Fundamental Issues in the Coalescence-Based Processing of Polymer Powders and Colloids
Final rept. 1 Oct 95-30 Sep 96
DU PONT DE NEMOURS (E I) AND CO WILMINGTON DE
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The processing of polymer colloids occurs under the influence of internal surface forces and externally applied tractions. Internal surface forces result from molecular volume-to-volume and surface interactions. A formulation for the computation of surface tractions resulting from these interactions has been developed. It generalizes and replaces Derjaguins approximation and consistently combines curvature-based and direct van der Waals contributions. In this formulation the influence of a body on any other is described by a second order inter-surface stress tensor. Its properties and physical significance have been explored. The formulation is general and applicable to many other phenomena where surfaces forces play an important role. It has been implemented as a surface finite element which allows its use in numerical simulations of deformation. Detailed finite element simulations of viscoelastic coalescence driven by surface forces have been conducted. They confirm the experimentally observed importance of viscoelastic rheology for coalescence of polymers. The consistent treatment of surface forces has exposed and resolved inconsistencies in the current understanding of elastic adhesion and viscous sintering. Finite element simulations of deformation of soft colloidal particles under DLVO forces have also been conducted. It is found that under suitable conditions, due to large contact deformation, during drying particles can continue to be separated by a liquid film. Experimental investigation on well-characterized particles over a range of particle size have established that coalescence of soft colloids is primarily by recoverable elastic deformation, in agreement with theoretical predictions.
- Polymer Chemistry
- Fabrication Metallurgy