Complex surface topography, substrate

Immiscible Substrates with Complex Surface Topography. As before, the substrate is assumed to be completely immiscible with the adhesive, so that adhesive-substrate interactions are limited to surface sites. However, the substrate surface topography is now complex, as depicted schematically in Fig. 1. Be-... 

Some form of substrate pre-treatment is almost always essential before adhesive bonding (see many articles herein entitled Pre-treatment of... ). The extent to which pretreatments increase the Roughness of surfaces and the connection between this and adhesion are complex issues that have interested scientists for more than 50 years (see Mechanical theory of adhesion). The advent of Scanning electron microscopy (SEM) in the late 1960s made much more detail of surface topography available. Some surfaces of metals can be seen in SEM to be covered with acicular projections with heights of the order of 1 p.m (Fig. 1). Such surfaces have been termed microfibrous . 

In the context of the fimdamental relation between surface topography and wetting behavior as modeled by Wenzel or Cassie and Baxter one has to consider the relevance of geometrical parameters for the complex porous and textured textile substrate. It is of interest in this context that a paper by Hsieh et al. [26], who studied the wetting of water and ethylene... 

In addition, the square of the surface order parameter is proportional to the chemical reactivity profile of the twin domain wall interface at the surface (Locherer et al. 1996, Houchmanzadeh et al.(1992). Intuitively, one would expect the chemical reactivity of the surface to be largest at the centre of the twin domain wall, falling off as the distance from the centre of the wall increases. Contrary to the expected behaviour, a more complex behaviour is found. The reactivity, a monotonic function of Q, is expected to fall off as the distance from the centre of the wall increases, but only after if has reached a maximum of a distance of - 3 IF from the centre of the domain wall. If such a structure is expected to show particle adsorption (e.g. in the MBE growth of thin films on twinned substrates) we expect the sticking coefficient to vary spatially. In one scenario, adsorption may be enhanced on either side of the wall while being reduced at the centre. The real space topography of the surface is determined by both sources of relaxation-twin domain wall and the surface. These are distinct and, when considered separately, the wall... 

Theories of partide-surface adhesion are available for idealised particles and surfaces. These theories need to be extended to real particles and surfaces. They need to take into account the complex nature of the particle surface as well as the topography of the substrate to which they become attached. Advances in experimental techniques for measurement of partide-surface adhesion with real particles and surfaces have been very slow and this hampered the development of adequate fundamental principles. 

As described in the preceding sections, the surfaces of A1 alloys, Zn and steel, when exposed to aqueous solutions containing sufficient levels of R salts to inhibit corrosion, with the exception of steel in add solution (I. Singh and M. Singh 1987), become covered with a film of R hydroxide or hydrated oxide. The presence of these films is assodated with significantly reduced rates of corrosion. It is clear therefore that these films inhibit corrosion. Detailed scanning electron microscopy (SEM) studies have indicated that the topography and structure of these films are complex, and that while the structure and composition of the film may differ with each spedfic substrate, the films possess many common features (Hinton and Amott 1989). 

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