqueous monodispersed systems, namely, to the attractive, neutral, repulsive character of the electrostatic interparticle forces. Once site percolation thresholds were correctly estimated it was shown that the assumption of percolation is compatible with the theoretical model when the solid PMMA mass concentration values are ranging just in the critical ranges experimentally obtained. Copyright 1997 Academic Press. Copyright 1997Academic Press
Mezzasalma
SA
Materials Science and Engineering Institute, University of Genoa, C.so Perrone 24A, Genoa, 16161, Italy