Rheology and Dynamics of Associative Polymers in Shear and Extension:  Theory and Experiments

Abstract

We investigate the steady and transient shear and extensional rheological properties of a series of model hydrophobically modified ethoxylate-urethane (HEUR) polymers with varying degrees of hydrophobicity. A new nonlinear two-species network model for these telechelic polymers is described which incorporates appropriate molecular mechanisms for the creation and destruction of elastically active chains. Like other recent models we incorporate the contributions of both the bridging chains (those between micelles) and the dangling chains to the final stress tensor. This gives rise to two distinct relaxation time scales: a short Rouse time for the relaxing chains and a longer network time scale that depends on the aggregation number and strength of the micellar junctions. The evolution equations for the fraction of elastically active chains and for the conformation tensors of each species are solved to obtain the total stress arising from imposed deformations. The model contains a single adjustable nonlinear parameter and incorporates the nonlinear chain extension, the shear-induced enhancement of associations, and the stretch-induced dissociation of hydrophobic chains. In contrast to earlier closed-form models, we are able to obtain quantitative agreement between experimental measurements and the model predictions for three different series of telechelic polymers over a range of concentrations. The scaling of both the zero shear viscosity and the effective network relaxation time shows good agreement with those measured in experiments. The model also quantitatively captures both the shear thickening and subsequent shear thinning observed in the rheology at high deformation rates and predicts transient extensional stress growth curves in close agreement with those measured using a filament stretching rheometer.

Assembly mechanism of recombinant spider silk proteins

“…Such behavior has been shown to be the dominant cause for aggregation for particles in the micrometer range (17) and to induce shear-activated irreversible aggregation (18). Once the colloidal silk spheres interact, the intrinsic characteristics of eADF3 and eADF4 contribute to a behavior that can be interpreted by a model originally developed for associative polymers in flow (19). Hydrophilic side chains presumably stick out of the spherical colloidal assemblies of eADF3 and form dangling ends that can interact with neighboring spherical colloidal assemblies (Fig.…”

“…5). If interactions are favored kinetically, shear thickening can be observed (19). Shear increases the collision rate of individual proteins or assemblies (20) by increasing the root-mean-square projection of the dangling end in the deformation direction.…”

Rate-Dependent Stiffening and Strain Localization in Physically Associating Solutions

“…In brief, the overall stress response of the solution is calculated from the deformation-dependent concentration of elastically active triblock copolymer strands in the macromolecular network, fundamentally similar to theory proposed recently by Tripathi et al 32 In the following subsections, we introduce the physical assumptions of our model, the method of solution, and the resulting predictions and implications of the model.…”

Extensional rheometry of cellulose ether solutions: flow instability

“…For fluids with shear viscosity\10 3 Pa s, Capillary break-up extensional rheometry (CaBER) has received much attention during the past few years Tirtaatmadja et al 2006;McKinley and Tripathi 2000;Kheirandish et al 2008;Tripathi et al 2006;Plog et al 2005;Arnolds et al 2010). In CaBER, a fluid filament is subjected to step-strain and the mid-plane diameter of the filament undergoing capillary driven thinning is recorded as a function of time (Fig.…”

“…CaBER technique has been used in the past for Newtonian fluids , shear-thinning viscoelastic fluids (Tripathi et al 2006;Clasen et al 2006b;Rodd et al 2005), nonshear-thinning viscoelastic fluids, i.e. Boger fluids (Plog et al 2005;Campo-Deano et al 2011;Anna and McKinley 2001), and yield stress fluids (McKinley 2005a, b;Niedzwiedz et al 2009) CaBER measurements for a number of systems containing biopolymers and their derivatives in aqueous media have been reported in the past literature, most notably for xanthan (Stelter et al 2002), hydroxypropyl ether guar (Duxenneuner et al 2008), methyl hydroxyethyl cellulose (HEC) (Plog et al 2005), alginate (Storz et al 2010;Rodriguez-Rivero et al 2014), scleroglucan (Japper-Jaafar et al 2009), cellulose acetate ?…”