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.

Surfactant amplifies yield-stress effects in the capillary instability of a film coating a tube

“…Beyond the application to airway modelling, the present theory could be used to study the effect of surfactant on other capillary flows of viscoplastic fluids. For example, one possible industrial application that has received recent modelling attention is ink-jet printing (Jalaal et al 2021;van der Kolk et al 2023), where the effects of surfactant have not yet been studied but may be important. The flow region maps that we have introduced (figures 2, 3a and 6) may also prove useful in other problems by illustrating the transitions between different types of yielding.…”

“…2021; van der Kolk et al. 2023), where the effects of surfactant have not yet been studied but may be important. The flow region maps that we have introduced (figures 2, 3 a and 6) may also prove useful in other problems by illustrating the transitions between different types of yielding.…”

“…Thin-film theory compared well with simulations for low Bingham numbers but less well when the film thickness increased. Thin-film models for the axisymmetric spreading of droplets (Jalaal, Stoeber & Balmforth 2021) and the spreading of long extruded filaments (van der Kolk, Tieman & Jalaal 2023) have been developed and used to predict the distances reached by spreading fronts, which decrease as the capillary Bingham number is increased. Whilst these studies all addressed the effect of viscoplastic rheology on capillary phenomena, surfactant effects were not incorporated in any of the models.…”

Dynamics of drying colloidal suspensions, measured by optical coherence tomography

“…Optical coherence tomography has recently been showing its potential for the study of soft materials. [26][27][28][29][30][31][32][34][35][36] While most 7, for initial particle concentrations of j 0 = 0.06 (dashed lines) and j 0 = 0.19 (solid lines). At the lower j 0 a long induction period of 78 min is observed, before any solid packed film appears, even though the evaporation rate (given by dx l /dt) is similar in both cases.…”

“…Optical coherence tomography was first developed for medical applications 25 but has been emerging as a powerful imaging method for applications in soft matter physics [26][27][28][29][30][31] and the heritage sciences. [32][33][34][35][36] Using OCT, dynamic measurements of surfaces or interfaces can be made, for example to monitor the roughness of a drying varnish layer, 33 or to measure the evaporation rates of droplets, 30 the spreading rates of extruded fluids, 31 and the formation and decay of wrinkles during dielectrophoresis. 29 Internal features like shear bands can also be visualised.…”