ROLE OF DYNAMIC SURFACE-TENSION IN SLIDE COATING

Gelatin solutions (5 wt %) with different dynamic surface tensions and elasticities were coated in the slide coater. The experiments, which consisted of either one or two layers, were performed at speeds in the range of 0.35-2.03 m/s and 40-degrees-C. The vacuum under the bead at the onset of rivulet was correlated to the dynamic surface tension and the curvature of the upper meniscus. The dynamic surface tensions were measured with a maximum bubble pressure technique at frequencies in the range of 0.5-5 bubbles/s and adjusted with commercial surfactants. The variation of the dynamic surface tension with respect to the bubble frequency was correlated to both the solution Gibbs surface elasticity and the vacuum range measurements at the onset of ribbing. The dynamic and rheological properties of the surface impact the wettability, the coatability window, and the surface forces that control flow and deformation.