Wetting and Adhesive Forces on Rough Surfaces – An Experimental and Theoretical Study

Abstract

It is well known that wetting plays a crucial role in many processes due to its impact on the emerging adhesive forces. In general, high wetting angles between solid and liquid lead to higher adhesive forces and vice versa. For ideal systems the calculation of these adhesive forces is possible using analytical approaches for van der Waals and polar forces. But there is still a lack of knowledge how to consider impacts like roughness and irregular shape of the solids during the calculation.The present paper aims to show the correlation between wetting behaviour and adhesive forces for non-ideal systems. Therefore, a model system is created wherewith the wetting angle can be changed in a high range. Coated alumina particles are used as solids in this model system. The coating leads to a low surface energy and consequently to a high wetting angle to water of 105°. The wetting angle is reduced by adding ethanol to the aqueous phase and thus the influence of wetting on the adhesive force can be investigated.To correlate the wetting angle with the adhesive force, both of them must be measured. Using a substrate with the same surface coating as the used particles the sessile drop method for the determination of the wetting angle can be applied. Subsequently, the calculation of the interfacial energy, which should be linked up directly to the adhesive force, is possible. The adhesive forces are determined directly by using an atomic force microscope (AFM). Therefore, a coated alumina particle is glued on the end of the cantilever to measure the particle-substrate force directly. The particle and substrate are entirely submerged into the surrounding liquid.As confirmed, measurements of the wetting angle show a decrease with higher ethanol fractions. This is due to the 46 Jörg Fritzsche and Urs A. Peuker / Procedia Engineering 102 ( 2015 ) 45 -53 lower surface energy of ethanol compared to water. Furthermore, the results show a selective adsorption of ethanol to the solid surface. This leads to an increased surface saturation of ethanol depending on the concentration in the liquid which can be described with a Langmuir isotherm. AFM measurements show a variation of adhesive forces caused by the high roughness of the substrate. This can be described with statistical distributions. Parameters of this distributions show a correlation to the ethanol saturation. Semi-empirical approaches using van der Waals and polar forces confirm this behaviour.

Method of surface energy investigation by lateral AFM: application to control growth mechanism of nanostructured NiFe films

“…There is no acceptable technique for estimating surface energy in a microscopic local area or on a separate NGs at present. The universal and accurate method of surface energy investigations is based on the assessment of the wettability of a surface 23 , 24 , but this allows us to estimate the total surface energy of the sample, but not a separate microscopic area or NG. The best contender for determining local specific surface energy is an atomic force microscope (AFM).…”

Interactions between Carbon‐Bonded Alumina Filters and Molten Steel: Impact of a Titania‐Doped Filter Coating

“…A rougher surface provides an increased surface area and is known to increase reactivity. The detailed influence of the surface roughness on the filtration process is yet unknown and challenging to calculate due to complex interactions . Nevertheless, Voigt et al reported an increased filtration efficiency of rough filters for aluminum filtration.…”

Fast preparation and recycling method for colloidal probe cantilevers in hydrophobic mapping applications

“…Colloidal probe atomic force microscopy (CP-AFM) was first reported by [1,2] and is nowadays used in multiple applications in various fields of research. One possible application are adhesive force mappings on a variety of samples including biological [[3], [4], [5]], mineral [6,7], ceramic [[8], [9], [10]] or wooden samples [3,11]. Beside possible sources of contamination during storing in ambient conditions as summarized by [12], the main source of colloidal probe contamination in an adhesive force mapping application on mineral surfaces experienced by the authors are inorganic particulate contaminations [13], as given in Fig.…”

“…A variety of methods for cantilever or colloidal probe functionalization have been reported in literature, the same applies for possible colloids attached to the cantilever like glass spheres [18], polystyrene particles [6,7,19], silica microspheres [14,19,20] Al 2 O 3 particles [[8], [9], [10]] or gold particles [14]. A broader overview of the colloidal probe method was compiled by [18], listing more possible probes like TiO 2 , MgO, ZnS, poly-(methyl methacrylate) and polyethylene.…”

“…The other method is the utilization of organosilanes in combination with hydroxylated surfaces, mostly silica spheres. Used reagents are alkyl or fluoroalkyl silanes in solvent or vapor phase deposition [[8], [9], [10],14,20,22].…”