Surface high-energy

It should be loted that with low-energy surfaces the sudden fall in the heat of adsorption is absent. This is illustrated in Fig. 2.15, where the contrast between the behaviour of nitrogen on the carbons (high-energy surfaces) and on the molecular solids (low-energy surfaces) is very clear. 

At sufficiently low temperatures the isotherm of argon on high-energy surfaces tends to assume a step-like character (cf. p. 86). 

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

The materials used to be employed for making tribo-pairs are metals or metal oxides that belong to a high-energy surface so that it will exert influence on the arrangement of lubricant molecules nearby the solid surfaces. This contributes mainly to the viscosity variety of lubrication oil near to the solid surface. 

Oxide surfaces are high-energy surfaces that interact with water molecules becoming covered by a carpet of OH groups. The latter, in contact with aqueous solutions, behave as weak acids or weak bases, giving rise to dissociation that is the main origin of surface charging ... 

Fox HW, Hare EF, Zisman WA (1955) Wetting properties of organic liquids on high energy surfaces. J Phys Chem 59 1097-1106... 

As Table 2 shows, non-treated fillers and reinforcements have high energy surfaces. During the almost exclusively used melt mixing procedure, the forces discussed in the previous section lead to the adsorption of polymer chains onto the active sites of the filler surface. The adsorption of polymer molecules results in the development of a layer which has properties different from those of the matrix polymer [43-47]. Although the character, thickness and properties of this interlayer or interphase are much discussed topics, its existence is now an accepted fact. 

High-energy surfaces bind enough adsorbed molecules to make ire significant. On the other hand, ire is negligible for a solid that possesses a low-energy surface. 

For high-energy surfaces, 7re > 0 owing to adsorption. Relationships have been derived that express yds in terms of gas adsorption. 

On low energy surfaces such as polyethylene, polypropylene, or polytetrafluoroethylene many liquids have finite contact angles and Tre values are generally zero (3). On high energy surfaces such as most mineral oxides most liquids have no contact angle, tt6 values are quite appreciable and... 

Since slower-curing epoxy adhesives systems flow over and wet high-energy surfaces very well, there is little chance for air to become trapped at the interface. As a result, mechanical abrasion is often recommended as a substrate surface treatment prior to application of the epoxy adhesive. The added surface area and the mechanical bonding provided by the additional peaks and valleys on the surface will enhance adhesive strength. If the adhesive does not wet the substrate surface well, such as in the case of epoxy resin on polyethylene, mechanical abrasion is not recommended since it will only encourage the probability of gas voids being trapped at the interface. 

Recently, experimental and theoretical evidence for a model of the active site of industrial methanol synthesis that combines the role of ZnO and defects in Cu has been presented [58]. Planar defects have been shown to lead to changes in surface faceting of the Cu nanoparticles (Figure 5.3.8C) associated with formation of steps and kinks that were assumed to represent high-energy surface sites of special catalytic activity. For a series of Cu/ZnO-based catalysts, a linear correlation of the defect concentration with the intrinsic activity of the exposed Cu surface was observed. In addition, (partial) surface decoration of Cu with ZnOx by SMSI has been... 

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