Speaker
Description
Macromolecules in polymeric liquids (polymer melts, solutions, foams and gels, polymer liquid crystals) are usually distributed randomly, but under large external loads, deformations and high temperatures they can change shapes and orientations. The oriented macromolecules can move with a high degree of friction anisotropy. How to determine anisotropic friction forces and moments acting on the macromolecules? In this contribution, making several assumptions, models of anisotropic internal friction in polymeric liquids are proposed in continuous and discretized forms. This follows from common approaches to systems of the oriented polymeric macromolecules on the microscopic scale. They are studied as continuum media or as assemblies of discrete models of individual macromolecules. The first approach - Langevin motion equations describe Brownian random movements of polymer macromolecules in stochastic dynamics. The Langevin equations have anisotropic viscous friction terms and stochastic noise terms. The proposed friction models include translational and rotational anisotropic viscous friction and various types of friction anisotropy. The anisotropic viscous friction is studied in the frame of continuum modelling. The second approach - the macromolecule systems are modelled as assemblies of a large number of isolated microscopic elements. Taking into account the single macromolecule the following problems are analysed: various discrete models of the macromolecules, different forms of their kinematics, and a presence of anisotropic dry friction in contact with a hypothetical base plane. Anisotropic dry friction forces and moments are investigated in the cases as follows: sliding of bead-like macromolecules (i.e. spheres connected by springs), rolling without or with slipping of rod-like macromolecules, spinning and sliding of disc-like macromolecules, snake-like sliding of long macromolecules. Macromolecule dynamics is usually investigated numerically with the aid of known computational methods e.g. molecular dynamics, multi-body dynamics, FEM and others. The anisotropic friction models have practical applications in predictions of structural and dynamical properties of polymeric liquids and in simulation models of the polymer processing (e.g. polymer controlled decompositions and recycling techniques).
