Slippage rough surfaces

Abstract In this chapter we discuss the results of theoretical and experimental studies of the structure and dynamics at solid-liquid interfaces employing the quartz crystal microbalance (QCM). Various models for the mechanical contact between the oscillating quartz crystal and the liquid are described, and theoretical predictions are compared with the experimental results. Special attention is paid to consideration of the influence of slippage and surface roughness on the QCM response at the solid-liquid interface. The main question, which we would like to answer in this chapter, is what information on... 

Mesoscopic roughness at the solid-liquid interface can greatly modify both interfacial flow and static wetting properties leading to two behaviors, either a decrease [45,64,102] or an increase [63,103] of surface slippage with roughness. 

The amount of dewetted material increased by increasing the thickness h of the film. As can be seen from Fig. 2.3, such increase in h had several consequences. The most prominent observation is that dewetting proceeded faster for thinner films. This observation is not surprising. For dewetting on non-wettable surfaces like the HDT-patches one may expect slippage of the polymer [71]. Accordingly, the hole diameter D initially increased with time t with an exponent of roughly 2/3, i.e. t. However, when the periphery of the non-wettable patches was... 

Let us turn now to the experimental studies which have been conducted to measure slippage effects on superhydrophobic surfaces. In line with the discussion presented in the theoretical section, two kinds of roughness patterns have been mostly used for theses surfaces stripes or pillars. 

When a tensile load is applied to a fabric seam, it has to overcome two types of frictional forces. One is the inter-yam frictional forces within a fabric, and the other is the frictional force of the stitch assembly. The former is dependent upon the crimp, yam diameter, fiber content, and number of cross-over points. The latter, however, is dependent upon the fabric properties like fiber content, type of yam (spun or filament), thickness, lateral compression, cover factor (threads per cm), bending, shear, tensile and surface roughness, and coefficient of friction. It is also dependent upon the properties of the sewing thread like fiber content, diameter, coefficiait of Mction, initial modulus, and extensibility. All of these properties, together with the machine variables like needle and bobbin thread tension and the stitch length, make up the frictional force of the stitch assembly. Thus different combinations of these would be expected to provide different frictional resistance and hence different loads at which seam slippage may take place. 

The boundary condition is controlled by the extent to which the liquid feels a spatial corrugation in the surface energy of the solid. This depends on a number of interfacial parameters, including the strength of the liquid-liquid and liquid-solid interactions, the commensurability of the substrate and the liquid densities, characteristic sizes, and also the roughness of the interface. In order to quantify the slippage effect, the slip length. 

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