Self-Organization of Polymeric Fluids in Strong Stress Fields

A V Semakov,A Y Malkin,V G Kulichikhin

doi:10.1155/2015/172862

Abstract

Analysis of literature data and our own experimental observations have led to the conclusion that, at high deformation rates, viscoelastic liquids come to behave as rubbery materials, with strong domination by elastic deformations over flow. This can be regarded as a deformation-induced fluid-to-rubbery transition. This transition is accompanied by elastic instability, which can lead to the formation of regular structures. So, a general explanation for these effects requires the treatment of viscoelastic liquids beyond critical deformation rates as rubbery media. Behaviouristic modeling of their behaviour is based on a new concept, which considers the medium as consisting of discrete elastic elements. Such a type of modeling introduces a set of discrete rotators settled on a lattice with two modes of elastic interaction. The first of these is their transformation from spherical to ellipsoidal shapes and orientation in an external field. The second is elastic collisions between rotators. Computer calculations have demonstrated that this discrete model correctly describes the observed structural effects, eventually resulting in a “chaos-to-order” transformation. These predictions correspond to real-world experimental data obtained under different modes of deformation. We presume that the developed concept can play a central role in understanding strong nonlinear effects in the rheology of viscoelastic liquids.

Highlights

The general task in understanding the rheology of polymeric liquids is constructing models that allow one to describe the behaviour of a material using the minimal number of physical parameters
Further development of the statistical approach for the rheology of concentrated solutions and melts was based on the concept of entanglements, which is a physical network with some characteristic lifetimes of local contacts, or nodes, formed by macromolecules [3–5]
Analysis of literature and our own experimental data show that high deformation rates in polymer systems lead to a flow-to-rubber-like transition in their behaviour

Summary

Introduction

The general task in understanding the rheology of polymeric liquids is constructing models that allow one to describe the behaviour of a material using the minimal number of physical parameters. This model operates with four parameters: vector of the l+1 shear field h, susceptibility to the action of shear stresses 1/k (where k is a relative angle at the iteration step), the value of a local field E, and the possibility of rotating in the field of neighbouring particles, 1/m The solution of this equation giving the deformation (or stress) and particle orientation distributions can be treated as the elastic and deformation behaviour of structural elements l−1 in a material. Equation (23) models the behaviour of an elastic liquid being transferred into a rubbery state (at high deformation rates) that is characterized by the following features: rotary degrees of freedom can be realized, orientation is possible, inherent friction (energy dissipation) is excluded, and movement of particles along the lattice is impossible

Discussion

Conclusion