Shear Banding in Telechelic Associative Polymers by Molecular Dynamics

Abstract

Results on the shear flow of telechelic associative polymers using nonequilibrium molecular dynamics (NEMD) are presented. The particle stream velocities can be calculated from the peculiar velocities and the imposed velocity profile using a novel approach. The constitutive relationship stress–shear rate becomes nonmonotonic when the interaction force between hydrophobic sites is increased. This condition induces a steady banding flow, which arises under transient conditions as a local instability originated from the breakage of micellar aggregates, thus promoting the migration of these aggregates to regions of low velocity gradients. Here, for the first time, NEMD simulations predict the banding flow of associative polymers.

Molecular simulation of structure formation and rheological properties of mixtures of telechelic and monofunctional associating polymer

“…A lot of theoretical and computational studies of rheological properties of physical gels consisting of APs have been reported . Tanaka and Edwards proposed a transient network theory to physical gels consisting of APs and explained the shear thinning under the steady shear flow and the Maxwellian behavior controlled by the dissociation of associating groups from micelles in the linear viscoelasticity regime .…”

Periodic “stick-slip” transition within a continuum model for entangled supramolecular polymers

“…In concentrated solutions of telechelic polymers, i.e. linear chains with stickers at both extremities that enable the formation of transient network, experiments [33,36,37] and MD simulations [38] showed that flow instabilities can occur.…”

Shear-Induced Heterogeneity in Associating Polymer Gels: Role of Network Structure and Dilatancy

“…Near the overlap concentration, sticker clusters can be bridged by polymer strands and form an interconnected volume spanning networka physical gel [1][2][3]. Such gels are found in both natural and synthetic systems, and display a striking array of rheological behavior, including strain stiffening [4], negative normal stresses [5], shear thickening [6,7], shear thinning [8], and shear banding [9][10][11][12][13][14][15].Despite the ubiquity and versatility of physical gels, a fundamental understanding of the interplay between their microstructure, dynamics, and rheological properties remains a challenging and open problem. For instance, while experiments and simulations of associative networks (including both AP [13][14][15] and colloidal [16] gels) under simple shear have observed spatial inhomogeneities in both shear rate and density, suggesting some form of sheargradient concentration coupling (SCC) [17][18][19][20], the microscopic mechanism for the instability is unclear.…”

“…Such gels are found in both natural and synthetic systems, and display a striking array of rheological behavior, including strain stiffening [4], negative normal stresses [5], shear thickening [6,7], shear thinning [8], and shear banding [9][10][11][12][13][14][15].…”

“…For instance, while experiments and simulations of associative networks (including both AP [13][14][15] and colloidal [16] gels) under simple shear have observed spatial inhomogeneities in both shear rate and density, suggesting some form of sheargradient concentration coupling (SCC) [17][18][19][20], the microscopic mechanism for the instability is unclear. Mean-field based models [21] of AP rheology have largely focused on chain elasticity and have not accounted for density inhomogeneity (e.g., chain migration) which would require a constitutive relation describing the solute pressure (the driving force for chain migration) as a function of shear rate and concentration.…”