(398a) Coalescence Dynamics in Composites and Cross-Linked Polyesters

Dynamics of sintering and coalescence of particles has application in a variety of industrial processes varying from rotational molding to digital printing.  For instance digital printing requires toner particles microns and nanometer aggregates to fuse under pressure and temperature with adequate viscosity and elasticity. Molecular dynamics and Finite Element Method have been used to model sintering of particles. Analysis of Molecular Dynamics shows that diffusion processes dominate the coalescence of particles especially nano-particles.  For unequal size particles, coalescence processes became faster when the ratio of two particle sizes (smaller/larger) approaches to zero. The Koch–Friedlander (KF) analysis predicts the coalescence time of two unequal sized particles when benchmarked against the MD simulation, and the characteristic coalescence times is independent of the volume ratio of the coalescing partners. In Finite Element Method (FEM) modeling, cohesive interaction takes place between particles with initial configuration consisting of several hundred particles.  Average aggregate projected area scale with equivalent number of constituent primary particles during sintering: from fractal-like agglomerates to aggregates and eventually compact particles. The driving force for sintering is a minimization of the free energy resulting in a reduction of surface area. The energy gained by surface reduction is dissipated by viscous flow, which sets the time scale for sintering. Composites and cross-linked polyesters made by extrusion were characterized for dynamic viscoelastic spectra comparing with an Upper Convected Maxwell Model for sintering.