Dependence of capillary forces on relative humidity and the surface properties of femtosecond laser micromachined titanium.
Capillary forces were measured with colloidal atomic force microscopy at different levels of relative humidity on femtosecond laser micromachined titanium surfaces. After laser machining at different intensity levels, the titanium surfaces show a nanoscale ripple topology or microscopic bumpy structures. Different machining environments were chosen to influence the surface chemistry in addition to topology: while machining in pure oxygen and water resulted in surfaces consisting of TiO2, a composite surface of TiO2 and TiN was obtained after machining in pure nitrogen. All samples were subsequently exposed to pure oxygen, carbon dioxide or water, and showed different levels of wettability and capillary force. We have introduced the concept of humidity sensitivity as the relative increase of the capillary force with respect to the measured force at 0% humidity. We report that samples with a nanoscale ripple topology machined in pure oxygen exhibit the lowest level of capillary force and the lowest sensitivity towards humidity in the environment. Surfaces with low sensitivity towards changes of the relative humidity are good candidates for technical applications, where capillary forces have to be controlled. This study contributes to the development of such surfaces, to a better understanding of how capillary bridges are formed on rough surfaces and ultimately to the exploration of the relationship between surface wettability and capillary forces.
Department of Chemical Engineering, McGill University, 3610 University Street, H3A 0C5 Montreal, QC, Canada.
Jorge
J
Lehr
Department of Chemical Engineering, McGill University, 3610 University Street, H3A 0C5 Montreal, QC, Canada.
Anne-Marie
AM
Kietzig
Capillary adhesion; Capillary forces; Femtosecond laser; Laser micromachining; Surface chemistry; Surface forces; Titanium; Wettability