Accession Number : ADA329669

Title :   Fundamental Issues in the Coalescence-Based Processing of Polymer Powders and Colloids

Descriptive Note : Final rept. 1 Oct 95-30 Sep 96

Corporate Author : DU PONT DE NEMOURS (E I) AND CO WILMINGTON DE

Personal Author(s) : Argento, Claudio ; Jagota, Anand ; Mazur, Stephen

PDF Url : ADA329669

Report Date : 26 NOV 1996

Pagination or Media Count : 207

Abstract : 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 Derjaguin's 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.

Descriptors :   *POLYMERS, *POWDERS, *COALESCENCE, *COLLOIDS, THERMOMECHANICS, SIMULATION, PARTICLE SIZE, FINITE ELEMENT ANALYSIS, VISCOELASTICITY, ELASTIC PROPERTIES, STRAIN(MECHANICS), SURFACE PROPERTIES, TRACTION, RHEOLOGY, SINTERING.

Subject Categories : Polymer Chemistry
      Fabrication Metallurgy
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE