Rheology Resulting from Shear‐Induced Structure in Associating Polymer Solutions

Abstract

SynopsisSolutions of poly(vinyl alcohol) (PVA) and polysaccharide with sodium borate (SB) are investigated as a model system for associating polymers which exhibit shear-induced fluid structure and shear-thickening rheology. Certain combinations of PYA and SB concentrations are shown to result in fluids that exhibit a viscosity maximum followed by shear thinning as shear rate is increased. Stress saturation is often observed in the shear-thinning region. A significant hysteresis is also reported in which higher viscosities and lower shear rate for the viscosity maximum are observed in steady-state measurements made while decreasing shear rate in a stepwise manner. Boron nuclear magnetic resonance spectra are shown to be useful for elucidating the nature of the borate/hydroxyl-dyad complexes, including their stereoselectivity. Boron resonance peaks allow quantitative determination of the number of complexes. Dynamic mechanical properties are included, and a physical picture of network structure building and breaking during flow of associating polymers is discussed.

Temporary networks in polymer‐modified asphalts

“…With respect to low-molecular-weight polymers, Duvdevani (49) was the first to report the shear-thickening for ionomers and explained it as due to chain stretching, which favors an increase in the number of crosslinks (ionic associations), thus forming larger temporary complexes. The effect of an applied shear stress was further investigated (50,51). Yamamoto (52) and Tanaka and Edwards (53) explained the shear-thinning in terms of chain detachment activated by the elastic force in the chain.…”

Comparison of galactomannan crosslinking with organotitanates and borates

“…Therefore it is unclear whether these studies can be directly applicable to understanding the mechanisms involved in gelling aqueous polymer solutions. Maerker and Sinton have used 11B NMR to study the structure formed in polyvinyl alcohol: sodium borate solutions [21] where crosslinking occurs through the hydroxyls. Using 2,4-pentanediol as a model compound for PVA, they were able to show that only the 2R, 4S and the 2S, 4S isomers can complex with tetrahedral monoborate while the 2R, 4R isomer cannot.…”

Shear thickening of halato-telechelic polymers in apolar solvents

“…Suspensions are an important type of dilatant systems, the rheological behaviour of which has recently been reviewed by Barnes [1]. Dilatancy has also been reported for various types of polymer solutions: solutions of high molecular weight polymers in solvents of high [2] and low viscosity [3]; aqueous solutions of polyvinyl alcohol)-borate complexes [4,5]; triblock copolymers [6,7] and partially hydrolysed polyacrylamides [8]; and solutions of anti-misting agents [9][10][11][12] and ionomers in apolar solvents [13,14]. The unusual solution properties of these systems are usually accounted for by the formation of longlived polymer associations under the flow.…”