A process model for latex film formation: Limiting regimes for individual driving forces

The deformation of particles, to produce a structure without voids, has bee n an issue of contention in the film formation community for many years. Fo ur different mechanisms have been proposed. Three involve homogeneous defor mation throughout the film, although all are built on the deformation of tw o isolated particles, described in the viscous limit by Frenkel and in the elastic limit by Hertz and Johnson, Kendall, and Roberts. We derive a linea r viscoelastic generalization of Frenkel's model that predicts the deformat ion of two spheres compressed by a force, F, and surface tension, gamma. Th e resulting Equation is then embedded in field equations governing the coll apse of macroscopic films. Assuming a uniaxial compression allows derivatio n of limits for the proposed modes of homogeneous deformation. These limits are shown as surfaces in parameter space. Since temperature alters most pr ofoundly the rheological response of viscoelastic polymers, the controlling deformation mechanism is defined as a Function of temperature. Wet sinteri ng requires slow evaporation or a low modulus polymer and is seen at high t emperatures. Capillary deformation requires the strain in the film to follo w evaporation and appears at intermediate temperatures. Dry or moist sinter ing is then seen at the lowest temperatures, when the modulus is high and d eformation is slow compared to evaporation.