Abstract
HypothesisA process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing. ExperimentsWe combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures’ morphology. FindingsThe results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles’ systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a “surface capturing effect”, while for silica, droplets evaporated in mixed stick–slip mode and a “confinement effect” was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates.
Highlights
The results demonstrate that a reduction in the dispense volume hinders the coffee-ring effect” (CRE) and inclination effect (IE) for both particles’ systems, even though the evaporation mode is different
Printing tailored photonic structures on such photovoltaics can potentially aid light harvesting by precise light management, enhancing their efficiency [1]. In another area related to high-temperature applications, photonic structures might pave the way to a potential new class of thermal barrier coatings (TBCs)
This coincides with the observed evaporation mode of each suspension: droplets of the PS suspension dried with a constant contact line radius, which indicates a self-pinning effect caused by PS particles at the contact line [37,38]
Summary
Several studies [28,30,31,32,33] revealed that particles can accumulate at the receding liquid–air interface of the droplet, forming a dense homogeneous layer, which eventually gets deposited on the substrate. This ‘‘surface capturing effect” at the droplet has been caused either by an attractive particleinterface interaction [31] or by an increased evaporation rate due to heating [32] that results in a faster droplet surface shrinkage. A minimum number of 10 repetitions were conducted
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