Effect of soluble surfactant on thermocapillary instability in falling film

We conduct a study to decipher how the soluble surfactant affects the different unstable temporal modes accountable for thermocapillary instabilities. The H-mode (surface mode), shear mode, and additional two thermocapillary S- and P-modes are identified. We see that the measure of the surfactant solubility parameter stabilizes all the H-mode, S-mode, P-mode, and shear mode instabilities by diminishing their unstable zones. However, the non-dimensional base surface surfactant concentration parameter exhibits both stabilizing and destabilizing roles in the H-mode, S-mode, P-mode, and shear mode instabilities. Moreover, a modal coalescence happens between the H-mode and the S-mode.