A multiscale model for the rupture of linear polymers in strong flows

Abstract

Polymer-containing solutions used across research and industry are commonly exposed to mechanically harsh fluid processes, for example shear and extensional forces during flow through porous media or rapid microdispensing of biopharmaceutical molecules. These forces are strong enough to break the covalent bonds in the polymer backbone. As this scission phenomenon can change the functional and fluid-flow properties as well as introduce reactive radicals into the solution, it must be understood and controlled. Experiments and models to date have only provided partial or qualitative insights into this behaviour. Here we build a link between the molecular-scale degradation models and the macroscale laminar flow of dilute solutions in any given geometry. A free-draining bead–rod model is used to investigate rupture events at the molecular scale. It is shown by uniaxial extension simulations of an ensemble of chains that scission can be conveniently described at the macroscopic scale as a first-order reaction whose rate is a function of the conformation tensor of the macromolecules and the velocity gradient of the flow. This approach is implemented in the finite volume code OpenFOAM by elaborating an appropriate constitutive equation for the conformation tensor. The macroscopic model is run and analysed for ultra-dilute solutions of poly(methyl methacrylate) in ethyl acetate and polyethylene oxide in water, using the geometry of an abrupt contraction flow and neglecting any viscoelastic effect. This multiscale approach bridges the gap between phenomenological observations of mechanically induced chemical degradation in large-scale applications and the rich field of molecular-scale models of macromolecules under flow.

Organic neuromorphic devices: Past, present, and future challenges

“…Scaling up while ensuring no reduction in functionality and stability under storage is a major challenge for advanced functional materials. 65 When printing functional macromolecules, it is important to understand the forces they experience as they flow through pipes, pumps, and ancillary equipment, and that the shear, extensional, or thermal forces are not having a deleterious effect, 66 as is also the case for flow through printheads and nozzles. 67,68 Once out of the nozzle, there are complex interdependencies between the formulation and printing actuation that determine if stable, repeatable drop or filament formation is feasible.…”

Laminar flow-induced scission kinetics of polymers in dilute solutions

“…Our model, first presented in Rognin et al. (2018), includes those three aspects in a way that is summarised below.…”

“…In our previous study we obtained a closed form for inspired by molecular simulations (Rognin et al. 2018). Although the original expression depends on Lagrangian time derivatives, here, we suggest the following simplified form: Here is a coefficient of the order of unity, is a critical strain rate and is a measure of the strain rate in the direction of polymer elongation.…”

“…We introduce a set of partial differential equations inspired by rheological constitutive equations and molecular simulations previously reported (Rognin et al. 2018). The equations are implemented and solved with the open source CFD library OpenFOAM.…”

Polymer Mechanochemistry: Manufacturing Is Now a Force to Be Reckoned With

“…We have begun to address this with the development of a mechanochemistry model coupled with fluid dynamics simulation software. 90 Closely linked to the polymer concentration and influence on viscosity is the important parameter of molecular weight.…”