The effect of solvent on convectively‑driven silica particle assembly: Decoupling surface tension, viscosity, and evaporation rate

The process of convectively self‑assembling particles in films suffers from low reproducibility due to its high dependency on particle concentration, as well as a variety of interactions and physical parameters. Inhomogeneities in flow rates and instabilities at the air‑liquid interface are mostly responsible for reproducibility issues. These problems are aggravated by adding multiple components to the dispersion, such as binary solvent mixtures or surfactant/polymer additives, both common approaches to control stick‑slip behavior. When an additive is used, not only does it change the surface tension, but also the viscosity and the evaporation rate. Worse yet, gradients can be formed in these three properties, which then lead to Marangoni currents. Here, we use a series of alcohols to study the role of viscosity independently of other solvent properties, to show its impact on stick‑slip behavior and interband distances. We show how mixtures of glycerol and alcohol, or poly(acrylic acid) and alcohol lead to more complex patterning. Marangoni currents are not always observed in co‑solvent systems, being dependent on the rate of solvent evaporation. To produce homogenous particle assemblies and control stick‑slip behavior, gradients must be avoided, and the surface tension and viscosity need both be carefully controlled.