Gap Effects in a Rheometrical Flow of a Hydrophobically Associating Polymer Solution: Apparent Slip or Material Instability?

Abstract

Abstract In this paper, we study gap effects and apparent slip phenomena in a torsional flow of a moderately concentrated hydrophobically modified associative polymer solution.Slip is investigated by varying the gap between concentric parallel disks, and the plate surface roughness.The onset of apparent slip is shown to occur when the associative network is destroyed, and the slip velocity to increase with increased shear stresses in the strong shear-thinning region of the flow curve.The apparent slip phenomenon is shown to be due to the associative character of the polymer solution; it has been attributed to the existence of clusters of associating polymers (microgels),which behave like soft particles in a low viscous dispersing medium once the associative network is destroyed.Apparent slip can be eliminated by using measuring plates with roughness of about 100µm, that is of the order of the characteristic size of the microgels.