Structuring during flow of polymer and colloidal systems

Abstract

This review presents the description of various cases and physical causes of self-organization (development of ordered structures) provided by the shear flow of polymer and colloidal systems that are characterized by complex rheological behavior. This description is based on the common basis that, as a general rule, micellar systems in many respects behave as polymer solutions. In contrast to the development of regular dynamic structures during the flow of low-molecular-mass fluids, when the viscosity of a fluid plays a key role, in the case of complex rheological media, structuring is provided by the elasticity of a medium and/or by the existence of diverse structural modifications of the material. They arise owing to shear deformation and show different rheological characteristics, a circumstance that, in particular, lead to multivalued flow curves of the medium. Various aspects of this mode of structuring reported in the literature are revisited. Feasible mechanisms of self-organization in polymer and colloidal systems and modes of their description are discussed in detail. Special attention is focused on the similar natures of structural phenomena in polymer and colloidal systems. Various theoretical approaches to the description of instability and structural organization in polymer and colloidal systems are considered. In many cases, the possible cause of structuring can be associated with ambivalent flow curves with a region where stress decreases with an increase in the shear rate. However, in micellar and polymer systems capable of elastic strain, elasticity is the main cause of instability. In this case, such systems can coexist in two structural modifications: flow and elastic (rubbery). It is proposed that the above phenomena can be described in terms of the granular model of a fluid.