2018-11-21
10:15 at HCI J 498

Massive flow of polymer solutions through porous media, orthogonal superposition rheology, and non-monotonic stress-relaxation of pre-sheared self-associating fluids

Wim Briels

Computational Biophysics, University of Twente

The presentation will address three different, unrelated subjects, a sin that can only be committed by retired professors.

In the first part of the talk I will present a simulation model in which Brownian polymers are coupled to a discretized Navier-Stokes fluid, also called Smooth Particle Hydrodynamics. The coupling will conserve local momentum. The polymer model may be chosen to the taste of the user. In the case of massive flow through porous media, the polymer model necessarily must be very simple. I will present examples of simulations with single particle polymer models. Plenty of room will be left for critical questions.

In the second part I will present simulations of a steadily sheared soft matter model, probed by an orthogonal oscillatory shear flow with its gradient along that of the steady shear flow. Our main concern will be if Boltzmann’s superposition principle will hold in this situation. According to the latter, the shear relaxation modulus obtained with oscillatory experiments is equal to the stress relaxation modulus after a strain step. We will find that this principle does not hold in the present application, not even when the imposed steady shear has an infinitesimally small rate. Plenty of room will be left for critical remarks.

If time permits, I will present experiments on self-associating fluids, in which the relaxation of stresses after cessation of a sufficiently strong shear flow, is non-monotonic. I will argue that, contrary to the opinion of many of our colleagues, this behavior does not violate the laws of thermodynamics. Plenty of room will be left for critical remarks.