Role of surface-tension additive in coating framing effect topography

Abstract

Materials are often coated with liquid coatings for functional or aesthetic purposes. However, liquid coating deposition may result in surface irregularities in the final film due to substrate topography or physico-chemical or thermo-capillary phenomena. The surface defect of interest in this work is the framing effect, a surface defect at the edges of coated substrates. This study enables an in-depth understanding of capillary phenomena near substrate edges during coating and evaporation. A particle tracking velocimetry (PTV) technique highlights coating flows resulting from hydrostatic pressure and thermo-capillary phenomena such as vapour recoil and surface-tension gradients. This fluid mechanics technique was coupled with topographical measurements to study and quantify the influence of coating flows on framing effect dynamics. Framing effect topography do not rely on coating surface tension but on the presence of surface tension additive at film free surface and of their behaviours toward evaporation conditions.