Viscoplastic lines: printing a single filament of yield stress material on a surface

Abstract

This study presents the spreading of a single filament of a yield stress (viscoplastic) fluid extruded onto a pre-wetted solid surface. The filaments spread laterally under surface tension forces until they reach a final equilibrium shape when the yield stress dominates. We use a simple experimental set-up to print the filaments on a moving surface and measure their final width using optical coherence tomography. Additionally, we present a scaling law for the final width and determine the corresponding prefactor using asymptotic analysis. We then analyse the level of agreement between the theory and experiments, and discuss the possible origins of discrepancies. The process studied here has applications in extrusion-based thermoplastic and bio-three-dimensional printing.