Thermocapillary convection and interface deformation in evaporating liquid films on a structured surface

In this study, the evolution of thin hydrofluoroether (HFE) films that evaporate on sinusoidally structured copper walls while experiencing thermocapillary and, in mixtures, solutocapillary stresses, is investigated experimentally. An open cell equipped with a chromatic–confocal line sensor and Schlieren imaging provides time-resolved liquid–gas interface deformation profiles for pure HFE-7100 films and for HFE-7100/HFE-7500 mixtures. Experiments show that the spatially averaged liquid–gas interface location decreases linearly with time, so that the average evaporation flux remains constant for each wall temperature. The interface adopts a quasi-steady cosine shape whose amplitude increases with increasing evaporation flux. In the investigated binary mixtures, thermo- and solutocapillary stresses oppose each other. Thermocapillarity remains dominant, yet progressive depletion of the volatile HFE-7100 leads to attenuation of the deformation, so that the amplitude approaches the pure HFE-7500 limit. The measured deformation of the pure HFE-7100 film is compared with predictions of a simple model based on long-wave approximation. • Thermocapillary stress drives deformation on structured walls. • Evaporation flux governs the steady interface amplitude. • Solutal stresses counteract thermal effects in binary mixtures. • Long-wave model accurately predicts pure liquid film shapes.