Slipping fluids: a unified transient network model

Abstract

Wall slip in polymer solutions and melts play an important role in fluid flow, heat transfer and mass transfer near solid boundaries. Several different physical mechanisms have been suggested for wall slip in entangled systems. We look at the wall slip phenomenon from the point of view of a transient network model, which is suitable for describing both, entangled solutions and melts. We propose a model, which brings about unification of different mechanisms for slip. We assume that the surface is of very high energy and the dynamics of chain entanglement and disentanglement at the wall is different from those in the bulk. We show that severe disentanglement in the annular wall region of one radius of gyration thickness can give rise to non-monotonic flow curve locally in that region. By proposing suitable functions for the chain dynamics so as to capture the right physics, we show that the model can predict all features of wall slip, such as flow enhancement, diameter-dependent flow curves, discontinuous increase in flow rate at a critical stress, hysteresis in flow curves, the possibility of pressure oscillations in extrusion and a second critical wall shear stress at which another jump in flow rate can occur. #

Molecular interpretation of the “stick–slip” defect of linear polymers

“…Even if theoretical models have been proposed for unifying both mechanisms of desorption and disentanglement [27][28][29], we will focus in this paper on this last mechanism to propose expressions of the critical shear stress and the critical shear rate at the onset of stick-slip. We will consider the molecular weight effect to propose a physical mechanism at the origin of this defect and a criterion of existence, based on the molecular weight distribution, as we already did for the sharkskin defect [30].…”

Polymer Flow Through Porous Media: Numerical Prediction of the Contribution of Slip to the Apparent Viscosity

“…To do so, different tools are available. Molecular dynamics approaches, often with simple molecules, are useful to understand the fundamental physics at the molecular level (Rouse 1953;Joshi et al 2000;Sochi 2011). However, simulations cannot yet be performed on sufficiently large volumes to model flow in porous media, especially in the case of polymer solutions.…”

Influence of Stereoregularity on the Wall Slip Phenomenon in Polypropylene

“…4 We have recently proposed a unified model for wall slip that combines the two mechanisms of slip into one mathematical framework. 5 Thus, although a lot is now known about the mechanisms of the interfacial slip, it is still not clear as to how the subtleties of molecular architecture influence the slip behavior. Thus, the effects of molecular structural parameters such as molecular weight, molecular weight distribution, tacticity, short-and longchain branching, and the branching distribution are still not completely understood.…”