Effect of Solid-Surface Wettability

Elwing, H. Askendal, A. Lundstrom, I., Competition between adsorbed fibrinogen and high-molecular weight kiniogen on solid surfaces incubated in human plasma (the Vroman effect) influence of solid surface wettability, J. Biomed. Mat. Res. 1987, 21, 1023-1028... 

The capillary effect is apparent whenever two non-miscible fluids are in contact, and is a result of the interaction of attractive forces between molecules in the two liquids (surface tension effects), and between the fluids and the solid surface (wettability effects). 

To sum up, the effects on static contact angles of the departures from ideality of solid surfaces are qualitatively well understood and some of these effects are used in practice to improve or reduce wettability. Moreover, for simple geometries, a semi-quantitative agreement is obtained between experimental results and theoretical predictions. For surfaces with random roughness, predictions of wetting hysteresis present a great difficulty because the relevant size of defects is not yet well-established. 

Wettability is a very important property of solid surfaces. In many cases, the surface wettability of mechanical components and devices strongly influences their operation. There are many reports on this topic. Borruto et al. [1] studied the effect of surface wettability of different materials (AISI 1050 and AISI420 steels, Pyrex glass, Teflon (PTFE) and carbon fiber) on the friction and wear behaviors during... 

In addition to the effect of the surface tension force at a fluid-fluid interface in droplets or bubbles, surface tension forces play a very important role in fluid behavior at a fluid-solid interface. The wettability of the surface determines the contact angle between the liquid and solid and therefore the magnitude of the resulting surface tension force. This angle has, in general, to be measured experimentally and such experiments have shown that the value is not a constant for a particular fluid-sohd pair but shows hysteresis effects, in that the contact angle changes between the cases... 

A broader study compared the effect of different surface chemistry and roughness on water flow (and thus wettability) in a CNT, a boron nitride nanotube (BNNT), a silicon nanotube, and a roughened nanotube. Figure 10.5 expresses the axial velocity profiles of each nanotube. The simulations found that there was a plug-like velocity flow profile with a "jump" in velocity at the solid-... 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

There are numerous techniques which provide information related to the surface energy of solids. A large array of high-vacuum, destructive and non-destructive techniques is available, and most of them yield information on the atomic and chemical composition of the surface and layers just beneath it. These are reviewed elsewhere [83,84] and are beyond the scope of the present chapter. From the standpoint of their effect on wettability and adhesion, the property of greatest importance appears to be the Lifshitz-van der Waals ( dispersion) surface energy, ys. This may be measured by the simple but elegant technique of... 

The Wilhelmy hanging plate method (13) has been used for many years to measure interfacial and surface tensions, but with the advent of computer data collection and computer control of dynamic test conditions, its utility has been greatly increased. The dynamic version of the Wilhelmy plate device, in which the liquid phases are in motion relative to a solid phase, has been used in several surface chemistry studies not directly related to the oil industry (14- 16). Fleureau and Dupeyrat (17) have used this technique to study the effects of an electric field on the formation of surfactants at oil/water/rock interfaces. The work presented here is concerned with reservoir wettability. 

Adhesion Tensions and Tar Sand Extraction with Tween Surfactants. Mea-surement of the adhesion tension (t) allows the determination of the wettability of a given solid by a given liquid or surfactant solution. Measurements of adhesion tension between both bitumen or clay surfaces and various surfactant solutions is thus highly relevant to a study of the effects of surfactants in the separation of bitumen from Athabasca tar sand. 

During the plasma surface reaction, the plasma and the solid are in physical contact, but electrically isolated. Surfaces in contact with the plasma are bombarded by free radicals, electrons, ions, and photons, as generated by the reactions listed above. The energy transferred to the solid is dissipated within the solid by a variety of chemical and physical processes, as illustrated in Figure 7.95. These processes can change surface wettability (cf. Sections 1.4.6 and 2.2.2.3), alter molecular weight of polymer surfaces or create reactive sites on polymers. These effects are summarized in Table 7.21. 

Rapid fluid flow cannot be achieved with active metal brazes because of the need to form solid wettable reaction product layers for their liquid fronts to advance. Equations (10.1) to (10.2) relating liquid flow rates to the opposed effects of surface energy imbalances and of viscous drag are not relevant. Actual penetration rates are so slow, usually of the order of 1 pm.s, that the usual practice is to place the active metal braze alloy within the joints rather than expecting it to fill them, and, as explained already, gap width is not the dominant consideration when designing ceramic-metal joints. 

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