Bonding liquids, wettability

The wettability of plasma deposited coatings can be compared with poly(tetrafluoroethylene) and poly(ethylene). When the cosine of contact angles obtained with non-hydrogen bonding liquids are plotted against their surface tension, extrapolation of the resulting straight line to cos 0=1 yields a term called the critical surface tension (CST) which is characteristic of that surface (ll). 

Some nine years ago, Ellison and Zisman [4] reported their study of the wettability of 6-6 nylon (polyhexamethylene adipamide) and compared their results to those previously obtained on polyethylene [7]. They found that the nylon was more easily wet than the polyethylene, especially by hydrogen-bonding liquids, and attributed these findings to the presence of amide groups in the nylon surface. 

It was expected that as the average nylon number increased, the contact angles exhibited by hydrogen-bonding liquids on the various surfaces would rise, approaching the wettability of polyethylene as an asymptotic limit (polyethylene might be regarded as nylon oo). Such... 

One of the most common rubber adhesives are the contact adhesives. These adhesives are bonded by a diffusion process in which the adhesive is applied to both surfaces to be joined. To achieve optimum diffusion of polymer chains, two requirements are necessary (1) a high wettability of the adhesive by the smooth or rough substrate surfaces (2) adequate viscosity (in general rheological properties) of the adhesive to penetrate into the voids and roughness of the substrate surfaces. Both requirements can be easily achieved in liquid adhesives. Once the adhesive solution is applied on the surface of the substrate, spontaneous or forced evaporation of the solvent or water must be produced to obtain a dry adhesive film. In most cases, the dry-contact adhesive film contains residual solvent (about 5-10 wt%), which usually acts as a plasticizer. The time necessary... 

In the first Section, attention is paid to distinguishing between reactive and non-reactive systems from the point of view of wettability. Then, after describing wetting and bonding of non-reactive couples, we discuss the effect on these characteristics of oxygen, which is the most common impurity in solid/liquid/vapour systems, as well as the effect of reactive and non-reactive alloying elements. Finally, in a short Section, we consider some results for the wetting of fluorides which like oxides are very ionic. 

The intermolecular attraction between like molecules in the liquid state, such as the water-water attraction based on hydrogen bonds, is called cohesion. The attractive interaction between a liquid and a solid phase, such as water and the walls of a glass capillary (a cylindrical tube with a small internal diameter), is called adhesion. When the water-wall adhesion is appreciable compared with the water-water cohesion, the walls are said to be wettable, and water then rises in such a vertical capillary. At the opposite extreme, when the intermolecular cohesive forces within the liquid are substantially greater than is the adhesion between the liquid and the wall material, the upper level of the liquid in such a capillary is lower than the surface of the solution. Capillary depression occurs for liquid mercury in glass capillaries. For water in glass capillaries or in xylem vessels, the... 

It is desirable to find a simple surface property that will induce an equally simple and hence predictable behavior of plasma and its proteins and then of blood and its platelets. Are simple guidelines for building non-thrombogenic materials available or even possible Wettability (96), flow (97, 98y 99,100), and the effects of air/liquid interfaces (101) all seem to be relatively simple, physical factors with a clear effect on platelet adhesion. Physical, hydrophobic bonding, e.g., a force imposed... 

Wetting The ability of liquids to spread equally on solid matters. In bonding technology, the property of an adhesive to spread equally on the surfaces of the adherends. The wettability of a system depends on the respective surface tension of the solid and liquid media. 

Changing the wettability of the liquid can also be used to decrease the capillary forces. Creating a water-repellent surface is a means to reach this goal. Two kinds of bonds, Si-H and Si-F, make the silica surface hydrophobic or partially hydrophobic. Precursors bearing these special functional groups can be found in the literature [20,21]. 

Solid surfaces have many irregularities, and since adhesion is a surface phenomenon, the adhesive must fill completely all pores and surface irregularities of the adherend at the moment of application. To accomplish this, the adhesive must be applied in a liquid or semiliquid state. The liquid adhesive must penetrate all the pores and crevices, eliminating any air pockets, to obtain a homogeneous bond between the adherend and adhesive. The adhesive needs to wet the adherend surface, and the better the wettability of the adhesive/adherend pair, the better the chance of producing homogeneous spreading of the adhesive. 

Adhesives must effectively wet and completely contact the surfaces to assure a strong bond. The ability to wet a surface, wettability, is related to the ease with which a liquid spreads on a solid surface and is essential in maximizing coverage and minimizing voids in the bondlines. Wettability is measured by the equilibrium contact angle, 6, which is defined by balancing surface-tension forces in Young s equation ... 

The wettability of a liquid on a substrate is an important property in a number of ceramic processes. With a decreased wetting angle, i.e. an increased wettability, densification is enhanced in liquid phase sintering and the bonding in brazing or soldering is improved. 

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