Investigations into the Complete Spreading Dynamics of a Viscoelastic Drop on a Spherical Substrate

Predicting the Dynamics and Steady-State Shape of Cylindrical Newtonian Filaments on Solid Substrates

The spreading of liquid filaments on solid surfaces is of paramount importance to a wide range of applications including ink-jet printing, coating, and direct ink writing (DIW). However, there is a considerable lack of experimental, numerical, and theoretical studies on the spreading of filaments on solid substrates. In this work, we studied the dynamics of spreading of Newtonian filaments via experiment, numerical simulations, and theoretical analysis. More specifically, we used a novel experimental setup to validate a 2D moving mesh computational fluid dynamics (CFD) model. The CFD model is used to determine the effect of processing and fluid parameters on the dynamics of filament spreading. We experimentally showed that for a Newtonian filament, the same spreading dynamics and final shape are obtained when the initial radius is constant, independent of the magnitude in printing parameters. In other words, the only important parameter on the spreading of filaments is the initial filament radius. Using a numerical model, we showed that the initial filament radius manifests itself in two important dimensionless parameters, Bond number, Bo, and viscous timescale, τμ. Furthermore, the results clearly show that the dynamics of spreading are governed by the static advancing contact angle, θs. These three parameters determine a master spreading curve that can be used to predict the spreading of cylindrical filaments on flat substrates. Finally, we developed a theoretical model that was parameterized using experimental data to correlate the steady-state shape of filaments with Bo and θs. These results are particularly applicable for predicting and controlling the dynamics of filaments in DIW and other extrusion-based processes.

Leveraging spreadsheet analysis tool for electrically actuated start-up flow of non-Newtonian fluid in small-scale systems

In this article, we demonstrate the solution methodology of start-up electrokinetic flow of non-Newtonian fluids in a microfluidic channel having square cross-section using Spreadsheet analysis tool. In order to incorporate the rheology of the non-Newtonian fluids, we take into consideration the Ostwald-de Waele power law model. By making a comprehensive discussion on the implementation details of the discretized form of the transport equations in Spreadsheet analysis tool, and establishing the analytical solution for a special case of the start-up flow, we compare the results both during initial transience as well as in case of steady-state scenario. Also, to substantiate the efficacy of the proposed spreadsheet analysis in addressing the detailed flow physics of rheological fluids, we verify the results for several cases with the corresponding numerical results. It is found that the solution obtained from the Spreadsheet analysis is in good agreement with the numerical results—a finding supporting spreadsheet analysis's suitability for capturing the fine details of microscale flows. We strongly believe that our analysis study will open up a new research scope in simulating microscale transport process of non-Newtonian fluids in the framework of cost-effective and non-time consuming manner.