NEW INVESTIGATIONS ON THE RUPTURE PROCESS OF THIN LIQUID FILMS AT THE PARTICLE-BUBBLE ADHESION

摘要

The dependence of the critical thickness of wetting films rupture and the three phase contact expansion after rupture on methylated glass surfaces and on modified and structurized LB layers as model for collector-adsorption layers at solid surfaces is discussed. Two rupture mechanisms can occur: 1. growing capillary wave due to attractive forces; 2. nucleation. The second mechanism is extremely fast. It is demonstrated that the heterogeneity of the adsorption layer plays a critical role for destabilization of wetting films because of the probable formation of tiny bubbles on hydrophobic places (hot spots) as nuclei for film rupture. This might be the reason for the very high rupture thickness observed on such surfaces. The heterogeneity of LB layers can be enhanced strongly by collapse structures introduced as additional nucleation sites and by nanometer scaled grooves due to sceletonization of LB layers. In contrast, when the adsoiption (LB) layer is more homogenous, then metastable wetting films can exist, because in this case the rupture occurs due to the capillary wave mechanism.