Influence of dye concentrations of internal reflection suppression and air entrainment dynamics of polymeric droplets.

In many studies that incorporate droplet impact imaging techniques such as total internal reflection microscopy (TIRM), dyes and particles are often used for visualization enhancement. For the bottom view techniques such as TIRM, which depends on grayscale intensity changes to directly measure the spatio-temporal shifts in narrow gaps, internal reflections induced by the collapsed top surface can be seen and negatively affect the image quality. In this study, we show that with concentrations of various dyes such as Methylene Blue reaches a limit at which the internal reflections are suppressed, yet the air film topology is also affected. We attribute the changes in the air entrainment dynamics to both optical and physicochemical processes.