Cross-scale Modeling of Polymer Topology Impact on Extrudability through Molecular Dynamics and Computational Fluid Dynamics

Understanding how polymer topology influences melt extrudability is critical for advancing material design in extrusion-based additive manufacturing. In this work, we develop a bottom-up, cross-scale modeling framework that integrates coarse-grained molecular dynamics (CGMD) and continuum-scale computational fluid dynamics (CFD) to quantitatively assess the effects of polymer architecture on extrudability A range of branched polydimethylsiloxane (PDMS) polymers are systematically designed by varying backbone length, sidechain length, grafting density, grafted block ratio, and periodicity of grafted-ungrafted segments. CGMD simulations are used to compute zero-shear viscosity and relaxation times, which are then incorporated into the Phan-Thien-Tanner (PTT) model within a computational fluid dynamics (CFD) model to predict pressure drop of PDMS during extrusion through printer nozzle. Qualitative analysis reveals that polymers with concentrated grafted blocks exhibit significantly higher zero-shear viscosity than stochastically branched analogs, while sidechain inertia drives longer relaxation time. However, for untangled and weakly entangled PDMS, relaxation time remains in the nanosecond range, making shear-thinning and elastic effects negligible. Consequently, zero-shear viscosity emerges as the primary determinant of extrudability. This cross-scale modeling strategy provides a predictive framework for guiding the rational design of extrudable polymer materials with tailored topologies.