Effect of added surfactant on convective assembly of monosized microspheres

Abstract

Convective deposition has become one of the common techniques for obtaining a colloidal assembly with a desired number of layers/thickness. Many applications in photonics and semiconductor industries demand only a single layer of colloids placed in a reproducible manner. In the convective deposition, a deposition velocity is typically inversely correlated with a number of layers. Obtaining a uniform monolayer reproducibly thus requires maintaining precise conditions such as the pH, volume fraction, ionic strength of the suspension, temperature, and humidity. Maintaining ideal conditions is one of the limiting factors for the scale-up of convective deposition. Likewise, the surface chemistry must also be reproducible. In the following study, we have demonstrated the effect of the sodium dodecyl sulfate (SDS) surfactant on convective deposition. We show that added SDS alters the flow patterns inside the thin film through Marangoni-driven surface stress, which then alters the time for the assembly. The added surfactant can permit more reliable conditions for monolayer coatings. This study using controlled amounts of the surfactant may give a broader understanding of variability of results found in the literature.