Ab initio study of the interaction of polyoxymethylene with polyoxymethylene, ammonium perchlorate, and the aluminum (100) surface

Self-consistent restricted and unrestricted Hartree-Fock calculations have been performed for the microscopic interactions in particle-filled polymeric suspensions. First, we have investigated the elongation and the torsion potential of a single infinite polyoxymethylene chain. It is found that the 9/5 helix is 4.5 kcal/mol lower in energy than the planar zigzag conformation. A Youngs modulus of 8020 GPa is obtained for the chain-direction deformation. The potential-energy curve for the van der Waals interaction between two 2/1 helical polyoxymethylene chains has a minimum for a chain separation of 4.3 A with a binding energy of 1.3 kcal per (CH2O)2 translational unit. For the chain-direction slip of two polyoxymethylene chains a barrier of 5.1 kcal is calculated. To study polymer-particle interactions, cluster calculations for the interaction of polyoxymethylene fragments with ammonium perchlorate and the aluminum (100) surface have been performed. The oxygen in the polyoxymethylene backbone forms a hydrogen bond with ammonium perchlorate. For an O-H distance of 1.62 A a binding energy of 23.7 kcal is obtained. This strong coordination of the ammonium ion with the oxygen in the polyether backbone is in agreement with the experimentally observed increase in viscosity of polyether lacquers upon dissolution of ammonium perchlorate. The potential energy curve for the bonding of a H3C-O-CH2-O-CH2-O-CH3 fragment at the on-top sites of an Al5 cluster has a minimum for an O-Al separation of 2.3 A with a binding energy of 17.1 kcal (8.55 kcal per O-Al bonding). This binding energy is of the same order of magnitude as the energy of 4.5 kcal per CH2O unit needed to stretch the polyoxymethylene 9/5 helix to a helix whose next-nearest oxygen atoms are commensurate with the aluminum lattice constant of 4.05 A. Therefore the coating of aluminum particles with polyoxymethylene polymers is possible. The quantum-mechanical results of these microscopic static-model studies provide an estimate for polymer-particle forces needed for a macroscopic dynamic model of particle-filled polymeric suspensions. © 1988 The American Physical Society

Stokesian dynamics simulation of polyether-coated particles in a shear flow

The development of a Lennard-Jones-type polymer-polymer interaction model is described, appropriate for monolayer polymer coatings on spherical solid particles suspended in a polymer fluid. This model is appropriate for polymer-coated particles interacting at very close proximity (angstroms). These molecular forces, derived from ab initio calculations for polyoxymethylene- polyoxymethylene interactions are added to the hydrodynamic forces of a Stokesian dynamics simulation in order to estimate the effect of a polymer coating on the behavior of suspended particles under sheared conditions. The relation between suspension microstructure, shear velocity, and their time evolution are studied in molecular-dynamics-like simulations. © 1990 The American Physical Society

Stokesian dynamics simulations in the presence of van der Waals forces

The development of a Lennard - Jones polymer - polymer interaction model is described, appropriate for monolayer polymer coatings on spherical solid particles suspended in a polymer fluid. This model is appropriate for polymer - coated particles interacting at very close proximity (Angstroms). The Lennard - Jones potential, determined from ab initio calculations for polyoxymethylene - polyoxymethylene interactions is added to a Stokesian Dynamics computational model in order to estimate the effect of a polymer coating on the behavior of suspended particles under sheared conditions. The relation between suspension microstructure, viscosity and their time evolution are studied in molecular dynamics - like simulations. © 1990