Tools for polymer design: predicting rheology from molecular weight distribution and branching topology

Polymers make wonderful, useful materials! Yet, their success and ubiquity has itself caused problems, provoking examination of their sustainability and recyclability, and of the energy efficiency of their processing. In this context, the design and optimisation of new materials and processes requires tools with the ability to predict material properties and behaviour on the basis of their molecular structure. This talk will present our efforts to address the challenge of predicting the flow properties (rheology) of polymeric liquids, and discuss the physics underpinning the software we have developed. The potential design space is vast: practical polymers are polydisperse (broad and variable molecular weight distribution) and may contain branches (with potential to control the statistics of branch placement). These molecular variables affect the response of the polymers to flow: whether the strands align, or stretch, and by how much, in a given flow field. These dynamics in turn gives rise to relevant processing phenomena such as extension hardening, or shear thinning. We will focus on polydisperse linear polymers, for which we have developed a constitutive model ("Rolie-Double-Poly") embedded in software (https://reptate.readthedocs.io/) that quantitatively predicts non-linear rheology from molecular weight distribution. We will also discuss how chain branching affects the physics, as encoded within our "BoB" software (https://sourceforge.net/projects/bob-rheology/).